Human Performance and Limitations

ATPL Human Performance and Limitations

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CHAPTER 1 Introduction to Human Factors Introduction ........................................................................................................................................1-1 Accidents and Incidents .....................................................................................................................1-2 Public Transport Accident Data..........................................................................................................1-2 The Meaning of Human Factors.........................................................................................................1-3 A Conceptual Model of Human Factors – The SHEL Model ..............................................................1-4 Human Error ......................................................................................................................................1-6 Pilot Error ...........................................................................................................................................1-7 James Reason Model ........................................................................................................................1-7 Confidential Human Factors Incident Reporting Programme (CHIRP) ..............................................1-8 Study and Sleep.................................................................................................................................1-9 Learning Styles ..................................................................................................................................1-9 Lecture and Revision Notes ...............................................................................................................1-9 Review of Notes...............................................................................................................................1-10 Methods of Learning ........................................................................................................................1-10 Revision Style ..................................................................................................................................1-11 Revision Method ..............................................................................................................................1-11 Relaxation ........................................................................................................................................1-12 Sleep................................................................................................................................................1-12

CHAPTER 2 Aviation Medicine - Respiration and Circulation The Atmosphere ................................................................................................................................2-1 Measurement of Atmospheric Pressure .............................................................................................2-2 The Standard Atmosphere .................................................................................................................2-2 Standard Atmosphere Pressures and Temperatures for Different Altitudes ......................................2-2 Physical Divisions of the Atmosphere ................................................................................................2-2 Gas Laws ...........................................................................................................................................2-4 The Human Need for Oxygen ............................................................................................................2-5 Respiration.........................................................................................................................................2-6 Inspiration and Expiration...................................................................................................................2-7 Gaseous Exchange............................................................................................................................2-7 Control of Breathing ...........................................................................................................................2-8 The Circulatory System......................................................................................................................2-9 Composition of the Blood .................................................................................................................2-11 Blood Circulation..............................................................................................................................2-12 Further Uses of Blood Circulation ....................................................................................................2-13

CHAPTER 3 Aviation Medicine - The Effects Of Altitude Introduction ........................................................................................................................................3-1 Tracheal air ........................................................................................................................................3-1 Alveolar Air.........................................................................................................................................3-1 Forms of Hypoxia...............................................................................................................................3-3 Oxygen Requirements .......................................................................................................................3-3 Alveolar Partial Pressure....................................................................................................................3-3 Summary of Oxygen Requirements ...................................................................................................3-4 Hypoxia ..............................................................................................................................................3-4 Signs and Symptoms of Hypoxia .......................................................................................................3-5 Stages of Hypoxia..............................................................................................................................3-6 Susceptibility to Hypoxia ....................................................................................................................3-6 Time of Useful Consciousness...........................................................................................................3-7


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©Atlantic Flight Training

Limitations of Time at Altitude ............................................................................................................3-7 Hyperventilation .................................................................................................................................3-8 Symptoms of Hyperventilation ...........................................................................................................3-8 Treatment of Hypoxia and Hyperventilation .......................................................................................3-8 Cabin Decompression........................................................................................................................3-9 Climb and Descent...........................................................................................................................3-10 Climb................................................................................................................................................3-10 Decompression Sickness.................................................................................................................3-10 Re-exposure ....................................................................................................................................3-11 Treatment of Decompression Sickness............................................................................................3-12 Flying and Diving .............................................................................................................................3-12 Descent............................................................................................................................................3-12 Sinuses ............................................................................................................................................3-12 The Ear ............................................................................................................................................3-13 Prevention........................................................................................................................................3-14

CHAPTER 4 Aviation Medicine – Health and Hygiene Introduction ........................................................................................................................................4-1 Joint Aviation Requirements ..............................................................................................................4-1 JAR-FCL and ICAO Annex 1 .............................................................................................................4-1 Medical Fitness ..................................................................................................................................4-1 Fitness ...............................................................................................................................................4-1 Requirement for Medical Certificate...................................................................................................4-2 Aeromedical Disposition.....................................................................................................................4-2 Decrease in Medical Fitness ..............................................................................................................4-2 Fitness to Fly......................................................................................................................................4-3 Blood Pressure ..................................................................................................................................4-3 Hypertension......................................................................................................................................4-5 Orthostatic Hypotension.....................................................................................................................4-5 Causes of Orthostatic Hypotension....................................................................................................4-5 Coronary Heart Disease.....................................................................................................................4-6 Atherosclerosis ..................................................................................................................................4-6 Risk Factors of Coronary Heart Disease............................................................................................4-7 Reducing the Risk of Coronary Heart Disease...................................................................................4-7 Detection and Treatment of CHD.......................................................................................................4-8 Stroke ................................................................................................................................................4-8 Anaemia.............................................................................................................................................4-8 Obesity...............................................................................................................................................4-8 Body Mass Index ...............................................................................................................................4-9 Effects of Obesity...............................................................................................................................4-9 Exercise ...........................................................................................................................................4-10 Hypoglycaemia ................................................................................................................................4-10 Tropical Diseases ............................................................................................................................4-11 Water ...............................................................................................................................................4-11 Food.................................................................................................................................................4-12 Diarrhoea .........................................................................................................................................4-12 Cholera ............................................................................................................................................4-12 Amoebic Dysentery, Amoebiasis .....................................................................................................4-12 Diseases Transmitted by Insects .....................................................................................................4-12 Insects and Insect vectors................................................................................................................4-12 Mosquito-Borne diseases.................................................................................................................4-13 Malaria .............................................................................................................................................4-13 Diseases Transmitted by Flies .........................................................................................................4-13 Other Insects....................................................................................................................................4-13 Hepatitis ...........................................................................................................................................4-14 Immunisations..................................................................................................................................4-14 Rabies..............................................................................................................................................4-14 Tobacco and Smoking .....................................................................................................................4-14


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Carbon Monoxide.............................................................................................................................4-15 Nicotine ............................................................................................................................................4-15 Drugs and Medication ......................................................................................................................4-16 General Health.................................................................................................................................4-16 Drugs ...............................................................................................................................................4-16 Allergic Reactions ............................................................................................................................4-16 Idiosyncrasies ..................................................................................................................................4-17 Synergistic Effects ...........................................................................................................................4-17 Effect of Drug Combinations ............................................................................................................4-17 Alcohol .............................................................................................................................................4-18 Unit of Alcohol..................................................................................................................................4-18 JAR-OPS 1.115 - Alcohol and Drugs ...............................................................................................4-19 Recommended Amounts of Alcohol.................................................................................................4-19 Alcoholism........................................................................................................................................4-19 Physical Problems ...........................................................................................................................4-20 Alcohol and Sleep ............................................................................................................................4-20 Toxic Materials.................................................................................................................................4-20 Toxicology........................................................................................................................................4-20 Aviation Gasoline (AVGAS) .............................................................................................................4-21 JP4-JP5 ...........................................................................................................................................4-21 Ethylene Glycol ................................................................................................................................4-21 Methyl Alcohol..................................................................................................................................4-21 Chlorobromo Methane (CBM) ..........................................................................................................4-21 Halon ...............................................................................................................................................4-21 Hydraulic Fluid .................................................................................................................................4-21 Plastics.............................................................................................................................................4-21 Mercury ............................................................................................................................................4-22 Incapacitation...................................................................................................................................4-22 Fits and Faints .................................................................................................................................4-22 Epilepsy ...........................................................................................................................................4-22 Faint .................................................................................................................................................4-23 Gastroenteritis..................................................................................................................................4-23 Acceleration .....................................................................................................................................4-23 Short Term Acceleration ..................................................................................................................4-23 Long Term Acceleration ...................................................................................................................4-24 Motion Sickness...............................................................................................................................4-24

CHAPTER 5 Aviation Medicine - Diet and Digestion Introduction ........................................................................................................................................5-1 Carbohydrates and Fats.....................................................................................................................5-1 Fats ....................................................................................................................................................5-2 Proteins..............................................................................................................................................5-2 Diet ....................................................................................................................................................5-2 Mineral Salts and Vitamins.................................................................................................................5-3 Mineral Salts ......................................................................................................................................5-3 Vitamins .............................................................................................................................................5-4 Trace Elements..................................................................................................................................5-5 Digestion ............................................................................................................................................5-5 The Alimentary Canal ........................................................................................................................5-5 Mouth .................................................................................................................................................5-5 Teeth..................................................................................................................................................5-5 Salivary Glands..................................................................................................................................5-6 Digestion in the Mouth .......................................................................................................................5-6 Pharynx and Oesophagus..................................................................................................................5-6 Swallowing .........................................................................................................................................5-7 Stomach.............................................................................................................................................5-7 Digestion in the Stomach ...................................................................................................................5-7 Small Intestine ...................................................................................................................................5-8


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Digestion in the Small Intestine..........................................................................................................5-8 Large Intestine ...................................................................................................................................5-8 Functions of the Large Intestine.........................................................................................................5-9 Defaecation........................................................................................................................................5-9

CHAPTER 6 Aviation Medicine - Metabolism, Excretion And Heat Regulation The Liver ............................................................................................................................................6-1 Functions of the Liver.........................................................................................................................6-1 Pancreas............................................................................................................................................6-1 Insulin ................................................................................................................................................6-1 Excretion and Regulation of Body Fluids ...........................................................................................6-2 Functions of the Skin .........................................................................................................................6-2 The Kidneys .......................................................................................................................................6-2 Functions of the Kidneys....................................................................................................................6-3 Micturation .........................................................................................................................................6-3 Body Heat Regulation ........................................................................................................................6-3 Heat Production .................................................................................................................................6-3 Heat Loss...........................................................................................................................................6-3 Fever..................................................................................................................................................6-4 Heat Stroke ........................................................................................................................................6-4 Climate and Heat Loss.......................................................................................................................6-4

CHAPTER 7 Aviation Medicine - The Eye Introduction ........................................................................................................................................7-1 Anatomy and Physiology of the Eye ..................................................................................................7-1 Visual Acuity ......................................................................................................................................7-2 Clarity of Vision ..................................................................................................................................7-3 Depth Perception ...............................................................................................................................7-3 Distance Estimation and Depth Perception........................................................................................7-4 Stereoscopic Vision ...........................................................................................................................7-4 Monocular Cues.................................................................................................................................7-4 Geometric Perspective.......................................................................................................................7-5 Motion Parallax ..................................................................................................................................7-5 Retinal Image Size.............................................................................................................................7-5 Known Size of Objects .......................................................................................................................7-5 Increasing or Decreasing Size of Objects ..........................................................................................7-6 Terrestrial Association .......................................................................................................................7-6 Terrestrial Distance of Objects Used to Determine Distance .............................................................7-7 Overlapping Contours or Interposition of Objects ..............................................................................7-7 Aerial Perspective ..............................................................................................................................7-8 Emmetropia........................................................................................................................................7-8 Myopia (Short Sightedness)...............................................................................................................7-8 Hypermetropia (Long Sightedness) ...................................................................................................7-9 Presbyopia .........................................................................................................................................7-9 Astigmatism .......................................................................................................................................7-9 Spectacles .........................................................................................................................................7-9 Contact Lenses ..................................................................................................................................7-9 Radial Keratotomy ...........................................................................................................................7-10 Colour Vision and Colour Blindness.................................................................................................7-10 Night Vision......................................................................................................................................7-11 Saccadic Eye Movement..................................................................................................................7-12 Sunlight and its Effect on the Eyes ..................................................................................................7-12 Empty Field Myopia .........................................................................................................................7-12 Glare ................................................................................................................................................7-12 Sunglasses ......................................................................................................................................7-13


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Flickering Light.................................................................................................................................7-13

CHAPTER 8 Aviation Medicine – Visual Illusions Introduction ........................................................................................................................................8-1 Spatial Orientation .............................................................................................................................8-1 Spatial Disorientation .........................................................................................................................8-3 Landing ..............................................................................................................................................8-4 Width of Runway................................................................................................................................8-4 Approach............................................................................................................................................8-6 Runway Gradient and Terrain ............................................................................................................8-7 Runway Slopes Up ............................................................................................................................8-7 Runway Slopes Down ........................................................................................................................8-7 Ground Sloping Down to the Runway ................................................................................................8-8 Ground Sloping Up to the Runway.....................................................................................................8-8 Visual Illusions in the Air ....................................................................................................................8-8 Lean on Cloud....................................................................................................................................8-8 Lean on Sun.......................................................................................................................................8-9 Black Hole Effect..............................................................................................................................8-10 Visual Factors at Night .....................................................................................................................8-11 Reaction Time..................................................................................................................................8-11 Visual Acuity ....................................................................................................................................8-12 Blind Spot.........................................................................................................................................8-12

CHAPTER 9 Aviation Medicine - The Ear - Hearing and the Vestibular System Introduction ........................................................................................................................................9-1 Noise..................................................................................................................................................9-2 Effects of Noise..................................................................................................................................9-3 Conductive Deafness .........................................................................................................................9-3 Cochlea..............................................................................................................................................9-3 Noise Induced Hearing Loss (NIHL) ..................................................................................................9-4 Protection Against Noise....................................................................................................................9-4 Presbycusis........................................................................................................................................9-4 Vibration.............................................................................................................................................9-4 The Vestibular System .......................................................................................................................9-4 Semi-Circular Canals .........................................................................................................................9-5 Otoliths...............................................................................................................................................9-6

CHAPTER 10 Aviation Medicine – Vestibular Illusions Illusions of Vestibular Origin.............................................................................................................10-1 The Leans ........................................................................................................................................10-1 Somatogravic Illusion .......................................................................................................................10-2 The Somatogravic Illusion in Yaw and Roll ......................................................................................10-2 Somatogravic Illusion in Pitch ..........................................................................................................10-4 G-Excess Illusion .............................................................................................................................10-6 The Oculogravic Illusion...................................................................................................................10-6 Elevator Illusions..............................................................................................................................10-7 False Perception of Angular Motion – Vertigo..................................................................................10-8 Somatogyral Illusion.........................................................................................................................10-8 Oculogyral Illusions ..........................................................................................................................10-9 Illusions due to Cross-Coupled (Coriolis) Canal Stimulation ............................................................10-9 Pressure Vertigo ............................................................................................................................10-10


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Summary of Disorientation.............................................................................................................10-10 Prevention......................................................................................................................................10-10 Practical Advice to Flight Crew ......................................................................................................10-11 Practical Advice on how to Cope with Spatial Disorientation when it Occurs.................................10-12

CHAPTER 11 Aviation Medicine – High Altitude Environment Radiation..........................................................................................................................................11-1 Risk to Flight Crew...........................................................................................................................11-2 Ozone ..............................................................................................................................................11-2 Humidity ...........................................................................................................................................11-2 Water Vapour...................................................................................................................................11-2 Relative Humidity .............................................................................................................................11-2 Humidity Control ..............................................................................................................................11-3 Pressurisation ..................................................................................................................................11-3 Pressurised Cabins ..........................................................................................................................11-3 Cabin Pressurisation Advantages ....................................................................................................11-3 Disadvantages of Pressurised Cabins .............................................................................................11-4 Aircraft Oxygen Systems..................................................................................................................11-4 All Aeroplanes on High Altitude Flights ............................................................................................11-4 Oxygen Regulator ............................................................................................................................11-5 Oxygen masks .................................................................................................................................11-5

CHAPTER 12 Sleep Introduction ......................................................................................................................................12-1 The Danger of Fatigue .....................................................................................................................12-1 Vigilance Effects ..............................................................................................................................12-1 Causes of Pilot Fatigue ....................................................................................................................12-2 Symptoms of Pilot Fatigue ...............................................................................................................12-2 Sleep and Sleep Deprivation............................................................................................................12-2 Sleep Credit/Deficit ..........................................................................................................................12-4 Sleep................................................................................................................................................12-6 Sleep Disorders ...............................................................................................................................12-7 Sleep Loss and Microsleep ..............................................................................................................12-7 Insomnia ..........................................................................................................................................12-7 Sleepwalking and Sleeptalking ........................................................................................................12-8 Sleep Apnoea ..................................................................................................................................12-8 Narcolepsy .......................................................................................................................................12-8 Sleep Hygiene..................................................................................................................................12-8 Napping............................................................................................................................................12-9 Drugs ...............................................................................................................................................12-9 Sleeping Tablets ..............................................................................................................................12-9 Melatonin .........................................................................................................................................12-9 Circadian Dysrhythmia – Jet Lag .....................................................................................................12-9

CHAPTER 13 Stress Introduction ......................................................................................................................................13-1 Stress...............................................................................................................................................13-1 Effects of Stress...............................................................................................................................13-2 Stress is Cumulative ........................................................................................................................13-2 Psychological Stressors ...................................................................................................................13-4 Effects of Stress...............................................................................................................................13-6


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Physical and Psychological Stress Reactions..................................................................................13-7 Physical Stress Reactions................................................................................................................13-7 General Adaptation Syndrome.........................................................................................................13-7 Psychological Stress Reactions .......................................................................................................13-8 Domestic Stress...............................................................................................................................13-8 Clinical Effects of Stress ..................................................................................................................13-8 Coping Skills ....................................................................................................................................13-9 Stress Management .......................................................................................................................13-10

CHAPTER 14 The Nervous System Introduction ......................................................................................................................................14-1 The Central Nervous System ...........................................................................................................14-1 Brain ................................................................................................................................................14-2 Spinal Cord ......................................................................................................................................14-2 The Peripheral Nervous System ......................................................................................................14-3 Sensory Nerves ...............................................................................................................................14-3 Motor Nerves ...................................................................................................................................14-3 Autonomic Nervous System.............................................................................................................14-3

CHAPTER 15 Human Information Processing Introduction ......................................................................................................................................15-1 Sense...............................................................................................................................................15-1 Perception........................................................................................................................................15-2 Confirmation Bias.............................................................................................................................15-3 Central Decision Making and Response Selection ..........................................................................15-3 Ultra-short Term Memory .................................................................................................................15-4 Cocktail Party Effect.........................................................................................................................15-4 Working Memory or Short Term Memory .........................................................................................15-4 Short Term Memory and its Limitations............................................................................................15-5 Environment Capture .......................................................................................................................15-6 Long Term Memory and its Limitations ............................................................................................15-6 Motor Memory..................................................................................................................................15-7 Action Slip ........................................................................................................................................15-8 Response Execution ........................................................................................................................15-9 Attention...........................................................................................................................................15-9 Selective Attention .........................................................................................................................15-10 Divided Attention............................................................................................................................15-10 Stress and Attention.......................................................................................................................15-10 Response Behaviour......................................................................................................................15-10 Skill Based Behaviour ....................................................................................................................15-10 Rule Based Behaviour ...................................................................................................................15-11 Knowledge Based Behaviour .........................................................................................................15-11 Feedback .......................................................................................................................................15-11

CHAPTER 16 Situational Awareness and Attention Introduction ......................................................................................................................................16-1 Situational Awareness .....................................................................................................................16-1 Building Situational Awareness........................................................................................................16-1 Personal Factors Affecting Situational Awareness...........................................................................16-3 Three levels of Situational Awareness .............................................................................................16-3 Situational Awareness Level 1: Monitoring ......................................................................................16-3


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Situational Awareness Level 2: Evaluating ......................................................................................16-4 Situational Awareness Level 3: Anticipating.....................................................................................16-4 Pilot Considerations .........................................................................................................................16-4 Briefing/Debriefing ...........................................................................................................................16-4 Conflict Resolution ...........................................................................................................................16-5

CHAPTER 17 Communication Communication ................................................................................................................................17-1 Effective Communication .................................................................................................................17-1 The Cost of Effectiveness ................................................................................................................17-2 Results of Poor Communication.......................................................................................................17-2 The good transmitter ........................................................................................................................17-2 The good receiver ............................................................................................................................17-2 Types of Communication .................................................................................................................17-3 Written Communication....................................................................................................................17-3 Visual and Pictorial Ambiguity..........................................................................................................17-3 Verbal Communication.....................................................................................................................17-4 Social Skills......................................................................................................................................17-4 Body Language................................................................................................................................17-4 Verbal Behaviour .............................................................................................................................17-5 Listening...........................................................................................................................................17-5 Non-verbal Response ......................................................................................................................17-7 Verbal Response .............................................................................................................................17-8 Closed Question ..............................................................................................................................17-8 Open Question.................................................................................................................................17-8 Leading Question.............................................................................................................................17-8 Limiting Question .............................................................................................................................17-9 Understanding..................................................................................................................................17-9 Active Listening................................................................................................................................17-9 The art of effective listening .............................................................................................................17-9 Status, Role and Ability ..................................................................................................................17-10 Status.............................................................................................................................................17-10 Role ...............................................................................................................................................17-10 Ability .............................................................................................................................................17-10 Atmosphere....................................................................................................................................17-10 Communication summary ..............................................................................................................17-11

CHAPTER 18 Personality and Behaviour Introduction ......................................................................................................................................18-1 Working Relationships .....................................................................................................................18-1 Intelligence.......................................................................................................................................18-2 Personality .......................................................................................................................................18-2 Assessment .....................................................................................................................................18-3 Behaviour.........................................................................................................................................18-3 Self Opinion .....................................................................................................................................18-4 Defence Mechanisms ......................................................................................................................18-4 Denial...............................................................................................................................................18-4 Introversion and Extroversion ..........................................................................................................18-4 Behavioural Styles ...........................................................................................................................18-5 Assertive Behaviour .........................................................................................................................18-5 Case For Assertiveness ...................................................................................................................18-8 Body Language................................................................................................................................18-8 Aggressive .......................................................................................................................................18-8 Non-Assertive ..................................................................................................................................18-8 Assertive ..........................................................................................................................................18-9


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Assertive Behaviour .........................................................................................................................18-9

CHAPTER 19 Leadership / Followership Introduction ......................................................................................................................................19-1 Leadership Qualities ........................................................................................................................19-1 Leadership Skills..............................................................................................................................19-1 The Person Goal (P/G) Model..........................................................................................................19-2 Leadership - The Leader..................................................................................................................19-4 Qualities Approach...........................................................................................................................19-4 Situations Approach .........................................................................................................................19-5 Effective Leadership ........................................................................................................................19-5 Attitudes to Leadership ....................................................................................................................19-6 Ineffective Leadership ......................................................................................................................19-7

CHAPTER 20 Decision Making Decision Making Process.................................................................................................................20-1 Reaction to Decision Making............................................................................................................20-1 Making and Taking Decisions ..........................................................................................................20-1 Decision Making Models ..................................................................................................................20-2 Group Versus Individual Decision Making........................................................................................20-3 Influences on Decision Making ........................................................................................................20-4 Summary..........................................................................................................................................20-5

CHAPTER 21 Error and Error Chains Introduction ......................................................................................................................................21-1 Levels of Human Error .....................................................................................................................21-2 Correction of Human Error ...............................................................................................................21-2 Group Attitudes ................................................................................................................................21-3 SHEL Model Interfaces ....................................................................................................................21-3 Links of the Error Chain ...................................................................................................................21-4 Breaking the “Error Chain” ...............................................................................................................21-5

CHAPTER 22 Learning and Learning Styles Introduction ......................................................................................................................................22-1 The Learning Cycle..........................................................................................................................22-1 Honey and Mumford ........................................................................................................................22-3 Flexible Learning..............................................................................................................................22-4 Maslow.............................................................................................................................................22-4

CHAPTER 23 Automation Introduction ......................................................................................................................................23-1 Flight Crew Functions ......................................................................................................................23-2 Human Factors Concepts in Design ................................................................................................23-3


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Common Problems with Automation ................................................................................................23-3 Industry Requirements .....................................................................................................................23-4 Flight Crew Responsibilities .............................................................................................................23-4 Automation Summary ......................................................................................................................23-5

CHAPTER 24 CRM & MCC Introduction ......................................................................................................................................24-1 What is CRM?..................................................................................................................................24-2 Why CRM training?..........................................................................................................................24-2 CRM Loop........................................................................................................................................24-3 Multi-crew Co-operation (MCC) .......................................................................................................24-3


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Chapter 1. Introduction to Human Factors “Errare humanum est” Introduction Flight safety is one of the major objectives of the ICAO and considerable progress has been made in the past few years. However, additional improvements are needed as it has long been known that approximately 75% of accidents result from less than optimum human performance. This indicates that any advance in the field of Human Performance will have a significant impact on the improvement of flight safety. This was recognized by the ICAO Assembly which adopted a resolution on "Flight Safety and Human Factors" in 1986. As a follow up to the Assembly Resolution, the Air Navigation Commission formulated the following objective for the task: "To improve safety in aviation by making States more aware and responsive to the importance of human factors in civil aviation operations through the provision of practical human factors material and measures developed on the basis of experience in States" Human behaviour and performance are cited as factors in the majority of aircraft accidents. To decrease accident rates, Human Factors in aviation must be better understood and the knowledge more broadly applied. The improvement of awareness in Human Factors presents the international aviation community with the single most significant opportunity to make aviation safer. To introduce you to Human Performance and Limitations this chapter includes: ¾

A possible meaning and definition of Human Factors

¾

A conceptual model of Human Factors

¾

The industry need for Human Factors

¾

The application of Human Factors in flight operations

¾

The levels of expertise required for flight safety in modern day operations

The human animal has only been flying since the early 1900's. In the quest for more safety in aviation, attention has been focused on the obvious deficiencies of man and machine. Since the early beginnings of flight, great technological advances have been made making aircraft much safer. But what about the human? Has he been forgotten? This subject deals with the Human Factors that are considered the most important in aviation. The information given should help in the understanding of the human animal and, hopefully, help make aviation safer.


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Accidents and Incidents Human error is, by far, the most extensive cause of accidents and incidents in what is now a technologically complex area. Some of the latest accident statistics show that 65% of all accidents in Public Transport aviation have been attributed to flight crew error. It also indicates that for the approach and landing phase of flight, which accounts for 6% of total flight exposure time and 49% of all accidents, flight crew error is cited in 70% as a casual factor.

Initial Initial Final Descent Approach Approach

Initial Landing

Percentage of Accidents





4.4%

7.2%

11.3%

24.2%

19.2%

Percentag e of Flight Time


Take Off

Initial Climb

Climb

Cruise




14.4%

10.4%

6.9%



Percenta Percentag Percentag Percentag ge of e of Flight e of Flight e of Flight Flight Time Time Time Time

1%

1%

Public Transport Accident Data Note:

Loading, Taxi and unload are allocated 2% of the flight time. No accidents are reported in this phase.

Studies have shown that pilot disregard of rules is the most common cause of approach and landing accidents, other causes cited are: ¾

Omission of an action/inappropriate action by a flight crew member eg descent below DH/MDH without the appropriate visual reference

¾

Lack of positional awareness of height above terrain

¾

"Press-on-itis", a decision to continue the approach when conditions are not suitable

The industry need for Human Factors is based on the interaction between the following: ¾

Effectiveness of the system

¾

Safety

¾

Efficiency


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¾

Well being of crew members

Almost everyone involved in Public Transport aviation, from the design of an aircraft to its operation, is concerned with the human element; all need some basic Human Factors training. An Airline will continuously publish bulletins on technical subjects that are likely to be effective because both flight crew and technical personnel realise the importance to the safety of the operation. A similar bulletin on Human Factors topics is unlikely to generate the same response and comprehension unless training is given to the importance of the subject. All airline staff should be exposed to a general level of Human Factors education. Better education means that the Human Element becomes more aware of human performance capabilities and limitations. Studies indicate that if all sources are included in aircraft accident statistics then 80 - 90% are attributable to human error in one form or another The Meaning of Human Factors The human element in aviation can be considered in asset terms as: ¾

The most reliable

¾

The most adaptable

¾

The most valuable

Unfortunately, the pilot is also the most vulnerable to outside influences that can adversely affect performance. Human Factors is not a single discipline, it draws information from all of the following areas: Psychology

The science of mind and behaviour

Engineering

Applying the properties of matter and the sources of energy in nature to the uses of man

Human Physiology

Deals with the processes, activities and phenomena characteristic of living matter, particularly appropriate to healthy or normal functioning

Medicine

The science and art of preventing, alleviating or curing disease and injuries

Sociology

The study of the development, structure and function of human groups

Anthropometry

Study of human body sizes and muscle strength

The above is not a comprehensive list, other disciplines engaged in Human Factors activities include: ¾

Education

¾

Physics


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¾

Biochemistry

¾

Mathematics

¾

Biology

¾

Industrial design and operational research

A Conceptual Model of Human Factors – The SHEL Model It is helpful to use models to aid in the understanding of Human Factors; this allows a gradual approach in the understanding of all factors. The SHEL concept is one such model (Edwards 1972) that lends itself to the aviation environment. The name is derived from the initial letters of the model Software, Hardware, Environment and Liveware. The idea of the model is to establish the concept of a man/machine - environment.

H S

E

L

L

Liveware

H

Hardware

E

Environment

S

Software

L For a basic understanding of the SHEL model consider a football game. Start with the central L, and then look at the match between interfaces: L

Your team, (Players, Coach, Trainer)

L-L

Opposing team (Players, Coach, Trainer), Referee

L-H

Ball, Playing surface, Goal

L-E

Stadium, Fans, Weather

L-S

Rules, Scoreboard, Match importance

The interfaces are not straight edged. Remember that a perfect match is never achievable in real life – is there a perfect football team that never loses?


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L - Liveware - The person - The pilot To understand the person we need to look at the basic human characteristics: Physical Size and Shape

Design of workspace from anthropometric data (Anthropometry).

Physical Needs

The requirement for nourishment (Physiology and Biology).

Input Characteristics

The sensory systems that collect information for the brain (Physiology, Psychology and Biology).

Information Processing

The limitations of human capability (Psychology).

Output Characteristics

Once information is processed, the way the human sends messages to the muscles to initiate responses (Psychology, Physiology and Biomechanics).

Environmental Tolerance

The body's capability to withstand temperature, pressure and humidity (Physiology, Psychology and Biology).

The liveware (Pilot) is the hub of the SHEL model. The rest of the model must be adapted and matched to this central component. Liveware – Hardware Cockpit design – will there ever be a perfect flight deck? This interface is the area considered when an aircraft is designed - yet why does the pilot still have problems with the layout and use of equipment On the BAC 1-11 flap/gear levers next to each other so that inadvertent operation became a common occurrence. Liveware – Software The non-physical aspects of a system - procedures, manuals or checklists etc. Do you keep your aviation documentation up to date? A Constellation on approach to Prestwick. An experienced pilot flying a radar to visual pattern. The maps on the aircraft showed masts, on the approach, up to 50 ft agl - in fact they were up to 500 ft agl. The aircraft crashed, hitting the masts, killing all persons on board. Liveware – Environment Errors associated with the environment - noise, heat, lighting and vibration. The earliest interface to be recognised in flying. The challenges of pressurisation, air conditioning, vibration and sound proofing have been


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understood and dealt with in most modern aircraft. New challenges such as the problems associated with sleep disturbance are now the major causes of concern. Liveware – Liveware The interface between people. Poor interaction means poor crew effectiveness. This relates to all aspects of an airline operation. Any person dealing with a flight must be considered in this area. Flight crew human factors training attempts to minimise the mismatches that occur with this interface. Human Error Mismatches occur with the interfaces of the SHEL model as no human is perfect. Even though aircraft have developed technologically over the last 50 years the human being has not evolved at the same rate. New equipment can surpass the human capability to effectively operate it. All humans make mistakes - All pilots make mistakes. But remember, not all mistakes lead to disasters. The simple error model below illustrates the effect a pilot can have on a flight: PILOT ⇒ ERRORn ⇒ DISASTER Where ERRORn is a sequence of more than one error. The F28 accident at Dryden, Ontario, in March 1989 is a good example of how this model works. On the face of it, this was a clear cut case of pilot error. The immediate cause of the crash was the failure of the flight crew to obtain adequate protection against wing icing prior to departure. The inquiry yielded a 6 volume report; probably the most exhaustive air accident report ever. The conclusion: “The accident was not the result of one cause but of a combination of several related factors. Had the system operated effectively, each of the factors might have been identified and corrected before it took on significance. This accident was the result of a failure in the air transportation system as a whole.” Each sequence of this model needs to be attacked. PILOT ⇒ ERRORn Remedy ¾

Training - manuals, simulator training.

¾

Cross monitoring, 2 pilot operation.

¾

Crew fatigue and stress.

ERRORn ⇒ DISASTER Remedy ¾

Technology - weight on wheels switches, computer control.


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27 November 2003

Cockpit/aircraft design.

¾ Pilot Error

The phrase Pilot Error is peculiar to aviation; there is no equivalent in the civilian world Doctor Error, Engineer Error etc. The phrase is “falling from grace” especially with the advent of better Human Factors training. However, there is a need to evaluate the human response to the above error progression. Crew Resource Management (CRM), Multi-Crew Cooperation (MCC) and Human Factors training all play a role in ensuring the safety of the aircraft, crew and passengers. CRM and MCC are discussed in a later chapter. In aviation terminology an "incident" is a dangerous event but with no serious consequences. According to Frank Bird, for every fatal accident there are 600 incidents with no accident potential.

1

Disabling Injury – Fatal Accident

10

Minor Injury – Accident/Incident

30

Property Damage – Incident

600

No Injury or Damage – Errors/Near Accidents

The conventional way to represent the role of Human Factors in accidents is to count each accident where there was clear human error involvement. Looking at fatal accidents, if we list the human factors contributions to these fatalities, the top 4 causes are: Controlled flight into terrain (CFIT)

2169

Maintenance and inspection

1481

ATC and Comms

1000

Approach and Landing without CFIT

910

To further explain the error model the James Reason Swiss Cheese Model is used. James Reason Model To explain the Frank Bird model we can break down the above diagram into a what is termed the Swiss Cheese Model. Aviation can be broken into two failure areas:


1-7


Active Failures

Errors and violations by the human element – the pilot

Latent Conditions Resident pathogens that may lie under the surface for years We cannot prevent the latent conditions, we can only make them visible to those who manage and operate the system. All decisions, even the good ones, will have a downside for someone, somewhere in the system. The resident pathogens are more difficult and this is where the model, shown below, is important. The resident pathogens may lie dormant for years. All pilots make errors. Put this with the immediate mental precursors of an error - distraction, preoccupation, forgetfulness --then the sequence of the Error model is being put into place. All that is needed is for the resident pathogens to occur together (Errorn). Then the holes in each part of the model line up and the accident will occur (Sequence a). Where the errors occur and the holes are not matched then the sequencing will stop - and no accident will occur (Sequence b).

Design and development Manufacture Acceptance into Airline Service Development of technical servicing procedures

Sequence b

Implementation of SOP's

Accident

Sequence a

Confidential Human Factors Incident Reporting Programme (CHIRP) A totally confidential reporting system about Human Factors incidents that do not get reported. CHIRP is a charitable company run from RAE Farnborough. Similar schemes are run on behalf of the national Civil Aviation Authorities throughout the world. CHIRP is outside the control of the CAA. Feedback, a 3 monthly magazine, is produced that covers a wide range of Human Factors topics such as: ¾

Sleep and Fatigue

¾

Stress

¾

Communication

¾

Operating difficulties

¾

Technological problems

This system relies on the honest reporting of any incident or occurrence. Flight Crew, Cabin Crew, Engineers and ATC controllers can make reports. For Example:


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27 November 2003

I had two early mornings on two consecutive days to do two European flights and I was rostered for a night standby the following day at 0830L and did not sleep again that day. At 1900L crewing phoned to call me in for a UK - Europe - UK on which the crew were already into discretion. All went according to plan and I still felt fine as we set off from Europe for the UK (0300L). Due to the overlap of duty times we had three pilots on the flight deck and as always there was more stimulation and conversation than usual and I didn't start to feel jaded until the last 90 minutes of flight. With one hour to go I really started to feel tired but thought I should be able to last the flight without falling asleep. At the top of descent my eyes closed for the first time and I was in somewhat of a dozy state during the descent. I still felt, however, that I could make a big final effort during the last 10 minutes of the flight when there was more activity. Going downwind for landing, the approach checks, RT calls and then the flap setting did increase the activity but I simply felt worse than ever. Commands/actions were followed immediately by falling asleep again. On final approach I found myself being woken up as the Captain was asking for gear down, flaps etc. When we finally landed I felt dreadful and possibly the worst in many years of flying. There are obvious safety implications from this incident not the least of which was my driving home (0830L) afterwards. The irony of the situation was that the two pilots in discretion had been accommodated by crewing and felt fine whereas I was still within my allowed FDP and felt like death. I think that standby duties during late evening/early morning are almost impossible to rest and prepare for properly but can be acceptable with good rostering. I swear I will never accept an early morning duty followed by late evening standby on the roster again. Study and Sleep Learning Styles Learning "Parrot Fashion" was once the only form of learning in most schools. Nowadays, this system has changed to one where the student is expected to learn, understand and apply the material taught. This is no different in ab-initio pilot training, you will be presented with copious amounts of material to help you pass your groundschool exams. But what is essential to pass the exams? Lecture and Revision Notes The following is written for a full time student but the revision techniques apply to all. However, the means of study and revision note taking apply to Distance Learning. Students have to develop a method of copying the information that a lecturer is trying to pass on. This is usually done by note taking. Taking notes does help people remember what was said, and taught, in lectures. To ensure that notes are effective takes practice; it is not an easily acquired skill. The initial difficulty any student has is to decide what to write down. A student cannot write down everything that is said; how do you sift out the wheat from the chaff? This chapter is designed to help a student make notes of value such that revision is made easier.


