Human Performance and Limitations Introduction Human Factors is about people in their living and working situations; about their relationship with machines, procedures and the environment. It is also about their relationships with other people. In aviation, Human Factors involves a set of personal, medical and biological considerations for operations. Medical Requirements (JAR-FCL Part 3) - Fitness:
The holder of a medical certificate shall be mentally and physically fit to exercise safely the privileges of the applicable licence. - Requirement: In order to apply for/exercise licence privileges, the applicant shall hold a medical certificate issued and appropriate to the privileges of the licence. - Disposition: After examination completion, the applicant shall be advised whether fit/unfit or referred to the Authority. The Authorised Medical Examiner (AME) shall inform the applicant of any condition(s) that restrict licence privileges. If 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. Decrease in Medical Fitness Licence holders/students shall not exercise the privileges of their licences etc. at any time when they are aware of any decrease in their medical fitness which might render them unable to safely exercise those privileges and shall without undue delay seek the advice of the Authority or AME when becoming aware of: - Hospital or clinic admission for more than 12 hours. - Surgical operation or invasive procedure. - The regular use of medication. - The need for regular use of correcting lenses. Every holder of a medical certificate who is aware of: - Any significant personal injury involving incapacity to function as a member of a flight crew. - Any illness involving incapacity to function as flight crew for a period of 21 days or more. - Being pregnant. Shall inform the Authority in writing of such injury/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 occurrence. For illness/injury the suspension will be lifted after medical examination and pronounced fit to function as a flight crew member. In case of pregnancy, the suspension may be lifted by the Authority for such period and subject to such conditions as it thinks fit. Will cease after pregnancy ended and pronounced fit to resume. Some additional factors which affect the normal working of a human body in flight: - Fatigue (sleep disturbances/jet lag) - Blood Donations - Nutrition - Drugs (including caffeine/nicotine) - Alcohol - Stress
Accidents Accident Reports Accident investigations improved aircraft design, and later also ATC, resulting in a steady decline in accidents. This continuous decline has been attributed to the constant improvement of equipment, better training and operating procedures. Today, 2 out of 3 accidents are caused by human related actions. Human Error Encompasses pilots, cabin crew, dispatchers, ground crew, maintenance personnel, ATC and manufacturers. Human Error accidents have increased. Current research indicates inadequate training is the main cause (but not technical training). Studies indicate more training in leadership, communication and teamwork are needed. Crew Resource Management (CRM) CRM covers a wide variety of skills:
- Interpersonal human skills. - Decision Making. - Teamwork. - Situational Awareness. - Stress. - Workload Management.
CRM represents an approach to improving aviation safety that was born from real-life experiences of airline pilots. They realised technical skills were not enough to safely manage a complex flight system. 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. Flight Safety Concepts The SHEL Model Illustrates the different elements of Human Factors. First developed in 1972 by Edwards. S – Software H – Hardware E – Environment L – Liveware Liveware The centre of the model is a person, the most critical and flexible component in the system. However, people are subject to significant variations in performance and suffer limitations but most are now predictable in general terms. The block edges are not straight and simple. The other components must be carefully matched to them if stress in the system is to be avoided.
Physical Size and Shape Vital role played in the design of the workplace and most equipment. Movements and measurements vary according to age, ethnic and gender groups. Normally aircraft are designed around 90% of the population (ignoring the top and bottom 5%). Anthropometry: The comparative study of sizes and proportions of the human body. Input Characteristics Humans have a sensory system for collecting information from surroundings enabling response to external events. However, all senses are subject to degradation. Information Processing Poor instrument and warning system design has resulted from failure to take into account the capabilities and limitations of the human information processing system. Output Characteristics Once information is sensed and processed, messages are sent to the muscles to initiate the desired response (physical control movement/communication). Liveware-Hardware Interaction Elements: Controls and Displays (design, interpretation, control, standardisation). Alerting/Warning Systems (false indications, distractions, response, selection). Personal Comfort (temperature, illumination, seat position, cockpit visibility). Skills: Scanning, detection,, decision making, situational awareness, vigilance. Liveware-Software Interaction Elements: SOPs, Written Materials/Software, Maps/Charts, Checklists/Manuals, Automation. Skills: Computer literacy, self-discipline, time management, task allocation. Liveware-Environment Interaction Elements: Temperature, Pressure, Humidity, Noise, Lighting, Radiation, Wx, Terrain, Time of Day. Skills: Adaptation, observation, stress/risk management, prioritisation. Liveware-Liveware Interaction Elements: Human Errors/Reliability, Workload, Information Processing, Attitude Factors, Experience. Skills: Communication, observation, listening, management, problem solving, perception. Atmosphere and Physics Gases of the Atmosphere Nitrogen (N₂) – 78.08% Most plentiful gas in the atmosphere but not readily used by the human body. Can cause evolved gas problems by saturating body cells and tissues. Oxygen (O₂) – 20.94% Second most plentiful gas in the atmosphere. A by-product of photosynthesis renewing the supply of oxygen in the atmosphere every 3,000 years. During metabolism, the human body uses oxygen to convert body fuels into energy.