1-9


One good way to start is to sort out what has to be learnt into: M

-

What I must Memorise

U

-

What I must Understand

D

-

What I must be able to Do

Common Problems ¾

The student has no control over how fast the lecturer delivers the lesson.

¾

How much material does the student need to write down; in note taking, more is not necessarily better.

¾

Too much detail means little time is spare for thinking about what is being taught.

Taking detailed, accurate notes, requires the student to pay attention to everything that is said. Therefore, the time that a student needs to think about what notes to take is as important as the time that attention is paid to what the lecturer is saying. Remember, borrowing notes is never as effective as writing the notes during a lecture. The starting point for any note taking must be the building of an effective framework from which to work. Note Framework: Subject Heading. The lecturer will always write or state the lesson objective. This must be the starting point. Sub Heading. The lecture will be split up into minor topics each with its own explanations. Calculations. Any calculation made by a lecturer must be included. Ensure that you copy all calculations exactly as they have been written on the board. Review of Notes Notes should be made by making connections with all the related material (MUD). It is important to review any notes as soon as possible after they have been taken. If this review is done at an early stage it is possible to relate them to text book material. Remember, the notes have to be used at a later date for revision. Methods of Learning As examinations approach, the student needs to be able to recall and use the information that has been taught. Common Problems

Unsuccessful students try to read the material straight off:


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27 November 2003

¾

No allowance is made for difficult sections of text.

¾

If a portion of text is not understood, then the student ignores it.

¾

Text is skipped over, not read comprehensively.

Revision Style Successful students monitor their performance. ¾

A study plan is made and followed.

¾

Difficult sections are re-read till understood.

¾

Periodic reviews are made of the material

Effective learners need to: ¾

Understand the material that has been taught.

¾

They must be able to relate the facts learnt to other course material.

¾

They must be able to organise this material into easily remembered, and easily accessible, facts.

Revision Method To help with revision the SQ3R method can be used. This method of revision is a successful way for remembering textbook material. The SQ3R way of learning is: SURVEY Do not begin by reading the material. Look at the subject headings, bold type headings or italic terms. Obtain an idea of how much material is to be learnt or discussed. Decide on how to split the text into easily learnt packages. QUESTION be learnt.

Before reading each section ask yourself questions about what is to

READ Read the text. Think about the material as it is read. Ask questions of understanding and complete calculations if necessary. If text is not understood - DO NOT PROCEED. Ask for help at this stage, from other course members or staff members. Make sure all the material is understood before progressing to the next part of the revision package. RECITE At the end of each major section recite the major points to yourself. Do not skip over any areas. As you become more familiar with the information being presented, then the temptation is to miss out large chunks of material that you think you know. REVIEW The most important section. Review all the material learnt by using reciting or questioning techniques. Using other course members, in question and answer sessions, helps to reinforce all the material learnt.


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Relaxation Make sure that you take breaks during the learning process. Revision can be tedious, especially if there is a lot of text to be learnt. Short breaks every hour make sure that you stay refreshed during the toil. Do not revise one subject a night, this will lead to boredom; aim to revise 2 or more subjects. Sleep Individuals require differing amounts of sleep. The older you are the less sleep you require. However, people in learning situations do require regular sleep patterns. An integrated flying course requires a student to both fly and carry out an intensive ground school phase. Pressures are such that students start to disrupt their sleep by late night study or worry. Sleep is covered in more detail during the later stages of HPL, this small section is designed to help make a student comfortable in his new environs. ¾

Make the room comfortable - pictures on walls, personal possessions. These all make an area feel comfortable - more like home.

¾

No strenuous exercise immediately before going to bed. This means no physical or mental exercise.

¾

A high level of study activity should be avoided immediately before trying to sleep.

¾

Ensure that after working there is sufficient time to relax. The brain needs time to wind down.

¾

Keep the room ventilated - not too warm, not too cold.

¾

Do not drink too much alcohol. Alcohol induces a coma like sleep where there is no body refreshment.

¾

Try a warm milky drink - NOT COFFEE or tea.

¾

Light reading or listening to music can help relax the mind and body.

Do not jump into bed, straight after finishing studying, and expect to fall asleep immediately. If you find that you are not sleeping well try to stay in bed where it is warm. There is some suggestion that you will get some relaxation and body revitalisation even whilst lying down. Finally DON'T worry.


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27 November 2003

Chapter 2. Aviation Medicine - Respiration and Circulation The Atmosphere The Earth is surrounded by a mixture of gases known as the atmosphere which is held in place by the force known as gravity. The mixture of the atmosphere remains constant and is found to cover the earth up to 30 000 ft at the poles and 60 000 ft at the equator. The boundary of the atmosphere is known as the tropopause.

30 000 ft

60 000 ft

Within the atmosphere there is normally a decline in temperature of approximately 1.98ºC/1000 ft. Pressure also decreases with altitude. Cold temperature increases air density; low pressure decreases air density. Pressure change is the dominant force and as such the air density decreases with altitude. In the atmosphere, small increases in height at low altitude will cause a much greater change in pressure than the same height change at altitude.

Outer Space – No Molecules High Altitude – High Density of Molecules Low Altitude – Very High Density of Molecules


2-1


Measurement of Atmospheric Pressure Standard atmospheric pressure, or barometric pressure, is the weight or force exerted by the atmosphere at any given point. This pressure is expressed in different forms by the method of measurement such as pounds per square inch (psi), millimetres of mercury (HG) and inches of mercury. Millimetres of mercury (mm/HG) are used in these notes. The Standard Atmosphere Continual fluctuations of temperature and pressure in the atmosphere create problems for engineers and meteorologists who require a fixed standard of reference for aircraft. This standard is known as the International Standard Atmosphere (ISA). Conditions throughout the atmosphere for all latitudes, seasons, and altitudes are averaged and published by ICAO. The resultant standard atmosphere has specified sea level temperature and pressure and specific rates of change of temperature and pressure with height. Standard Atmosphere Pressures and Temperatures for Different Altitudes: Sea level

760.0 mm/HG

+15°C

10 000 ft

522.6 mm/HG

-05°C

18 000 ft

379.4 mm/HG

-21°C

33 700 ft

190 mm/HG

-52°C

40 000 ft

140.7 mm/HG

-56.5°C

Physical Divisions of the Atmosphere The divisions of the atmosphere are primarily physical or meteorological in nature. From meteorology we are familiar with both the troposphere and the stratosphere; both of which are important to the aviator and aviation. To look at the Physiological Effects associated with flight the atmosphere can be split into four zones: Physiological Zone This area extends from sea level to approximately 12 000 ft. It represents the area of the atmosphere to which the human body is more or less adapted. Only minor physiological problems exist when flying within this zone. Pilots who go higher than their acclimatized levels notice common symptoms such as middle ear blockage and sinus blockage difficulties, shortness of breath, dizziness and headache. Above this zone we are in an environment to which our body is unaccustomed. Physiological Deficient Zone Existing from 12 000 ft to 50 000 ft this zone, along with the previous zone, is the area in which most flying takes place. Oxygen deficiency becomes an ever increasing problem as we ascend due to the reduced atmospheric pressure. Partial Space Equivalent Zone This zone extends from 50 000 ft to 120 nm, where pressure changes become very small. The problems for flight over 50 000 ft are the same as those encountered in space. Sealed cabins, pressure suits are


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27 November 2003

necessary as problems now occur with blood and body fluids boiling over 63 000 ft. Gravitational changes on the body make this a space equivalent zone. Only Concorde has operated in this zone. Total Space Equivalent Zone True space, this zone extends outwards from 120 nm. The physiological problems of this zone are similar to the previous zone. The air is composed of a mixture of gases of nearly constant proportions: Oxygen

20.94%

Nitrogen

78.08%

CO2

0.03%

Other gases

1%

These proportions remain the same at all levels within the troposphere and up to an altitude of 60 000 ft. ICAO has defined the standard atmosphere which assumes: Pressure

1013.2mb

Temperature

15ºC

Density

1225 gm/cubic metre

The temperature lapse rate of 1.98ºC/1000 ft continues up to 36 090 ft. Above this altitude the temperature remains constant at –56.5°C. Pressure falls 1 hPa per 30 ft gained in the lower levels of the atmosphere (acceptable in the first 5000 ft) A temperature change of 3°C or a 10 hPa change in pressure will change the density by 1%.


2-3


700 600 500 PRESSURE (mmHg) 400

300 200 100 0

0 10 20 30 40 50 60 ALTITUDE (x1000 FEET)

Gas Laws The human body is adapted for life at sea level. If exposed to an altitude of 40 000 ft then a person will become unconscious in a few seconds and dead a few minutes later. Knowledge of the gas laws is essential in explaining the effects of reduced Barometric Pressure on the body. Boyle’s Law For a fixed mass of gas at constant temperature (T), the pressure (P) is inversely proportional to the volume (V). If the pressure on a gas decreases, its volume increases and vice versa. This law, when applied to the body, explains the expansion of gases trapped within the body in areas such as the middle ear, sinuses and gastro-intestinal tract. PxV=C Where:

P

Pressure

V

Volume

C

Constant.

Charles’s Law If the volume of a gas remains constant, the pressure will vary directly with the temperature. Algebraically

PV = RT or PV

/T = R

P

Absolute pressure

V

Volume

R

Universal gas constant


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27 November 2003

T

Temperature

Dalton’s Law In a mixture of gases, the pressure exerted by one of the gases is the same as it would exert if it alone held the same volume. From this the partial pressure of oxygen in the atmosphere can be derived for any altitude, since the pressure at that altitude can be measured and the proportion of oxygen in the atmospheric air is constant. This is of great importance to aviation especially when we discuss Hypoxia. To determine the partial pressure of each gas in the mixture we use the following: Ptotal = ppA + ppB + ppC…. Where Ptotal represents the total pressure of the mixtures of gases and ppA, ppB, or ppC represents the partial pressure of each gas in the mixture. Graham’s Law A gas of high pressure will exert a force towards a region of lower pressure and if a membrane separating these regions of unequal pressure is permeable or semi-permeable, the gas of higher pressure will pass through the membrane into the region of lower pressure. This will continue until the unequal regions are nearly equal in pressure. This law explains the transfer (diffusion) of oxygen, CO2 and other gases from one part of the body to another. Henry’s Law The amount of gas in solution varies directly with the pressure of that gas over the solution. When the pressure of a gas over liquid decreases, the amount of gas dissolved in the liquid will also decrease, or vice versa. This gas law is applicable when Decompression Sickness is discussed when Nitrogen comes out of the blood. General Gas Law A combination of Boyle’s Law and Charles’s Law where P and T signify absolute pressure and temperature, respectively. P1V1 = P2V2 T2

T1

The general gas law applies to "ideal" gases where the molecules are assumed to be perfectly elastic. For practical purposes we accept that the law applies to all gases. The Human Need for Oxygen To live, the human being must produce heat and energy from food eaten. Eaten food is converted into simple food products and transferred to the tissues by the blood. It is then oxidized to provide this heat and energy. To oxidize the food, oxygen has to be supplied to the living cells in the body. The waste product, carbon dioxide, is then carried away from the tissues and expelled from the body. This process is respiration. The definition of respiration is given below:


2-5


“The exchange of the respiratory gases, O2 and CO2, between the organism and its environment.” Respiration The breathing process consists of two phases: Breathing In

Inspiration

Breathing Out

Expiration

The respiratory system is made up of the following: ¾

Mouth and nose

¾

Trachea

¾

Bronchus

¾

Bronchiole tree

¾

Alveoli.

GAS EXCHANGE

AIR

TRACHEA

BRONCHUS

ALVEOLI CAPILLARY NETWORK

BRONCHIOLE

When a human breathes, air is drawn in through the mouth or nose to the Pharynx. The Pharynx, which is found at the back of the throat, warms, humidifies and filters the air before it passes down the trachea into the two bronchi. The bronchi split into the bronchiole tree as the air passes into the lungs. The lungs are set inside the chest cavity, or thoracic cavity, wrapped in an airtight sac called the pleura. At the ends of each branch of the bronchiole tree are air sacs, alveoli. These air sacs are very small and are surrounded by capillaries which are small blood vessels. The thin walls of the alveoli and capillaries allow oxygen to diffuse into the blood and CO2 into the alveoli. The lungs in the average man can hold approximately 6 litres of air, a woman, 4 litres. Tidal Volume The volume of air breathed in and out in a single breath. When resting this is approximately 500 cm3


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27 November 2003

The maximum volume that can be breathed in and out is approximately: Men

2500 cm3

Women

1500 cm3

Inspiration and Expiration The chest cavity is surrounded by the ribs on the sides and separated from the abdominal cavity by the diaphragm, a large flat sheet of muscle. The chest cavity has only one opening. Any change in volume to the chest cavity will ventilate the airspace in the lungs. The chest size is altered by a muscular action that raises and lowers the diaphragm and by contraction and relaxation of the muscles between the ribs. Inspiration and expiration circulate air in and out of the lungs efficiently. 8

4

5

1 7

3

6 2

EXPIRATION 5 RIBS RETURN 6 DIAPHRAGM RELAXES 7 LUNGS RETURN TO ORIGINAL VOLUME 8 AIR EXPELLED

INSPIRATION 1 RIBS RAISED 2 DIAPHRAGM DEPRESSED 3 LUNGS EXPAND 4 AIR DRAWN IN

Gaseous Exchange The constant turnover of air provides the mechanism for both O2 to diffuse into the blood and CO2 to diffuse into the lungs. This gaseous exchange can be explained by looking at the partial pressure each gas exerts. In air outside the lungs the partial pressure of O2 is 160 mmHg. Carbon Dioxide has a low partial pressure in outside air of approximately 0.3 mmHg. The difference in pressure of these gases between the alveoli and the blood is how the gaseous exchange between the lungs and the bloodstream occurs. ¾

Blood entering the lungs has a lower ppO2 than the alveolar air, so oxygen diffuses into the blood


2-7


¾

The ppCO2 is higher in the blood entering the lungs than in the alveoli, so CO2 diffuses out of the bloodstream and into the lungs

TRACHEA (WINDPIPE)

RESPIRATORY BRONCHIOLE

CO 2 CO 2 O2 O2

PULMONARY ARTERY

LUNG

CO 2

O2 CO2 O2

BRONCHI BROCHIOLES

ALVEOLI PULMONARY VEIN DEOXYGENATED BLOOD OXYGENATED BLOOD

Most of the oxygen is taken into the blood, and carried, by the protein haemoglobin. Haemoglobin is found within the red blood cells and is an Iron rich compound. The Haemoglobin bond ensures that the body can receive enough Oxygen for the body’s needs. If blood diffused directly into the blood solution only, then the body would be starved of sufficient Oxygen necessary for the human to survive. Oxygen remains bound to the haemoglobin until it reaches the tissues of the body, an area of low oxygen tension. This oxygen is then released into the tissues to oxidize food. About 95% of the oxygen is transported by haemoglobin, as an oxy-haemoglobin bond, and the remainder is diffused directly into the blood solution. Some Carbon Dioxide binds to the haemoglobin but the majority diffuses into the blood and is carried in solution as carbonic acid. Both Oxygen and Carbon Dioxide bind weakly to the Haemoglobin as a strong bond would result in difficulties in releasing the gases to either the tissues or the lungs. Control of Breathing Control of breathing is centred in the respiratory centre of the brain. The human requires no conscious effort to breathe; although the rate of breathing can be altered voluntarily. Inspiration is the active phase of breathing; expiration the passive phase. The rate and depth of breathing can be adjusted to meet any change in the consumption of oxygen and expiration of carbon dioxide. Under normal conditions the body is slightly alkaline (pH7.4). During respiration: ¾

The partial pressure of carbon dioxide elevates


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27 November 2003

¾

The acidity level increases

¾

The pH value lowers to less than 7.4

Any increase in the CO2 concentration in the blood stimulates an increase in the ventilation rate. As blood flows through muscle capillaries the dissociation of oxy-haemoglobin to release oxygen is increased by: ¾

Low O2 concentration in muscle tissue

¾

High CO2 concentration

¾

High temperature

Too little CO2 causes the blood to become more alkaline and the pH value to rise. The human body maintains the equilibrium within narrow limits, any shift in the blood pH and ppCO2 levels are sensed by the respiratory centres of the brain. When unusual levels occur, chemical receptors trigger the respiratory process to help return the ppCO2 and pH levels to normal limits. For the uptake of O2 by the blood and the release of that O2 to tissues the extreme limits of the pH of the body are regarded to be 7.2 to 7.6. The brain monitors the levels of both carbon dioxide and oxygen in order to make any changes in the respiration rate. Note:

A healthy body is more sensitive to changes in the carbon dioxide balance of the body than to oxygen.

The Circulatory System The circulatory system is concerned with the transportation of blood throughout the body. The blood has the following functions: ¾

The carriage of oxygen and the carriage of carbon dioxide

¾

The carriage of food

¾

The carriage of nitrogenous waste

¾

The carriage of hormones or chemical messengers

¾

The protection of the body against disease

¾

Regulation of body temperature

The circulatory system centres on a muscular pump - the heart. The heart is a hollow organ with a wall made of three layers: The Pericardium

The outer layer

The Myocardium

The middle layer

The Endocardium

The inner lining of the heart cavities


2-9


This heart is made up of four chambers; Two atria which are thin walled, the suction chambers, and two ventricles which are thick walled, the discharge chambers. The Ventricles The left ventricle, which pumps blood around the body, has a much thicker wall than the right ventricle, which only pumps blood to the lungs Separation of the Atria and the Ventricles separated by the atrio-ventricular valves:

The

atria

and

ventricles

Tricuspid Valve

Separates the right atrium from the right ventricle

Mitral Valve

Separates the left atrium from the left ventricle

are

HEART AND BLOOD FLOW

Right Atrium Two veins enter the right atrium, the inferior vena cava and the superior vena cava. These veins bring blood back to the heart from all of the body except the lungs. Blood from the right atrium passes into the right ventricle and then into the pulmonary artery to the lungs Left Atrium Blood from the four pulmonary veins runs into the left atrium. This blood is passed into the left ventricle which is connected to the main artery which passes blood to all parts of the body except the lungs. This main artery is known as the Aorta The blood is circulated around the body by a network of flexible tubes, the blood vessels Arteries Strong, muscular and elastic walled vessels, arteries carry mainly oxygenated blood. All arteries flow away from the heart. The exception is the pulmonary artery which carries de-oxygenated blood from the heart to the lung.


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Veins Thin walled vessels, with one way valves, veins carry mainly de-oxygenated blood back to the heart. The exception is the pulmonary vein which carries oxygenated blood from the lungs to the heart. Capillaries Arteries sub-divide to form a dense network of fine thin-walled blood vessels known as capillaries. The thin capillary walls allow the exchange of gases and other material between the cells of the body and the blood. The capillaries eventually rejoin passing through the tissues to become veins. Composition of the Blood Blood is a complex tissue made of different kinds of cells, free proteins, other chemicals and factors and water. The average adult has about 6 litres of blood circulating in the body. Blood consists of a clear yellow fluid (plasma) and solids. Approximately 90% of the plasma is water, in which other substances are dissolved or suspended. The most important solids in suspension are Red blood cells The red blood cells are formed in the bone marrow and contain a red pigment, haemoglobin. This is also the protein that carries oxygen to the tissues. Haemoglobin is an iron-containing compound. The iron that is in the haemoglobin molecule is responsible for the chemical affinity of haemoglobin for Oxygen and Carbon Monoxide. White Blood cells Several kinds of cells found in the blood are colourless or white in appearance. All of these cells play a role in protecting the body from disease. The white blood cells are formed from “stem cells” found in the bone marrow. These cells mature into the specialized forms that protect the body from infection. Although these white cells are located in the blood, they function as part of the body’s immune system. Platelets Platelets help the blood clot. When a blood vessel is severed or torn the damaged ends constrict and retract in order to minimize blood loss. Almost immediately the blood that is escaping from the damaged vessel begins to clot. Platelets congregate at the site of the injury and release clotting factors. These clotting factors start to convert one of the blood substances, fibrinogen, into the protein, fibrin. Fibrin forms a dense weblike structure that in turn traps more platelets. This forms into a jelly like clot taking about 10 minutes. As the clot hardens it begins to shrink, releasing a watery substance, serum. The serum carries antibodies to combat infection and specialized cells that begin the process of repair. Together the above cells account for 45% of the blood’s total volume the remainder is called plasma. Plasma Plasma is a yellow, slightly alkaline fluid consisting of 90% water and 10% solid matter. The composition of the plasma is controlled mainly by the kidneys, these solids include:


2-11


¾ Proteins ¾ Amino acids ¾ Fats ¾ Glucose ¾ Urea and other nitrogenous waste ¾ Salts Blood Circulation The cycle of blood flow through the body is as follows: ¾

Blood from the right atrium is pumped into the right ventricle

¾

From the right ventricle the blood goes into the pulmonary artery which carries blood to the lungs

¾

In the capillaries of the lungs, gaseous exchange occurs: ¾

Oxygen is taken into the blood

¾

Carbon dioxide is passed into the lungs

¾

The freshly oxygenated blood returns to the left atrium of the heart via the pulmonary veins

¾

The left atrium empties into the left ventricle which is connected to the aorta

¾

Contraction of the left ventricle forces blood into the aorta, the major artery which is connected to the rest of the body save the lungs

¾

The aorta divides into arteries that carry the blood to the tissues. These arteries divide into capillaries which give off the oxygen and take up carbon dioxide before the blood returns to the heart

¾

All blood returning to the heart collects in the superior or inferior vena cava which feed directly into the right atrium


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27 November 2003

OXYGENATED BLOOD DEOXYGENATED BLOOD DIRECTION OF

HEAD AND ARMS

FLOW BLOOD

AORTA

LUNG

PULMONARY ARTERY

VENAE CAVA E

LUNG

PULMONARY VEIN LEFT ATRIUM RIGHT ATRIUM LEFT VENTRICLE

RIGHT VENTRICLE

LIVER

INTESTINE

HEPATIC PORTAL VEIN

KIDNEYS

LEGS

Further Uses of Blood Circulation As the blood passes through the body the following organs carry out the following functions: Stomach

Nutrition from food is picked up and carried along to the tissues

Spleen

Old blood cells are taken out of circulation

Liver

Removes toxins and adds proteins to the blood

Kidneys

Adjust the water content and remove waste products

Bone Marrow Helps renew white blood cells


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Intentionally Left Blank


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27 November 2003

Chapter 3. Aviation Medicine - The Effects Of Altitude Introduction The atmosphere is a mixture of gases of constant proportions up to an altitude of 60 000 ft. The approximate figures are: Oxygen

21%

Nitrogen

78%

Other gases

1%

As altitude increases, pressure and density decrease and the amount of Oxygen available to the red blood cells decreases. Two gases cause further complicating factors: Water Vapour

Ever present in the atmosphere, water vapour content varies depending upon the climatic conditions. In the lungs, the alveolar air is always saturated with water vapour. This accounts for 6% of the volume of air in the lungs at sea level.

Carbon Dioxide

The amount of carbon dioxide in the atmosphere is approximately 0.03%. In the lungs, because of the respiration process, the amount of CO2 is higher; equivalent to 5.5% of the available volume at ground level.

These gases have to be taken into account when considering the amount of Oxygen available to the respiration process. At sea level, because of the amount of water vapour and CO2, the volume of Oxygen in the lungs available for the respiration process is reduced to 14.5%. Tracheal air When inhaled air is drawn into the respiratory passages, it becomes saturated with water vapour and is warmed to body temperature. This water vapour has a constant pressure of 47 mmHg at normal body temperature. This is regardless of the barometric pressure. The inspired gases available for the respiration process are reduced by the amount of water vapour present. Alveolar Air The tracheal air enters the lungs and Oxygen and CO2 are exchanged in the respiration process. The expired air has less Oxygen and more carbon dioxide content. The partial pressure of O2 (ppO2) in the alveoli varies with the CO2 partial pressure. A constant,


3-1


ventilation rate creates a CO2 partial pressure of approximately 40 mmHg. Using these values the ppO2 at any altitude can be calculated. Where:

P

Ambient barometric pressure in mmHg

F

The fractional percentage of the inspired gas

ppH2O(tr)

Water vapour partial pressure constant at 47 mmHg at 37oC

ppO2(tr)

Tracheal Oxygen partial pressure

ppCO2(alv)

Alveolar carbon dioxide partial pressure constant at 40 mmHg with normal ventilation rate

ppO2(alv)

Alveolar Oxygen partial pressure

To calculate tracheal gas: ppO2(tr) = (P - ppH2O(tr)) x F In the transition from tracheal air to alveolar air, the ppO2 is reduced and ppCO2 is increased. We assume that the ppN2 remains constant. To calculate alveolar gas: ppO2(alv) = ppO2(tr) - ppCO2(alv) Example

At 10 000 feet the air pressure is 523 mm Hg, using 21% as the percentage O2. What is the alveolar partial pressure of O2?

Step 1

Calculate the tracheal gas: ppO2(tr) = (P - ppH2O[tr]) x F ppO2(tr) = (523-47) x 0.21 = 99.96 mm Hg

Step 2

Calculate the alveolar gas: ppO2(alv) = ppO2(tr) - ppCO2(alv) ppO2(alv) = 99.96 mm Hg - 40 mm Hg = 60 mm Hg The calculated alveolar partial pressure of Oxygen in the lungs is 60 mm Hg at 10 000 ft altitude.


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27 November 2003

A pressure gradient is required to ensure that Oxygen diffuses from the alveoli into the red blood cells. If this pressure gradient falls, Oxygen movement into the blood is impaired. Some degree of protection is given to the body up to 10 000 ft because of the affinity of haemoglobin for Oxygen. The body has a “surplus” of Oxygen for use to this height. Above 10 000 ft the partial pressure of Oxygen in the alveoli falls off rapidly and the over protection is lost. The body begins to suffer from a lack of Oxygen; a process known as Hypoxia. Forms of Hypoxia Hypoxic Hypoxia. Caused by an insufficient partial pressure of Oxygen in the inspired air. This reduction of Oxygen becomes apparent above an altitude of 10 000 ft. Most likely in aviation when an aircraft has a decompression. Anaemic Hypoxia. Anaemic Hypoxia, also known as Hypaemic Hypoxia, is caused by a reduction in the Oxygen carrying capacity of the blood. This reduction can be caused by a lowering in the amount of circulating haemoglobin, Anaemia. Haemoglobin forming a bond with carbon monoxide produces the same result. Stagnant Hypoxia. Defined as an Oxygen deficiency in the body due to poor blood circulation. Caused by a failure of the circulatory system. When flying, this type of Hypoxia, can be caused by problems such as pressure breathing or excessive "G" forces. Histotoxic Hypoxia The inability of the body to utilize Oxygen. Caused by a failure of the body tissues to use the available Oxygen efficiently because of impairment to cellular respiration. Poisons such as drugs and alcohol are the usual cause. Oxygen Requirements As altitude increases the Oxygen pressure decreases: ¾

By 8000 ft the atmospheric pressure is only ¾ of the sea level pressure

¾

At 18 000 ft the atmospheric pressure is ½ that at sea level

¾

By 33 500 the atmospheric pressure is ¼ of the sea level pressure

As altitude increases, the percentage of Oxygen that needs to be added to the gas a pilot breathes needs to increase to ensure that the alveolar partial pressure is maintained. Alveolar Partial Pressure: Sea Level

103 mm Hg

10 000 ft

61 mm Hg


3-3


Above 10 000 ft extra Oxygen needs to be added. The percentage of Oxygen added increases until 33 700 ft where 100% Oxygen is required to give the equivalent alveolar partial pressure to that at sea level (103 mmHg). Above this height the partial pressure can be allowed to fall to the 10 000 ft equivalent of 61mmHg - this occurs at 40 000 ft. Above 40 000 ft positive pressure breathing, the forcing of Oxygen under pressure into the lungs, is required. Summary of Oxygen Requirements HEIGHT

OXYGEN REQUIREMENT

ALVEOLAR PARTIAL PRESSURE

0 - 10 000 ft

Air only

103 mm Hg

10 000 - 33 700 ft

Increasing percentage of Oxygen required

61 mm Hg As % of 02 increases so the equivalent partial pressure increases

33 700 - 40 000 ft

100% Oxygen required

103 mm Hg falling to 61 mm Hg by 40 000 ft.

40 000 ft +

100% Oxygen supplied by pressure breathing

-

The above figures refer to the actual height. Modern aircraft are pressurised to a cabin altitude of approximately 6 - 8000 ft. The temperature is easily controlled and mental functions can be retained. Some older people or those who suffer from respiratory disease may suffer from Hypoxia at these levels. In an ideal world, the aircraft would be pressurised to sea level. In reality this is impracticable because of the weight and strength parameters that would have to be achieved. Hypoxia Hypoxia occurs when the Oxygen available in the blood supply is insufficient to meet body tissues needs. The greatest risk of Hypoxia to a pilot is normally a result of a rise in altitude associated with a fall in pressure. Early signs of Hypoxia are related to the higher mental functions and are similar to those of alcohol. The rate of onset depends on the altitude: 15 000 ft

The signs and symptoms are relatively slow in onset and difficult to detect.

40 000 ft

The signs and symptoms are so quick that an individual may not recognise what is happening.

In 1979 a Beech Super King Air was flying westwards at FL 310 along the south coast of England on a conversion exercise. As it approached Exeter the crew asked ATC for permission to practise an emergency descent. This was granted and they were instructed to execute a right hand turn and contact Exeter ATC as they initiated descent. The crew acknowledged this instruction, adding that they 'would be out of contact for a few seconds as they would be donning masks and things'. Shortly afterwards the aircraft entered a turn to the left, which became a left orbit. The aircraft continued to orbit left for the next 6 hours, slowly


3-4

27 November 2003

drifting southwards with the wind until it crashed in north east France. No further contact had been made with the crew. During the investigation into the accident it was discovered that the training captain had, whilst conducting such flights with previous students, actually depressurised the aircraft and Oxygen masks had been really necessary. Examination of the wreckage revealed that the pilots had donned their masks but that the mask hoses had not been fully connected to the Oxygen supply system. Further testing in an identical aircraft depressurised at FL 300, with descent initiated as soon as the test commenced, revealed that a doctor taking his mask off at such an altitude was rendered incapable after 15 seconds and unconscious after 30 seconds. In this accident when the crew were breathing air these test times would have been reduced by a significant amount, causing rapid onset of Hypoxia with death following in a few minutes. Signs and Symptoms of Hypoxia Mild Hypoxia may produce a state similar to drunkenness. More serious cases will result in coma. All episodes of Hypoxia are damaging to tissues. If exposure is prolonged then damage may be permanent; the most vulnerable area being the brain. At normal body temperatures the brain is unable to tolerate total lack of Oxygen for more than 3 minutes without irreversible damage. The symptoms of Hypoxia are many and individuals will differ in their reactions to the onset. The symptoms are listed below: Personality Change

Changes in behaviour occur. The mild mannered may become aggressive in nature. A “Laissez Faire” attitude is also apparent at this stage.

Impaired Judgement

Lack of self-criticism. The sufferer is usually the last person to see any deterioration in performance.

Muscular Impairment The pilot begins to lose muscular co-ordination. Accurate flying becomes difficult. Minor errors quickly turn into major events. Memory Impairment

Short term memory is lost. Simple arithmetic problems become difficult and accuracy in calculation is difficult. Long term memory actions can still be accessed.

Sensory Loss

Colour vision is affected very early in the onset of Hypoxia. Touch becomes dull,hearing becomes limited and spatial orientation problems may occur.

Cyanosis

The extremities of the body become blue in colour. Haemoglobin in the de-oxygenated state gives the capillaries this bluish tinge.

Hyperventilation

As a pilot begins to suffer from the onset of Hypoxia the need for Oxygen results in a tendency to overbreathe.


3-5


Other sensations include tingling or warm sensations, sweating, headache and nausea. All the above symptoms will be experienced by a person suffering from Hypoxia; however, each person will exhibit his own symptom pattern which occurs on each exposure to Hypoxia. Impairment of Consciousness As Hypoxia progresses so does an individual's level of consciousness. Initial confusion is followed by semiconsciousness and unconsciousness. Without Oxygen, DEATH will follow. Stages of Hypoxia There are four stages of Hypoxia which vary according to the altitude and the severity of symptoms. Indifferent Stage Night vision shows the effects of Hypoxia. A loss of 40% of night vision can be experienced at altitudes as low as 4000 ft. Compensatory Stage The circulatory and respiratory system provide a defence against Hypoxia. Pulse rate, systolic blood pressure, circulation rate, and cardiac output increase to offset the lack of Oxygen. Respiration will increase in rate and depth. At 12 to 15 000 feet the effects of Hypoxia on the nervous system are increasingly apparent. After 10 to 15 minutes, the impairment in efficiency becomes obvious. Crewmembers start to become drowsy and frequent errors of judgement are made. Simple tasks become difficult, especially those requiring alertness or moderate muscular co-ordination. At these altitudes Hypoxia is slow in onset and is difficult to detect especially in the hard working environment of the modern cockpit. Disturbance Stage The body can no longer compensate for the Oxygen deficiency. Occasionally, pilots become unconscious from Hypoxia without undergoing the subjective symptoms; Fatigue, sleepiness, dizziness, headache, breathlessness, and euphoria are the symptoms most often reported. However, the symptoms above are all valid. Critical Stage Within three to five minutes, judgement and co-ordination usually deteriorate. Subsequently, mental confusion, dizziness, incapacitation, and unconsciousness occur. Susceptibility to Hypoxia Susceptibility to Hypoxia can be increased by the following: Altitude

At higher altitudes Hypoxia onset can be measured in seconds not minutes.

Time

The longer the pilot is without Oxygen the greater the effect.

Exercise

Exercise increases the need for the body to produce more energy. Hence, the need for more Oxygen.


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27 November 2003

Cold

When cold, the body uses energy to get warm. To warm the body heat is generated from the oxidation of food.

Illness

Illness increases the demands on the body’s need for energy..

Fatigue

Tiredness and fatigue lower the body’s resistance to the onset of Hypoxia.

Drugs/Alcohol Hypoxia impairs the body’s higher mental functions. Drugs and alcohol have a similar effect. The combination of the two has an obvious cumulative effect. Smoking

CO has a greater affinity for haemoglobin than Oxygen. By reducing the amount of haemoglobin available for an Oxygen bond the body is already part way to being Hypoxic.

Time of Useful Consciousness The definition of the Time of Useful Consciousness is accepted as: “The time available to a pilot to recognise the development of Hypoxia and do something about it” This is not a time to loss of consciousness. ALTITUDE

TIME OF USEFUL CONSCIOUSNESS

45 000 ft

12 Seconds

40 000 ft

10 - 20 Seconds

35 000 ft

30 seconds

30 000 ft

45 - 75 Seconds

25 000 ft

2 - 3 Minutes

18 000 ft

30 Minutes

Limitations of Time at Altitude An aircraft not equipped with Oxygen should not fly at altitudes above 10 000 feet for extended periods of time. Specific time and altitude restrictions are stated in JAR-OPS. An unpressurised aircraft should not exceed 14 000 ft without supplemental Oxygen being used.


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Hyperventilation The respiratory controls of the body react to the amount of CO2 in the blood. During exercise the body uses more Oxygen and more CO2 is produced. This means that an excess of CO2 will be present in the blood. The respiratory centre, in the brain, reacts to this surplus and the rate of breathing increases in both depth and rate. This increase in breathing rate removes the excess CO2 from the body. Once this excess is removed the breathing rate returns to normal. Hyperventilation is an increase in the rate of breathing which removes carbon dioxide from the body faster than is required. This induces a lowering of the acidity of the body. Hyperventilation may be a side effect of Hypoxia, but the following can induce an attack: ¾

Anxiety or emotional stress

¾

Pain

¾

Motion sickness

¾

Heat

¾

Turbulence

¾

Vibration

Symptoms of Hyperventilation ¾

Dizziness and light headedness

¾

Tingling in the hands, feet and around the face

¾

Stiffening of hands and fingers and increasing stiffness of other limbs and muscles

¾

Visual Disturbance including tunnelling or clouding of vision

¾

Hot or cold flushes

¾

Anxiety and worry causing a vicious circle of effect and cause.

¾

Impaired performance

¾

Loss of consciousness leading to collapse. In the case of collapse respiration returns to normal and an individual recovers.

Treatment of Hypoxia and Hyperventilation The symptoms of Hypoxia and Hyperventilation are so similar that to differentiate between them can be difficult. Use the following guidelines: Above 10 000 ft

Assume Hypoxia, Oxygen must be given to the sufferer. A descent below 10 000 ft is essential.

Below 10 000 ft

Hypoxia should not be a problem except in those people who are old or have respiratory problems. The rate and depth of breathing should be slowed down. If hyperventilation is identified as the problem then re-breathing the expired air


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27 November 2003

can help the recovery. Restricting the breathing by use of a sick-bag or Oxygen mask are common methods used. Cabin Decompression Cabin pressurisation failures can occur at any time during flight. The rate of loss of pressure can be: ¾

Very slow which allows time for a pilot to recognise and deal with the problems promptly, or

¾

Very rapid if the decompression is due to the loss of a door or window.

For a Public Transport aircraft like the B747: Loss of a door

The pressure will equalise in approximately 12 - 20 seconds.

Loss of a window

The pressure equalises in approximately 60 - 90 seconds.

In smaller aircraft the pressure will equalise in a much shorter time. During a rapid decompression there will be a sudden explosive bang and the cabin will fill with fog, dust and flying debris. The fog occurs due to the rapid drop in temperature and the change in Relative Humidity. Normally the ears will clear automatically. Belching and the passage of intestinal gas will occur. Air escapes from the lungs through the mouth and nose. In such a case the crew are immediately exposed to the following problems; ¾

Hypoxia

¾

Cold

¾

Decompression Sickness

Oxygen is needed to avoid Hypoxia and a descent is required to a safe altitude below 10 000 ft. Where structural damage has occurred, the descent must be made at a rate that the damage allows. Emergency descents are not normally made in Public Transport aircraft for a rapid decompression as supplementary Oxygen is provided. During rapid decompression the cabin altitude may rise above aircraft altitude due to a venturi effect. Aerodynamic suction occurs where the air on the outside, passing over the defect in the hull pulls air out of the cabin. The difference between cabin and aircraft altitude can differ by as much as 5000 ft. If flying in a pressurised aircraft, which has a rapid decompression, then the Time of Useful Consciousness will be reduced. The rapid reduction of pressure in the aircraft will affect the body. Oxygen is exhaled from the lungs due to this pressure change. The partial pressure of


3-9


Oxygen in the blood is reduced and the Time of Useful Consciousness can be reduced by up to ½ the normal time eg

For a rapid decompression at 30 000 ft the Time of Useful Consciousness will be 25 - 30 seconds (The time for 35 000 ft).

In the event of a decompression or suspected pressure loss the first action that the crew must take is to ensure a sufficient oxygen supply by donning their own oxygen masks. Climb and Descent Any air or gas contained within the body will expand or contract with any change in pressure. Climb The following problems can occur when there is an increase in altitude: Lungs and Intestine

Gas collects along the gastro-intestinal tract because of:

Eating

When we eat, air is swallowed with the food we eat.

Bacteria

Gas is formed in the intestines by the action of bacteria on food.

The gas in the stomach or intestines expands during a rapid decompression. If this gas is not released to the atmosphere, severe pain can be experienced. Damage to the lungs, or even rupturing (pneumothorax - air between the lung and chest wall) can occur if pressure changes are extreme. Normally the rib cage will protect the respiratory system. Teeth Good dentistry ensures that teeth are filled correctly and the oral health of the pilot is maintained to a high standard. Poor oral hygiene can result in abscesses, poor dentistry can lead to air pockets being left in filled teeth; both can cause pain during a decompression due to the expansion of gases. Decompression Sickness Decompression sickness is caused by inert gases, mainly nitrogen, coming out of solution into the body's tissues due to exposure to reduced atmospheric pressure. When breathing air at sea level, the body is normally saturated with nitrogen. When the ambient pressure is reduced by increasing altitude, the body becomes super-saturated with nitrogen. Some of this nitrogen can come out of solution as bubbles in joints, the skin or the chest. Depending on the location, and the extent of bubble formation, the symptoms can vary. The common names for Decompression Sickness and the location in the body are listed below: Bends

Painful joints such as the knees or elbows


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27 November 2003

Creeps

Itching in the skin that may be accompanied by a rash.

Chokes

Pain in the chest with a dry hacking cough.

Nervous System Effects

Possible paralysis and a loss of vision.

Staggers

Loss of balance which is similar to the actions of a drunk.

Collapse

Unconsciousness, death may occur.

Certain conditions make decompression sickness more likely: Altitude

Cabin altitudes greater than 18 000 ft. Above 25 000 feet the chances of suffering from decompression sickness are greatly increased.

Duration

The longer a person is at altitude the more likely the chance of decompression sickness

Age

Age seems to affect the onset

Weight

Obese and overweight people are more susceptible.

Diving

Diving allows the body to “super saturate” with Nitrogen. An increased altitude allows this Nitrogen to come out of solution.

Rate of Climb The faster the rate of climb the faster the onset. Exercise

The parts of the body that are most used in exercise are those that are most susceptible.

Other Factors Fatigue, Alcohol, Hypoxia and cold Re-exposure Flying within 24 hours of suffering from Decompression Sickness will increase a pilot’s susceptibility of contracting the problem again. 48 hours should be the minimum time allowed to elapse before flying again.


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Treatment of Decompression Sickness Decompression sickness can be avoided by pre-oxygenation (breathing 100% Oxygen before flight) and then breathing 100% Oxygen during flight. This saturation of the body with Oxygen reduces the Nitrogen saturation and reduces risk of Decompression Sickness. If Decompression Sickness does occur: ¾

Descend immediately

¾

Land as soon as possible.

¾

Use 100% Oxygen.

¾

Keep the patient warm.

¾

Recompression in a barometric chamber may be required after landing.

¾

Do not rub affected parts.

Flying and Diving Diving before flight increases the risk of Decompression Sickness. If compressed air is used under pressure, the body's store of nitrogen is increased. As an ascent is made, nitrogen comes out of solution - thus causing Decompression Sickness. Do not fly within 24 hours of SCUBA diving. Decompression Sickness can occur as low as 6000 ft after diving. Modern passenger jets are pressurised to altitudes between 6 - 8000 ft. Descent The ear and the sinuses are parts of the body that suffer most in the descent. Sinuses

FRONTAL SINUS

MAXILLARY SINUS


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27 November 2003

Sinuses are air filled cavities in the bones of the skull that form the upper part of the face. They help resonate the voice and make the skull lighter. The frontal sinuses are in the brow of the forehead above the eyes. The maxillary sinuses are larger cavities in the cheek bones. Other sinuses are found in the deeper bones of the skull, separating the nasal passages and the floor of the skull. The sinuses are lined with mucous membrane and are connected to the nasal cavity by small openings. These openings, sinus canals, allow the air pressure to be equalised to the atmosphere. The sinus canals vent air to the atmosphere as the altitude increases. The lining of the canals is made up of a soft mucous membrane which expands when a person is suffering from colds or flu. Air can still vent to the atmosphere in the climb; but in the descent the inward passage of air is impossible. During the descent, severe pain and injury can result. This is known as a sinotic barotrauma or Barosinusitis. The Ear The ear has three main areas which are discussed in detail in a later chapter: ¾

Outer ear

¾

Middle ear

¾

Inner ear

Outer Ear

Inner Ear Middle Ear

The outer ear is exposed to atmospheric pressure.


3-13


The middle ear is an air filled cavity bordered by the ear drum and the Cochlea. It is connected to the back of the throat by the Eustachian tube. The walls of the Eustachian tube are made of soft tissues, with the opening into the throat acting as a flap valve. During ascent, air can vent to the atmosphere. This flap valve can stop air returning into the middle ear during a descent when the pilot suffers from an infection.

Below Atmospheric Pressure

Atmospheric Pressure Ear Drum pulled inwards

Eustachian Tube blocked

Colds or flu can cause the soft tissue, of the Eustachian tube, to expand. Therefore, in a descent the ear cannot equalise the middle ear pressure to the outside pressure. Severe pain and injury (possible rupturing of the ear drum) can occur. This is the otic barotrauma or Barotitis Media. Prevention Do not fly with any of the following: ¾

Cold

¾

Flu or

¾

Hay fever.


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27 November 2003

Chapter 4. Aviation Medicine – Health and Hygiene Introduction A delicate subject to all of us because once qualified, you are going to spend your working life in close contact with other pilots. To this end the problems of body odour and bad breath have to be discussed. Simple courteous acts such as brushing the teeth, bathing daily and using deodorants should be first nature. As an airline pilot you are the representative of your company and the consideration of dress and habits must also be addressed. Appearing clean and tidy for duty give the appearance that you are the professional pilot. Of more importance is how you stay healthy. A pilot requires a medical certificate in order to exercise the privileges of the licence. Joint Aviation Requirements The Civil Aviation Authorities of certain European States have agreed common comprehensive and detailed aviation requirements, referred to as the Joint Aviation Requirements (JAR). JAR-FCL and ICAO Annex 1 Joint Aviation Requirements for Flight Crew Licensing (JAR-FCL) relate to flight crew licensing. ICAO Annex 1 gives the standards and recommended practices for personnel licensing and has been used to provide the structure of the JAR-FCL. JAR-FCL and ICAO Annex 1 both require a licence applicant to demonstrate theoretical knowledge of human performance limitations relevant to licence sought. JAR-FCL Part 3 details the medical requirements for each licence. This document details the requirements for obtaining and maintaining a medical certificate. ICAO documents provide the basic structure for the JAR requirements. Additions are made where necessary by making use of existing European regulations. Medical Fitness Fitness The holder of a medical certificate shall be mentally and physically fit to exercise safely the privileges of the applicable licence.


4-1


Requirement for Medical Certificate In order to apply for or to exercise the privileges of a licence, the applicant or holder shall hold a medical certificate issued in accordance with the provisions of JAR-FCL Part 3 (Medical) and appropriate to the privileges of the licence. Aeromedical Disposition After completion of the examination the applicant shall be advised whether fit, unfit or referred to the authority. The authorized medical examiner (AME) shall inform the applicant of any condition(s) (medical, operational or otherwise) that may restrict flying training and/or the privileges of any licence issued. In the event that a restricted medical certificate is issued which limits the holder to exercise PIC privileges only when a safety pilot is carried; the authority will give advisory information for use by the safety pilot in determining their function and responsibilities. Decrease in Medical Fitness Licence holders or student pilots shall not exercise the privileges of their licences, related ratings or authorizations at any time when they are aware of any decrease in their medical fitness which might render them unable to exercise safely those privileges and they shall without undue delay seek the advice of the authority or AME when becoming aware of: ¾

Hospital or clinic admission for more than 12 hours

¾

Surgical operation or invasive procedure

¾

The regular use of medication

¾

The need for regular use of correcting lenses

Every holder of a medical certificate issued in accordance with JAR-FCL Part 3 (Medical) who is aware of: ¾

Any significant personal injury involving incapacity to function as a member of a flight crew, or

¾

Any illness involving incapacity to function as a member of a flight crew, or

¾

Being pregnant

shall inform the authority in writing of such injury or pregnancy, and as soon as the period of 21 days has elapsed in the case of illness. The medical certificate shall be deemed to be suspended upon the occurrence of such injury, or the elapse of such period of illness, or the confirmation of the pregnancy, and ¾

In the case of injury or illness the suspension shall be lifted upon the holder being medically examined under arrangements made by the authority and being pronounced fit to function as a member of the flight crew, or upon the authority exempting, subject to such conditions as it thinks fit, the holder from the requirement of a medical examination, and


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27 November 2003

¾

In the case of pregnancy, the suspension may be lifted by the authority for such period and subject to such conditions as it thinks fit and shall cease upon the holder being medically examined under arrangements made by the authority after the pregnancy has ended and being pronounced fit to resume her functions as a member of the flight crew

Fitness to Fly You are the judge as to whether you are fit to fly. Illnesses that are trivial on the ground can cause that fatal accident in the air. With the availability of new “over the counter” drugs problems such as: ¾

The power of the drug, and

¾

The side effects and symptoms

become important. A medical certificate is the most important attachment to the licence; lose it – lose the job. Most pilots neglect the body for many reasons, favourites are: ¾

Poor diet

¾

Lack of fitness

¾

Alcohol intake

¾

Drug Intake

¾

Smoking, and

¾

Ignorance

But these are also the cause of many accidents. Blood Pressure The maximum arterial pressure is achieved when the left ventricle contracts to force blood out of the heart. Known as the Systolic Pressure, this is the pressure at which the blood leaves the heart through the Aorta. When the heart relaxes, the pressure in the left ventricle will fall and the valve from the heart is closed off. Elastic recoil in the Aorta and the arteries maintains the pressure so that a steady flow of blood is achieved towards the capillaries.


4-3


Original Position Stretched Position

Aorta

Blood Flow

During the Systolic phase: ¾

The ventricles contract

¾

Pressure in the heart increases

¾

The aortic valve is forced open

¾

Blood is forced down the aorta

¾

The aorta stretches to make room for the blood

The minimum pressure in the arteries is the Diastolic Pressure. This pressure reflects the resistance of the small arteries and capillaries to the blood flow. This resistance is the load against which the heart must work. During the Diastolic phase: ¾

The ventricles relax

¾

The pressure within the heart decreases

¾

The aortic valve is forced shut

¾

The elastic walls of the aorta recoil and return to their original position

¾

Even though the heart is at rest the blood is still propelled through the rest of the body

Blood pressure is determined by using a sphygmomanometer where the blood pressure is given in mmHg. Measurement is taken from the upper arm in a sitting position. Typically, the values of blood pressure are given as two figures eg 120 over 80 meaning: Systolic

120 mmHg

Diastolic

80 mmHg


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27 November 2003

The World Health Organisation (WHO) classification of blood pressures is listed below: Category

Blood Pressure mmHg Systolic

Diastolic

Below normal

< 100

< 60

Normal

100 – 139

60 – 89

Borderline

140 – 159

90 – 94

Hypertension

> 159

> 94

Hypertension If the systolic and diastolic pressures are high when the body is at rest then this is an indication that the heart is working hard at pumping blood. This high blood pressure increases the risk of stroke and coronary heart disease especially when the blood pressure is higher than 140/90. Long term hypertension imposes strain on the cardio-vascular system that in turn can lead to heart failure. The cause of high blood pressure is generally unknown but can be linked to: ¾

Moderate to excessive intake of alcohol.

¾

Smoking

¾

Obesity

¾

Salt in the diet

¾

Genetic factors

Hypertension has a reputation as the silent killer because of the lack of warning of impending heart failure or heart attack. Orthostatic Hypotension Orthostasis means upright posture, and hypotension means low blood pressure. Orthostatic hypotension consists of symptoms of dizziness, faintness or light-headedness that appear on standing, and are caused by low blood pressure. Symptoms that often accompany orthostatic hypotension include chest pain, trouble holding the urine, impotence, and dry skin from loss through sweating. Causes of Orthostatic Hypotension Blood pressure is maintained by a combination of several factors. The heart is the central pump, and a weak or irregular heart can cause orthostasis. Conditions such as arrhythmia heart failure, deconditioning, and pregnancy are examples where the heart may not be able to provide an adequate blood pressure. The heart pumps blood, and if there is too little blood volume (anaemia, dehydration, dialysis), the pressure drops. The blood vessels in the body also can constrict to raise blood pressure, and if this action is paralysed, blood pressure may


4-5


fall. Heat, such as a hot shower or from a fever, can also dilate blood vessels and cause orthostasis. Both Hypo- and Hypertension can lead to the loss of a pilot’s licence. Coronary Heart Disease Coronary heart disease (CHD) kills an estimated 10 000 000 people worldwide. CHD is a general term that refers to any disease that results in a restriction or blockage of the coronary blood supply to part of the hearts wall. Any restriction or blockage causes a partial or total deprivation of oxygen to the affected part. This may cause death in the muscle cells. Any sudden irreversible damage of this kind is termed a myocardial infarction. Where a large part of the heart is affected then a person may die. If only a small region is affected then the person may make a complete recovery. The first two branches of the aorta are the left and right coronary arteries. These vessels spread out over the surface of the heart and divide into a dense network of capillaries supplying the muscle of the atria and ventricles.

Aorta

Coronary Arteries

Atherosclerosis The build up of a fatty material in the lining of the coronary arteries causes them to narrow. Initially the fatty material lines the inner coat of the artery wall. As time passes, lipid and cholesterol molecules from the blood enlarge the fatty material. Eventually, calcium deposits harden this fatty material. The larger these deposits become, the more the restriction in the blood vessel. The heart has to work harder to force blood through the arteries which in turn may cause the blood pressure to rise. Where CHD develops it normally takes one of three forms: Angina Suffered by people who have their coronary arteries narrowed by atherosclerosis. The main symptom is severe pain in the centre of the chest radiating


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27 November 2003

out to the left arm and up to the neck and jaws. Normally brought about by exertion or stress, the pain goes when the sufferer relaxes. There is no death of muscle tissue involved. During exercise or stress the heart beats faster and the demand for oxygen by the cardiac muscle cells increases. This demand cannot be met by the reduced flow through the narrowed coronary arteries and so angina results. Heart Attack Also known as Myocardial Infarction or Coronary Thrombosis. The fatty lining on the inside of an artery makes the surface uneven and this results in a disturbance of the smooth blood flow. This provides sites where blood can clot slowly (thrombus). If a clot breaks loose it follows the blood flow until it reaches a narrower blood vessel. This can severely restrict or even stop the blood flow. This blockage causes the heart muscle to be starved of oxygen and leads to a myocardial infarction. Sudden and severe heart pain results which may be fatal. Heart Failure The blockage of a main coronary artery leads to gradual damage of heart muscle with the result that the heart becomes weaker and fails to pump blood efficiently. Risk Factors of Coronary Heart Disease The main risk factors in their order of importance are: ¾

Family history

¾

Smoking

¾

Raised blood pressure

¾

Raised blood cholesterol

¾

Lack of exercise

¾

Diabetes

Other conditions such as obesity are not fully understood. Reducing the Risk of Coronary Heart Disease By avoiding the main risk factors the risk of CHD can be minimised. You can help yourself by: ¾

Stopping smoking

¾

Leading a less stressful lifestyle

¾

Being careful with the diet, eating a low cholesterol and low fat diet

¾

Keeping your weight to a normal Body Mass Index

¾

Exercising at least three times a week for a minimum of 20 minutes. The exercise must be vigorous enough to double the pulse rate.


4-7


Detection and Treatment of CHD Tests do not give an accurate indication of the health of the coronary arteries. An ECG can give some indication of the electrical activity of the heart muscle to show abnormalities such as an infarct, or narrowing of the arteries. For partial blockages arteriography would have to be used. Stroke A stroke occurs when the blood supply to an area of the brain is cut off. Two types of stroke can occur: Haemorrhagic An artery in the brain bursts so that blood leaks into brain tissue – a brain haemorrhage, or Ischemic

There is a blockage due to atherosclerosis

Anaemia A blood deficiency involving an abnormal reduction of the haemoglobin content of the red blood cells. These are the cells that carry oxygen to the various locations of the body. Those who are anaemic develop symptoms caused by the inadequate delivery of oxygen to their body tissues. Symptoms include low energy, dizziness, shortness of breath, pallor and digestive disorders. Obesity Any food that is eaten in excess of that required is stored as fat. Obesity is associated with a high fat intake in the diet and lack of exercise. Obesity increases the risk of developing the following diseases: ¾

Diabetes

¾

Hypertension

¾

Coronary heart disease

¾

Arthritis

¾

Cancer – especially of the colon, rectum, prostrate in men and uterus, cervix and breast in women

¾

Stroke

Obesity also increases the likelihood of developing hernia, varicose veins and gallstones. Obesity is defined as when a person: ¾

Is 20% or more above the recommended weight for height

¾

Has a Body Mass Index greater than 30


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27 November 2003

To lose weight a person must reduce their intake of food. Body Mass Index The Body Mass Index (BMI) is calculated as: BMI = Body mass (Kg) Height (m)2 BMI

Category

Male

Female

< 20

< 19

Underweight

20 – 25

19 - 24

Acceptable

> 25 – 30

>24 - 29

Overweight

> 30

> 29

Obese

Effects of Obesity Diabetes Diabetes is a metabolic disorder that changes the way the body breaks down sugars and starches. In normal people insulin, which is a hormone produced in the pancreas, helps to convert sugar to energy. This is stored by the body cells or used instantaneously. Diabetes is diagnosed as: Non-Insulin Dependent Diabetes The pancreas produces insulin but the body is not able to make use of it effectively. Insulin Dependent Diabetes The sufferer must have insulin injections because of a lack of insulin being produced. Non-insulin-dependent diabetes is linked to a person’s body weight; most non-insulin diabetics are 20% over their ideal body weight. Non-insulin diabetes can disappear when weight is lost. Coronary Problems A contributor to heart failure. Obesity causes changes in the heart’s left ventricle, which raise the risk of sudden death. Gout Gout is a disorder in where the body produces an excessive amount of uric acid or where the kidneys are unable to eliminate the uric acid formed. The uric acid is deposited in tissues and joints in the form of needle like crystals. This causes inflammation, swelling and severe pain. Joints most often include the knee, ankle, foot, hand, hip, and shoulder. Attacks can begin suddenly and the joint becomes inflamed, swollen, red and tender. If left untreated the problem can last for weeks. Arthritis Arthritis is an inflammation and stiffening of the joints often causing great pain. As the joints become stiff and painful, movement is difficult. Arthritis is an


4-9


illness that progressively disables and handicaps a person. Where the sufferer is obese, extra stress is put on the joints of the body, especially the knee and hip joints. Exercise Exercise does not help a person lose weight although it is an excellent way to reduce the risk of CHD. To be effective exercise has to be regular: ¾

It must be sufficient to double the resting pulse.

¾

Be carried out for at least 20 minutes three times a week

Hypoglycaemia A condition where the sugar content of the blood has fallen to a dangerously low level. Symptoms include; ¾

Physical or mental tiredness

¾

Lightheadedness

¾

Collapse and unconsciousness

Initially the brain and nervous systems are affected which manifest as personality changes such as: ¾

Anger

¾

Lack of ability to exercise judgement

¾

Poor decision making

Hypoglycaemia can occur as a result of a diabetic taking an overdose of insulin. In fit people hypoglycaemia can occur when: ¾

No food has been eaten for a few hours

¾

Subjected to sudden mental anxiety or physical exercise

Pilot’s are their own worst enemies, so before flying: ¾

Do not skip meals

¾

Always have a meal before flying

A quick fix to hypoglycaemia is to take a sweet drink or eat sweets.


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27 November 2003

Tropical Diseases Where public health control is poor personal protection from Tropical Diseases must rely on preventive measures and personal hygiene. The term tropical disease refers to diseases or conditions encountered in areas with high temperature and humidity. This is assumed to be an area bounded by the Tropics of Cancer and Capricorn. Tropical diseases are well understood. They are preventable and curable by modern drugs. If proper attention is given to personal hygiene combined with simple safeguards, there is no reason why problems should occur. Flight crew have to be alert and must follow: ¾

Simple rules of hygiene

¾

Sanitary precautions

Water Contaminated drinking water is one of the most frequent sources of intestinal infection such as: ¾

Diarrhoea

¾

Dysentery

¾

Typhoid and paratyphoid fevers

¾

Cholera

¾

Schistosomiasis and worm infections.

These can develop into chronic diseases for which the cure is difficult. All can be prevented if sensible precautions are taken with regard to water and food. Do not: ¾

Drink water straight from the tap

¾

Have drinks with ice cubes

¾

Brush the teeth with tap water

¾

Drink water from pre-opened bottles

To purify water boil it for 3 - 5 minutes. Hot tea or coffee and undiluted citrus fruit drinks are also safe. If water cannot be boiled purify with a chemical tablet. Drinks from well-reputed manufacturers that are bottled under strict licensing control are usually safe. Outdoor swimming in salt water is safe, except where beaches are next to freshwater outlets. Freshwater can be the source of serious tropical disease and bathing should be avoided.


4-11


Food Most diseases caused by contaminated water may also be acquired from contaminated food. This is the principal source of simple diarrhoea and food poisoning. In tropical countries it is not unusual for human excreta to be used as fertiliser. Irrigation of crops is by the use of open springs or sewers. Do not eat raw vegetables or fruit unless you peel them yourself. Avoid salads as they are usually washed in the local water. Milk and milk products can also be the cause of certain ailments. Food poisoning is a general term applied to some gastrointestinal infections. The risk to flight safety is by the sudden onset of incapacitating symptoms. Food poisoning does occasionally occur on board aircraft or during flight and flight crew should not consume food from the same source prior to or during a flight. Diarrhoea Diarrhoea (travellers’ diarrhoea) is a worldwide illness where the body excretes watery stools. The rapid dehydration that occurs may cause serious flight safety problems. Cholera Cholera is an acute enteric infection caused by Vibrio Cholerae. Spread by the intake of water and foods contaminated by the excrement of infected persons. Untreated, mortality may exceed 50 per cent. Control is by purification of water supplies and proper sewage disposal. Cholera vaccine provides some protection for a period of six months. Amoebic Dysentery, Amoebiasis Infection is by cysts from faeces of infected persons and is transmitted by hand to mouth, polluted water, and contaminated raw vegetables. Severe complications can affect the liver and lungs. The disease may be encountered anywhere in the world. Diseases Transmitted by Insects Insects and Insect vectors High temperatures, humidity and long hot seasons ensure that insects flourish in tropical environments. Exposure to insects is predominantly due to outdoor or primitive living conditions. Insects can affect the health of a person in the following manner: ¾

By transmitting or disseminating the disease

¾

Some insects are parasitic in or on the human body, and

¾

Some are directly poisonous in that they may inject powerful, even lethal irritants or venom.


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27 November 2003

Mosquito-Borne diseases The most important of mosquito-borne diseases is malaria. Mosquitoes require blood in order to reproduce. Other important mosquito-borne diseases include: ¾

Yellow fever

¾

Dengue Fever

¾

Filariasis

Malaria Malaria is an acute recurrent, febrile disease characterised by chills followed by high fever and sweating. The incubation period is usually eight to nine days but can be up to 12 months. Deaths due to malaria are reported every year among international travellers. These occur because: ¾

Travellers are unaware of, or underestimate, the danger of contracting malaria abroad

¾

Lack of prevention measures such as taking the required medication

Malaria still kills more people than any other tropical disease. Diseases Transmitted by Flies Gastro-intestinal diseases are transmitted by the housefly in unhygienic or unsanitary environmental conditions. Biting flies are responsible for dissemination of bartonellosis, pappataci fever and Leishmaniasis that may be prevalent in certain tropical areas. Tsetse flies are vectors of trypanosomiasis (African sleeping sickness) in central Africa. Other Insects Assassin bugs (Reduviidae) are vectors of Chagas disease found in Central and South American areas. Fleas are vectors of plague, murine or endemic typhus and some tapeworms. Ticks are vectors of such diseases as Rocky Mountain spotted fever, Q fever, Colorado tick fever, encephalitis and tularaemia, and can cause tick paralysis. Soft ticks transmit relapsing fevers. Mites and lice are transmitters of typhus and encephalitis fevers.


4-13


Cockroaches and bedbugs are looked upon with suspicion because they usually indicate unsanitary environments but they are not natural vectors of disease. Hepatitis Inflammation of the liver caused by infectious or toxic agents. Infectious agents include viruses, spirochetes protozoa and bacteria. The incubation period is two to six weeks and the infection can be prevented by immune serum globulin injections. Immunisations Medical requirements for immunisation of flight crew on international flights differ from country to country. Requirements are usually company dependent. Rabies Rabies is an infectious fatal disease spread to humans by the bite of an infected animal. The incubation period for rabies is between 3 weeks to 120 days. The disease is nearly always fatal unless a vaccine is given. Stay away from all animals especially cats and dogs. Rabies is a common problem in many countries around the world. Tobacco and Smoking In the 1950s the link between smoking and lung cancer was recognised. In the 1960’s, smoking was found to be a risk factor in CHD. Tobacco smoke is composed of: Mainstream Smoke

Smoke from the filter or mouth end of a cigarette

Sidestream Smoke

Smoke from the burning tip

Approximately 85% of smoke in a room is sidestream smoke. Most of the 4000 different chemicals in cigarette smoke are found in a higher concentration in the sidestream smoke than the mainstream smoke. This must put others as well as the smoker at a greater risk of developing smoking related diseases. This is known as passive smoking. Three main components of cigarette smoke pose a threat to the human being: ¾

Tar

¾

Carbon Monoxide

¾

Nicotine

Tar is implicated in the blocking of the bronchiole tree and tarring of the alveoli. Sufferers experience difficulty in breathing because of the blockage of the airways and the progressive destruction of the alveoli. The blockage of the airways is caused by chronic bronchitis. Where


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27 November 2003

a person has been smoking for a long time the chronic bronchitis can be accompanied by emphysema: Chronic Bronchitis The cleaning action of the lungs is inhibited by the tar in tobacco smoke. As the tar passes through to the lungs through the airways more mucus is secreted. This mucus accumulates in the bronchiole tree and may block the passage of air. Any dirt, bacteria or virus will collect in the mucus – this is the cause of what is known as “smoker’s cough”. Emphysema Where the lung is affected by chronic bronchitis infection will become more commonplace. Inflammation occurs and an enzyme called elastase is produced. This enzyme destroys the elasticity of the alveoli which eventually burst. Thus there is less surface area for any gaseous exchange. In extreme cases a person will need continuous oxygen to stay alive. Carbon Monoxide Carbon monoxide (CO) is a product of the incomplete combustion of carbon compounds and is absorbed by inhalation. The relative toxicity of CO increases with altitude. Carbon Monoxide (CO) is absorbed by the blood in the alveoli and competes with oxygen for haemoglobin. The haemoglobin has a greater affinity for the CO than it does oxygen (approximately 200 times). The stable compound carboxy-haemoglobin is formed and because of this the amount of oxygen available for absorption is reduced by as much as 10%. CO is deadly; being colourless, odourless and tasteless. It has a four hour half-life in air. Carbon monoxide does not naturally occur in any quantity in the atmosphere. Its effects can be cumulative and are not easily corrected. Oxygen does not bring quick relief and several days may be required to rid the body completely of carbon monoxide. The presence of carbon monoxide results in hypoxia where it can have the same effect as an altitude increase of 8 to 10 000 feet. The symptoms of carbon monoxide poisoning are headache, dizziness, weakness, nausea, rapid heart beat, respiratory failure and death. After death a person shows a redness in the lips and cheeks. Nicotine Nicotine stimulates the sympathetic nervous system by reducing the diameter of the arteries which stimulates the release of adrenaline from the adrenal glands. Nicotine is absorbed into the blood and will reach the brain within a few seconds. The release of adrenaline increases the heart rate and blood pressure. The narrowing of the arteries decreases the blood supply to the extremities such as the hands and feet. This lack of Oxygen can lead to the amputation of limbs due to the onset of gangrene.


4-15


Drugs and Medication The term drug is a difficult one to define; in the widest sense a drug is a chemical substance which is taken into the body or applied to the skin. More commonly the term is used to describe substances which interfere with some aspect of the body’s metabolism. These drugs are taken to alter the: ¾

The progress of a disease, such as a painkiller or antibiotic

¾

The working of the nervous system such as LSD, Heroin or even Alcohol

General Health The person who, for whatever reason, does not feel well should not fly. General discomfort is not conducive to safe flying. Self-medication is also hazardous and the best recommendation to flyers is not to take any drug and fly. Drugs and flying do not mix. The side effects of most medications can be disabling in the air. If illness or pain requires treatment then a pilot will not perform normal flying tasks well. Drugs The safest rule is to take no medicine while flying, except on the advice of an authorised medical examiner. The condition for which the drug is required may be hazardous to flying. Specific drugs associated with aircraft accidents are: ¾

Antihistamines (widely prescribed for hay fever and other allergies)

¾

Tranquillizers (prescribed for nervous conditions, hypertension, and other conditions)

¾

Reducing Drugs (amphetamines and other appetite suppressing drugs can produce sensations of well being which have an adverse affect on judgement)

¾

Barbiturates, nerve tonics or pills (prescribed for digestive and other disorders, barbiturates produce a marked suppression of mental alertness).

Legitimate medications taken for minor ailments can jeopardise safe flight by their subtle or unpredictable effects on the pilot. This includes both prescribed medications and over-thecounter medicines. Allergic Reactions Some people may experience an exaggerated or allergic reaction to a medicine. The allergic response to a drug can arise unexpectedly and dramatically causing incapacitation.


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27 November 2003

Idiosyncrasies An individual may react in an unusual and unexpected way to a particular medicine. Synergistic Effects When a drug is taken in combination with another drug the total effect may be exaggerated. Effect of Drug Combinations Two drugs taken at the same time can: ¾

Cancel each other out

¾

Render each other more potent, or

¾

Cause a side reaction

Drugs may have side effects which contribute to pilot error, and accidents. Some are listed below: Antihistamines Widely prescribed and readily available for sufferers of hay fever, allergies and colds. Drowsiness and dizziness are a common side effect. Decreased reaction time and orientation problems may occur. Nasal decongestants Can cause nasal burning and stinging, sneezing and increased nasal discharge. Aspirin Side effects include, irregular body temperature, variation in rate and depth of respiration, hypoxia and hyperventilation, diarrhoea, gastrointestinal problems and decreased clotting ability of the blood. Antacids Allow the formation of carbon dioxide at altitude that can cause acute abdominal pain due to the distension of the stomach. Sleeping Pills and Tranquilizers Cause sleepiness, nausea, depression, reduced alertness, affected reaction time and concentration, visual disturbances, severe mental disturbances and predisposition to heat stroke. Reducing Agents and "Pep" Pills Drugs generally containing amphetamines. They produce a feeling of high spirits and false confidence, while actually crippling one's judgement and leading to reckless errors. Barbiturates and Pain Killers Used to relieve anxiety or reduce pain. These drugs suppress mental alertness.


4-17


Cough Medicine Cause central nervous system depression, reduced reaction time and high probability of overdose. Motion Sickness Drugs Cause drowsiness and depressed brain function, and temporary deterioration of judgement making skills. Diuretics

Change the osmotic balance of the body.

Alcohol Alcohol can produce subtle effects on the perception and performance abilities of a pilot. There is no known threshold level for these effects. Alcohol, taken even in small amounts, produces a dulling of judgement which results in: ¾

Reduction of reaction time

¾

Lack of accurate flying

¾

Lack of self criticism

¾

A decrease in spatial orientation

Unit of Alcohol A unit of alcohol is equivalent to: ¾

A standard glass of wine

¾

A single spirit, or

¾

½ pint of beer

Specifically it is defined as 15 ml or 9 grams pure alcohol which is equivalent to a bottle of beer. Alcohol is absorbed very rapidly into the blood and tissues of the body. The body metabolises alcohol at the rate of one to one and a half units per hour. Binge drinking increases this time drastically. Alcohol is also absorbed into the fluid of the inner ear. The fluid metabolises alcohol much slower than the rest of the body causing problems with the vestibular system. The presence of alcohol in the blood interferes with the normal use of oxygen by the tissues causing histotoxic hypoxia. Because of reduced pressure at high altitudes and the reduced ability of the haemoglobin to absorb oxygen, the effect of alcohol in the blood during flight at high altitudes, is much more pronounced than at sea level. The effects of one drink are magnified 2 to 3 times over the effects the same drink would have at sea level.


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27 November 2003

Alcohol acts as a depressant and an anaesthetic. Binge drinking the night before flight is dangerous as a pilot will still be acting under the influence of alcohol. JAR-OPS 1.115 - Alcohol and Drugs The operator ensures that no person enters an aeroplane when under the influence of alcohol or drugs where the safety of the aeroplane or its occupants is likely to be endangered. JAR OPS state that a pilot shall not: ¾

Consume alcohol less than 8 hours prior to the specified reporting time for flight duty or the commencement of standby

¾

Commence a flight duty period with a blood alcohol level in excess of 0.2 promille

¾

Consume alcohol during the flight duty period or whilst on standby

If large amounts of alcohol are consumed then the period should be increased to over 24 hours. Recommended Amounts of Alcohol The following are the recommended Health Council limits for alcohol: Men

21 units per week

Women

14 units per week

If a man’s intake is more than 6 units per day/30 units per week, women 4 units per day/20 units per week, then there is a greater than 50% chance of an alcohol related illness. Blood Alcohol Levels commonly used as guides to impairment: 0.05% - exhilaration - loss of inhibitions. 0.11% - slurred speech and staggering gait. 0.20% - euphoria - marked gait impairment. 0.30% - confusion. 0.40% - stupor 0.50% - coma. 0.60% - respiratory paralysis and death. Alcoholism Alcoholism is a disease. Of the many definitions given the World Health Organisation definition is most accepted:


4-19


Alcoholics are those excessive drinkers whose dependence upon alcohol has reached such a degree that it results in noticeable mental disturbance or in an interference with their bodily and mental health, their interpersonal relations, their smooth social and economic functioning, or those who show the signs of such developments. Physical Problems Problems include: ¾

Digestive system disorders such as ulcers

¾

Inflammation of the pancreas

¾

Cirrhosis of the liver.