Carbon Dioxide (CO₂) – 0.03% Although small in amount, it is still critical to life. Plants use carbon dioxide for photosynthesis and is a by-product of human metabolism. The carbon dioxide supply is renewed every 8 years. Other Gases Argon (Ar) – 0.93% Neon, Helium, Krypton, Xenon, Hydrogen, Ammonia – 0.95% The Standard Atmosphere Barometric Pressure: The weight/force exerted by the atmosphere at any given point. ISA: The average conditions for all seasons/latitudes/altitudes in the atmosphere. - Relationship between pressure and altitude. Standard Atmospheric Pressures and Temperatures Altitude (ft) 40,000 33,700 27,500 18,000 10,000 Sea Level
Pressure (mmHg) 141 190 253 378 (50% compared to SL) 523 760
Temperature (°C) -56.5 -52 -40 -21 -05 +15
Partial Pressure Each gas in a mixture of gases behaves as if it alone occupied the total volume and exerts a pressure. Physiological Zone (Sea Level – 10,000ft) The atmospheric zone in which the human body is well adapted. Changes in pressures with rapid ascents/descents within this zone can produce ear/sinus trapped gas problems. Physiologically Deficient Zone (10,000 – 50,000ft) Decreased barometric pressure results in sufficient oxygen deficiency to cause hypoxia. Additional problems may arise from trapped/evolved gases. Protective oxygen equipment is necessary. Space Equivalent Zone (60,000ft – 120 miles) Supplemental 100% oxygen no longer protects humans from hypoxia (pressure suits and sealed cabins are required). Unprotected humans may suffer radiation effects and boiling of body fluids. Dalton’s Law (Relations of Partial Pressures) The sum of the partial pressures of individual gases is equal to total pressure.
P
L
=
+
+
To calculate pp of one of the gasses: Divide the gas % by 100 x Total pressure (at that altitude).
Pressure Change Effects The human body can withstand enormous changes in barometric pressure as long as the air pressure in the body cavities equals ambient air pressure. Difficulty occurs when the expanding gas cannot escape to allow equalisation. Body gas expansion causes dysbarism (gas expansion manifestations – trapped/evolved). Trapped Gas Disorders If gas expansion is impeded, pressure builds up within the cavity and pain is experienced. Barotrauma: Abdominal, ear, sinus pain or toothache. oyle’s Law (Relation between Pressure and Volume) The volume of a gas is inversely proportional to the pressure exerted upon it (temperature constant). PxV=C
P = Pressure P P
V = Volume
=
C = Constant
OR
V V
Gastrointestinal Tract Trapped Gas Disorders Severe pain experienced above 25,000ft caused by distension of stomach, large and small intestines. Source of gas is swallowed air and as a result of digestion. Can produce marked lowering of blood pressure and loss of consciousness if distension is not relived. Watch for pallor/signs of fainting. Diet Foods which produce gas include: onions, cabbages, apples, radishes, cucumbers, melons. Crew participating in high altitude flights should avoid these foods as well as carbonated drinks. Irregular and hasty eating (or eating while working) makes individuals more susceptible. If trapped problems exist in the gastrointestinal tract at high altitude, belching/passing flatus relieves the pain (eating/drinking aggravates discomfort). Ear Trapped Gas Disorders (Ohitic Barotrauma) As pressure reduces during ascent, the air in the middle ear is intermittently released through the Eustachian tube into the nasal passages. As inside pressure increases, the eardrum bulges and some air is forced out of the middle ear causing a pop/click (eardrum resumes normal position). During descent, the pressure changes may not occur automatically (Eustachian tube resists opposite direction flow). The pressure difference causes the eardrum to be forced inwards. This can make opening the Eustachian tube impossible causing pain. The eardrum could rupture. Pain could increase with further descent and ascent could be required for pressure equalisation before a slow descent. Greatest pressure changes between sea level and 5,000ft. Delayed Ear Block Caused by saturation of middle ear with oxygen (when breathing pure oxygen) and can develop several hours after landing. The pressure inside the ear becomes less than outside causing mild pain. Can be relieved by performing the Valsalva.