Alcohol and Sleep The use of alcohol as a relaxant is widely used by flight crew. The odd social drink will not affect a person’s well being. Large amounts of alcohol induce a coma like sleep where both the slow wave and REM sleep are badly affected. Prolonged use of alcohol will induce extreme fatigue because of the lack of proper sleep. Toxic Materials All pilots will be exposed to a variety of chemical agents that are toxic. A general knowledge of the effects of these materials is required. Toxicology Toxicology is defined as: The study of the nature and mechanism of toxic effects of substances on living organisms and other biological systems. Toxicity depends on: ¾

The amount of exposure

¾

The dose, and

¾

The duration of exposure

Toxic materials can affect any organ of the body. The major organs that can be affected are the lungs, liver, kidney, skin, eyes, nervous system, reproductive system, heart and immune systems.


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27 November 2003

Aviation Gasoline (AVGAS) Exposure may occur during handling, storage, or engine maintenance. It may be inhaled or absorbed. AVGAS fumes are an upper respiratory irritant. Rapid vaporisation of AVGAS can cause chemical skin burns if next to the body. JP4-JP5 JP4 and JP5 are jet engine fuels; JP4 is 65% kerosene and 35% gasoline, while JP5 is kerosene. They may cause headache, nausea, confusion, drowsiness. Prolonged skin exposure can lead to second degree burns. Ethylene Glycol Used in antifreeze, hydraulic fluids, condensers and heat exchangers. Ingestion can be fatal. Methyl Alcohol Methyl alcohol causes disturbances of vision, headache, vertigo, nausea and vomiting. Methyl alcohol is found in de-icing fluid. If drunk in large amounts then blindness can occur. Chlorobromo Methane (CBM) A constituent chemical used fire extinguishers. Absorb by inhalation and skin absorption. CBM is considered safe for flight crew. Halon Halon is a generic term meaning halogenated hydrocarbon. The gas is a CNS depressant. Used as a flooding agent to extinguish fires in simulator buildings. Hydraulic Fluid Hydraulic fluid is petroleum based and inflammable. When burned, phosgene is formed. This toxic gas affects the respiratory system. Inhalation is possible when a hydraulic line breaks under pressure. Plastics Plastic burns to CO and other toxic gases. Absorption is through inhalation. Burning plastic creates a black, choking, toxic smoke that quickly incapacitates.


4-21


Mercury Mercury is a metal liquid at room temperature. The vapour can be absorbed by inhalation Incapacitation In-flight pilot incapacitation is known to have caused accidents and occurs frequently enough for flight crew to train for the possible consequences. Despite strict medical standards incapacitation still continues to occur. Temporary incapacitation may be less dramatic than a total collapse but is just as much of a problem. Most temporary collapses are caused by gastrointestinal upsets. Incapacitation can be divided, “obvious” and “subtle” incapacitation. Obvious Incapacitation Obvious incapacitation is immediately apparent to other flight crew members. Occurring suddenly, attacks are usually prolonged and normally result in that flight crew member being useless for the rest of the sortie. Sudden incapacitation may not be preceded by any warning. Subtle Incapacitation Subtle or insidious incapacitation is harder to identify because it is not obvious. Subtle in its onset it is hard to predict or notice. This form of incapacitation can be dangerous because of the time it takes for a crewmember to notice the effects. Fits and Faints A sudden loss of consciousness disqualifies a pilot from holding a flight crew licence. An explanation is given as to the difference between Fits and Faints. One may impose a permanent loss of licence; the other suspension or restrictions. The term fit (seizure) is usually reserved for some manifestation of epilepsy. Faint (syncope) refers to a change of consciousness caused by disturbance of the brain’s blood supply. Epilepsy Epilepsy is just a collective term for a set of symptoms caused by electrical activity in the brain and often classified as minor or major. An EEG (electroencephalogram) test, recording routine brain activity, will often detect epilepsy. The fit is usually termed: Grand Mals Normally a major uncontrolled physical movement

attack

accompanied

by

convulsions

and

Petit Mals A minor attack which lasts for a few seconds and is associated with loss of attention


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27 November 2003

Epilepsy will mean a permanent withdrawal of licence. Faint Faints are more common because an otherwise healthy person may faint from shock, loss of blood, stress, lack of fluid or food. The basic mechanism of a faint is a sudden reduction of the blood's oxygen supply to the brain. Faints can be caused by any of the following: ¾

Shock

¾

Loss of blood

¾

Hypoglycaemia

¾

Stress

Where the cause of fainting can be identified then it will not normally affect a person’s fitness to fly. There is a possibility that restrictions may be made on the licence eg two pilot operation only. Gastroenteritis Gastroenteritis is generally caused by food poisoning and is most common in travellers. The symptoms are nausea, vomiting, diarrhoea, abdominal cramps and fever. The conditions are usually short lived and a pilot is unfit to fly whilst he is affected. The symptoms usually settle within 2 – 3 days. However, if the problems last longer than 72 hours a doctor must be consulted. Acceleration The body is able to withstand the effects of acceleration up to certain thresholds. These thresholds depend upon both the intensity and duration that the forces are applied. Normally, acceleration is divided into 2 areas: Short Term Acceleration Impact acceleration forces that last less than one second. The forces the body can withstand are directly related to its own strength: ¾

In the vertical axis the body can withstand 25G

¾

In the fore and aft axis 45G

¾

In the lateral (side) axis 10-15G

Any force above these levels cause injury.


4-23


Long Term Acceleration Forces that last more than one second. As a human being we are used to the effects of gravity. When we fly we are subject to the acceleration forces that can be applied when flying the aircraft. The value of long term acceleration is usually given as either “positive G” or “negative G”. Positive G Perceived as an increase in body weight, the more the G pulled the harder it becomes to move freely. If enough G is pulled then organs can be displaced from their normal position. As seen earlier we measure the blood pressure in the upper arm as this equates to the blood pressure in the heart. If we were standing it would be fair to say that the blood pressure in the head will be less than that in the heart and that the blood pressure in the feet will be greater than that in the heart. If G is applied then the blood pressure in the head will be reduced because the force will drive the blood to the lower half of the body. The blood supply can be cut off meaning that the eyes and the brain are starved of blood. As G increases we notice the effect on the eyes firstly by greyout (gradual greying of the vision) and followed by unconsciousness. Greyout will appear at approximately 3.5G if the pilot is totally relaxed. By using straining manoeuvres the delay of greyout and unconsciousness can be up to 7-8G. The military use G-suits to help the pilot in long term acceleration. G tolerance is reduced by many factors such as: ¾

Hypoxia

¾

Hyperventilation

¾

Heat

¾

Low blood sugar

¾

Smoking

¾

Alcohol

Negative G The effects of negative G are the opposite of those for positive G. Negative G manoeuvres in an aircraft are much more uncomfortable than positive G manoeuvres. Facial pain can be experienced and in extreme cases small blood vessels can burst. Negative G is associated with the term “redout”, where the lower eyelid is pushed up under the eye. Maximum negative G is considered as –3G and then for short periods only. Motion Sickness Although motion sickness is uncommon among experienced pilots it does occur. It can jeopardises your flying efficiency especially when concentration is needed eg Instrument Flying. Student pilots are more susceptible to the effects of motion sickness which is caused when the body is subjected to a real or apparent motion that is unfamiliar. Motion sickness is caused by continued stimulation of the inner ear which controls balance. Symptoms are progressive and include problems such as:


4-24

27 November 2003

¾

Over salivation

¾

Perspiring heavily

¾

Feeling nauseous and disoriented

¾

A tendency to vomit

In extreme cases if the air sickness becomes severe a pilot can be incapacitated. Do not fly if taking anti-sickness drugs. These drugs affect the central nervous system and reduce a pilot’s efficiency. When suffering from airsickness the following may help: ¾

Open air vents

¾

Loosen clothing

¾

Use supplemental oxygen

¾

Keep the eyes outside the aircraft and try and fly straight and level for a period.

¾

Avoid unnecessary head movements

¾

Land as soon as possible.


4-25




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27 November 2003

Chapter 5. Aviation Medicine - Diet and Digestion Introduction All living cells require energy. This is obtained from the digestion of food. Food has to be eaten to provide the human body with the required energy. Foods fall into three distinct categories: ¾

Carbohydrates

¾

Fats and oils

¾

Proteins

To form a complete diet, mineral salts, vitamins, trace elements, water and roughage (fibre) are also required. The amount of food taken must supply enough energy to: ¾

Keep the body alive, both at rest and play

¾

Allow energy to be stored in the body for use when we are not eating

Carbohydrates and Fats Carbohydrates are compounds that contain carbon, hydrogen and oxygen and are the most immediate source of energy found in the body. Carbohydrates are: ¾

The main fuel used by the muscles, and

¾

The only fuel that can be used by the central nervous system

They can be sub-divided into three groups: ¾

Simple sugars

¾

Complex sugars

¾

Starch

All carbohydrates are converted to glucose by the body. If carbohydrates are not available in the body then poisonous substances, ketones, are produced. Carbohydrates are required to carry out the satisfactory oxidation of fats in the body. Foods high in carbohydrates include bread, rice and potatoes. When eaten in excess, carbohydrates are converted and stored in the body as fats.


5-1


Fats Fats also contain carbon, hydrogen, and oxygen; but less oxygen than carbohydrates. Fats produce energy by oxidation, however, for every 2 grams of fat it takes 1 gram of carbohydrates to carry out this process. Fats are less bulky than carbohydrates and for the same weight produce twice as much energy. However, fats do take much longer to digest than carbohydrates. Proteins Proteins, like fats and carbohydrates, contain carbon, hydrogen and oxygen as well as nitrogen and sulphur. They are essential for the diet as they produce amino acids which help the body build up new protoplasm. Protoplasm All human beings consist of microscopic units, known as cells. These cells are made up in part by a living matter, protoplasm. Amino Acids The acids that form the component parts of proteins. Proteins can be sub-divided into two groups: First Class Proteins Those proteins found in meat, fish, eggs, milk and cheese. These foods contain all the essential amino acids. Second Class Proteins The foods, like vegetables, that do not carry all, or are poor in, the essential amino acids. Diet Our diet has to be adequate to supply all our energy needs. When planning a diet, the amount of energy produced by different foodstuffs should be taken into account. To survive, the body must produce: Heat Energy To maintain the body temperature at 36.9° C. Mechanical Energy

To enable us to perform efficiently at work.

The whole energy requirement of the body could be provided by carbohydrates. This would most probably be indigestible because of the bulk required. Proteins, as they may be used as a source of energy, could also provide the body's total energy requirement. However, to satisfy our needs, approximately 5 kg of meat would have to be consumed daily - quite an expense. Fat alone will not give us our energy requirements as we also need carbohydrates to break it down into a usable form. Generally when people talk about a balanced diet, all three forms of food have to be eaten. A suggested diet could include:


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27 November 2003

Intake

Calorie Intake

Proteins

125 g

500

Fats

125 g

1125

Carbohydrates

400 g

1600

Total Calorie Intake

3225

Mineral Salts and Vitamins Both mineral salts and vitamins are essential for the complete diet and a healthy body. Mineral Salts All of us realise that we require an intake of common salt, sodium chloride. In addition, numerous other minerals are essential for the body to function correctly. Calcium Important for the formation of teeth and bone and required for muscle contraction. Nearly 30% of our bone is calcium. Calcium is present in most tissue fluids, green vegetables and milk. Phosphorus Phosphorus combines with calcium to form calcium phosphate, an essential salt in the formation of healthy bones and teeth. Phosphorus is found in certain proteins. Magnesium Magnesium is necessary for the formation of the skeleton and efficient cell functioning. Meat is the body's main source of magnesium. Potassium

Helps muscle function and the conduction of nerve impulses.

Sodium Helps keep the osmotic balance of the body as well as aiding muscle function and the conduction of nerve impulses. Sodium Chloride Taken into the body in the form of common salt. Sodium chloride is an important constituent of our blood. The osmotic pressure and tissue fluid are both regulated by its presence. Sodium chloride is also necessary to provide the stomach with the material to form hydrochloric acid, an essential fluid within the stomach. Salt can be excreted by both the kidneys and the skin, as sweat. If the body loses a large amount of salt then it must be replaced to maintain body equilibrium. Potassium Chloride Potassium is found in most vegetables and like sodium chloride helps maintain intracellular osmotic pressure. The body must maintain a sodium chloride/potassium chloride balance. If there is a lack of sodium chloride, the potassium chloride replaces it in the blood stream. An excess of which has a harmful effect on the heart.


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Iron An important constituent of haemoglobin. Lack of iron in the diet can lead to anaemia. Anaemia A deficiency in the number of red blood cells or their haemoglobin content. Iron is present in meat, fruit and green vegetables. Iodine Iodine is necessary for the correct function of the thyroid glands. These glands control the body's metabolism and growth. Zinc A constituent of some enzymes, and is involved in wound healing and the functioning of insulin. Vitamins Vitamins are essential, in small quantities, for the normal functioning of the metabolism of the body. The major vitamins are: Vitamin A Vitamin A provides for the proper functioning of the retina in the eye. Found in milk, fat, butter, liver, oils, egg and green vegetables. When Vitamin A is deficient: ¾

Night blindness can occur

¾

Young people do not grow correctly

¾

Drying of the mucous membrane of the eye lids and cornea allow Keratinisation (a coating of the surfaces by a hard film)

Vitamin B Complex A large group of water soluble vitamins found in yeast, liver, milk, green vegetables and flour. Three of the vitamins are found to be essential in the human diet, Vitamins B1 , B2 and Nicotinic Acid. Lack of Vitamin B1 can cause diseases such as Beri Beri. Lack of Nicotinic Acid causes Pellagra, a disease characterised by inflammation of the mouth and skin and mental impairment. Vitamin C Vitamin C helps the proper functioning of the skin and mucous membrane. Found in fresh fruits and very lightly cooked vegetables. Lack of Vitamin C causes scurvy, a disease in which bleeding occurs in all parts of the body. Vitamin D A fat soluble vitamin found in cod liver oil, egg, butter and cream. The body can produce its own Vitamin D by exposure to sunlight. Lack of Vitamin D leads to the onset of rickets in children, a disease where the bones of the body become deformed. In adults, osteomalacia can result, or softening of the bones. Without Vitamin D, calcium and phosphorus cannot combine to form calcium phosphate which is essential for healthy bones and teeth.


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27 November 2003

Vitamin E Found in cereals, meat and lettuce. The effects of its absence are not really understood, but a deficiency is thought to cause sterility. Vitamin K the diet.

Vitamin K is essential for the clotting of blood. It is seldom lacking in

Trace Elements Other elements fluorine, manganese, cobalt, zinc and copper are required in minute quantities for special purposes. For a complete diet, a person must also take in water and roughage. Water is an essential constituent of protoplasm, and is necessary for the balance of body fluids; the body is in effect 70% water. Because water is continually lost from the body in sweat, urine and respiration, continuous replacement is required to avoid dehydration. Roughage is the indigestible part of food and is passed through the stomach and the gastrointestinal tract. If roughage is allowed to remain in the alimentary canal for any period of time then poisonous toxins can be produced which eventually pass into the blood. Digestion Before food can be utilised by the body it has to be converted into soluble diffusable substances. These substances must be able to pass through the walls of our small intestines into our blood stream. The preparation of food for absorption, and the excretion of waste, is the process known as digestion. This takes place in the Alimentary Canal; a long canal that begins at the mouth and ends at the anus. The Alimentary Canal Mouth The mouth is an oval cavity with an opening to the outside. It consists of two parts: ¾

The outer part which is the space outside the teeth and within the lips and cheeks

¾

The inner part or true cavity of the mouth

Teeth Within the mouth are the teeth. Each tooth is covered by enamel, a hard substance containing phosphate and calcium. Under this enamel is a thick layer of bony substance, Dentine. After losing the temporary milk teeth, each jaw has: ¾

4 incisors or cutting teeth

¾

2 canine or eye teeth


5-5


¾

6 molar or chewing teeth

Salivary Glands The mouth contains three pairs of salivary glands: ¾

Parotid glands

¾

Sub-maxillary glands

¾

Sub-lingual glands

Digestion in the Mouth Food is divided up into small pieces by the teeth and mixed with saliva, which flows out of the salivary glands. Saliva flows as two secretions: ¾

A flow due to a mental stimulus ie the watering of the mouth due to the sight or smell of food.

¾

A second flow when the food is in the mouth

Saliva is a colourless, slimy liquid which is slightly alkaline. Consisting mainly of water, it also contains salts, Mucin and Ptyalin. The saliva has important digestive functions: ¾

It moistens and lubricates food, so facilitating swallowing

¾

It dissolves part of the food, making taste possible

¾

Taste stimulates ¾

The saliva glands into producing more saliva

¾

Other glands into producing other digestive juices

¾

Ptyalin digests starch by converting it into sugar

Correct chewing of food is important as: ¾

More food is subject to the action of saliva

¾

More of the food area can be subjected to other digestive juices later in the process

Pharynx and Oesophagus To the back of the mouth is a cone shaped cavity, 12 - 14 cm long, the pharynx. This leads into the oesophagus which is approximately 25 cm long. The oesophagus lies between the trachea and spinal column. Passing through the thorax, the oesophagus goes through the diaphragm and enters the abdomen, joining the stomach at the cardiac orifice.


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Swallowing Food is passed down the oesophagus by a muscular action, peristalsis. This is a wave like relaxation and contraction of the muscular walls of the oesophagus.

Stomach The stomach is located in the abdomen, immediately below the diaphragm. The size of the stomach varies with the amount of food it contains. Digestion in the Stomach Food arrives in the stomach from the oesophagus. The presence of the food stimulates the gastric glands into secreting gastric juices. The gastric juices are clear, colourless and strongly acidic, which: ¾

Digest proteins

¾

Allow the acid contents of the stomach to kill any germs

¾

Clot any milk products

The food is converted into a semi-liquid mass, acid chyme. Gradually, the acid chyme is allowed to flow into the duodenum, the first stage of the small intestine. The gradual flow of food is necessary as the acidity of the food needs to be made alkaline by the fluids of the duodenum.


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Small Intestine The small intestine is approximately 6 m long and consists of the duodenum and the coiled part. The duodenum is approximately 25 cm long and circles the pancreas. Openings into the duodenum come from: ¾

The bile duct from the liver and gall bladder

¾

The pancreatic duct from the pancreas

The long coiled part of the small intestine lies in the central and lower part of the abdomen Digestion in the Small Intestine When the acid chyme enters the duodenum a hormone called secretin is produced. This hormone pours into the blood and stimulates the pancreas to secrete its juices. Pancreatic Juices A colourless, alkaline fluid containing solids in solution. These solids act upon fats, proteins and starch. At the same time, the acid chyme stimulates the intestinal glands to: ¾

Secrete intestinal juice which converts the acid chyme into a digestible form.

¾

Stimulates the gall bladder into emptying its bile. Bile is produced in the liver and stored in the gall bladder. A yellowish-green fluid, bile is purely an excretory substance which is produced from broken down red blood corpuscles. Bile is important to digestion as it helps emulsify fats. Bile also acts as a weak antiseptic lubricating the contents of the duodenum.

Large Intestine The small intestine joins the large intestine, which is approximately 1.5 m long. The large intestine extends from the ileum to the anus and is divided into 3 sections: The Caecum The caecum is a large sac, from which the appendix hangs. The appendix is important in vegetable eating animals for the digestion of cellulose. In man it has no function. The Colon The first part of the colon runs up the right lumbar region. Just below the liver it turns across the front of the abdomen and then descends to the left lumbar region of the abdomen. The Rectum and Anus The colon becomes the rectum, a tube approximately 12 cm long. The last 3 cm of the rectum is known as the anal canal. The opening to the exterior is called the anus, an area protected by the sphincter muscles.


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Functions of the Large Intestine Undigested food passes, in a liquid state, from the small intestine into the large intestine. In the large intestine, water is absorbed into the blood, faeces are formed and the mass becomes more solid. Movement along the large intestine is by peristalsis. The faeces take approximately 16 hours to move along the large intestine. Defaecation Defaecation is the act of passing faeces to the exterior. Faeces Faeces are a semi solid mass consisting of approximately 70% water. Coloured by a pigment stercobilin, which is formed from bile pigments. The solid matter consists of waste products from the process of digestion.


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27 November 2003

Chapter 6. Aviation Medicine - Metabolism, Excretion And Heat Regulation The Liver The liver is the largest gland in the body, weighing approximately 1.5 Kg. During respiration, when the diaphragm is depressed, the liver is compressed. This compression aids the circulation of blood through the organ. For this reason, exercise is important for the correct functioning of the liver. Connected to the upper surface of the liver is the gall bladder. Functions of the Liver The functions of the liver are: ¾

The storage of excess carbohydrates as glycogen

¾

The regulation of the amount of glucose in the blood

¾

The preparation of fat for utilisation as a source of energy

¾

Converting nitrogenous waste into urea, which is passed through the blood to the kidneys

¾

Production and secretion of bile

¾

Release of Vitamin B12 which stimulates red blood corpuscle production

¾

Storage of iron

¾

Body temperature regulation

Pancreas The pancreas has two important functions: ¾

The secretion of the pancreatic juices

¾

The secretion of insulin.

Insulin circulates around the body in the blood. Without insulin, no glycogen can be stored in the liver and glucose cannot be released to produce energy. Insulin Without insulin the body cannot get its energy by the oxidation of sugars. Fats and amino acids are converted in to glucose, but this form of glucose cannot be stored, and is thus excreted by the kidneys. In effect, the body wastes away. The disease that results from this lack of insulin is known as diabetes.


6-1


Excretion and Regulation of Body Fluids During the activity of the body, waste substances are produced. Accumulation of these substances can be harmful and so they must be excreted from the body. There are three excretory organs within the body: The Skin salts.

The body excretes by the process of sweating out water and mineral

The Kidneys and Other Urinary Organs waste, mineral salts and water. The Lungs respiration. The Skin

These organs excrete nitrogenous

The lungs excrete CO2, water and other waste products of

The outer covering of the body consists of two layers:

¾

The outer epidermis

¾

The inner dermis

Functions of the Skin Sweat Glands Sweat glands continuously give out water which contains small quantities of salts and organic matter. This sweat is not normally seen as it evaporates as it is formed. Protection organs.

The skin is the outer layer of the body and as such protects the inner

Regulation of Body Temperature Sense Proprioceptive receptors are found in the skin. These nerve sensors give us the senses of touch and temperature recognition. The Kidneys Urine, containing nitrogenous waste, is produced in the kidneys. These waste substances are extracted from the blood continuously. The urine is passed to the bladder, which is emptied through the urethra.


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Functions of the Kidneys The kidneys: ¾

Excrete waste products of the body

¾

Control the concentration of certain salts within the blood plasma

¾

Control the osmotic pressure of the blood

¾

Maintain the alkalinity of the blood

¾

Remove abnormal substances when found

Micturation Micturation is the action of passing urine from the bladder to the exterior. Pressure is built up within the bladder by the continuous collection of urine. Once a certain pressure is reached, then the urge to micturate is felt. Body Heat Regulation Man is a warm blooded mammal, with an internal temperature of approximately 36.9° C. Body temperature is kept stable by the balance of heat production and heat loss. Heat Production Heat is produced by the cells of the body, particularly the muscles and the liver. Blood leaving the liver is warmer than that entering. It is the blood leaving the liver that distributes these heat gains to the body. Heat Loss Heat is lost from the body by: The Faeces and Urine This heat loss is constant. Respiration

This heat loss varies with temperature and humidity.

The Skin

Heat loss varies dependant upon blood flow and sweat.

Heat loss from the faeces, urine and respiration cannot be controlled by the body. Heat loss from the skin is controlled by the temperature of the body: ¾

If the body is cold, the blood vessels in the skin constrict, blood flow is reduced, and heat loss is reduced.


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¾

If the body is warm, the blood vessels dilate, more blood flows through the skin. This allows more heat to be lost to the air.

Fever Where a rise in body temperature occurs, a person may have become infected, and fever may result. The symptoms of fever are: ¾

Initially, the skin becomes dry and heat production is increased. Shivering and a chilled feeling may soon follow.

¾

As the fever advances, the skin becomes hot and flushed and profuse sweating occurs.

¾

Headache and generalised aches and pains are experienced.

Heat Stroke A condition that can occur suddenly when the body heat regulation mechanism fails and the sweat glands cease to function properly. Symptoms include: ¾

Headache

¾

Confusion and restlessness

¾

Hot, flushed possibly dry skin

¾

High body temperature

Climate and Heat Loss Climate

Healthy/Unhealthy

Reason

Hot and moist

Unhealthy

The body is not cooled by sweating because of the humidity of the air.

Hot and dry

Healthy

The dry air increases the evaporation of sweat

Cold and moist Unhealthy

Moist air holds a great deal of heat, so that heat loss from the body is relatively high.

Cold and dry

Heat loss from the body is low.

Healthy


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Chapter 7. Aviation Medicine - The Eye Introduction Vision is the most dominant sense, the eyes are approximately 25 times more sensitive than any other organ in the body. Although good vision is essential for pilots and is tested during the medical assessment of a pilot; perfect eyesight is not required. Anatomy and Physiology of the Eye The eyeball lies in a bony socket within the skull (the orbit) with two eyelids which protect and clean the surface of the eye. The eyeball is connected to the skull by 6 muscles, which move the eye up and down and from side to side.

PUPIL

IRIS

LENS CORNEA

RETINA

OPTIC NERVE

Light is refracted by the transparent cornea at the front of the eye onto the lens. The lens then focuses the remaining light onto the retina. The lens can vary its focal length by the movement of the ciliary muscle which surrounds the lens. By using a process of contraction and relaxation the lens’ focal length is varied. This is the process which allows the eye to focus on both near and far objects. ¾

70% of the focussing process is refraction as light passes through the Cornea

¾

30% of the focussing process is carried out by the variable focus lens


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Between the cornea and the lens is the iris, a circular sheet of muscle fibre; this muscle sheet gives the eye its colour. The pupil is the opening in this muscle sheet. Contraction and dilation of the Iris: ¾

Increases and decreases the depth of focus

¾

Controls the amount of light falling on the retina.

The retina, the light sensitive covering on the inside of the eye, contains two types of photoreceptor cells: Rods

Sensitive to low light illumination and relative movement at the extremes of vision.

Cones

Colour sensitive the cones are associated with both vision in good light and fine detail.

The focal point of the retina is called the fovea, this area contains cones and no rods. This is the point of highest visual acuity. Decreasing numbers of cones and increasing numbers of rods occur as the distance from the fovea increases. Colour discrimination is limited to small areas around the central fovea. Both rods and cones are connected to the brain by nerve fibres (neurones) which then combine to form the optic nerve. Each cone has a single neurone; clusters of rods share the same neurone. The nerve fibres combine as the optic nerve, the blind spot. After detection of light on the cones or rods nerve impulses travel along the optic nerve to the optic chiasma. This is where the optic nerves from both eyes meet. From the chiasma the impulses travel to an area of the brain known as the visual cortex, where the information from the eyes is interpreted into a usable message. Visual Acuity Visual acuity is the ability to perceive shape and detail. The highest visual acuity occurs when the retinal image is focused within 2° of the fovea. Light focused on the retina away from the fovea is less well defined and visual acuity falls rapidly towards the periphery of the eye. Peripheral vision is sensitive to movement but in order to distinguish detail an object must be looked at directly.


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6/6

VISUAL ACUITY

6/12

6/60 60

40

20

0

20

40

60

DEGREES AWAY FROMFOVEA

Relative visual acuity is measured by the Snellen's Test. A test type card is placed at 6 metres and the test is based on what a normal eye can see at that distance: 6:6 Vision

The ability to see at 6 metres what an average individual can see at 6 metres – average vision.

6:4 Vision

The ability to see at 6 metres what an average individual can see at 4 metres - better than average vision.

6:20 Vision

The ability to see at 6 metres what an average individual can see at 20 metres - worse than average vision.

Clarity of Vision Clarity of vision does not fully depend on visual acuity. External factors that can affect a persons clarity of vision include: ¾

Time of day

¾

Size, shape and contrast of an object with relation to its surroundings

¾

The distance an object is from the viewer

¾

Relative motion to the viewer

¾

Visibility – whether clear or hazy

Depth Perception To see clearly at different distances the eye makes two adjustments: ¾

A change in the refractive power of the lens to enable the eye to focus, and

¾

A change in the convergence of the eyes - binocular vertege.

For the brain to make judgement of depth certain cues are used:


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¾

Binocular vision (two eyes), people who are monocular make adjustments which compensate for the loss of one eye

¾

The relation, size and clarity of the object.

¾

The relative movement and texture of the object.

Distance Estimation and Depth Perception Cues to distance estimation and depth perception are easy to recognise when pilots use vision under good illumination. As the light level decreases, the ability to judge distance accurately is degraded and the eyes become more vulnerable to illusions. Pilots can judge distance at night if they understand the problems in obtaining accurate cues to distance estimation and depth perception. A pilot normally uses subconscious factors to determine distance where either single or a variety of cues is used. Accurate estimates of distance can be gained if the pilot is aware of the factors to be aware of. Cues to distance or depth perception are either monocular or binocular. Stereoscopic Vision The human being is able to focus both eyes on a single object. This is called stereoscopic vision. Each eye sees an object at a slightly different angle (binocular cues). The images seen are merged together and the human being sees a three dimensional object. Stereoscopic vision does not play a major role in depth perception over a distance of 12 m, beyond this range other static and dynamic cues are used. Binocular Cues Binocular cues depend on the slightly different view each eye has of an object. Consequently, binocular perception is of value only when the object is close enough to make a difference in the viewing angle of both eyes. When flying, most distances outside the cockpit are so large that the binocular cues are of little value. Binocular cues operate on a more subconscious level than the monocular cues. Monocular Cues Several monocular cues aid in distance estimation and depth perception such as: ¾

Geometric perspective

¾

Motion parallax

¾

Retinal image size and

¾

Aerial perspective.


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Geometric Perspective Where an object appears to have a different shape when viewed at varying distances and from different angles. The types of geometric perspective are explained in the following paragraphs. Linear Perspective Parallel lines, such as railway lines, tend to converge as distance from the observer increases.

Apparent Foreshortening A problem where distant objects appear elliptical due to their distance from the viewer. For example, a lake may look elliptical from a distance but the real shape is revealed as the distance to the lake reduces. Binocular vision is not essential for flying - there are one eyed airline pilots. Motion Parallax Considered the most important cue in depth perception. Motion parallax is the apparent, relative motion of stationary objects when viewed by an observer moving across the landscape. Near objects appear to move past; distant objects seem to move in the direction of motion or remain fixed. The rate of apparent movement depends on the distance the observer is from the object. For example, when driving a Go-cart the ground underneath appears to be moving fast; when flying at altitude the ground underneath seems to move slowly. Motion parallax can cause problems to pilots taxiing: A pilot who changes from a low cockpit height aircraft will taxy at a specific speed. The ground movement outside is one cue he takes his taxiing speed from. If the pilot changes to a high cockpit aircraft he will tend to taxy too fast as he uses the relative speed of the ground as his cue for the taxy speed. Retinal Image Size An image focused on the retina is perceived by the brain to be of a certain size. The factors that aid in determining distance using the retinal image are explained below: Known Size of Objects The nearer an object is to the observer, the larger its retinal image. The brain adapts to estimate the distance of familiar objects by using the size of their retinal image. The diagram


7-5


below shows how this method is used. A structure projects a specific angle on the retina, based on its distance from the observer. If the angle is small, the observer judges the structure to be at a greater distance. A larger angle indicates to the observer that the structure is close. In the case below, the observer can judge the distance from the object by the relative size. If no experience exists, an object’s distance would be determined primarily by motion parallax.

500 metres Eye 30 ft 10°

1000 metres

Eye

5°

30 ft

Increasing or Decreasing Size of Objects Using common sense, if the retinal image: ¾

Increases in size - the object is moving nearer the observer

¾

If the retinal image decreases - the object is further away. If the retinal image is constant, the object is at a fixed distance.

Terrestrial Association Comparison of objects, such as an airport with an aircraft flying, will help to determine the relative size and apparent distance of the object from the observer. Objects associated together are judged to be at approximately the same distance. In the diagram below, an aircraft that is observed near an airport is judged to be in the traffic pattern and, therefore, at approximately the same distance as the airport.


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Eye

Terrestrial Distance of Objects Used to Determine Distance Overlapping Contours or Interposition of Objects When objects overlap, the overlapped object is farther away as shown in the picture below. G-FIND must be the closest of the aircraft as it obscures the aircraft behind.


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Aerial Perspective The clarity of an object and the shadow cast by it are perceived by the brain and are cues to estimating distance. To determine distance with these aerial perspectives, most pilots use the areas discussed below: Fading Colours or Shades Objects viewed through haze, fog, or smoke are less distinct and appear to be at a greater distance than they really are. If an object is seen more distinctly in clear air it appears to be closer than it actually is. Loss of Detail or Texture Distant objects become less discrete. If a ploughed field is viewed from a distance it appears brown. As the observer closes, not only does the colour appear brown but also the ruts of the ploughing become visible. Position of Light Source and Direction of Shadow All objects cast a shadow if lit. The direction of the shadow depends on the position of the light source. If the shadow is toward the observer, the object is closer than the light. Emmetropia The healthy state of the eye when fully relaxed. Parallel rays of light are focused on the retina.

NORMAL

Myopia (Short Sightedness) In short sightedness the eye is longer than normal and this results in an image focusing in front of the retina. Accommodation (focusing) by the lens cannot overcome this deficiency.

SHORT SIGHTED (MYOPIA)

Distant objects will be out of focus, with close up vision being satisfactory. To correct short sightedness a concave lens is used.


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Hypermetropia (Long Sightedness) In long sightedness a shorter than normal eye results in the image being focused behind the retina.

LONG SIGHTED (HYPERMETROPIA)

Close up vision is blurred yet long distance vision is usually clear. To correct long sightedness a convex lens is used. Presbyopia Close up vision deteriorates with increasing age. Hardening of the lens in people over 40 results in a mild form of long sightedness. This is known as presbyopia. Difficulty in reading fine print in poor light is normally the first sign of the onset of presbyopia. Half Moon spectacles are used to correct the defect; corrections for middle and distant vision can be made by using bifocal, trifocal or even quadrifocal lenses. Hardening of the lens may also result in clouding of the lens. This clouding is associated with cataract formation. Pilots with early cataract problems may see an eye chart, but can have difficulty in bright light. Due to the scattering of light as it enters the eye this sensitivity may be disabling under certain circumstances. Any clouding of the eye should be investigated immediately. Astigmatism An optical defect caused by abnormalities to the surface of the cornea or lens. In a healthy state the cornea is spheroidal, like a football. The astigmatic cornea is oval shaped, like a rugby ball. Errors caused by astigmatism can be corrected by a cylindrical lens. Spectacles Variable focus lenses are an alternative to bifocal or multifocal lenses. There is no clear demarcation between upper distance vision to near vision correction in the lower portion of the lens. Distortion also occurs near the periphery of vision. Because of these problems varifocal lenses are not advised for use in flying. Contact Lenses Contact lenses provide better peripheral vision and are not subject to misting. There are a some problems associated with flying with contact lenses. The cornea does not have its own blood supply and obtains oxygen from the ambient air, the contact lens may starve the cornea


7-9


of the oxygen required. Mild hypoxia and dehydration, caused by the low humidity on the flight deck also increase the potential for corneal damage. Cabin decompression can result in bubble formation. Rubbing of the eyes may dislodge a contact lens. Before a medical certificate can be annotated approving the wearing of contact lenses the applicant must provide a report from an ophthalmologist or contact lens practitioner. If all requirements are met then the use of contact lenses is approved; the certificate usually carries an annotation stating that a pair of ordinary spectacles must be carried in flight whilst the contact lenses are being worn. Bifocal contact lenses, for the correction of presbyopia, are unsuitable for flying. During a rejected take-off in a B747 the flight engineer lost visual co-ordination between the throttles and EPR gauges and advised the captain that the number three engine was losing thrust. The cause of the engineer’s action was attributed to his multifocus lens spectacles which he was wearing for the first time. The above example shows the importance of wearing the correct spectacles and the time it takes the eye to adapt to them. Radial Keratotomy Radial keratotomy is a surgical procedure that creates multiple radial, spoke-like incisions on the cornea of the eye to produce better visual acuity. Glare sensitivity can be a complication of the procedure which may be troublesome at night. Other complications include fluctuating visual problems because of corneal swelling and increased susceptibility to injury. Possible long-term complications of this procedure are unknown and no pilot should undergo the treatment. Colour Vision and Colour Blindness People with normal colour vision can distinguish up to 120 different colours and over 1000 differing shades of these colours. 8% of the male population and 1% of the female population cannot distinguish between red and green. There are 4 types of red/green colour blindness: Protanopia

Blue-green appears grey; red-purple appears grey

Protanomalia

Blue-green appears an indistinct grey; red-purple appears an indistinct grey

Deuteranopia

Green appears grey; purple-red appears grey

Deuteranomalia

Green appears an indistinct grey; purple-red appears an indistinct grey


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Total colour blindness is rare but can be found in both males or females. Two types of total colour blindness are known: Typical

The person has no colour discrimination and sees everything as black or white. If a person suffers from this type of colour blindness then they usually suffer from other types of visual impairment.

Atypical

A condition where only very clear colours can be discerned.

Colour vision is affected in people who do not have colour blindess by: ¾

Yellowing of the cornea and lens due to old age.

¾

Smoking and alcohol.

Normal colour vision is not essential for flying. However, there is a need to be able to distinguish between red, green and white lights in order to comply with: ¾

The rules of the air by night

¾

Light signals from the ground

¾

Aerodrome signs and markings

¾

The changing colours associated with glass cockpit displays

Night Vision If the amount of light entering the eye changes then any initial coarse adjustment is made by the iris to close or open the pupil which allows more or less light into the eye. Because the pupil has only a limited capacity a second process is required. Chemical changes which involve both the rods and cones take place. As light intensity decreases colour discrimination of the cones is difficult. It is at this stage that the rods, which are sensitive to low level illumination take over vision from the cones. The rods contain a pigment, visual purple (Rhodopsin) which is bleached by bright light. The chemical change takes a finite time as the light decreases. This dark adaptation time is approximately: ¾

30 minutes for the rods

¾

7 minutes for the cones - the fovea contains no rods so maximum visual acuity at night is achieved by looking at objects off-centre.

Best night vision is achieved after this 30 minute adaptation period. Night vision is lost immediately when the eye is exposed to bright light. The major factors that affect night vision are: Hypoxia As low as 4000 ft night vision begins to deteriorate, by 14 000 ft it is possible that up to 40% of night vision will have been lost.


7-11


Smoking Carbon monoxide in tobacco smoke, forms a strong bond with haemoglobin. The carboxyhaemoglobin produced reduces the amount of oxygen that is carried by the blood. A heavy smoker can suffer from hypoxia well below 10 000 ft with a consequent loss in night vision. Other factors include, age, alcohol intake, illness and the use of stimulants Saccadic Eye Movement When the eyes are not tracking a moving target they move in a series of jerks called a saccade. This movement takes approximately 1/3 second. As a result of saccadic eye movements, it is not possible to make voluntary, smooth eye movements while scanning featureless areas. Autokinesis A problem that occurs because of the saccadic movement of the eye. If a person stares at a single point of light such as a star then after about 5 to 10 seconds the star will appear to move. This can appear to the pilot as another aircraft in the sky. Sunlight and its Effect on the Eyes Very high levels of light are encountered at high altitude, especially when an aircraft is flying over a flat sheet of cloud. Two parts of the light spectrum can cause damage to the eye: Blue Light

Long term exposure may cause cumulative damage to the retina.

Ultra Violet (UV) Light Prolonged exposure to UV wavelengths can also cause damage. UV rays are absorbed by the lens and cause a painful swelling, accompanied by extreme sensitivity to light better known as snowblindness. It is produced only after prolonged exposure to high-intensity sunlight, such as that reflected into the eyes by cloud. Ultraviolet burns do not normally produce permanent damage to the eye. UV wavelengths are normally filtered by the cockpit windshield. Empty Field Myopia When flying at altitude, at night or above cloud where there is no definite pattern of earth or sky to focus upon, the eye adopts a resting focus of 1 - 2 metres away. Distant objects have to be relatively large to be seen. Effort is needed to refocus the eye on infinity. In order to see objects outside the flight deck the eyes should be focussed on objects such as the wing tips or clouds. Glare Glare is caused when flying above a layer of cloud or flying into a low sun. The brightness contrast outside and inside the cockpit can make it difficult to read the instrument panel. Photochromatic lenses are now commonly used by pilots but these adapt to ambient light slowly. A problem may occur when changing from bright light to relatively darker backgrounds


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27 November 2003

eg sunlight to cloud. Pilots should be aware of the possibility of ending up flying blind without realising. Sunglasses Cumulative damage to the retina can occur over a number of years due to glare. Good quality sunglasses give protection by filtering out both blue and ultra violet light. Flickering Light Bright flickering light can cause epileptic type fits. Helicopter passengers have suffered fits because of the rotor blades turning in bright sunlight and causing a flicker effect. An individual may feel uneasy or suffer discomfort in this flicker environment. Precautions can be taken by a sufferer such as wearing sunglasses. It is possible that the warning symptoms of mental unease or discomfort can last for a few minutes, but this cannot be relied upon. The following suggestions are made with reference to flickering light: Pilots If a pilot suffers from flickering light effect: ¾

Wear sunglasses.

¾

Turn away from the sun to reduce the flicker effect.

¾

Land immediately.

Passengers Affected passengers are usually on the sunny side of the aircraft. To reduce flicker effect: ¾

Wear sunglasses.

¾

Cover adjacent windows.

¾

Cover or close the eyes.

¾

Move to a seat which is not affected by the sun.


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7-14

27 November 2003

Chapter 8. Aviation Medicine – Visual Illusions Introduction This chapter discusses the problems of visual illusions. Vestibular illusions are discussed in a later chapter. Who needs instruments he said, with perfect eyesight like me? My approach seems just right, he thought one black night and calmly flew into the sea. Anon Spatial Orientation Changes occur as we grow from being a baby into early childhood. Gradually a baby learns about the forces that affect our orientation in the world. From that early age we begin to understand the force of gravity (G) and how it always acts vertically down. It is later in life that we learn that the force of gravity exerts a force of 1G, and that our visual horizon is horizontal with this force. When pilots determine spatial orientation they use different senses: ¾

The eyes

¾

The vestibular system in the inner ear

¾

The proprioreceptive sensors in the skin that confirm our position with the vestibular and vision senses – “seat of the pants”

To determine visual orientation other factors are taken into account, some of which are listed below: ¾

The colour of an object

¾

The size and shape of the object

¾

The perspective

¾

Hue (shade) and parallax

¾

The groupings of objects

Problems with spatial orientation begin with the eye – brain interface. “Seeing is believing” is often used, unfortunately, the eye does not always transmit enough information to the brain for us to interpret the truth. When dealing with Human Information Processing (HIP) we shall use the term “perception”. This part of the HIP process is built on past experience and expectation. So we can say in some instances that the eye is confused because perception has made its best attempt at telling us the truth.


8-1


The two pictures that follow show how easy it is to confuse the brain. The reversible goblet is a simple example of how perception is not a static process. You see a candelabrum or two faces looking at each other. The brain does not fix on one image, but constantly reminds you of each picture. In reality, you are unable to concentrate on one of the interpretations; both the candelabra and faces are continuously interpreted.

A more difficult interpretation is the Toulouse Lautrec picture shown below.

Within the picture is an old lady and a young lady. Once unlocked it is difficult to concentrate on just one of the depictions in the diagram. In both pictures you have been given no depth clue. The next diagrams are included for interest and rely on you believing that the flat plane is in fact 3-dimensional.


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27 November 2003

The circles diagram uses the concept of relative size. The centre circles are the same size but the one on the right looks larger. The tuning fork is an impossible diagram if looked at closely.

The two line diagrams are viewed as perspective drawings and the central two lines are seen as curves. Both lines are straight and parallel. Sight is the most powerful sense. However, in the diagrams above, you have been easily deceived into believing what is obviously false. In the next pages we look at how this deficiency translates into the airborne environment. Spatial Disorientation Since the 1920’s when the Royal Air Force designed the first blind flying panel the problems of instrument flying have been recognised. The standard “T” of instruments that you use in modern aircraft was in fact developed in 1927. By training and technological innovation, the number of accidents attributed to disorientation has fallen over the past few years. It must be remembered that if the power of vision is removed then the pilot will lose control of the aircraft. The USAF demonstrated this by using a simple test. Three experienced pilots flew simple manoeuvres with their visual and instrument clues removed. The results in the diagram below show that in straight and level flight control could only be maintained for approximately 60 seconds.


8-3


Pilot 1

80

Time From Loss of Visual Cues to Loss of Control (Seconds)

Pilot 2 Pilot 3

60

40

20

Straight and Level

30° AOB Turn

Landing During training to take-off and land a pilot determines his position with reference to cues around the airfield. These can include: ¾

The size and shape of familiar objects

¾

The speed at which these objects pass in the peripheral vision

¾

The gradient of the terrain

¾

The covering of the terrain (English Countryside, water, desert etc)

¾

The brightness of the terrain

¾

The visual angle between the horizon and the touchdown point

¾

The rate of closure of the touchdown point

No pilot will use all the cues all of the time, unconscious attention is paid to their own individual “favourites” that are cultured during training. When one or more of the cues is removed or altered then difficulty in landing or taking-off may occur. Width of Runway The pilot uses the PAPI or VASI system to judge the visual angle of approach at most airfields. Where these aids are not available then the pilot has to revert to basic visual cues taught in training.


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27 November 2003

Low Approach

Normal Approach

High Approach

Assuming that the above diagram is for the same width runway a pilot should have no problems in believing that: ¾

If the aircraft is low then the runway appears flat and short

¾

If the aircraft is high that the runway appears long and thin.

The considerations change when the three runways have a different width. For example, if the first runway is very wide, the middle runway is normal and the one on the right is very narrow. All the approaches could in fact be normal for their respective runway width.


8-5


This can compound the errors during an approach where no PAPI or VASI are fitted. If the pilot is on an approach to a runway that is narrower than the one normally used, then the thin runway may be interpreted as being farther away than the normal width runway or that the aircraft is high. The aircraft may be descended early and land short. Approach During a 3° approach the angle between the pilot’s eye and the touchdown point must be 3°. Visual Horizon 3°

Visual Touchdown Point

The pilot aims the aircraft at the touchdown point and as it approaches the runway, just before landing the ground seems to flow away from a central visual impact point.

The visual impact point and the touchdown point are different. The aircraft will touch down on the runway before the visual impact point. Landing cues are used as the aircraft gets nearer the ground, these include the apparent: ¾

Speed that the ground passes the peripheral vision

¾

Size of objects on the ground


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27 November 2003

These cues are easily lost when the approach is made at night, over water, desert or snow it is then that problems occur. Runway Gradient and Terrain Where the runway slopes to the threshold, or the terrain slopes into a level runway, the pilot may misinterpret his approach height. The diagrams below give both the side view and the view of the runway that the pilot may expect. Normal Approach The pilot sees the “correct” picture for the runway and the correct approach path is made.

View of Runway

Runway Slopes Up With a runway that has an upslope, the pilot will see the runway as long and thin and may believe that he is too high. A possible action is to correct to what the pilot believes is the correct approach path, which will involve the aircraft descending and possibly landing short. View of Runway

Runway Slopes Down A runway with a downslope will be seen as short and fat. The pilot may believe that the aircraft is too low and fly the aircraft high to achieve what he believes is the correct approach. The aircraft will be high with the possibility of landing long.


8-7


View of Runway

Ground Sloping Down to the Runway As the aircraft approaches the runway the terrain appears to be too close to the aircraft. The feeling is one of being too low and the aircraft is climbed.

Apparent Height

Real Height

Ground Sloping Up to the Runway The impression on the approach is that the aircraft is high because the terrain appears to be too far away. The aircraft may be descended in this case.

Real Height

Apparent Height

Visual Illusions in the Air Lean on Cloud Clouds are not like the visual horizon that a pilot flies to. It is possible for the cloud to have slope. Pilots who believe that the cloud is level are liable to align the aircraft with the horizon given by the cloud and sky.


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27 November 2003

The worst possibility occurred over New York in 1965, where a B707 and L1049C collided. The pilot of one aircraft levelled his aircraft to the visual horizon given by a flat sheet of cloud, the other aircraft flying straight and level appeared to be turning in towards his aircraft. Turning to take evasive action caused the aircraft to collide. Lean on Sun A partial visual illusion because the aircraft is in cloud. Where an aircraft is flying close to the top of cloud it is possible to make out the position of the sun. The pilot interprets this brightness as the sun being vertically above the aircraft. The sun is rarely directly above and in the diagram below it is positioned to the left of the pilot. In this case the aircraft is banked left to bring the aircraft into the perceived vertical position.


8-9


Black Hole Effect During night flying accidents occur because the pilot’s visibility is determined by the greatest distance that lit obstacles can be seen. Darkness degrades or eliminates most of the visual cues so depth perception is degraded or totally removed. Lit objects are seen at a greater distance at night than by day. When a pilot approaches a runway over terrain that does not have any lights such as desert or water judgement becomes difficult – known as the Black Hole Effect. Where an approach is made over unlit terrain such as water or desert the pilot sees the runway lights at a greater distance than the runway would be seen during the day. The perception is that the aircraft is high on the approach to the runway. Under these conditions it is possible to misjudge the approach and land short of the runway. At night bright lights and good visibility lead to an under-estimation of the distance. Conversely low light and poor visibility lead to an over-estimation of the distance. A pilot on a “Black Hole” approach varies the descent profile by reference to the visual perspective this can also be aggravated by other factors (Kraft and Elworth): ¾

If a long, straight approach is made to an airport located near to a small town

¾

The pilot is not familiar with the runway length/width combination

¾

The airport is at a slightly lower elevation than the surrounding terrain

¾

The airport does not have a good lighting system


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27 November 2003

¾

Small settlements are spread over an area around the airport

Visual Factors at Night Other factors that mislead pilots flying at night: ¾

A brightly lit runway will make the runway appear closer than it really is. This may cause the pilot to descend early.

¾

Flying in clear air at night, brightly lit objects appear closer than they really are.

¾

If the horizon is obscured scattered lights can be mistaken for stars. This can give the pilot the sense that the aircraft is nose high and a correction nose down is made.

¾

If the horizon is obscured then the distant lights of a city may make the horizon seem to be lower than it actually is.

¾

Rain on the windshield can convince a pilot that he is too high due to the refraction of light. It is possible that an error of 200 ft per nautical mile can occur.

¾

When an airport is viewed through a rain shower the runway lights bloom and appear bigger than they really are causing the pilot to believe that the aircraft is high.

¾

Flying over a dark sea at night when no stars are visible it is possible that the pilot may misinterpret fishing boat lights below the aircraft as stars. The misconception is that the aircraft is upside down and the pilot rolls the aircraft to put these “stars” above him.

Reaction Time Where an aircraft is approaching head on the retinal size of the approaching aircraft is small until a short time before impact. Where a target is moving across the visual field the “pick up” time is much shorter. 3 SEC ½°

1.5 SEC/1°

.75 SEC/2°

.1 SEC/ VERY BIG INDEED


.38 SEC/4°

8-11


Peripheral vision is good at picking up the movement across the eye by using the rods. In the diagram below two aircraft on a collision course are on a constant bearing at a constant speed.

B

A If the constant bearing is maintained and there is no relative motion then aircraft B will be stationary in aircraft A’s visual field. The movement needed to stimulate the rods is absent and the pilot in aircraft A will not see aircraft B until shortly before the collision. The aircraft subtends such a small angle on the retina till it is within 0.4 seconds of impact. Probably too late for any corrective action. Visual Acuity Visual acuity has been described as the capacity of the eye to resolve detail. The acuity across the eye reduces rapidly as soon as we are more than 2° away from the fovea. Blind Spot The eye has a Blind Spot. In normal vision a person does not notice any deterioration in vision because of the position of the blind spot. Compensation is made by the saccadic motion (a jerk/rest cycle of 1/3 second) of the eye. The saccadic movement can be demonstrated by the following experiment. On a dark clear night, stand still and concentrate on a single bright star, after 5 to 10 seconds the star will start to move. A process known as Autokinesis.


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27 November 2003

To illustrate the blind spot look at the diagram below from about 30 cm. Then: ¾

Close the left eye

¾

Focus the right eye on the cross

¾

Move the picture slowly towards the face

As the picture gets closer the aircraft will disappear and then re-appear.


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27 November 2003

Chapter 9. Aviation Medicine - The Ear - Hearing and the Vestibular System Introduction The ear has two functions: ¾

The sense of hearing.

¾

The sense of balance.

The ear is divided into three parts; ¾

The outer ear

¾

The middle ear, and

¾

The inner ear.

The outer and middle ear react to vibration and are solely involved in hearing. The inner ear is divided into two parts: Cochlea

Responsible for the transduction of the atmospheric vibrations into electrical energy transmission to the brain.

Vestibular Apparatus

Responsible for balance.

Ossicles

Semi-circular Canals Otoliths Cochlea

Tympanic Membrane (Ear Drum) Eustachian Tube


9-1


Sound waves travel through the outer ear and cause the ear drum (tympanic membrane) to vibrate. The vibrations are amplified and conducted across the middle ear (the conductive system) by the Ossicles (Malleus, Incus and Stapes) to the inner ear. The cochlea converts the vibrations to nerve impulses which are then relayed to the brain and interpreted as sound. The middle ear is an air filled cavity and connected to the back of the nasal passage by the Eustachian Tube. This tube provides the means of equalising pressure between the outer ear and the middle ear. Noise Sound vibrations or pressure waves (noise) have two variable factors which directly affect any damage to the ear: Intensity of Sound

This depends on the amplitude of the sound waves and is registered as loudness.

Frequency

The number of cycles per second, this is pitch.

The frequency range of human hearing extends from 20 - 20 000 Hertz. 50 - 100 Hz

The hum from a mains voltage system.

256 Hz

Middle C on the piano.

300 - 500 Hz

Speech range.

8000 Hz

The upper level of the speech range

Sound intensity is usually registered in decibels (dB). A list of sounds and their noise rating are given below: 0 dB

Threshold of hearing.

15 dB

Whisper.

30 dB

Conversation.

45 dB

Conversation in a busy office.

60 dB

An orchestra playing loud music.

90 dB

Pneumatic drill.

120 dB

Piston aircraft engine a few feet away.

125 dB

Disco.

130 dB

Jet aircraft noise a few feet away.

150 dB

Jet aircraft with afterburner selected.


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27 November 2003

Effects of Noise Damage to the ears depends on: ¾

The intensity of the noise

¾

The duration of the noise

If the hearing system is subjected to noises in excess of 85 dB temporary hearing loss can occur. Where there is exposure above 85 dB for more than 8 hours a day over a long period permanent hearing loss may occur. Excessive exposure to noises above 120 dB for several hours a day for 3-6 months will cause Noise Induced Hearing Loss (NIHL) or deafness. With noises above 120 dB: ¾

120 dB

Discomfort to the ears.

¾

140 dB

Pain to the ears.

Other problems associated with noise include: ¾

Where 100 dB is heard: ¾

A frequency below 100 Hz causes the body to sweat

¾

High intensity noise can affect mental and physical co-ordination, and lead to disorientation

¾

High intensity noise below this danger level must be regarded as a stress factor and can lead to a decrease in efficiency

Conductive Deafness Deafness because of damage to the middle ear can be caused by: ¾

The perforation of the eardrum, or

¾

Infection to the middle ear, or

¾

Displacement of the Ossicles.

This damage can often be repaired and does not necessarily result in hearing loss; if permanent hearing loss occurs it is known as conductive deafness. Cochlea Damage to the cochlea is more serious and can be irreversible. Cochleal implants are possible and these return some of the hearing loss. The cochlea is full of sensitive membranes connected to nerve ends which respond to vibrations. This vibration generates movement in the nerve impulses which the brain translates as sound.


9-3


Noise Induced Hearing Loss (NIHL) If the membranes in the cochlea are “over vibrated” then they can be permanently damaged. These hairy membranes are bent over permanently and are unable to recover. High frequency acuity is usually the first area of the auditory range to be lost; known as high tone deafness. Protection Against Noise Hearing protection is simple and should be used by pilots. The effects of jet engines, engineering sheds, car noise, discotheques or even personal stereos can damage the hearing. Ear defenders (ear muffs) or ear plugs are very effective in attenuating (weakening) noise: Ear Plugs

Protection of up to 25 dB

Headset or Ear Defenders

Protection up to 45 dB

Presbycusis Presbycusis is the loss of hearing that gradually occurs in most individuals as they grow older. Hearing loss is a common disorder associated with aging. About 30-35% of adults between the ages of 65 and 75 years have some hearing loss. Age reduces the effectiveness of the auditory system; high frequency acuity is usually affected first. Vibration Vibration affects both the visual and psychomotor performance. Where frequencies between 1 – 20 Hz are experienced the following physical symptoms may occur: 1 – 4 Hz

Breathing problems

4 – 10 Hz

Possible chest and stomach pains

8 – 12 Hz

Lumbar region pains

10 – 20 Hz

Headaches and possible eyestrain

The Vestibular System The vestibular system of the ear consists of: ¾

The semi-circular canals which detect angular accelerations of the body, and

¾

The otolith organs, the utricle and saccule, which detect linear acceleration or deceleration.


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27 November 2003

Semi-Circular Canals There are three fluid filled semi-circular canals in each ear. The canals are set in three planes at right angles to each other and are named the Lateral Canal, the Anterior Canal and the Posterior Canal.

SEMICIRCULAR CANALS

VESTIBULAR NERVE TO BRAIN UTRICLE

AUDITORY NERVE

SACCULE

COCHLEA

At the base of each canal is a sensory organ, the cupola. The cupola is a saucer shaped valve anchored at one end to the semi-circular canal, detecting movements of the fluid it contains. These movements are turned into electrical signals - since there are 3 canals at right angles the brain can use these signals to give 3-dimensional information to help control balance and tell us which way up we are.

With no acceleration the cupula remains vertical

During any lateral motion the fluid in the canal begins to move. The cupula is then deflected in the direction of fluid movement.


9-5


As a state of equilibrium is reached the cupula overcomes the movement of the fluid and returns to a state of rest.

When rotation stops the fluid within the canals, because of the inertia, will cause a deflection of the cupula in the opposite direction.

Since the semi-circular canals are at right angles to one another the forces of acceleration in yaw, pitch and roll can be detected. In the absence of visual cues, the brain will interpret these stimuli as: ¾

Acceleration as movement

¾

Simple acceleration

¾

Changes of acceleration

¾

Constant velocity

In general terms, the semi-circular canals sense any angular movement by the body. Otoliths The otoliths are sensitive to linear movement and the force of gravity. The two Otoliths, positioned below the semi-circular canals in the inner ear are made of calcium carbonate. Movement in a linear sense can give a false impression of climbing or descending.


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Chapter 10. Aviation Medicine – Vestibular Illusions Illusions of Vestibular Origin The Leans A term used to describe a false sensation of bank when the aircraft is, in level flight. This illusion can occur in both VFR and IFR flight:

The aircraft is initially flying straight and level

The pilot allows a wing to drop at a rate that is below that required to stimulate the fluid in the semicircular canals The pilot still believes that the aircraft is flying straight and level The pilot detects the error and returns the aircraft to straight and level. The rate of roll is fast enough to stimulate the fluid in the semicircular canals

The fast roll induces the pilot to believe that he is in a turn in the direction of the roll


10-1


The false sensation of bank may persist for up to an hour, but this is unusual. To overcome the sensation flying must be referenced to the instruments. This can be draining especially if the sensation lasts for a long time. In some cases the pilot may align his body with the apparent vertical, rather than the normal axis of the aircraft. In a two pilot aircraft control should be always given to the other pilot. Somatogravic Illusion Somatogravic illusions occur when the Otoliths are stimulated by a linear acceleration. When standing still the perception is that gravity acts vertically down. In the Somatogravic Illusion any accelerating force can cloud this perception. When short term linear acceleration is experienced then the pilot can easily distinguish between that and gravity. If the acceleration is long term, as an aircraft accelerating, the brain is unable to distinguish between the resultant acceleration and the acceleration due to gravity. The acceleration is combined with that of gravity to give a resultant force.

Force (F) Resultant (R) Gravity (G)

The Somatogravic Illusion in Yaw and Roll During a prolonged visual turn the pilot knows that the aircraft is turning because of the visual clues given by the instruments and the visual horizon. If the visual clues are taken away, the pilot will still sense the turn because of the stimulation of the fluid in the semi-circular canals. As soon as a steady turn is achieved the fluid in the semi-circular canals reaches an equilibrium and the cupola returns to the normal position. The pilot loses all sense of a turn and the perception is that the aircraft is flying straight and level.


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27 November 2003

Perceived Resultant Force

F

R G

Where: F

Inertial force of radial acceleration

G

Gravity

R

Resultant force


10-3


In a flat turn, the opposite occurs; the pilot believes that the aircraft is banking in a turn.

Perceived Resultant Force

F

G

R

Somatogravic Illusion in Pitch Of greater importance is the somatogravic illusion in pitch. Where the speed is linear and there is no acceleration the pilot will sense the forces below.

Up

Down G


G

10-4

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27 November 2003

During a sustained acceleration, the pilot feels that the aircraft is in a nose-up attitude because of the resultant force. The illusion takes approximately one minute to develop fully.

Acceleration

Up Pitch Up

F F R

F R

G

Down

G

R

G

Where: F

Inertial Force due to Acceleration/Deceleration

G

Gravity

R

Resultant Force

Even a brief acceleration, such as a catapult launch (5g for 2-3 seconds), can give rise to an apparent nose-up attitude of 5°, which may take a minute or more to die away. Conversely, during a sustained deceleration such as applying airbrakes, the aircraft may appear to pitch down.

Deceleration

Up

Pitch Down F R G

F F

Down

G R

G

R

The somatogravic illusion can occur during take-off or on a missed approach and is a particular danger at night or in poor visibility. The natural response of any pilot is to counteract the pitch up sensation by pitching the aircraft nose down. This increases the acceleration because of the unloading of stick forces and the sensation becomes worse. The more the pitch down the greater the sensation of pitch up and hence the worsening of the illusion. Note: If an aircraft is fitted with an air driven artificial horizon, as the aircraft accelerates, the indications given will support the somatogravic illusion ie a pitch up indication.


10-5


The diagrams below taken from an accident report show how the aircraft was bunted into the ground. The pilots sensed that the aircraft had pitched up and flipped onto its back.

G-Excess Illusion A sensation of angular movement can be induced in a turning aircraft. The movement of the head in a turn when looking down at the instrument side panel can induce a tumbling sensation. Neither the movement, whether forward or backward, nor the rate, is consistent between individuals. Experiments have shown that a forward head movement in pitch made during a pull up from a dive produces a sensation of tumbling forward in pitch. The illusion occurs because of: ¾

A cross coupled stimulation of the semi circular canals, or

¾

A transient stimulation of the Otoliths

The Oculogravic Illusion The oculogravic illusion is regarded as a visual component of the somatogravic illusion. During acceleration the pilot can experience a pitch up sensation. This can be accompanied by the apparent upward movement of objects within the visual field. On deceleration, the visual field may appear to move downwards. The mechanism is not primarily because of eye movement, but the perception of how the brain has interpreted the sensation. If the external visual field is well defined the illusion is not a problem.


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At night, when only a few stars or isolated lights are visible, or where external visual cues are largely inadequate, such as flight over water or desert, the oculogravic illusion can cause spatial disorientation. The apparent movement and transient displacement of light sources in the external visual scene may be interpreted by the aviator as a change in aircraft attitude, Alternatively, the apparent movement of an isolated light may be misinterpreted as the light of another aircraft. In normal flight the lights of the runway appear to be below the aircraft.

Horizontal

As the aircraft accelerates the resultant force gives the illusory movement of the lights upwards. The pilot may assume this is a nose down change in attitude and counteract with a pitch up to what he believes is a safe attitude. The perception is in the opposite direction to that of the somatogravic illusion but is produced by the same change in the direction of the resultant force vector.

ACCELERATION

Apparent upward motion of lights

If there are no external visual cues, the somatogravic illusion is dominant. Elevator Illusions Visual illusions can occur when there is a change in the magnitude of the vertical forces. These are termed Elevator Illusions, as they were first experienced in the high speed lifts built in America in the 1920’s. In an updraught the gravity vector increases and there is a sensation of moving up. This is confirmed by an apparent up movement of the visual field. The converse happens in a downdraught.


10-7


False Perception of Angular Motion – Vertigo Vertigo is defined as an illusory sense of turning. Unfortunately, the term has now become synonymous with spatial disorientation. Somatogravic and oculogravic refer to linear motion, for angular or rotating motion the terms somatogyral and oculogyral are used: Somatogyral Illusion The semi-circular canals sense angular acceleration. During a prolonged turning manoeuvre at constant angular speed such as: ¾ A co-ordinated turn ¾ A sustained roll, or ¾ A spin the correct information is sensed for the first few seconds.

O

2-3 Seconds

15 Seconds

Roll Right Angular Motion Starts

Cupola Returns to Normal Position

Cupola Deflection

The initial sensation of a right turn will be lost after approximately 15-30 seconds. This depends upon: ¾ The speed of rotation ¾ The axis of rotation ¾ Cues from other sensory organs, and ¾ The extent to which the pilot is familiar with the motion Figures given by the USAF state that, for a typical spin pilots will be unable to perceive rotation by purely vestibular means after 15-30 seconds. Spin direction can be determined from the blurred view of the outside world or by checking cockpit instruments.


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Visual cues are usually adequate to allow the appropriate recovery action. Recovery produces an angular acceleration in the opposite direction to that on spin entry.

15 Seconds

18 Seconds

30 Seconds

Roll Left Recovery Starts

Cupola Deflection

Cupola Returns to Normal Position

The sensation of turn in the recovery is in the opposite direction to that of the spin. This illusion occurs when the pilot is deciding whether the rotational component of the spin has ceased so that the recovery can be completed. The only reliable means of detection is reference to the visual references or instruments. If the rotation has been fast vision may have been degraded. It normally takes a pilot several seconds after the spin has ceased, for full visual acuity to be restored. The presence of false sensations and impaired vision can cause problems in the spin recovery. The pilot may sense that the spin has stopped before the full recovery is complete. If the pilot tries to pull the aircraft out of the dive then the aircraft may be overstressed. After recovering correctly, the pilot may make believe that the spin is now in the opposite direction. By attempting a recovery the aircraft may re-enter the original spin. This may result in a graveyard spin, the aircraft repeating the cycle several times. Oculogyral Illusions Where impairment of visual acuity is caused by rotation, the semi circular canals may pass illusory signals to disorientate the pilot. These take the form of apparent motion and errors in the position of visual objects. Not a problem in well defined visual conditions, but if external cues are poor, illusions can persist for a few minutes. When the rotational movement has stopped a light that can be seen clearly will appear to rotate with the observer. Illusions due to Cross-Coupled (Coriolis) Canal Stimulation Complex motion will stimulate more than one semi-circular canal simultaneously. This can cause interactive sensations causing spatial disorientation. Interactive illusions involving the


10-9


otolith organs may occur such as g excess illusion. Head movements made during an aircraft manoeuvre are the main cause of this type of illusion. Head movements made during the initial part of a turn, do not give any false sensations, because the semi-circular canals sense the movement correctly. During this time, each canal senses the angular velocity correctly. The imposed rotation and the angular motion of the head are sensed correctly. Any movement of the head after this initial period can result in the cross-coupling of the senses and the illusion occurs. Turning the head to change a radio frequency or Squawk is a common cause of Coriolis. Pressure Vertigo Pressure Vertigo is caused by pressure changes within the middle ear normally when clearing the ears in the climb or in the descent. The vertigo sensed is intense, with blurring of vision and apparent movement of the visual field. The duration is short and will last no longer than 10-15 seconds. Summary of Disorientation Prevention This can be considered under three headings: Aircraft Factors: Instrumentation: Quality of displays. Instruments which can be read quickly and un-ambiguously by night and day. Instruments adequate for manoeuvres and conditions expected. Reliability. Clear malfunction indication, Use of head up displays to assist transfer from external to internal cues and reduce head movements. Display should reduce perceptual conflict when external cues are uncertain. Flightdeck: Position ancillary instruments and controls so that head movements are reduced during critical flight phases. Configuration - a lack of well-defined aircraft frame of reference, contributes to break-off and leans.


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27 November 2003

Presence of sloping edge of canopy and instrument panel not aligned with transverse axis of aircraft, does not assist pilot to maintain level attitude when flying on external visual references. Operational Factors Recognise manoeuvres and flight environments which carry a high disorientation risk. Flight crew should fly only those aircraft, those manoeuvres and in those flight conditions which are commensurate with training, experience and proficiency. Flightcrew Factors Training and experience are of paramount importance: ¾

Selection. This is important because of the large difference between individuals in apparent susceptibility to disorientation in flight.

¾

Health. Disorders affecting vestibular and visual systems should result in grounding.

¾

Drugs. Susceptibility to disorientation increases when drugs are used eg hypnotics (sleeping pills) and especially barbiturates, anti-histamines (for hay fever), anti-motion sickness tablets (hyoscine) and alcohol. Many stay in the body for more than 24 hours.

Practical Advice to Flight Crew Preventative Advice: ¾

You cannot fly by the seat of your pants.

¾

Don’t allow control of the aircraft to be based at any time on seat of your pants sensations, especially when deprived temporarily of visual cues

¾

Do not mix instrument flying with flying by external visual cues unnecessarily.

¾

Make an early transition to instruments in poor visibility. Once on instruments, stay on instruments, until external cues are unambiguous.

¾

Maintain a high proficiency at flight in IMC.

¾

Be particularly vigilant in high risk situations - night, poor visibility, etc.

Do Not Fly: ¾

With an upper respiratory tract infection (common cold, ear or sinus infection).

¾

Under the influence of drugs or alcohol.

¾

When mentally or physically debilitated for any reason.

Make your first flight after a period off flying a simple VMC sortie. Experience does not make you immune. CROSS CHECK YOUR INSTRUMENTS AND TRUST THEM, THEY CANNOT ALL BE WRONG


10-11


Practical Advice on how to Cope with Spatial Disorientation when it Occurs ¾ You can dispel persistent minor illusions (eg leans) by redirecting attention to other aspects of flying. ¾ When suddenly confronted with strong illusory sensations: ¾ Get on instruments ¾ Maintain instrument reference and correct scan pattern ¾ Control aircraft to make instruments display desired flight pattern ¾ Don’t mix external visual and instrument references ¾ Seek help if disorientation persists, from co-pilot, ground control, etc. ¾

Finally, remember that disorientation is a normal response to the unnatural environment of flight.


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27 November 2003

Chapter 11. Aviation Medicine – High Altitude Environment Introduction The effects of high altitude have already been detailed in an earlier chapter. The aim of this chapter is to detail the effects of other high altitude problems such as: ¾

Radiation risks to flight crew

¾

Ozone

¾

Humidity in pressurized aircraft

¾

Pressurisation

¾

Oxygen and oxygen systems

Radiation JAR OPS lays out rules with respect to Cosmic Radiation. The only aircraft affected is Concorde. All aeroplanes operated above 15 000 m (49 000 ft) — radiation indicator All aeroplanes intended to be operated above 15 000 m (49 000 ft) carry equipment to measure and indicate continuously the dose rate of total cosmic radiation being received and the cumulative dose on each flight. The display unit of the equipment shall be readily visible to a flight crew member. Cosmic radiation consists of particulate radiation and photons produced when charged particles interact with the nitrogen, oxygen and other constituents of the earth's atmosphere. These charged particles enter the solar system and produce secondary radiation known to us as cosmic radiation. The sun continuously ejects charged particles. In normal conditions the charged particle from the sun is too weak to enter the atmosphere and has no effect on the public transport flight crew. At certain times, the solar particles have enough energy to penetrate the atmosphere and substantially increase the dose equivalent rate at these altitudes. The earth's magnetic field deflects a large percentage of the charged particles approaching the earth. This protection is most effective at the geomagnetic equator near the geographic equator. At the magnetic equator the lines of force are nearly parallel to the surface of the earth and provide a shield which repels the charged particles. Where the magnetic lines of force are perpendicular to the surface of the earth the shielding effect is minimum. This is found at the magnetic poles. Tests show that the dosage rate over the poles is twice that of the equator. Most airlines operate great circle routes over the poles.


11-1


Risk to Flight Crew Cancer is the main risk from exposure to Cosmic Radiation. Although low, the risk for flight crew is there. For 1000 flight crew who fly the Atlantic between London and New York for 20 years it is perceived that 6 will die because of work related cancer. In the normal population of 1000 people, approximately 250 would be expected to die of cancer. Hereditary risk is also possible. Where a parent has been exposed to radiation it is possible that a child will inherit any radiation induced genetic defects. Ozone Ozone is a highly toxic gas. In small amounts it is an irritant to the lungs. If large amounts are inhaled then it is deadly. Stratospheric ozone is formed by the action of ultraviolet light on oxygen. Ozone is found in large quantities around 115 000 ft. The amount of Ozone reduces as the altitude is reduced. Below 40 000 ft there is little or no free ozone in the atmosphere. At the altitudes that Concorde cruises it is possible, in Polar Regions, that the Ozone content of the atmosphere can reach 1 - 2 parts per million (ppm). This Ozone still has to penetrate the pressurized cabin. Ozone is destroyed by heat and by the catalytic action of materials such as nickel. To totally destroy the Ozone bond the temperature required is 400°C. The air in the cabin pressurization system is heated above this temperature thus removing the Ozone before the air is used in the cabin. Problems may occur when the engine power is reduced for the descent. Tests have shown that the content of Ozone in the cabin can reach a level of no more than 0.5 ppm. The length of exposure and the low concentration of the gas have no long lasting effect. Humidity Water Vapour Water vapour is always present in the atmosphere as a gas. The concentration of this gas varies dependent on the climate and conditions. The body needs to have a moist atmosphere to function normally. To function correctly the lungs need to be constantly moist. The amount of water vapour in the atmosphere is measured in terms of Relative Humidity. Relative Humidity Relative Humidity is the amount of water vapour present in the atmosphere and is measured as a percentage. Amount of Water Vapour in the Atmosphere

/ Total Amount of Water Vapour the Atmosphere can hold x 100 (%)

Temperature is the major determining factor. Warm air can hold more water vapour than cool air. Air at high altitudes is cold and therefore holds less water vapour than air at low altitude.


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27 November 2003

For maximum comfort the water vapour should be approximately 40 – 60%. When flying long haul it is possible for the humidity to drop to as low as 5%. Humidity Control Humidifiers provide a means of increasing the moisture content of the air received into the system when operating at high altitudes. This reduces the discomfort caused by the action of excessively dry air. Humidifiers are normally located in the fuselage ducting just down-stream of the heating and refrigeration equipment. Pressurisation Pressurised Cabins Modern transport aircraft are pressurized to a cabin altitude of between 6000 to 8000 ft. This gives the passenger and crew: ¾

Protection from high altitude problems such as Hypoxia and Decompression Sickness

¾

A comfortable environment in which to exist

Most modern aircraft have a rate of climb in the order of 2000-3000 fpm, for comfort the cabin pressure changes at a rate of about 150-300 ft/min. This allows the body to equalize pressure slowly and comfortably as the aircraft climbs. Some people may still have problems with ears blocking or gas expansion in the stomach and intestines. Cabin pressurisation is taken from the engine compressor, it is then cooled and fed into the cabin. The pressure level is then set by controlling the rate of escape of the compressed air from the cabin by means of a barometrically operated relief valve. Cabin Pressurisation Advantages Advantages of pressurization are: ¾

Protection from Hypoxia and Decompression Sickness

¾

Oxygen is only needed in emergencies

¾

The pain from the expansion of stomach and intestinal gases is reduced.

¾

Temperature can be warmer than the outside environment.

¾

Movement is possible within the cabin.


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Disadvantages of Pressurised Cabins The advantages of pressurization outweigh the disadvantages: ¾

Contamination of the cabin is easy

¾

With rapid decompression the occupants are exposed to all the rigours of the high altitude environment.

Aircraft Oxygen Systems Aircraft oxygen systems provide diluted or 100 percent oxygen for breathing. JAR-OPS determines certain criteria for aircraft on high altitude flights. All Aeroplanes on High Altitude Flights Approximate altitude in the Standard Atmosphere corresponding to the value of absolute pressure used in this text is as follows. Absolute Pressure

Metres

Feet

700 hPa

3000

10 000

620 hPa

4000

13 000

376 hPa

7600

25 000

An aeroplane intended to be operated at flight altitudes where the atmospheric pressure is less than 700 hPa in the cabin is equipped with oxygen storage and dispensing apparatus capable of storing and dispensing the oxygen supplies required. An aeroplane intended to be operated at flight altitudes where the atmospheric pressure is less than 700 hPa where the cabin is pressurized above 700 hPa in personnel compartments is provided with oxygen storage and dispensing apparatus capable of storing and dispensing the oxygen supplies required. Pressurized aeroplanes introduced into service on or after 1 July 1962 and intended to be operated at flight altitudes where the atmospheric pressure is less than 376 hPa are equipped with a device to provide positive warning to the pilot of any dangerous loss of pressurization. An aeroplane intended to be operated at flight altitudes at which the atmospheric pressure is less than 376 hPa, or which, if operated at flight altitudes at which the atmospheric pressure is more than 376 hPa, cannot descend safely within four minutes to a flight altitude at which the atmospheric pressure is equal to 620 hPa and for which the individual certificate of airworthiness is first issued on or after 9 November 1998 is provided with automatically deployable oxygen equipment to satisfy the requirements.


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27 November 2003

The total number of oxygen dispensing units has to exceed the number of passenger and cabin attendant seats by at least 10 per cent. Oxygen Regulator Flight crew use an oxygen regulator to control the flow of oxygen into the oxygen mask. This reduces the oxygen pressure to a breathable level. Regulators may include diluter demand for diluting the supplemental oxygen with ambient air to extend the duration of the oxygen supply or automatic positive pressure for flights above 30 000 feet. Continuous flow regulators are used for portable oxygen bottles and in some passenger cabin systems. Diluter demand regulators used by flight crew incorporate: ¾

A pressure gauge

¾

A flow indicator, and

¾

An air valve lever.

Most operate in the altitude range from 0 to 37 500 ft. Oxygen is delivered to the pilot in response to breathing. The regulator provides either an air oxygen mixture, or 100 percent oxygen, depending upon the mode of operation selected. Oxygen masks Flight crew use a full face mask which provides a seal to the outside atmosphere. In conditions where cabins are filled with smoke this is thought to be essential. Passenger oxygen masks are not as efficient. The mask delivers 100% oxygen continuously. There is no seal to the outside atmosphere and as such there is no smoke protection.


11-5




11-6

27 November 2003

Chapter 12. Sleep Introduction The aviation industry is a 24-hour activity in order to meet the demands of the modern world. Flight crew are required to support this 24 hour operation. With the demands of both long and short haul operations fatigue in aviation is recognised as a serious safety concern. Fatigue and lack of sleep may not be apparent to a pilot until serious errors are made. Pilots routinely experience fatigue throughout their aviation careers and many crewmembers consider it an occupational hazard. Commercial pressure is ever increasing and these demands with the ever present “press on itis” quickly fatigue even the most fit pilots. Sleep is a real concern and this section outlines: ¾

How fatigue occurs

¾

How to help combat fatigue

¾

Sleep and sleep disorders

The Danger of Fatigue Fatigue is a danger to both the long haul and the short haul pilot. Because of its insidious nature an individual does not initially feel the onset of fatigue. A fatigued pilot may not be aware of the gradual and cumulative effect and consequently, may be unaware that their performance has become degraded. Because of the slow onset the pilot may not recognize the degradation of his performance. A fatigued pilot loses the ability to self criticize and is more willing to accept inaccurate flying and poor judgment. As fatigue increases, decision making skills are lost with a slowing down of the whole thinking process. Information may have to be checked and checked again because of these problems. Reaction time is increased, irritability and mood swings easily block communication and hamper teamwork. Apathy eventually sets in and the fatigued pilot becomes indifferent to the outcome of the flight and the operational performance. Where a person goes without sleep for up to 24 hours the effects are similar to those of having up to 8 units of alcohol. Vigilance Effects Any task that requires vigilance is suspect to the effects of fatigue. Fatigue can be described as: Short Term Fatigue (Acute) The effects of normal everyday living. Acute fatigue is the tiredness a person feels after physical or mental strain. Co-ordination and


12-1


alertness become dulled and performance reduced. Good rest and sleep combined with proper nutrition and exercise prevent acute fatigue. Long Term Fatigue (Chronic) If sufficient recovery time is not allowed between bouts of acute fatigue then chronic fatigue may occur. The only recovery is a prolonged period of rest. During chronic fatigue performance and judgement can lower to a dangerous level. Causes of Pilot Fatigue Pilot fatigue is normally caused by: ¾

Circadian Dysrhythmia – Jet Lag.

¾

Short haul rostering – multi leg flying days

¾

Poor rostering – long standby periods, long duty periods

¾

Sleep lost because of domestic worries

Other factors do have an effect, but the above may be taken as the main causes. Symptoms of Pilot Fatigue We know when we are fatigued, but can we recognize it in others. A few symptoms are listed below: ¾

Slow reaction time, both physically and mentally.

¾

Errors becomes the norm

¾

Lack of self criticism.

¾

Fixation on a single source of information or task.

¾

Short-term memory loss

¾

Impaired judgment leading to poor Decision Making.

¾

Distracted easily from the main task.

¾

Inaccurate flying

¾

Lethargic

¾

Limited Situational Awareness.

¾

Poor communication skills.

Coffee, concentration or will power do not get rid of fatigue. They may delay the onset but the normal result is one of worsening the effect. Sleep and Sleep Deprivation Chronobiology is the scientific name for the study of biorhythms. The human body follows certain biological rhythms some of which have a period of 24 hours, these are termed


12-2

27 November 2003

Circadian Rhythms (Latin: Circa - about, dies - a day). Other biorhythms, however, display different periods eg., the female menstrual cycle - 28 days, children's rest/activity cycles - 90 minutes. One of the most studied of Circadian Rhythms, that is useful to pilots, is the sleep/wake rhythm. The body's temperature is approximated at 37°C. During a 24 hour period it cycles between 36.2°C and 36.9°. The sleep/wake cycle is bound to this change in body temperature: ¾

When the temperature is rising the body is waking

¾

When the temperature is falling the body is ready to sleep

In the diagram below the time of minimum temperature and maximum temperature are annotated on the body temperature cycle. Note that there is a dip in the temperature after the lunch time period. Body Temperature Minimum 0500

36.5°C Maximum 1800

Time of Day

Post Lunch Dip

This sleep/wake cycle is controlled by the body’s internal clock. In America deprivation tests were carried out on an individual in a room with no time clues such as light or dark. Initially allowed a clock the individual was asked to rise at 9 am each day. After 3 days the clock was removed. Initially the person woke at 9 am. On subsequent days the waking time was delayed by one hour – on day 4 waking at 10 am, day 5 at 11 am etc.


12-3


WITH A CLOCK

DAYS

ASLEEP

AWAKE

1 2 3 WITHOUT A CLOCK

4 5 6 7 8 9 10 11 12 13 14 15

0

6

12 TIME OF DAY

18

24

The circadian rhythm of the body has adjusted to 25 hours, a condition known as free run. The body is contracted into a 24 hour day by the constraints of our working lives. We react to the night and day and to other time clues known as Zeitgebers (German for time giver) The problems of the body temperature cycle and the circadian rhythms do have an affect on the pilot. Sleep Credit/Deficit Using a simple system of allowing +2 points for every hour asleep and -1 point for every hour awake we can show how easy it is for the body to go into sleep debt. The system is not infallible, as it does not take into account: ¾

The type of sleep

¾

Whether the person is on long haul flight

During a normal night if we assume that an individual has 8 hours sleep then when they wake they will have amassed +16 points. If that individual then stays awake for 16 hours then they will lose –16 points. Thus finishing the day with 0 points. On subsequent days the same occurs and the points score never goes below the 0 line – the individual is in sleep credit.


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27 November 2003

+16

+8 SLEEP CREDIT 0 00 00

0800

1600

0000

0800

1600

0000

0800

1600

0000

SLEEP DEFICIT -8

-16

Now assume that the cycle is broken by a period on night shift. Assuming a normal night’s sleep: ¾

The individual wakes with +16 sleep points (A)

¾

Assume they stay awake for 8 hours (B) and from 1600- 1800 hrs manage to get a two-hour nap (C) before reporting for duty

¾

Duty starts at 2000 hrs through to 0600 hrs.

¾

At 0600 hrs they return home but are unable to sleep because the body temperature is rising

¾

Finally they sleep at 1200 hrs (D). They sleep until 1800 hrs (E) when it is time to prepare for work

¾

The cycle repeats itself and the person gets further and further into sleep deficit. This situation is termed cumulative sleep debt. +16 B

A

C +8 SLEEP CREDIT

E

D 0 00 00

0800

1600

0000

0800

1600

0000

0800

1600

0000

SLEEP DEFICIT -8

-16

By the time the third shift is started the sleep credit is 0 before they start work. Now translate this to the pilot on a flight in the early hours of the morning with little to do but monitor the autopilot. Most pilots use coffee to stop sleep but this is only a short term measure.


12-5


Sleep The precise functions of sleep are not fully understood. Experiments have shown that sleep has a restorative function for both the body and the mind. Sleep has been investigated extensively over the last sixty years and much is known of its nature. In experiments three main measurements are recorded: Brain wave activity

EEG (electroencephalogram)

Eye movement

EOG (electroculogram)

Muscle tension

EMG (electromyogram)

The recording of these three measurements has shown scientists that the body initially goes through four linked stages of sleep termed quiet sleep. During these 4 stages there is a gradual slowing of the brain’s activity as the body goes into a deeper sleep. Stages 3 and 4 of quiet sleep are known as slow-wave sleep because the EEG records little or no brain activity. Following the Quiet Sleep is another stage of sleep called REM (rapid eye movement) sleep. Also known as Paradoxical sleep. During this sleep: ¾

The EEG records similar brainwaves to those recorded when someone is awake

¾

The EOG records rapid eye movements (hence REM sleep) as if searching for something

¾

The EMG records total muscle relaxation; the mind is awake but the body is asleep – hence the term paradoxical sleep

Quiet sleep is thought to be body restorative and that REM sleep allows the brain to store what has been learned during that day and also to check and create new neural pathways. The evidence supporting this theory is that children (and adults who are in learning situations) show a higher REM sleep percentage than average. Each full cycle of sleep takes approximately 90 minutes, successive cycles showing increasing amounts of REM sleep. In general, during a normal 8 hours sleep, the first four hours are mainly slow-wave sleep (body-restorative) and the latter four hours mainly REM sleep (mind-restorative). If the first four hours (slow-wave) or the second four hours (REM) sleep are interrupted then both are made up on the next night. CYCLE STAGES 1-4 SLEEP REM SLEEP

TIME OF DAY

23

24


1

2

12-6

3

4

5

6

27 November 2003

Dreams occur mainly in REM sleep but sleepwalking and nightmares occur in slow-wave sleep, hence, people remember dreams but not sleepwalking. Alcohol affects both Quiet Sleep and REM sleep. ¾

Moderate amounts affect REM sleep

¾

Large amounts affect both types because of the coma like affect of alcohol

Sleep Disorders The common sleep disorders include: ¾

Microsleep

¾

Insomnia

¾

Sleepwalking and sleeptalking

¾

Sleep Apnoea

¾

Narcolepsy

Sleep Loss and Microsleep Any loss of sleep will begin a sleep debt. Fitful sleep overnight may also produce the same effect. Sleep debt is only cured by sleep. Sleep debt and fatigue may lead to what is termed a microsleep. Microsleeps are uncontrolled spontaneous episodes of sleep that last for a few seconds up to a few minutes. During a microsleep a person becomes detached from reality and will be unresponsive to outside influences. Insomnia Insomnia can be divided into two types: Clinical Insomnia Clinical Insomnia is suffered by people who are unable to sleep even in the most favourable conditions. Symptoms include: ¾

Difficulty in falling asleep

¾

Difficulty in maintaining sleep

¾

Waking unrefreshed

¾

Daytime fatigue


12-7


¾

Irritability

¾

Lack of concentration

Situational Insomnia Aircrew can suffer situational insomnia; it is an inability to sleep due to irregular work/rest patterns. Jet lag being the most common cause. Sleepwalking and Sleeptalking Common in childhood and less common but present in some adults are sleepwalking (somnambulism) and sleeptalking (somniloquism). Neither are a health hazard but excessive cases need investigation. Sleep Apnoea A condition which affects people who snore excessively, especially those who are overweight. During sleep the snoring affects the back passages of the throat and air can be cut off from the lungs for a short period. The person effectively stops breathing. In extreme cases a person could die. The condition is treated by the use of a mask which the sufferer wears during the night. Air is passed through the mask by a compressor which ensures a positive pressure in the throat at all times. Narcolepsy The inability to stay awake. Sufferers have the tendency to fall asleep at any time whether they are tired or not. Sleep Hygiene Individuals require differing amounts of sleep. The older you are the less sleep you require. People in learning situations do require a regular sleep pattern. When studying the pressures are such that late night study or worry can disrupt the sleep pattern. But a few helpful hints are given below: ¾

No strenuous exercise immediately before going to bed. This means no physical or mental exercise.

¾

A high level of study activity should be avoided immediately before trying to sleep, rest for at least 30 minutes before going to bed

¾

Keep the room ventilated - not too warm, not too cold.

¾

Do not drink too much alcohol. Alcohol induces a coma like sleep where there is no body refreshment.

¾

Try a warm milky drink - NOT COFFEE OR TEA.

¾

Light reading or listening to music can help relax the mind and body.


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27 November 2003

Napping Most people feel tired during their waking hours. Napping is a way of refreshing the body quickly and efficiently. In experiments it has been shown that a short nap can be as restorative as a longer period of sleep. Drugs To sleep or to stay awake some pilots will resort to drugs. To stay awake the most common drug used is Caffeine; the antidote for sleepiness being a strong, black coffee. To relax and sleep alcohol is used. Caffeine The harmful and addictive effects of excessive caffeine should be noted and are well-documented. Alcohol Alcohol is a central nervous system depressant which interferes with sleep, particularly REM sleep. In small amounts alcohol does promote well-being and can relieve stress and promote relaxation. But like all drugs addiction can bring problems. Sleeping Tablets With normal medication, cold and flu remedies induce drowsiness because of their nervous system depressant action. Some drugs can remain in the system for hours and affect performance the next day. The half-life of a drug is an important factor that pilots must take account of. The half-life of a drug is the time it takes for a drug to decay to one half of its peak concentration. Half-life figures are not available publicly. In order to ensure that any drug you are using is safe always consult a GP before use. Sleeping tablets have a long half-life and can affect a waking person for a few hours after rising out of bed. Newer sleeping drugs are always coming onto the market and before use a doctor should be consulted. Contrary to a lot of opinion, sleeping tablets are only meant as a short term sleeping problem fix. Melatonin Melatonin is a depressant currently being promoted in some countries as a natural hormone, which allegedly induces sleep in shift workers or elderly people. The drug is now marketed as an aid to combat Jet-Lag. Melatonin is not legal in several countries and is certainly not recommended for use by pilots. There are problems with quality control, potency and monitoring of this supplement. The biological effects and the long-term use of Melatonin are not known. Circadian Dysrhythmia – Jet Lag Abnormal shift work can result in a cumulative sleep debt. Longhaul pilots have the added problem of their body adjusting to new time zones. New Zeitgebers confuse the body ie new light/dark, new meal cues as time zones are crossed. For the long haul pilot it is better to be travelling westwards than eastwards. Westwards travel involves a lengthening of the day and


12-9


the Circadian Rhythm is better at lengthening its cycle than shortening it. Remember that the body rhythms free-run at 25 hours. The body’s Circadian Rhythms adjust at different rates at between 1 – 1½ hours per day for every hour’s difference in time zone. The result of this slow resynchronization is that you may find yourself beginning the next leg of your flight before your biorhythms have resynchronized. It is estimated that some long haul pilots spend their entire flying careers suffering from Circadian Dysrhythmia and only adjust fully when on extended periods of leave or illness. Two methods are suggested to combat Jet Lag. Method 1 Stay awake for 2 hours after landing; then rest/sleep for 4 hours; then sleep for 8 hours before reporting for duty. Method 2 zone cues.

If the lay over is less than 24 hours then remain on the original time

The effects of Circadian Dysrhythmia are well known and include: ¾

A general lack of well-being.

¾

Below par performance.

¾

Stomach disorders.


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27 November 2003

Chapter 13. Stress Introduction Stress affects all human beings. It is the perception of what the stress is that determines whether the human copes. Overstress a person and their ability to reason and function correctly is reduced. Not enough stress will cause boredom and complacency. The right amount of stress and optimum performance levels are achieved. Stress Stress can be defined as: Excessive and aversive environmental factors that produce physiological responses in an individual The strain and pressure that is exerted on a human can be related to the scientific use of the term where effectively a body is bent and eventually breaks if overstressed. Stress is present in all humans. It is important to accept that in all walks of life that we all suffer some stress whether good or bad. The pilot needs to be aware of the problems of stress and how to cope with the rigours it puts the body through. This helps the person recognise the negative impact on performance caused by overstress such as: ¾

Fatigue

¾

Personal problems, and

¾

High workload

Remember, the pilot is his own worst enemy. Peer pressure over the years has instilled in most pilots a fear that admission of overload is a weakness. The stress that the body is subjected to can be broken down into three areas. Remember that these problems may be singular or cumulative, for simplicity we look at each separately. Physical

Environment we live in; conditions such as, noise, vibration and stages of hypoxia

Physiological Fatigue, physical fitness, poor diet Emotional

The domestic, social and emotional factors related to living. Work related activity such as leadership or decision making.


13-1


Stress can be defined as either: Chronic Stress

Acute Stress

The long term demands of a person’s lifestyle such as work, health or domestic security Short term stress caused by the issues of the day.

Effects of Stress Acute stress is dealt with by the body immediately. Adrenaline is released into the bloodstream and charges the body: ¾

Raising the heart rate

¾

Increasing the blood pressure

¾

Increasing the breathing rate, and

¾

Increasing the blood sugar level

A condition known as the "fight or flight" syndrome. This allows the person to react quickly to a given situation. Chronic stress is different, the body has to take a long term view of the stress that it is being put under. Chronic stress can make a situation that we normally cope with difficult. Chronic stress will exaggerate the effects of acute stress and in the long term threatens a person’s health. Stress is Cumulative Long term stress over a period of time can affect the individual’s ability to perform in stressful situations. In a pilot this can result in: ¾

Inaccurate flying

¾

Communication difficulties

¾

Leadership and command problems

A simple model like the one shown below can help describe the effects of stress.

Stressor

Stress Mediation

Stress Reaction

Where: Stressor

A situation or event that causes a stress


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27 November 2003

Stress Reaction

The physical, physchological or emotional response of the body

The interaction of stressors and the resultant stress reactions are not straightforward. We all react differently to different stresses in life. What seems minor to one person may be a life crisis in another. To misquote Kipling: “if you can keep your head when all around you are losing theirs, you don't understand the problem!” Any stress reaction is related directly to the evaluation of the stress and the perceived ability a person has in coping. Solely psychological these are our stress mediators and can be good or bad depending on our perception of the problem. To extend the simple stress model used before.

Stress Mediation

Stressor Change

Coping Skills

Frustration

Perception of Stress

Conflict

Predictability

Stress Reaction Physical Psychological Emotional

Pressure Boredom Trauma

Listed are some of the major stressors in life. These pass through a mediation phase that then is felt by the body as a stress reaction. Mediation should lessen the effect of stress. As we learn to cope with the R/T and flying the aircraft at the same time both become inbuilt into our sub-conscious and are no longer worried about. However mediation may not work: Example

Assume that you are on an approach to London Heathrow. The weather is poor. The cloud base is on the ground, the crosswind is on limits. There are two possibilities.


13-3


One

You cope with the approach and do a good job

Two

You “cock it up”

One week later you are flying into London Heathrow in exactly the same conditions. If you succeeded last time stress mediation will have taken place and you will not be so worried about the approach and most probably you will make a good approach again. If you failed last time your brain will be telling you that you failed last time and that you can’t do it. In this case mediation is worse and you will most likely fail. Psychological Stressors The stressors that are related in the simple stress model can be experienced as shown below. Frustration

Where obstacles stand in the way of our progress such as holding because of problems on the ground

Pressure

Whether self inflicted or external we all get the feeling so much to do and so little time to do it Last minute cramming for the examinations?

Boredom

A problem in that a bored person does not work at peak performance and can be left wanting in an emergency

Trauma

A physical or emotional experience that leaves the body in shock

Conflict

Domestic or work, conflict can make the life of the sufferer miserable.

Change

Change is related in this chapter by the use of Life Change Units. The events listed are measured relative to each other for a Northern European adult. If you accumulate more than 120 LCU's/12 months or 200 LCU's/2 years, then you may suffer a minor life crisis.


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STRESS EVENT

VALUE IN LCU's

DEATH OF A SPOUSE

100

DIVORCE

73

MARITAL SEPARATION

65

IMPRISONMENT

63

DEATH OF CLOSE FAMILY MEMBER

63

PERSONAL INJURY OR ILLNESS

53

MARRIAGE

50

DISMISSAL FROM WORK

47

MARITAL RECONCILIATION

45

RETIREMENT

45

CHANGE IN HEALTH OF FAMILY MEMBER

44

PREGNANCY

40

SEX DIFFICULTIES

39

GAIN OF NEW FAMILY MEMBER

39

BUSINESS READJUSTMENT

39

CHANGE IN FINANCIAL STATE

38

CHANGE IN NUMBER OF ARGUMENTS WITH SPOUSE

35

MAJOR MORTGAGE

32

FORECLOSURE OF MORTGAGE LOAN

30

CHANGE IN RESPONSIBILITIES AT WORK

29

SON OR DAUGHTER LEAVING HOME

29

TROUBLE WITH IN-LAWS

29

OUTSTANDING PERSONAL ACHIEVEMENT

28

WIFE BEGINS OR STOPS WORK

26

BEGIN OR END SCHOOL

26

CHANGE IN LIVING CONDITIONS

25

REVISION OF PERSONAL HABITS

24

TROUBLE WITH BOSS

23

CHANGE IN WORK HOURS OR CONDITIONS

20

CHANGE IN RESIDENCE

20

CHANGE IN SCHOOLS

20

CHANGE IN RECREATION

19

CHANGE IN CHURCH ACTIVITIES

19

CHANGE IN SOCIAL ACTIVITIES

18

MINOR MORTGAGE OR LOAN

17

CHANGE IN SLEEPING HABITS

16

CHANGE IN NUMBER OF FAMILY REUNIONS

15

CHANGE IN EATING HABITS

15

HOLIDAY

13

CHRISTMAS

12

MINOR VIOLATIONS OF THE LAW

11


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For the pilot, as well as the domestic changes that are listed above there are certain events specific to the job in hand: ¾

Medicals

¾

Training and line checks

¾

Time schedules and late passengers

¾

Other crew members

¾

Company pressure

¾

Fatigue etc

There are many more, these are but a few. Effects of Stress Stress affects our motivation and performance. Small amounts of stress are needed to make the body move. This can be related in a simple performance/ arousal graph. As the amount of stress increases we are initially: Optimum Arousal

Performance Loss

Performance Low Arousal

Arousal

¾

In a low arousal state. This can be thought of as just waking up or being over fatigued. The central nervous system is not functioning fully and any information processing is slow and inaccurate. Motivation to react to stimuli is low and the body is inattentive. Think about what your actions are when you wake to the alarm clock. Get up straight away or press the snooze button?

¾

As the day progresses the arousal increases as does the performance. Under optimum conditions the central nervous system is functioning correctly. To carry out complicated tasks the body needs to be in this state of optimum arousal: ¾

One where a task will stimulate and interest the brain but not be so complicated so as to push us into an overload situation.


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Once the limit of capacity is reached then the performance falls rapidly.

¾

Physical and Psychological Stress Reactions Stress reactions are the physical, psychological or emotional response to the stressor. The reactions are not independent of each other but can be interrelated. For simplicity each is discussed separately. Physical Stress Reactions Think of what happens to you when you have a sudden shock. Pulse and breathing become rapid, possible sweating and trembling. The fight or flight syndrome is an animal reaction to danger and results in the release of certain hormones (Adrenaline and Nor-adrenaline) into the bloodstream. The commands to release these hormones come from the Sympathetic Branch of the Autonomic Nervous System. As the danger passes, the Parasympathetic Branch calms the body down. The long term effects of stress are better explained by the General Adaptation Syndrome. General Adaptation Syndrome

Resistance

Alarm

Exhaustion

Three stages occur: The Alarm Stage A stressor causes a fall in our resistance. measures are taken by the body and it starts to act against the stress.

Defensive

The Resistance Stage Once mediation has taken place the body prepares a resistance phase. This is a time limited phase as the body can only cope with so much.


13-7


The Exhaustion Stage Eventually resistance will fail if the mediation has not been successful. Prolonged exhaustion can be fatal. More common are ailments such as hypertension, organ failure, cardiac arrest, ulcers, or renal failure. Psychological Stress Reactions Stress is related as the way that a person feels and responds to a situation. These feelings are divided into three simple categories: Emotional Responses Common emotional reactions to stress include anger, anxiety, fear, depression etc. In extreme cases emotional responses can be come uncontrollable and cause such problems as anxiety attacks. Cognitive Responses Stress affects the ability to concentrate on the task in hand. To think clearly and logically defence mechanisms are used to cope with the stressors. Behavioural Responses The changes in the way a person acts when stressed. Fidgeting or shaking when worried is just one example. In the pilot the most common response to stress is the use of alcohol. Domestic Stress The one stress we all suffer from at some stage in life. By using the LCU table you can determine how life is affecting you. Domestic stress does affect the workplace no matter who you are. Clinical Effects of Stress The body reacts in differing ways to cope with stressors. Both psychological and physiological responses are made: Physical Effects The “Fight or Flight” syndrome where Sympathetic Branch of the Autonomic Central Nervous System is activated.

the

Health Effects will cause hypertension.

Increased heart rates and the release of adrenaline

Behavioural Effects

The problems of the over use of drugs or alcohol.

Cognitive Effects Lack of concentration and lack of attention to detail lead to the inability to deal with problems clearly and logically.


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27 November 2003

Emotional Effects The body releases tension in many ways which may include aggression or moodiness etc. Coping Skills To cope with stress the person needs to accept that a stress is causing problems. The next stage is to choose a coping strategy that best helps. Some coping is carried out subconsciously. If the sub-conscious does not work then there are strategies that can be adopted. To cope with a stress the person must accept that they are under stress and want to do something about it. These conscious coping strategies are: Action Coping The reduction of stress by direct action. Implementation usually includes some or all of the following: Assessment

Find the sources and effects of the stress

Set Goals

Find the stressors and stress reactions that need to be attacked

Plan

Make a plan of action on how to cope

Action

Carry out the plan

Evaluation

Check to see if the plan is working. If not, try again or revise the plan.

Cognitive Coping Cognitive coping is a method in changing the way we think about a problem. Methods used include: Distraction

Concentrate on other tasks to take away the pressure of the stressor

Redefining the Situation

Try to make the stress more acceptable

Direct Action By thought the decision may be to use action planning Catharsis

An emotional outburst to release the stress

Acceptance

Decide to accept the problem and do nothing about it

Symptom-Directed Coping


The use of external coping skills:

13-9


Physical Exercise A healthy person copes with stress better than an unfit person. Stress can be released in the aggression of sport – is that golf ball your bosses’ head? Relaxation Techniques Use of areas such as meditation or hypnosis to counteract the ravages of life. Other Coping Strategies include: Religion

The help of the church and someone to talk to is a good way of helping with stress

Counselling

Not only professional counselling but talking with a friend can help.

Stress Management The way that a person decides to cope with a stress. To carry out stress management the person must first accept that stress is causing a problem. It is easy to recognize the signs of stress in oneself, but what about others? If a person does not manage stress, stress will manage the person. Life events do not create stress; the perception of the stress is created in our minds. The source must be identified before it can be addressed and reduced or eliminated. Make a plan and stick to it. The aim is to control or to eliminate the effects of stress. Be realistic and practical. This may call for you to be flexible and willing to adapt. Rest is essential as a tired mind and body give quickly. Humour and perseverance help.


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27 November 2003

Chapter 14. The Nervous System Introduction The nervous system is a communication system which allows the body to adapt itself to an ever changing environment. It includes: ¾

The spinal cord with the spinal nerves

¾

The brain and its cranial nerves

¾

The autonomic nervous system

¾

The sense organs ¾

The eye

¾

The ear

¾

The organs of taste in the mouth

¾

The epithelium in the nose which is sensitive to smell

¾

The sense organs of the skin and muscles which are sensitive to touch

The Central Nervous System

Cell Body

Axon

The basic unit of the nervous system is the neurone (nerve). The neurone consists of: ¾

A cell body

¾

Dendrites which conduct nerve messages to the cell body

¾

The axon, a slender thread which conducts nerve messages away from the cell to the central nervous system

The brain and spinal cord make up the central nervous system, a collection of neurones connected to each other by dendrites and axons.


14-1


Brain The brain is the master controller of the body, more complex than any computer. Consisting of a mass of nervous tissue the brain is responsible for: ¾

Our senses

¾

How we learn

¾

Our memory

Specific areas of the brain monitor and control the different areas of the body. The Cerebrum, the largest division of the brain, is where information processing occurs. The Cerebellum is the structure of the brain that helps a person maintain their balance while standing. Below the cerebrum and cerebellum lies the brain stem; this connects the brain to the spinal cord. Spinal Cord The spinal cord is nearly cylindrical and runs down the middle of the vertebrae of the spine. The spinal cord contains billions of nerve fibres which transmit signals to and from the brain. Branching out from the spinal cord are the spinal nerves. Each nerve leaves the spinal cord as two roots which join once clear of the vertebrae. These nerves connect all of the body's areas and tissues below the head to the central nervous system. Some of these nerves are connected to each other, as well as to the brain. These connections allow a loop to be formed which does not depend on the brain for a response. Known as a "reflex" the loops allow for a faster and simple reaction in critical situations eg placing a hand on an electric hot plate, the hand is automatically pulled away such that the response is completed before the brain has had time to think about it.


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The Peripheral Nervous System Peripheral nerves emerge in pairs from the spinal cord and pass to all parts of the body. Like telephone cables they are capable of relaying both incoming and outgoing signals. These nerves can be grouped into three divisions: ¾

Sensory nerves

¾

Motor nerves

¾

Autonomic nervous system

Sensory Nerves Sensory nerve fibres carry information received by the senses to the brain. Sensory nerves are designed to detect stimuli from: ¾

Touch

¾

Pressure

¾

Pain

¾

Temperature

¾

Position

Motor Nerves Motor nerves carry the orders sent by the brain to the muscles. The motor system controls the body's motor functions or more simply, movement. Motor nerves are attached to the muscles of the body, impulses are sent from the brain which signal the muscle to contract or extend, placing the skeleton into the position required. If more control is needed then more motor nerves are required eg in finger control. The majority of the motor nerves are voluntary. This means that a person must think about moving a muscle. Autonomic Nervous System The autonomic nervous system supplies those organs of the body that are not under the control of the will eg contraction of intestinal muscles to push food along. There are two divisions of the autonomic system: ¾

Sympathetic system

¾

Parasympathetic system

The two systems effectively work against each other sending opposite signals to the organs: ¾

If the heart is beating too slowly the sympathetic system will send signals to increase the heart rate


14-3


¾

When the heart is beating too fast the parasympathetic system will send signals to slow the heart down


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27 November 2003

Chapter 15. Human Information Processing Introduction During the day a person makes hundreds of decisions. Flying an aircraft is no different, the pilot must use his decision making skills continuously. An American diplomat once said: Only total inactivity will cause no errors Edward Phelps – US Diplomat The pilot, unfortunately, cannot follow this course of action as the aircraft will eventually run out of fuel. The use of information and decision making is a complicated process. The neural pathway through the brain where information is received, a decision taken and a response executed are too complicated for this course. A simple model of what is called Human Information Processing (HIP) follows. Sense A physical stimulus has to be received by the receptors. Stimulus

Receptor

Sight

Eyes

Sound

Ears

Taste

Tongue

Touch

Proprioreceptive System

This raw energy is unusable to the brain and needs to be converted (transduced) into electrical impulses.

Transduction

Stimulus


Receptor

15-1

Sensory Memory


Initially the information is sent to the Short Term Semsory Memory. The time that the information is stored is limited and depends upon the attention that can be paid. Information from the two main senses are held in: Iconic Memory

Visual sensory store which lasts for 0.5 to 1 second

Echoic Memory

Auditory sensory store which lasts for 2 to 8 seconds

Once there is enough processing capacity in the brain then the information is passed on to the area of perception. Attention is paid during each of the following processes. The amount of attention that can be paid to each piece of information is limited as will be seen later in this chapter. Perception An interpretation or impression based on one’s understanding of something Perception is the process by which the brain recognises and interprets the transduced stimulus which has been held in the short term sensory memory. In the perceptive stage the mind starts to build up a mental model. This entails building a 3-D model which builds pictures in our minds of: ¾

Where we are

¾

Where we are going

¾

Where we have been

It is true to say that our mental model is our conceptual way of understanding: ¾

What an object is

¾

How that object works

¾

What effect that object is going to have in our life

Transduction

Stimulus


Sensory Memory

Receptor

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Perception

27 November 2003

Perception is based on the information we sense and our expectations of the world. Perception is based on the following inputs: ¾

The processing capacity of the brain

¾

Past experience

¾

Expectation

Unfortunately, once we have reached the perceptive process it is difficult for us to change our minds. It is at this stage that the human being is most likely to fall into the problem of Confirmation Bias. Confirmation Bias Confirmation Bias is part of the human error process that occurs when a false perception is made. It is a situation where a person has made a decision and only believes information that confirms that decision. Any contradictory information is ignored. For example: In a two engined aircraft where there is a burning smell in the cockpit. If one engine is shut down and the burning smell goes then it might be fair to assume that the correct engine has been shut down. If in the above case the conditioning system is taking air from both engines then the burning smell might have gone for another reason and the incorrect engine shut down. In this case the pilot may be tempted to believe that he has shut the correct engine down and Confirmation Bias has been started. Central Decision Making and Response Selection Once perception is completed then a decision has to be made. Impulsive or immediate response can be made or the HIP continues with the brain using: ¾

The working memory and long term memory, or

¾

The motor memory system


15-3


Transduction

Stimulus

Perception

Sensory Memory

Receptor

Decision and Response

Ultra-short Term Memory If an immediate response is required then the brain replies on impulse using the “ultra short memory”. This memory can retain sensory inputs for about a second. This does depend on external factors such as strength of impression. In the ultra-short term memory, material is processed very quickly according to its current importance. Importance or priorities will vary from person to person and with the situation. Cocktail Party Effect Cocktail party effect is one way that the brain uses this ultra short memory. A crowded Friday night bar where you are in conversation with friends. You are concentrating on your group when a person behind you says your name. Without altering expression you immediately change your attention to the other group. Working Memory or Short Term Memory Both terms are frequently used. Consider the following. If a pilot hears a warning bell on a flight deck then they will probably react in one of two ways: ¾

Switch off the sound in which case an immediate response has been made.

¾

Hold the information in memory whilst a search is made in order to identify the problem.


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27 November 2003

The above uses a continuous process where information is constantly entered and recalled from memory. During this period a decision has to be made where the information is stored – the short term memory or retrieval from the long term system. The central decision and response channel can only work one problem at a time and is thus a choke point within the brain.

Transduction

Sensory Memory

Receptor

Stimulus

Perception


Long Term Memory

Short Term Memory

Short Term Memory and its Limitations When the brain accesses the short or long term memory system the short term memory will store information for a short time. Used to retain information that is not needed in the long term memory, the short term memory only retains information for a limited period and its capacity is limited to: ¾

7± 2 unrelated items of information that can be held for approximately 10-20 seconds unless active rehearsal is used to retain the information.

¾

A process called “chunking” can increase the number of items.


15-5


eg

the use of telephone numbers ¾

A telephone code 041 is held as one item not three

¾

An area code 01455 is held as one item not 5

¾

01455 477686 would be retained as 2 items not 11 which would overload the short term memory

Short term memory is prone to interference and any interruption can and will cause the loss of information. For example: You need to phone a person but do not know the number. You look it up in the phone book and start rehearsing it as you go to the phone. Before getting to the phone you are interrupted for about 30 seconds by something. The short term memory loses the phone number and you have to start all over again. Environment Capture The short term memory is prone to a problem known as environment capture. A frequently operated skill in the same environment (a habit) where the pilot has not made a conscious decision to operate the skill. For example: When flying in the traffic pattern. Pilots who delay undercarriage selection somehow have this information dislodged from the working memory especially if the delay is by some form of interruption like ATC instructions. The event will generate a standard response from what becomes a boring activity, flying several uneventful circuits. The pilot may make the final gear down call because he always makes it at this time. The mental model is completed and the pilot believes he has selected gear down. Only when the aircraft scrapes down the runway does the pilot realise that he has failed to select the gear. Long Term Memory and its Limitations Long term memory has two distinct parts: Semantic Memory This is the store associated with what we know and do: the understanding of a word; how to fly an aircraft; facts - London is the capital of England. This area of the brain stores all the information that is learnt, including that information we will never use. If a word or fact is forgotten it is because the neural pathways are forgotten, not that the information is lost. The information is stored in an area of the brain that has not been accessed for a long time.


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Episodic Memory Episodic memory is a fluid memory that remembers events that have been experienced. It is coloured by our desires and expectations. Stories are not remembered factually but reviewed and changed to suit the teller’s needs. In eye witness reports episodic memory can have problems. Think about the reporting of aircraft crashes: ¾

All aircraft burst into flames before they crash

¾

All pilots fly the aircraft away from schools, hospitals and houses before they crash

Other problems occur with the “expert” witness. A pilot witnessing an aircraft crash has expectations of what was happening in the cockpit and will relate these as what he saw. A non-expert witness is more likely to give a better account. Children give the best eye witness reports as their episodic memory has not yet developed. Motor Memory When a new action is learnt then it initially seems difficult. Like riding a two wheel bike for the first time. Piloting is exactly the same, initial impressions of flying, ATC etc seem to make the task impossible when training is started. Like most actions which are well practised flying is eventually executed by a motor programme. Non conscious actions are used to fly the aircraft whilst talking on the radio uses conscious thought through the decision and response channel. The motor programme is by-passing the central decision and response channel.


15-7


Transduction


Perception

Response Execution

Short Term Memory

Long Term Memory

Sensory Memory

Receptor

Stimulus

Motor Memory

A motor programme can be used when an action has been well practised and is repetitive. The performance of this action becomes automatic and no conscious thought need be applied. The process by which motor programmes operate is complex but as soon as the flying becomes difficult eg landing, the central decision and response channel has to be used to fly the aircraft. Action Slip The advantages of using motor memory is obvious, as it extends our capabilities. Action slip is an error process that is caused by the brain using motor memory. For example: Pouring a cup of tea, whilst watching TV, and then adding sugar to the cup. If there is some distraction on the TV we can find ourselves pouring tea into the sugar bowl. The action of pouring the tea is being carried out by a motor programme, with no conscious thought being applied. With the distraction the process of pouring the tea carries on and we start pouring the tea into the sugar bowl because the brain thinks it has progressed to the sugar stage, or: BAC 1-11; My first officer was flying the leg. After T/O I carried out the usual checks. Brakes, U/C up, PAX notices off etc. Weather lovely, blue sky. W/V 270/18, temp +30C! At 1500 ft I


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27 November 2003

noticed the flaps were retracted. I thought the F/O had retracted them early. Usually the flap is retracted at 200 ft plus in VFR or 3000 ft noise abatement. Almost immediately he mentioned that the flaps were retracted. "Oh, I see you have brought the flaps in" he said. "No", I replied, "I haven't touched them". He said that he hadn't either. Shortly after this he noticed the U/C was still extended. I raised it. There can be no doubt I raised the flap instead of the U/C after take-off. I had no memory of this. Why would I do this potentially dangerous thing on an aircraft with which I was completely familiar? I have no idea; no sickness, no stress, nothing dramatic personally. Response Execution Once the memory has been used the brain has to make a response. How appropriate the response depends upon the pressure that a person perceives that he is under. The following apply to decision making in all walks of life: ¾

If a delay is dangerous then a person will feel that they are under pressure to make a quick decision

¾

Quick decisions are usually made before all information is processed

¾

Where there is stress then a fast but less accurate response is made

¾

Sound stimulates the mind better than sight

¾

Where a person plans for the expected then it is possible that if there is any change then pressure will make the brain reply with the planned response A crew planning for runway 13 from take off to landing. Only when they contact tower is runway 31 given as the landing runway yet they still land on runway 13.

¾

An old person may react more slowly than a young person yet the response is usually more accurate

Attention Attention is a limit to HIP, it depends upon certain factors: ¾

The limit to the number of items working memory can hold.

¾

The rate at which information can be passed through the central processing system.

Whether attention is paid to a stimulus depends upon: ¾

The importance of the stimulus

¾

The available attention


15-9


Attention can be described in two ways. Selective Attention Selective attention is where inputs are sampled and given a priority. Detailed processing can only be carried out on one complex task. If there are too many demands on the attention then information will be lost. In 1972, a Tristar on approach to Miami experienced a minor undercarriage malfunction. The crew selected the auto-pilot and looked into the undercarriage problem. Unfortunately, the auto-pilot setting was such that the aircraft entered a shallow descent. As the aircraft approached the ground, ATC, other aircraft, visual and audio warnings tried to attract the crew's attention to their danger. The crew's attention was focused on their undercarriage problem and were filtering out all other warnings, until it was too late to do so. The aircraft crashed killing all on board. Divided Attention Divided attention can be used to carry out two tasks that do not overload the HIP. Motor programmes, which are run with no conscious thought, can be consciously checked by a pilot who diverts his attention away from the major task in order to check a sequence of operation. Stress and Attention Stress focuses the attention processes. Thus to complete a task, under stress, we focus entirely on that task in hand. This is always to the detriment of other problems. Response Behaviour Once a response has to be made the brain will use one of the three response behaviours. Skill Based Behaviour Skill based behaviours are procedures acquired through practice and that are executed without conscious thought. Skill based behaviour is obtained in two distinct manners: ¾

Concentration on the individual parts of a skill, giving them attention, until practice makes the individual processes second nature.

¾

Practising the whole skill with concentration on the final product. Eventually a motor programme is made which carries out the skill based response.


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27 November 2003

Once these skills are acquired then they seem to possess certain characteristics: ¾

The skill is not easily explained to others. This may cause difficulties if a pilot wishes to pass on the skill.

¾

If the skill needs to be modified then the component parts must be broken down and re-learnt.

Because of the uses of motor programmes in skill based response a pilot operating a skill makes the decision to do so and then has the attention to monitor the task. But if a distraction is introduced then the pilot may make an inadvertent operation. Environment Capture can also occur in skill based response. All actions need to be consciously checked, especially those that are using sub-conscious thought. The errors of skill do not normally happen to the student pilot; they happen to a pilot with experience. Rule Based Behaviour Rule based behaviour uses the short and long term memory to carry out actions. Rule based behaviour is stored in the long term memory and involves the use of the central decision and response channel. By using conscious thought the error problems that occur with motor memory skills are bypassed. Simulator, procedural training or similar work that involves the use of Flight Reference Cards and checklists or plates are examples of this type of behaviour. The only problem relates to the well known saying: Garbage in – Garbage out Knowledge Based Behaviour Knowledge based behaviour is based on the reasoning powers that a person can use to arrive at a decision. The pilot is able to use his own thinking processes to evaluate and then reach a decision. Feedback When carrying out a task then we must continuously monitor the consequences of our actions. To enable the information to be processed, both internal and external feedback mechanisms are used.


15-11




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27 November 2003

Chapter 16. Situational Awareness and Attention Introduction “Stay ahead of the Aircraft”. How many flight instructors have used this term to tell a student to think about his flying? Does he mean that the student’s Situational Awareness is lacking? When we look at aircraft accidents we have to ask ourselves this question: Why does a well motivated crew, in an aircraft fitted with all the latest equipment, fail to perform at a critical point during a flight? Situational Awareness It is difficult to define personal or crew situational awareness. Below are some definitions that other people have used: ¾

Situational awareness is the perception of the elements in the environment within a volume of time and space, the comprehension of their meaning and the projection of their status in the near future (Endsley 1987)

¾

Situational awareness refers to the up to the minute cognisance required to operate or maintain a system (Adams, Tenney and Pew 1995)

¾

Situational awareness is adaptive, externally directed consciousness. At a very simple level, situational awareness is an appropriate awareness of a situation (Smith and Hancock 1995)

The above definitions are really definitions for the single crew. For the crew: ¾

Team situational awareness involves two critical but poorly understood abstractions; individual situational awareness and team processes in a highly interactive relationship (Salas, Prince, Baker and Shrestha 1995)

¾

Team situational awareness is the crew’s understanding of flight factors that affect (or could affect) the crew and aircraft at any given time (Wagner and Simon 1990)

Building Situational Awareness To help build situational awareness we need to build a 3 D model which pictures in our mind: ¾

Where we are

¾

Where we are going, and

¾

Where we have been


16-1


This mental model is our conceptual way of understanding: ¾

How or why something is working

¾

Why something is happening

¾

Why a person is behaving in the way they are

There are numerous factors that affect Situational Awareness. The diagram below lists but a few: Crew

Task

Aircraft Dynamics of the Situation Performance System Status Sensors Avionics

Goals Constraints

Intent Standard Behaviour Individual Behaviour Resources

Situational Awareness

Air Traffic Control Clearances Instructions Information

Active Monitoring Cockpit Senses ATC Other Flight Crew

Environment Navigation Data Weather Other Traffic

The mental model that a pilot prepares is created by both experience and expectation. It is therefore, a perception of events. The problem with perception – has the pilot picked up the reality of the situation or is it imagination? To ensure that the crew situational awareness is equal all crewmembers must remember that: ¾

In the modern flight desk “knowledge is not power”

¾

All information must be shared

¾

Effective communication ensures that the correct message is sent

There is a need for an accurate perception of the factors and conditions that affect the aircraft and flight crew before, during and after the flight.


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Personal Factors Affecting Situational Awareness Vigilance Most tasks require constant monitoring without lapses in attention. Vigilance can be defined as attention to the task in hand such as continuously scanning for other aircraft during a long flight. Vigilance is decreased by factors such as: ¾

Fatigue

¾

Loss of sleep

¾

Boredom

Arousal Defined as “to awaken from sleep”. In the aviation sense it can be taken as maintaining preparedness for a task. As seen in the chapter on stress a high level of arousal is needed for optimum performance. It is fair to state that a high arousal state requires a high vigilance state. Low arousal leads to low vigilance and very poor performance. Hypervigilance A state of panic. This worrying state can manifest itself quickly and for no apparent reason. The sufferer becomes illogical in the way that attention is paid to all tasks. Minor problems may take a disproportionate amount of a pilot’s attention leading to major problems being missed. Three levels of Situational Awareness The pilot requires the skills of not only coping with what is happening now but with the skills of anticipating what is going to happen in the near future. This can be broken down into three Situational Awareness Levels: Situational Awareness Level 1

Monitoring

Situational Awareness Level 2

Evaluating

Situational Awareness Level 3

Anticipating

Situational Awareness Level 1: Monitoring There are limits to how much a pilot can see and hear at the same time. Monitoring is an art where the pilot needs to be aware of the present needs and be able to ignore the unwanted. Easy to say – difficult to act upon. Let us look at some techniques that can move us towards this goal. Attention is like a searchlight. It can be focussed in one direction. Attention can become so narrow that a pilot can ignore all outside influences to ensure that he concentrates on the task in hand. Narrowly focused attention is useful when solving difficult problems. But who is flying the aircraft?


16-3


If the attention is widened too far the pilot will be aware of all aspects of the flight and its environs. The pilot’s job requires the ability to focus on a problem and to keep the big picture. Too wide a span and overload is a possibility. In two crew aircraft, redundancy allows for one crewmember to focus on a problem whilst the other is “flying the aircraft”. It is easy to fall into the problem of being sidetracked. These distractions have to be sorted into those that matter and those that don’t. Distraction is an easy way to fall into the first stages of an error chain. As a pilot you need to be able to: ¾

Keep the big picture.

¾

Pay attention to detail.

¾

Not get sidetracked or distracted.

Situational Awareness Level 2: Evaluating To fall behind the task in hand is one of a pilot’s worst nightmares. In this level the pilot needs to evaluate and comprehend the numerous inputs associated with the flying job in hand. In addition to monitoring inputs there must be comprehension as well. This allows the pilot to have a Situational Awareness of the task in hand. The majority of problems in this category come from difficulties with automation. To stay on top of the situation we must utilise all sources of information. Situational Awareness Level 3: Anticipating The pilot not only needs the awareness of what is happening now but needs to be able to anticipate what is going to happen in the future. This stage ensures that crews have the same awareness of a problem and can both work to the same goal. The crew that anticipates usually stays away from the problems that high workload situation brings. Pilot Considerations “What if” is the question a pilot should continuously ask. This question can help in the management of the cockpit environment which includes Situational Awareness. Both pilots need the knowledge of “what”, “where”, “when”, and “who” during any portion of a flight. Briefing/Debriefing A NASA study showed that those crews that brief and debrief a flight are much more effective than those who don’t. Both briefing and debriefing allow pilot’s to plan the sortie. This plan is the initial basis on which Situational Awareness is built. The brief is the initial sharing of knowledge.


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27 November 2003

Conflict Resolution By monitoring, another crewmember’s mistakes can be quickly recognised and dealt with. SOPs help by designating the responsibilities of both the pilot flying and the pilot non-flying. Each pilot will have certain responsibilities but must also monitor the situation with the other pilot.


16-5




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27 November 2003

Chapter 17. Communication Introduction Communication can be defines as a process where: Information, thoughts and feelings are exchanged in a readily and clearly understood manner Communication is essential in the modern day transport aircraft in order to maintain Situational Awareness. Karl Marx wrote: he who communicates, leads Communication Effective Communication Why should we communicate effectively? Consider the words below: Captain:

Take-off power

Engineer:

Responds by pulling the power back on all four engines. Good thing it was at the take-off point

On the flight deck the pilots need to communicate ideas, concerns and information effectively. How effectively this is done depends not only on the sender but the receptiveness of the receiver. Do not assume that everything you say is clearly and immediately understood. The opposite is often true. Hearing is not synonymous with understanding and without understanding there is no effective communication. Effective communication is vital for the safe conduct of flight operations, but, what is effective communication? How can we define it? Consider other words beginning with the same 6 letters, ie., community, communism, communion, communal etc, all imply sharing. Communication could be defined as the sharing of information. We are concerned, however, with effective communication. Is the sharing of information, therefore, enough for us to have communicated effectively? Any message starts with a sender. It is eventually received by the receiver. To be effective this message must be sent and received with the minimum of change to its meaning.


17-1


The Cost of Effectiveness All communications have a price. To ensure that the message has been correctly received a check of understanding must be carried out. Results of Poor Communication Look at the Company angle rather than the flight deck, what are the results of poor communication? Low Production

By poor rostering you fail to fly an economic number of hours for the company. Such as missing a flight to Inverness because the company failed to ring you.

Apathy

"Well they didn't tell me about the 0630 Inverness shuttle last week, who knows if they will bother this week".

Mistakes Occur

"I thought I was on the 0730 to Heathrow".

Non-Cooperation

"Well if they can't be bothered to tell me anything, then they can get stuffed".

Grapevine Abounds

"I hear Captain Bloggs is for the chop for missing the 0630 to Inverness ".

We have all experienced something similar in life at some stage. The key to good communication is whether the sender is a good transmitter and the message is sent to a good receiver. The good transmitter ¾

Passes clear and easy to understand instructions

¾

Has a clear voice

¾

Transmits when the receiver is ready

¾

Ensures that the message is understood and that a feedback system is in operation

The good receiver ¾

Pays attention to the whole message

¾

Tells the transmitter if they are not ready

¾

Acknowledges the receipt and understanding of a message


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27 November 2003

Types of Communication Communication comes in many forms: verbal, written, pictorial etc. Each type of communication needs to be looked at separately to discover the positive and negative aspects. Written Communication Written communication is provided to the pilot in many forms such as; checklists; JAR-FCL OPS; UKAIP; Ops Manuals; letters; memo's etc. The advantages of written communication is obvious; letters and memos can be distributed quickly; checklists and publications can be amended quickly if mistakes occur. Negative aspects are that the communication is impersonal; it is one-way and subject, therefore, to ambiguity and misinterpretation; no check of understanding can be carried out; is the document up to date? Written communications have to be well structured and simple to use to be effective. Think of an insurance policy and all the small print. The length of sentence and the legalese used may mean that you have forgotten what you first read before you get to the end of the sentence. Survey has shown how the number of words in a sentence affect understanding: The Number of Words

% Who Understand

in a Sentence

After the First Reading

27

4

15

70

12

86

8

94

Shortening the sentence does not mean that the sentence is any easier to understand. Think of the double meaning of both the sentences below: If you find any of our goods unsatisfactory you should see our Manager! The Area Manager has passed all water used in our batteries. Visual and Pictorial Ambiguity Pictures tell a thousand words. Yet in the chapter on visual illusion we can see how easy it is to become confused. In 1979, an Air New Zealand DC10 flew inexplicably (seemingly) into the side of a 13 000 ft active volcano in Antarctica. The weather in the area was declared VMC; the aircraft was in controlled flight; there was no alarm expressed by the crew recorded on the cockpit voice recorder, so why did the DC10 crash? Visual ambiguity in true whiteout conditions was a major causal factor.


17-3


Verbal Communication Verbal communication is face to face and with body language aids the interpretation of a message. Most verbal communication is two-way, allowing questions to be asked to achieve clarity. Verbal communication can be ambiguous and because there is no written record may be difficult to refer to. Social Skills Social skills refers to the basic behavioural mechanisms that we use between each other. One of the main areas is body language. Body Language There has been a lot written on the term body language. Below are listed some of the general principles that help to maintain good relations on the flight deck. In the diagram below the way that we carry out normal communication is shown in a piegraph. Note how little attention is paid to the words and how much is paid to the body language.

Normal Communication

The words

7%

55%

38%

The way the words are said Body language

The main methods by which we communicate using body language are: Eye Contact Do you believe someone who constantly looks away from you while you are talking to them? Not only does it show a lack of interest in the conversation but is rude. Staring on the other hand can be used as a form of aggression. Facial Expression We all show happiness, sadness, content etc with our facial expression. On the flight deck it is easy to show contempt, disgust etc.


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27 November 2003

Touch Touch is an important means of communication. In the Arab states the handshake is a long protracted affair which if not carried out shows lack of interest. In the UK, the handshake is little more than a grasp of hands. It is easy to forget the importance of touch to some cultures. Body Orientation and Posture The way that you sit, the way that you place your body in respect to others communicates your feelings towards them. Crossed arms, crossed legs all give different messages. Physical Separation There is an approximate 50 cm space around the body that is sacrosanct. Any invasion in this space is usually countered by a movement away. Verbal Behaviour The way in which words are said holds nearly as much importance as body language. The emotions are easily betrayed by the speed, pitch and tone of the voice. Suffice to say that the words themselves mean little in a general conversation. As soon as the crew are on a flight deck then there is a block to the normal communication state. As soon as the flight crew enter high workload areas of flight then the communications are forced and the body language takes on a much lesser importance.

Forced Communication

The words

10%

35%

55%

The way the words are said Body language

It is at the high workload times that most communications errors that cause accidents are made. It is important that the pilot realises that: ¾

There is a change in the preferred means of communication

¾

75% of accidents occur in the take-off/landing phase of any flight (high workload)

¾

The words and the way they are used are critical at this stage of flight

Listening 40% of our day is spent listening and is a most vital area of communication. We all think that we are good listeners but do we listen or do we hear? All too often the “noise” does not


17-5


penetrate into the brain and accuracy and meaning are lost. Problems in effective listening are: ¾

We speak at approximately 125 words per minute, maximum 180 words per minute

¾

We have the capacity to listen at 500 words per minute

The person uses the excess brain capacity for: Planning

Preoccupation with formulating a response and not listening to what the sender is saying

Wandering

Waiting for a key word and when it comes up, taking the conversation into another area of interest

Debating

Taking the opposite point of view.

Turning Off

The receiver does not listen because it is felt that the message is not important.

Listening is a skill. How many times have you been accused of hearing only those things that you wish to hear? I know you thought you understood what I said; but what bothers me is that what you heard is not what I meant The reasons behind poor listening lie in the Human Information Processing system itself. The only way that we can converse quickly is by our perception process playing a guessing game as we will see below. The brain attempts to guess what the other person is about to say, in order that an answer can be prepared. The two processes below are often confused:

Hearing

The physical comprehension of a sound

Listening

The process of interpreting physical, emotional and intellectual inputs

Look at the diagram below. Reply Person 1 Person 2

Listening

Planning

Level of Attention

Evaluating


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27 November 2003

This is a simple representation of an everyday conversation. Person 1 is speaking, Person 2 initially listens but soon wishes to become the centre of attention. As soon as the evaluation starts the level of attention drops and no notice is paid to the conversation. Evaluation is being carried out on the small portion of the conversation heard. Eventually Person 2 has his reply formed and they interrupt to have their say. To be a good listener then active listening needs to be practised. The process of active listening can be split into 4 stages: Stage 1 ¾

Awareness of the sound

¾

Making sense of the sound

¾

The ability to distinguish words

¾

Understanding begins

¾

The listener starts to concentrate

¾

The distinguishing of fact from fantasy

¾

True analysis of information

¾

Dependence on knowledge and past experience

¾

Stage 3 plus the added dimension of empathy

Stage 2

Stage 3

Stage 4

To help the above consider the following: Non-verbal Response ¾

Face the speaker, smile, look relaxed.

¾

Maintain eye contact.

¾

Encourage the other to speak.


17-7


Verbal Response Use questions to check the understanding: ¾

Restrict the range of possible responses.

¾

Useful in getting specific information quickly.

¾

Improper use can make a person feel like they are being interrogated.

Questions are asked for many reasons such as: ¾

To obtain information

¾

To obtain information or views

¾ ¾

To show interest To check understanding

There are four types of popular question. Two are acceptable in an aviation environment, two are not. Closed Question A question that invites a simple yes or no answer. This question is good for: ¾

Obtaining information

¾ ¾

Giving information Checking understanding What is the capital of France?

Open Question A question that allows another person to give their views. What do you think about the approach into Heathrow? Leading Question Where the question gives the answer. I think Luton’s our best diversion, don’t you?


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27 November 2003

Limiting Question Similar to the above yet gives a limit to the answers. Where shall we divert, Luton or Coventry? Understanding Once a question has been asked then there must be a degree of understanding. Remember, that compliance is the norm in the human. Compliance is the psychological term which describes a person's tendency to prefer to agree rather than disagree. The answer to our question will invariably be yes, even if there is no understanding of the subject. By use of the first two questions above there is the chance that effective communications can be maintained. Remember the following that Rudyard Kipling wrote: I have six faithful serving men They taught me all I know Their names are what and why and when And how and where and who. Use them to phrase your question and you are part of the way there. Active Listening Active listening is: ¾

The genuine desire to understand another person's perception

¾

Listening and expressing understanding of what another person has said

¾

Sensitivity to another's thoughts and feelings

Active listening is not: ¾

Passive

¾

Giving agreement or disagreement

¾

Judgmental

¾

Argumentative

The art of effective listening Being an effective listener takes practice and a sincere effort on behalf of the listener.


17-9


The effective listener is: ¾

Trustworthy and caring

¾

Accepting

¾

Allows others to talk

¾

Focuses on thoughts and feelings

¾

Is constructive

¾

An active listener

Status, Role and Ability Status Status on the flight deck usually depends on two variables: ¾

Who is the captain

¾

Who is the first officer

The relationship between the two can be defined as leadership/followership. In status, the captain has no difficulty in questioning the first officer; can the same be said about the transfer of information the other way? The problem can be exacerbated when the captain is a training captain and the first officer is just starting his career. When crew are of an equal status, such as two Captains flying together or two Flying Instructors, even two students. Those of equal status are reluctant to question the ability of the other; there is a reluctance to appear to be taking over. Role The role of a pilot changes continually dependent on whether he is the handling or nonhandling pilot. Pilots are reluctant to take control in situations that appear to be dangerous because they do not wish to show a lack of faith in the other. Ability We consider other pilots by our judgement of their ability. The Captain may well be a good commander, but if we consider him a poor pilot then our relationship with him will be coloured. Atmosphere A good flight deck is one that has the right atmosphere created by both crewmembers. This leads to effective 2-way communications. The atmosphere is created by: ¾

Correct attitudes for the Leadership/Teamwork job


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27 November 2003

¾

Interest is shown in the opinions of other crewmembers as much as the completion of the task

¾

Open and frank discussion is encouraged

¾

Active listening is used and consideration given to an answer before the reply is made

¾

Empathy is given to other crewmembers

¾

An explanation of answers and decisions is given to encourage an open cockpit

Communication summary As the phrase says: You cannot not communicate To be an effective communicator the sender or receiver must be: ¾

An active listener

¾

A good questioner

¾

A clear and concise orator


17-11




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27 November 2003

Chapter 18. Personality and Behaviour Introduction All people are different. Unfortunately, this can and does complicate our working life. We begin to notice differences from an early age: ¾

Initially, the physical differences are those that are obvious

¾

Psychological differences are then noticed, areas such as: ¾

Personality

¾

Behaviour

¾

Intelligence

The differences in personality and behaviour that we show in everyday life are important in aviation. Especially important are the behavioural traits we show when first meeting someone. We all want a pleasant flight deck atmosphere. We all want to be sympathetic to other peoples needs. A friendly relaxed flight deck atmosphere helps to: ¾

Foster good communications, which

¾

Helps Situational Awareness, which

¾

Leads to a safer flight

A lot is said about personality and behaviour, in simple terms: Personality

Is what we are

Behaviour

Is what we exhibit

Working Relationships The most important aspect of flightdeck operations is the relationship built up between the pilots. As a human we constantly: ¾

Build relationships with people

¾

Break relationships

¾

Adapt ourselves to the change in our environment.

A pilot though is not only concerned with the building of relationships with other pilots. From the minute they are at work, the process of building relationships start with:


18-1


¾

Car park attendants

¾

Operations personnel

¾

Cabin crew

¾

Dispatch

¾

Engineering

¾

ATC

In communications it was shown how important the way that words are said and body language are. The importance of the following cannot be underestimated as well: ¾

First impressions

¾

Personality clash

¾

Cultural or religious differences

It is important that the pilot recognises the following traits to help flight deck communications: ¾

A person's personality

¾

A person’s style and their attitude to life

By recognising the above traits there is the chance to respond positively and enhance the flight deck relationship. Intelligence There are no selection criteria for a person to train to be a pilot. There may be a selection procedure within a company when sponsorship is involved but most pilots self improve and hence are not selected. Intelligence does not affect whether you can become a pilot or not. But, what is intelligence? A great deal of work has gone into defining and quantifying the subject. Intelligence Quota (IQ) tests are the benchmark most people think of when assessing intelligence. Unfortunately, intelligence is sometimes mixed with the general world wise traits of the human. Personality Personality can be described as the inner person. It is personality that makes you the individual that you are. Personality is: ¾

What you are born with, and

¾

What you acquire over your formative years from: ¾

Family

¾

Friends


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27 November 2003

¾

Education

Once the formative years have passed personality is fixed. However, it can be changed by a traumatic influence such as brain damage after a car crash. Assessment There are times when it is necessary to assess a person's suitability for a task. This is normally achieved in three ways: Interview

A subjective way of assessing a person. This is a person’s view of another. Most people judge and assess on the first impression and appearance. It is difficult to modify these thoughts even with the passage of time.

Questionnaire

Where a questionnaire is used techniques such as factor analysis help with the construction of the document. Questions may seem repetitive but the findings are linked and give an assessment of the person.

By using the factor analysis technique, a valid questionnaire for assessing personality traits is constructed and this builds a profile of that individual. One such questionnaire being the Myers-Briggs profile which is widely used within the aviation industry. Behaviour Behaviour is similar to the clothes we choose to wear. Think of the clothes you would wear at the following two occasions: ¾

A funeral

¾

A barbecue

Behaviour is very much the same. You choose your behaviour to a particular situation like the clothes you wear. If you choose your behaviour, then you are responsible for your behaviour. Unfortunately, you are judged on the way that others see you. In reality the two statements below dictate behaviour: First Impressions Last

You never get a second chance to make a first impression

Behaviour Breeds Behaviour If you shout at someone, they will normally shout back


18-3


Self Opinion We all have a picture of what we think we are. This picture is composed of certain values such as: ¾

Thoughts

¾

Attitudes

¾

Moral values, and

¾

Commitments

These values are influenced by our past experiences and expectations on life. These can include events that are both successes and failures. This includes the way that others have reacted to these events especially during our formative years. We live to these values and more importantly judge others with these values. Defence Mechanisms To help in our self opinion we employ inbuilt defence mechanisms. These also help us in our coping strategies against stress. The defence mechanisms are set to disguise the presence of a weak or undesirable quality by the emphasis of a more positive quality. In stress coping they may reduce tension by accepting and developing a less preferred but more attainable lifestyle. These defence mechanisms can also relegate the blame for such problems as shortcomings or mistakes by attributing them to others. The student pilot who fails a test blames the instructor for not teaching the correct techniques. Denial We are all guilty of turning our back on the unpleasant side of life. With pilots it is the embarassment of watching our own errors when played back on a video screen. Remember “Errare Humanum Est”. No pilot has ever flown a perfect sortie, flying is a continuous correction of errors. Introversion and Extroversion Introversion and extroversion are diametrically opposite. The prefix ‘intro’ means into or toward, and ‘extro’ means from or away. Introverts turn inwards to their own thoughts and can be viewed as shy or being socially reserved. Extroverts turn their thoughts outwards, demonstrating gregarious behaviour and confidence. Introversion and extroversion are personality traits formed by deeply held beliefs. Behaviour is affected by introversion and extroversion, and although it is possible to alter ones behaviour through activity and training, the effects are generally short lived, with deep rooted personality traits emerging when fatigued or under pressure. Most of us fall somewhere into the middle ground of introversion and extroversion with a slight preference one way or the other. In


18-4

27 November 2003

order to study grades of introversion and extroversion it is simpler to look at extreme examples. An extreme introvert would try to avoid unnecessary contact with others, preferring to be left to their own devices, not being challenged by those around them. The true introvert would be happy with his or her lot, enjoying solitude and rarely seeking self improvement. Extreme introversion is usually coupled with a lack of confidence and self-empathy. An extreme extrovert requires constant attention from others, needing interpersonal stimulation and often adulation from those around them. Extroversion usually requires a high level of self confidence, but conversely, a strong extrovert may also not enjoy being challenged by colleagues or work related tasks. This may manifest itself as overconfidence, and occasionally arrogance. To enable a person to change their behaviour by choice, first they must alter their beliefs. This can be more difficult than it sounds. Rarely can an individual change their beliefs to alter their behaviour over a long term. The first step is to become aware of the behaviour that they feel requires changing. This must then be linked to the relevant belief that causes the behaviour. Once the belief and behaviour have been identified, the individual must accept the required change, and this may involve a period of denial followed by anger. Only then can an individual change their personality. Beliefs, personality traits and behaviour can be altered by external circumstances. Indeed, an individual’s beliefs and personality traits will change with time as they experience life, and it is these experiences that will alter behaviour. The most obvious changes occur following life threatening or near death experiences and can be very dramatic, but every thing that one sees hears and does will have an impact on behaviour no matter how small. Behavioural Styles Past experience and expectation can have an influence on our behaviour. Behaviour is influenced not only by the accumulation of these experiences but also by the attitudes and awareness of maintaining a friendly relaxed attitude within the flight deck Psychologists divide behavioural styles into two basic categories Relationship Oriented The first consideration is the feelings of others, which rank high in the Decision Making process. A person who is high relationship oriented and low task oriented is considered to have a caring or nurturing style of behaviour. Task Oriented The first consideration is given to the task or goal in the Decision Making process. A person who is high task oriented and low relationship oriented is considered to have an aggressive style of behaviour. Assertive Behaviour Assertive behaviour has a bad reputation mainly because of its association with aggression. In some ways aggression is a hostile act. It can be argued that an assertive person intends to hurt or injure, maybe even destroy another. In truth, assertion is a device used to ensure that the maximum potential for reaching a goal has been attained. In some ways the following define assertiveness:


18-5


¾

The ability to use words positively and with conviction

¾

The ability to defend one’s own rights

Personal assertiveness is required to ensure that: ¾

A person can take the initiative in any task

¾

They can translate this initiative into an action

¾

No implication of aggression is perceived

Over-assertion is regarded as: ¾

Improper

¾

Provocative

¾

Unusual in certain cases

The above feelings are felt by people who are subject to over-assertive action. Their reactions can be categorised into three areas: ¾

Discomfort

¾

Resentment

¾

Retaliation

In its most vulgar form assertiveness can be used as an unscrupulous device to extract total obedience. To achieve “the norm” a person must ask certain questions of themselves. The most important being “What do I understand as the meaning of assertiveness?”. We can split assertive behaviour into three categories: Non-Assertion Where a problem is taken up and a person fails to say anything about the difficulties that it may create Lack of self respect Aggression

Doing things in such a way that other peoples rights are violated

Lack of respect for others Assertion

Doing things in such a way that other peoples rights are not violated

Respect for both oneself and others Following are listed a few advantages and disadvantages of each behavioural style.


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27 November 2003

Non Assertiveness Advantages

Disadvantages

The appearance of being virtuous

Eventually others lose their respect.

The non assertive may feel more comfortable being used

Resentment may take its place

The idea that non assertiveness leads to a quiet life

The non assertive gets what they want; but not what they need

People take advantage of the situation

Self respect is eventually lost Aggressive Advantages

Disadvantages

The less aggressive do what the aggressive wants

Others resent the aggressive

The aggressive can get the admiration of other people The aggressive feels all powerful


Retaliation is always likely after aggressive behaviour In the long term people revolt against the aggressive

18-7


Assertive Advantages

Disadvantages

Others understand what the assertive wants

The assertive risks being given the answer “NO”

There is never a feeling of being manipulated Both long achievable

and

short

term

goals

are

Confrontation is sometimes inevitable

Self respect is always maintained

It is fair to say that a lack of confidence in oneself will usually lead to non-assertive behaviour. The pilot must be able the express an opinion and be able to influence others without aggression. Case For Assertiveness Suppression of an aggressive is essential to ensure that conflict is kept to a minimum. Assertive action leads to an inward belief and awareness of one’s own abilities. Non assertive action combined with low confidence lead to misunderstanding and resentment. Body Language The importance of body language and assertiveness is summarised in the next few paragraphs: Aggressive General

Exaggerated show of strength, flippant and sarcastic style, air of superiority.

Voice

Tense, shrill, loud, shaky, cold, deadly quiet, demanding, superior, authoritarian.

Eyes

Expressionless, narrowed, cold, staring, not really seeing you.

Stance

Hands on hips, feet apart, stiff and rigid, rude, imperious.

Hands

Clenched, abrupt gestures, finger pointing, fist pounding.

Non-Assertive General

Actions instead of words, hoping someone will guess what you want, looking as if you do not mean what you say.

Voice

Weak, hesitant, soft, sometimes wavering.


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27 November 2003

Eyes

Averted, downcast, pleading.

Stance

Lean for support, stooped, excessive head nodding.

Hands

Fidgety, flutter, clammy.

Assertive General

Attentive listening, assured manner, communicating, caring, strong.

Voice

Firm, warm, well modulated, relaxed.

Eyes

Open, frank, direct, eye contact without staring.

Stance

Well-balanced, straight on, erect, relaxed.

Hands

Relaxed motions.

Assertive Behaviour Assertive behaviour, takes the best of aggressiveness (without the put-down negatives) and the best of non-assertiveness (without loss-of-self.). Assertive action is a genuine direct communication of ideas, wants and needs. Put with conviction a position can be expressed strongly without domination. Assertive behaviour becomes easier the more it is used. When we respect these rights in ourselves, we are also more likely to act in a manner that respects these rights in others. Aggressive behaviour denies the rights of others and non-assertive behaviour overlooks these rights in ourselves.


18-9


Chapter 19. Leadership / Followership Introduction Leadership is a term which applies to the whole flight deck. For there to be a leader there must also be a follower. True leadership and command must not be confused; command is normally assigned where as leadership is an acquired art. All flight crew must recognise their own leadership responsibility in the decision making process. Leadership is a way of focussing and motivating a group in order to achieve the task. On the flight deck the commander, as the designated leader, has the authority and responsibility for the flight. In modern public transport operations the pilot flying can be termed a functional leader; one who carries out a specialised task on a temporary basis. Leadership Qualities A leader should be able to: ¾

Provide continuity and motivation

¾

Remain flexible at all times

Normally a leader should be one step ahead of his team; too far ahead and the team can be lost. The effective leader has to use the ideas and actions in such a way that they influence the thoughts and behaviours of the team. The leader is the pivot through which change and influence are implemented. Leadership Skills Leadership skills begin developing as soon as a pilot sits on a flight deck for the first time. These skills are determined by certain factors which can be good or bad depending upon the formative years on the flight deck. Most leaders perform 4 primary functions: Regulation of the flow of Information The leader must be able to regulate the flow of information, ideas and suggestions. The leader can either be the commander or the pilot flying in this case. ¾

Communication of flight information

¾

Asking for opinions, suggestions


19-1


¾

Giving opinions, suggestions

¾

Clarifying communication

¾

Providing feedback

¾

Regulating participation

Directing and Coordination of Crew Activities processes the information below.

The

commander

usually

¾

Direction and coordination of crew activities.

¾

Monitoring and assessing of the crew performance as a whole. This may include self criticism

¾

Providing planning and orientation

¾

Setting of priorities, whether task or people orientated

Motivation of Crewmembers A positive climate generated by the reasoning below helps in keeping performance standards high. ¾

Creation of a happy working environment

¾

Maintenance of an "open" cockpit atmosphere

¾

Good conflict resolution through assertive actions

¾

Maintenance of positive relations

¾

Providing non-punitive critique and feedback at all times. Accepting critique and feedback from other crewmembers

Decision Making ¾

The leader is ultimately responsible for decisions

¾

Assuming responsibility for Decision Making

¾

Gathering and evaluating information from all sources

¾

Formulating decisions

¾

Implementing decisions and relating why the particular action has been chosen

¾

Gathering feedback on all actions

The Person Goal (P/G) Model One way of depicting interaction is to construct a model where the dimensions are peopleorientation (P) and goal-orientation (G).


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27 November 2003

Person

P+G-

P+G+

Goal

P-G-

P-G+

Acceptable Behaviour Unacceptable Behaviour

In this model we are looking at the balance between the concern for achieving the goal (G) and the concern for people (P). P+G- Democratic Leader The friendly leader who has little concern for the task. Conflict resolution is kept to a minimum where others are left to have their own way. The types of word that describe the democrat are: ¾

Reactive

¾

Understanding

¾

Sensitive

¾

Nice

¾

Protective

All are commendable but in extreme can lead to a dysfunctional flight deck. P-G- Timeserver Other names applied to this type of leader are laissez-faire or autonomous leader. This type of leader cares little for the job or for the people in it. This style of leadership generates the poorest team performance because of the willingness to accept poor leadership styles by: ¾

Rule bending

¾

Failure to achieve or trying to achieve objectives

¾

Low morale within the team

The negative traits shown are: ¾

Indifference

¾

Apathy

¾

Passiveness


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P-G+ Autocratic Leader The aggressive leader. Task orientated to the extent that the feelings of others are ignored. The over-bearing nature of this type of leader ensures that the experience of others is ignored. In extreme cases those in the team become disinclined to offer any help at all. The autocrat gives directions, expects unquestioning obedience from juniors and is abrasive and demeaning. The unacceptable traits shown are: ¾

Overbearing

¾

Autocratic

¾

Dictatorial

¾

Tyrannical

¾

Ruthless

P+G+ Ideal Leader By definition this person must be assertive. Concerned for both the goal and the person this leader will earn the respect and commitment of the team. The atmosphere enables all to contribute ideas which are recognised and considered. Traits observed are: ¾

Constructive

¾

Straightforward

¾

Direct

¾

Expressive

¾

Assertive

Leadership - The Leader Wherever a group of people are found certain expectations exist of the person in charge of that group. What makes an effective leader? The old saying: Leaders are born, not made! Some people are born with the aptitude for leadership, but they are few in number. But how is leadership taught? Qualities Approach By examining the personal qualities (PQ's) of born-leaders it is possible to define the qualities that made them effective. The result is a list of those qualities that give both a positive and a negative relationship. Below is a table summarising the percentage of positive and negative relationships between personality traits and leadership. Adapted from Mann (1959)


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Traits

Number

% Giving A

% Giving A

% Yielding

Of

Positive

Negative

No

Findings

Relationship

Relationship

Relationship

Intelligence

196

46

1

53

Adjustment

164

30

2

68

Extroversion

119

31

5

64

Dominance

39

38

15

46

Masculinity

70

16

1

83

Conservatism

62

5

27

68

Sensitivity

101

15

1

84

From all the qualities seen there is no positive way of teaching which combinations are effective and those which are not. Situations Approach Following the failure of the PQ's theory, an alternative, the situations approach, was fielded. It stated that leaders were born for situations; people like Winston Churchill. In all leadership programmes where a situations approach to leadership was adapted it was found that, where a person was appointed at random to be the leader, after a short period the others in the group started to behave as if the appointed leader was the natural leader. If, the leader is appointed such as on the flight deck then the foundations for leadership have been laid; the leader still needs to be effective. Effective Leadership The following characteristics are generally accepted as those recognised in an effective leader: Competence

Professional competence is required by the leader on the flight deck. The technical skills shown along with the piloting skills should be good and inspire confidence in the rest of the crew.

Communication

Communication should be clear and concise interspersed with good listening skills so that interpretation and evaluation is possible. Personal emotion is kept out of transactions.

Decision Making

Decisions are based on the situation at that time. All information is used and a logical decision making sequence is used to form the solution (DECIDE).


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Perseverance

A leader who sticks to the task in hand regardless of the difficulties encountered. The effective leader is always confident that a solution can and will be found.

Emotional Stability

Self control is maintained in the most trying conditions. Personal emotions never cloud decision making.

Enthusiasm

Where the leader is committed then the follower will usually give their best.

Ethics

The highest standard of professional conduct is expected at all times.

Recognition

Acknowledgement is given to the help of others.

Sensitivity

Stress and fatigue should be recognised in both self and others to ensure overload situations are not allowed to develop.

Flexibility

Adaptation of styles to the problem in hand must be possible. No two emergencies are the same.

Humour

One man’s humour is another’s sarcasm. Well directed humour is an effective tool in the management of the flight deck. Badly directed humour is hurtful and can destroy effective teamwork.

Attitudes to Leadership The likes and dislikes of a human being that can destroy the effective team at any time. Most are formed from personal belief about situations or events. Most attitudes are from the subconscious and are apparent in the behaviour that we show. Extremes of attitude are dangerous in the flight deck environment: Anti Authority

The person who hates anybody telling them what to do. Where this person regards rules and regulations as stupid or unnecessary then an unsafe cockpit atmosphere can be engendered. All pilots have the prerogative to question authority if they think it necessary.

Impulsive

The flying “arms in the cockpit” type. The person who has to react to any problem immediately. The lack of thought can in extreme cases cause Confirmation Bias.


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Invulnerable

The “it’ll never happen to me” brigade. Accidents happen to others but not me. The pilot who has this attitude is more likely to take risks and chances that are unsafe.

Macho

Thought to be a male problem only but in fact females are just as susceptible. The type who has to prove that they are better than anyone else.

Resignation

The “Who cares” or “What’s the use” pilot. The pilot who does not believe that they make any difference to the situation. This type will follow the more assertive pilot which may lead to the acceptance of unreasonable risks.

Complacency

With high levels of automation crews are beginning to accept what the computer does as the norm. Monitoring and checking is left because the “computer is always right”.

Ineffective Leadership Ineffective leaders will tend to: ¾

Over control all situations

¾

Focus on the task only and ignore the person

¾

Avoid conflict

¾

Distance themselves from the other crew

¾

Behave inconsistently

¾

Ignore inputs from other crewmembers, by either demeaning or totally ignoring them

¾

Be sarcastic or belittling

¾

Be devious or indirect

Most captains do not use this style of leadership. Most will develop a very shallow cross flight deck gradient which encourages the assertiveness of others.


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Chapter 20. Decision Making Decision Making Process Decision Making can be broken down into a series of steps or actions that the pilot follows: ¾

The recognition that there is a problem. Note that no action is taken at this stage

¾

The gathering of information in order to assess the situation. This is undertaken by all crewmembers

¾

The information required and where that information can be located needs to be established. How this information can be verified is set at this stage

¾

The options that are identified and the alternative solutions are now risk evaluated. Advantages and disadvantages are weighed to give the best solution

¾

Decision implementation and any actions are executed. Remember, doing nothing can be an action

¾

Review the consequences by use of feedback. Evaluation and revision may be necessary

Reaction to Decision Making The following actions are not a comprehensive list of addressing the decision making problem. The intent is to give a logical safe progression to a problem: ¾

Fly the aircraft

¾

Never assume that you do not have the time

¾

Identify the problem

¾

Assess the situation using all resources

¾

Select and carry out the correct procedure

¾

Continue evaluating the situation

¾

Inform the cabin crew

¾

Inform the passengers? Good idea or bad – will it cause panic.

Making and Taking Decisions There are very few situations in an aircraft that require an immediate decision. There is not an infinite time period in which a problem can be solved; the aircraft will eventually run out of fuel. Therefore, certain principles need to be applied to decision making. They can be described as below: Inquiry

What is wanted. Priorities and timescale need to be defined


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Advocacy

Consultation of all participants

Conflict Resolution Commitment to a plan of action and being able to resolve this with other members of the crew Decision Making

All decisions must be explained. At this stage, why there was rejection of any plans must also be explained

Critique

A review of the situation is needed to ensure that the plan is working. At this stage checks for Confirmation Bias should be made.

Decision Making Models Most airlines use simple acronyms to ensure that a logical process, like the above, is followed. British Airways use DODAR. ¾

Diagnosis

¾

Options

¾

Decide

¾

Assign

¾

Review

It does not matter what model is used, all have the same intent and format. All are closed loop situations which allow a continuous evaluation of the problem and its consequences. Atlantic Airlines use DECIDE: Detect

Estimate

Choose

Identify

Evaluate


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27 November 2003

Detect

The pilot detects the fact that a change has occurred that requires attention The emergency occurs

Estimate

The decision making team have to estimate the significance of the change to the flight What is the problem

Choose

The team now choose a safe outcome What are the options

Identify

The team identifies actions that will control the change What is the best course of action

Do

The team do action on the best option Carry out the action

Evaluate

Evaluation of the effect of the change is monitored continuously Review of the situation

Group Versus Individual Decision Making A crew as opposed to an individual will usually make a better decision. It is one reason why committees are formed. A crew working as a team, where knowledge and experience are combined, can be very effective. To be effective all must be confident and comfortable in raising doubts or opinions. Each crewmember must be confident that their opinion is a valued one. In team decision making the following guidelines can be used: ¾

Use all the available resources.

¾

Differences of opinion can be expected. This must be regarded as helpful not a hindrance.

¾

Avoid arguing. All problems must be approached logically.

¾

Majority voting is acceptable in committees. In the aircraft there is one Captain. The final decision must rest with him.

¾

All inputs have to considered as important.


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¾

Why a solution has been taken has to be explained to all.

Influences on Decision Making Certain factors have to be taken into account where group or individual pressure can influence pre-decision thinking. These factors are listed below. Compliance Most people will tend to comply with decisions rather than question them.This is true when the decision is made by someone of a perceived higher status. Compliance can also occur when a person has disagreed with a previous decision and does not wish to seem obstructive. Conformity Peer pressure. A person will tend to conform with the group's decision because they wish to be the same as the rest of the team. If 2 or more people have given an answer to a problem then it is likely that a third will give the same answer. Status affects conformity. Differences must be voiced at this time. Confirmation Bias Confirmation Bias is the natural tendency for a person to accept information which agrees with their ideas about what is happening and to reject that information which does not agree, as spurious. Group Polarisation (Risky Shift) The tendency for a particular attitude to prevail within a group. A group decision reflects an extreme rather than a norm. The problem is worst when a pilot who likes taking risks flies with a pilot who is similar in attitude. The tendency for the pair is to take greater risks. A phenomenon known as “Risky Shift”. Conversely, cautious pilots would make a more cautious decision. Other factors affect the decision making processes of a pilot. These are more social influences than the effects of the above: Vigilance

With a normal person as workload increases so does vigilance. Vigilance is a degree of activation of the body. It is different from attention which depends upon the capacity of the brain to deal with problems. Where boredom or monotony occur, hypovigilance can lead to a state of near sleep where decision making is difficult.

Judgement

Where a pilot is vigilant then judgement is usually sound. Good judgement is learnt through the flying processes and can be said to be based upon experience. What matters with judgement is the outcome. Judgement depends upon the decision to act and the response given. Judgement in a pilot is the recognition of all the variables that effect decision making and their outcome.

Attitude

What does the term “Safe Pilot” mean. Is it someone who is over cautious or someone who weighs up all eventualities and their outcome. Attitude is a part of the mind you as a pilot put to all


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processes of flying. Hence its affect on decision making. A good attitude does not necessarily mean good decision making but it does help. Summary Decision making depends upon evidence given to us by certain senses, it is based upon: ¾

Our expectations and desires which can distort the perceived information

¾

Any erroneous mental modelling in building our situational awareness

No matter how we perceive a problem it is essential that in the decision making process we always hold an open mind. We must: Hope for the best; but plan for the worst


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27 November 2003

Chapter 21. Error and Error Chains Introduction We have all experienced part of another person’s accident For example: ¾

How many readers have had an accident when driving a car?

¾

How many readers have nearly had an accident when driving a car?

Human error is attributed as the main cause factor in 65 – 75% of all aviation accidents. Each accident can be said to be the activation of an error chain being activated. The knowledge of how an error chain works or how to mitigate the effects of human error are essential to the modern pilot. No pilot flies a perfect sortie. It could be said that a flight is a sequence of errors occurring one after another. Each error being linked like a chain. In most cases the links of the chain are broken by the pilot correcting each or most errors which leads to a safe flight. Where the links of the chain are not severed then the error progression is followed and an accident is possible. The Chain is broken SAFE FLIGHT

The Chain is intact POSSIBLE ACCIDENT


21-1


Levels of Human Error Because of the nature of flying there is always the possibility of errors occurring. The error chain is a result of human error and should not be linked with flying alone. Three levels of human error can be classified: Slip

Slips occur when the incorrect information is sent or poor communication is used. A slip is often a response to a well formed habit. Normally a slip is seen as a visual or auditory response which can also be an indication of a raised stress level.

Mistake

Planning failures. Mistakes generally occur because of the perceived time an individual thinks they have to complete a task. Rushing causes the pilot to misread simple tasks such as track and time etc.

Error

Errors occur because of incorrect actions. The incorrect action can be based on either correct or incorrect information flow. Because the error is an action it is classed as the most dangerous form of human error.

Correction of Human Error Each of the above levels can be corrected as they occur: Slip

By letting the person who made the slip know that the error has been made.

Mistake

By questioning the plan at the time the misconception is announced. This can be during the planning, briefing or execution stage.

Error

By using two flight crew who are alert to the possibility of errors occurring. However, each pilot must be capable of using assertive action to alert others that an error has been made.

To ensure that the above are carried out some form of error management process is required. James Reason suggested that to be effective that any error management system would have to cover the following: The Operator

Any person who is involved with the operation of the aircraft

The Task

What the aircraft is doing

The Flight Deck

The pilots and their interaction with the aircraft

The Organisation

The company and its peripheral services


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Human error can occur at any time. Most airlines train to what they think may happen or has happened in the past. The airline SOPs are written to cover most eventualities in an attempt to eliminate the possibility of human error. SOPs do not cover every eventuality and the pilot may have to revert to a knowledge based response in order to deal with occurrences. Group Attitudes Errors are induced by any of the following: Peer Pressure Doubts are suppressed because of the need to be part of the group and the pressure of wanting to be “one of the boys” Vulnerability

Risky Shift, where team members agree to the more adventurous approach

Knowledge

“Knowledge is power”. Members of the team withhold information because they feel that to have more knowledge is to have more power

Rationalisation“It’ll be alright on the night” SHEL Model Interfaces In Chapter 1 the SHEL Model was introduced as a conceptual model of human interaction.

H S

E

L

L

Liveware

H

Hardware

E

Environment

S

Software

L The interfaces are frequent sources of error because of the mismatch between the central Liveware and the outer components of the model:


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¾

The Liveware-Hardware interface where switches and levers are poorly located or improperly coded

¾

The Liveware-Software interface where delays and errors may occur while seeking vital information from confusing, misleading or excessively cluttered documentation and charts. Problems can also be related to information presentation and computer software design.

¾

The Liveware-Environment interface related to factors like noise, heat, lighting, air quality and vibration. This area also covers fatigue caused by the disturbance of the body’s biological rhythms.

¾

The Liveware-Liveware interface where the interaction between people is investigated

Links of the Error Chain Certain clues can be used to identify and break the links of any error chain. For simplicity the error chain can be broken into two areas: Operational Errors Failure to Meet Targets

Failure to meet the flight targets such as ETA, airspeeds, approach minima etc. The operational procedures required by the company are ignored or missed.

Non-Standard Operations

Whether intentional or not, deviation from the SOPs can lead the aircraft into a dangerous situation. The SOPs are developed to lead the flight crew through a logical approach to any problem solving. The SOPs may not cover all aspects of flight but they offer the pilot an effective means of problem solving during periods where time may be critical.

Violation of Minima

Whether intentional or unintentional any violation of minima or operating standards can lead the aircraft into a dangerous situation.

No One Flying the Aircraft

During all stages of flight the aircraft’s progress needs to be monitored. If the aircraft is left to its own devices then accidents can and will happen.

Human Errors Poor Communication


Whether the problem involves incomplete messages or the lack of communicating information poor communication is an area that still causes concern. As soon as there is a difference in knowledge level then there will be a difference in situational

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awareness. Ambiguity in Instructions

Where sources of information do not agree there is the possibility of the crew falling into Confirmation Bias. Sometimes it is better to check the negative in order to find out what is happening.

Discrepancy in Situational Awareness

Where information is constantly changing it is important that all flight crew members are kept up to date with all changes.

Distraction and Attention

Once attention is focused on one problem the brain focuses and deals with this problem alone. Because of the attentional capacity in HIP there is the possibility that information will be lost. Distraction can be the result of outside influence and inattention is paid to the process of flying the aircraft.

Confusion

Where confusion reigns it is important that the flight crew do not seek solace in each other. It is at this time that the problems of leading questions and the need for confirmation come to the fore.

There will be other component parts to the operational and human errors outlined above. The ones shown are the main areas of the error chain that need to be broken. Breaking the “Error Chain” To break the Error Chain the crew first has to detect the presence of a problem. Action needs to be taken in order to ensure a safe flight: ¾

Identify the problem

¾

Communicate what the problem is

¾

Achieve agreement as to what the problem is

¾

Decide on an action to solve the problem and break the chain of events

¾

Evaluate the action to ensure that the problem does not reappear


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Chapter 22. Learning and Learning Styles Introduction As a learner you have probably never thought about the principles that may affect your learning. In general there are certain principles that guide us in how we learn. These can be split into two areas: ¾

The material presented to us for the course, and

¾

How we learn it

The Learning Cycle A training programme is usually devised to suit a training need. In this case Human Performance and Limitations as part of the JAR-FCL theoretical knowledge course. Most of our learning process is either theoretical or practical: ¾

We are given a subject to learn and then apply the knowledge practically We use these notes to pass the Human Performance Examination

¾

We get the practical knowledge by the result of an action We learn by experience that on a cooker that when the ring is red it is hot, black means cold

Kolb (1984) further expanded this process into a learning cycle. This is just a simplified model which represents a person’s process of learning.


22-1


What has to be learnt

Individual learner

Training Plan

Evaluation of the programme

Delivery of training

Assessment of the individual

This model is not as complicated as it looks. The learning cycle can be joined at any point and the circle completed. The Kolb cycle can be further simplified by cutting down to four elements.

Experience

Reflection

Preparation

Theory

The four areas can be expanded in the following way: Experience A learning process that can happen by chance. It is our process of everyday learning. The experience can be by a formal teaching method. This is an active stage where information for a task is fed to our sensors.


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Reflection The point in the cycle where a learner starts to think about what has been experienced. This is a passive stage. A person will reflect on the subject that has been learned. In some way this is the stage where a person begins an inner discussion with themselves. Effectively “the wheat is sorted from the chaff”. Theory Not many people are natural theorists. In most cases we all use other peoples ideas to help with our own instruction. This is a stage where new information is taken in and compared with what we already know. Preparation A planning stage. When a new piece of information has been learnt then the information is normally reflected upon. Once this reflection has occurred then it is time to move on to the next point in the cycle. Honey and Mumford (1982) Honey and Mumford redesigned the Kolb Learning Cycle to produce a model of learning styles.

Experience Activist Reflection Reflector

Preparation Pragmatist Theory Theorist

The Kolb cycle is modified by linking it to the 4 types of person who are happiest working at a particular stage of learning. Activist

The type of person who enjoys things as they happen and look forward to an experience with enthusiasm. The activist will rush into things without thinking of any drawbacks. The people who use this learning style prefer to be centre stage where the action is. Once the activity is completed they become bored. This type of person likes to learn through games, teamwork etc.

Reflector

A person who takes a cautious, thoughtful approach to learning. This person is a listener who will tend to take a back seat in any discussions. The reflector only acts once all information has been gathered. Kelly (1955) described this stage in the following statement:


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When new information is received, if it fits in with our beliefs then we confirm what we already know. The problem arises when we receive information that is contra to our beliefs. At this stage we have two choices, rejection or reflection to accommodate or disregard this new information The more mature learner is normally found in this stage. In summary the reflector is a person who likes learning by observation or by selfinstruction by investigation. Theorist

A person who learns by rote. The theorist is very much a vertical learner with little lateral thinking. Most of us are not born as logical thinkers and the process of theory has to be learned in itself. The theorist learns by rules, using the rules. This is a very effective way of learning because this style leads to learning accuracy.

Pragmatist

The person who is happy putting an idea into practice. This learning style describes the person who gets on with the job and is only interested if it works. This is the practical down to earth workman who enjoys learning from life’s experiences.

Flexible Learning By looking at the above styles it is easy to categorize yourself or others. In most cases we all use a mixture of the styles to get “our balanced form of learning style”. The knowledge of your or other peoples learning styles can help on the flight deck in the understanding necessary to achieve an effective team. Maslow (1943) To satisfy the human needs there is an order of priority. Maslow introduced a triangle of human needs. The lower order motives are aroused first and must be satisfied first. Once a need is satisfied then the next level in the hierarchy can be satisfied. The triangle of needs starts with basic physiological needs up to those related to ego. Eventually the person reaches self-fulfilment. The hierarchy of needs is shown in the diagram below.


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1

Self Fulfilment

2

3

4

Self Esteem Needs

(prestige, status, achievement and domination)

Belonging and Affection Needs

(friendship and love)

Safety and Security Needs

(freedom from pain and danger)

Physiological Needs

5

Reference:

(expression of capacities and talents)

(hunger, thirst, oxygen requirements)

The Manual of Learning Styles, Peter Honey and Alan Mumford Peter Honey Ardingly House 10 Linden Avenue Maidenhead Berkshire SL6 6HB


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Chapter 23. Automation Introduction Since the introduction of the basic instrument flying T designed by the Royal Air Force in 1927, manufacturers have been developing systems that reduce pilot workload.

Air Speed Indicator

Attitude Director

Altimeter

Machmeter

Horizontal Situation Indicator

Rate of Climb

The above instrument panel has now been developed into the glass cockpit designs that pilots in modern aircraft have become accustomed to. A simple design is shown below. Note that the basic T is still adhered to. ATTITUDE AIRSPEED

ATTITUDE ALTITUDE

AIRSPEED VERTICAL SPEED

17

18

HEADING

15


19 20

16

21

180

23-1


Operating an aircraft has changed as automation has increased. Automation provides the pilot with: ¾

Alternate methods of accomplishing tasks

¾

Having more capacity to spare for the job in hand

With the increased use of automation it is essential that: ¾

The automatics work reliably and in a predictable manner

¾

The instruments are easy to read with little or no chance of misunderstanding

¾

The pilots understand the operating limits and limitations of the system

Part of the problem of difficulty in reading and understanding instruments can be shown with the three pointer altimeter below:

100

FEET 0 9 1000 FEET 1 10000 FEET

8

FEET

7

2

3 6

60000FT

1013

4

¾

The instrument is difficult to read

¾

Making an error in reading the altitude is easy

¾

However, the instrument is accurate

Flight Crew Functions Flight crew perform 4 primary functions during flight (Abbott1993): Flight Management


Flying the aircraft

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Communications Management

Monitoring and response to internal and external communications during the flight

Systems Management

Monitoring and actioning of all systems during flight

Task Management

The management of tasks and resources needed in the conduct of the flight

Human Factors Concepts in Design The primary functions of the flight crew must be taken into account. Most designers and manufacturers take into account the following when designing aircraft automatics: ¾

Integration of fail safe concepts for the flight crew

¾

Adapting the automatics for minimal workload for the crew

¾

Easy to understand systems which allow easy monitoring

¾

Better Liveware – Hardware interfacing

¾

Comprehensive information flow

¾

Easy to correct instruments and systems

¾

Sensible error tolerance factors

Automation has to be seen as a partial, or even total replacement, of the pilot. Obviously, the amount of pilot – machine interface depends upon the level of automation required. Common Problems with Automation The advance in computer technology has meant a rapid advance in cockpit automation. There are obvious benefits in the new technology but there are still serious accidents where flight crew management of the systems is inadequate. Corrections are made for these deficiencies, as a problem is uncovered. The most significant areas where there is a breakdown are: Training Training can cover the essentials of operating the system in normal flight; but is the training sufficient to operate the system in a degraded mode. Over use of the computer can result in a degradation of the pilot’s flying skills, especially on NDB approaches. Design Philosophy There is still the perennial problem of the designer not consulting the pilot. There must be consultation to ensure that problem areas can be dealt with before manufacture. Radical changes have occurred over the last few years with the introduction of concepts such as side stick control. Situational Awareness and Complacency To maintain situational awareness is essential in all flights. The reliability and accuracy of modern systems lead pilots into


23-3


an over-reliance on what they think is a no fail system. Boredom results and the pilot becomes inattentive. Reaction times to an emergency when a pilot is in this low— aroused state are slow and prone to errors. Design Protection Different manufacturers take different approaches to this problem. Some design systems which are intolerant of human error, others allow margins for human error. In either system there must be a crew warning system to ensure that the computer and pilot work together and not against each other. Manual Override If the situation deteriorates there must be a method of manual reversion for the pilot. Accidents have occurred where the pilot has not been able to revert to manual control and the aircraft has continued on its computer flight path. Information Management Too much information can confuse and overload the pilot. The time taken to input information means less time to the tasks of lookout and communications. In some aircraft deciding what to display can distract from the task in hand. Automation Management Communication and procedures.

The computer is always right!

Lack of awareness leads to breakdowns in communications

Industry Requirements To ensure that the implementation of new systems meets the performance standards required industry must follow certain guidelines: ¾

Design reviews and evaluation of automation must be carried out before manufacture

¾

Some form of human factors certification of automation must be possible

¾

Validity of all designs must be proven

¾

The role of the pilot must be specified including his task management responsibilities

¾

Training courses have to be developed to ensure that both normal and degraded operations are covered in depth

¾

Standards should be developed for all displays and the colours to be used

Flight Crew Responsibilities To ensure that the operation remains safe and that for both normal and emergency procedures the pilots carry out the required task: Normal Operations All selections and actions are checked by both pilots. One pilot actions the other pilot checks. It must always be remembered:


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¾

The autopilot is not a pilot but an aid to help workload and situational awareness

¾

Flight parameters must be continuously monitored

Emergency Procedures actioned:

The aircraft must be flown and the following

¾

Time should be taken in identifying the problem

¾

ECAM actions should be followed

¾

Where an irreversible action has to be completed then there must be a positive check by both pilots

Automation Summary There are both advantages and disadvantages to automation. Whether you are for or against the automation of the flight deck it must always be remembered that both the computer and the human being are not infallible. Listed below are some of the advantages and disadvantages: Advantages ¾

Performs most of the control tasks allowing the pilot to perform other higher mental functions

¾

Removes the human element from day to day performance

¾

Can reduce the crew size

¾

Better control of systems making the aircraft more economic

Disadvantages ¾

Is the pilot reduced to a button pusher?

¾

Does the pilot lose interest in the job?

¾

Removes the most flexible asset who can resolve non-SOP problems

¾

Automation does cause accidents

¾

Increases the mental workload with the need to monitor the system carefully

¾

Handling skills are infrequently practiced

¾

Complacency and boredom set in

A recent FAA survey listed the main contributory factors in automated aircraft accidents: ¾

Pilot’s who have an insufficient knowledge of the systems they are using

¾

Confusion involved when not knowing the mode of flight


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¾

Liveware – Software design mismatches

¾

Systems behaviour when modes are changed – what information is being shown

¾

Over reliance on the computer

¾

Non SOP operations

Note that most of the above are problems with the human element. Automation at its best should help the pilot; at its worst it kills. To make the best of the systems provided the pilot needs to be both trained and motivated to operate at a high performance level.


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Chapter 24. CRM & MCC Introduction From the beginning of flying to the present day the majority of accidents have been attributed to the pilot. The term “pilot error” has been used to categorise all accidents possible. In the last few years this term is becoming less predominant and the term “human error” is becoming more common. Using the statistics for the First World War it is not surprising that so many pilots crashed because of human error

World War 1 Statistics

8%

2% Pilot Error Technical Defect Enemy Action 90%

When the statistics are brought up to date.

Air Transport Accidents 1994

4%

7% Human Error

16%

Technical Defect Weather 73%

ATC

We can see that the largest proportion of blame is to human error.


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Studies have shown that there is a real need for effective crew training. Hence the advent of Cockpit Resource Management (CRM). What is CRM? We have been flying for over 90 years, why CRM now? The concept of CRM is not new but it remains a fact that accidents related to external sources have decreased, whilst accidents attributed to human weaknesses have increased. Why CRM training? Crew Resource Management represents one approach to improving aviation safety. Technical skills alone are not enough to manage the modern public transport aircraft. CRM programmes have gone into widespread use since the early 1990’s. The value of these programmes can be shown by using real incidents. One of the best examples is the Sioux City DC-10 accident. Captain Al Haynes and his team were faced with a hopeless situation when his United Airlines DC-10 suffered a loss of all three hydraulic systems at FL 370. The crew used all resources available in the air and on the ground while manoeuvring the DC-10 by differential thrust from the two remaining engines. A crash landing was done at Sioux City airport saving 186 of the 296 passengers. Commander Haynes commented: "United started something called CRM in 1980. It really helped us. We would not have made it without it". The list of critical situations where good human performance and teamwork saved the day is lengthy. There have been many accidents where the cockpit and cabin crew’s hard efforts have saved many lives. CRM training has already proved its value many times. CRM training can only be considered fully effective when it comes to light as improved everyday behaviour through practical actions. CRM and Human Factors training for airline crew members is now mandatory. ICAO detailed certain markers that define what CRM is and is not. CRM Training is: ¾

A comprehensive system for improving crew performance

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It addresses the entire crew population

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It is a system that can be extended to all forms of flight crew training

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It concentrates on attitudes and behaviours and their impact on safety

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It is an opportunity for individuals to examine their behaviour and make individual decisions on how to improve cockpit teamwork

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It uses the crew as the unit of training


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27 November 2003

CRM Training is not: ¾

A quick fix that can be implemented overnight

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A training programme administered to only a specialised few or "fix-it" cases

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A system that occurs independently of other on-going training activities

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A system where crews are given a specific prescription on how to work with others on the flight deck

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Another form of individually centred crew training

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A passive lecture style classroom course

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An attempt by management to dictate cockpit behaviour

A pilot should remember that: CRM is not, and never will be, a substitute for the mechanical skills of flying. It is here to help you understand what is required in the modern day airliner CRM Loop Approximately 70% of air accidents are caused by human error and problems occur because of four main failings. ¾

Poor decision making

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Ineffective communication

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Inadequate leadership

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Poor management

CRM training was further reduced into 7 major training areas: ¾

Communications

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Situational Awareness

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Problem Solving/Decision making

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Leadership/Followership

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Stress Management

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Interpersonal Skills

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Critique

Multi-crew Co-operation (MCC) JAR-FCL now requires a pilot to undergo MCC training before the first type is annotated to an licence. The MCC skills required to work together in a multi-crew environment are difficult to distinguish between those required for CRM. The regulations however, do make a clear distinction between CRM and MCC. JAR-FCL requires MCC training before the first type rating is issued. JAR-OPS requires CRM training on a continuous yearly training basis. CRM training is often given to both pilots and other personnel.


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The objectives of MCC training are: ¾

Optimum decision making

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Communication

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Division of tasks

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Use of checklists

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Mutual supervision

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Teamwork, and support throughout all phases of flight

Listed below are some of the advantages of multi-crew operations versus single pilot operations, MCC helps to enhance these skills: ¾

There will be another pilot to fly if one should be incapacitated

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Reduced workload and hence better situational awareness

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Monitoring of other’s reactions

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Correct use of checklists

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More efficient operation

Disadvantages are usually the fault of the crew not because of the deficiencies in the system: The use of the multi-crew concept is required by regulations for many aircraft and it has proved itself as a fundamental tool in achieving safe and efficient operations of aircraft.


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27 November 2003

Human Performance and Limitations

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