- Pressure change effect on the middle ear Complications from Pre-existing Physical Conditions Eustachian tube inflammation/infection from a head cold, sore throat, middle ear infection, sinusitis, or tonsillitis can cause the middle ear to not be adequately ventilated. Forceful opening of the tube could carry the infection to the middle ear. If flight is essential, slow descents are preferred. Malposition of the temporal bone and jaw may cause ear pain. Swallowing or yawing can equalise the pressure during descent. If this does not work them perform the Valsalva (NEVER during ascent). If middle ear/ambient pressures have not equalised after landing and pain persists consult a doctor since barotitis media can occur. Sinus Trapped Gas Disorders Sinuses are air-filled, relatively rigid, bony cavities lined with mucous membranes connected to the nose by small openings. If normal, air passes into/out of the cavities without difficulty equalising the pressure. If obstructed (infection/allergic condition) this causes a pressure differential which sometimes causes severe pain. Like ears, they are most affected in the later stages of descent. Frontal: Pain extends over the forehead above the bridge of the nose. Maxillary: Pain either side of the nose (cheekbones) and possibly in the upper jaw. Perform Valsalva during the descent. If pain is noticed on ascent, any further climb should be avoided. Same for descent. If oxygen equipped, use under positive-pressure to ventilate the sinuses. If not clear after landing, consult a doctor.
- Location of sinus and cavities
Teeth Trapped Gas Disorders (Aerodontalgia) Toothache usually results from an existing dental problem. Generally occurs from 5,000-15,000ft. The altitude at which this takes is consistent for the individual. Descent will bring relief from pain but also often disappears at the same altitude which it first occurred.
Evolved Gas Disorders Occur in flight as a direct result of a reduction in atmospheric pressure. Gases dissolved in body fluids at sea-level pressure are released from the solution and enter a gaseous state as bubbles when ambient pressure is lowered. This causes various disorders (decompression sickness). Henry’s Law The amount of gas dissolved in a solution is directly proportional to the pressure of the gas over the solution. Nitrogen Saturation (Decompression Sickness) Tissues and fluids of the body contain 1 – 1.5 litres of dissolved nitrogen. As altitude increases, the partial pressure of atmospheric nitrogen decreases and nitrogen diffuses from the body so equilibrium can be reached. If this change is rapid, there is a lag in recovery of equilibrium leaving the body supersaturated. The excess nitrogen diffuses into the blood. With rapid ascent to >30,000ft the nitrogen forms bubbles especially in tissues with fat. Symptoms: Pain in joints/related tissues, shortness of breath, sensation of suffocation, bluish skin colouration, skin itching, cold, headache, partial paralysis, loss of consciousness. Evolved gas disorders are considered medical emergencies. The risk can be reduced by pre-oxygenation (pilot breathing 100% pure oxygen for a period prior to high altitude exposure). If symptoms appear in flight, descent to ground level must be immediately conducted and place the affected individual on 100% oxygen to remove excess nitrogen from the system. Bends: Bubbles in the joints (shoulder, elbow, wrist, knee, ankle, rarely hips) Creeps: Bubbles in the skin. Chokes: Bubbles in the lungs. Staggers: Bubbles in the brain.
Pressurisation of Cabin Usually maintained at a pressure equivalent to an altitude of ≤10,000ft. The altitude threshold for the onset of decompression sickness is 18,000ft. Scuba Diving If you fly in an aircraft following scuba diving or any underwater activity using compressed air, excess nitrogen can have been absorbed into the blood and tissues (depends on depth/duration of exposure). Individuals should not fly within 12 hours following diving using compressed air. The time limit increases to 24 hours if the dive depth is greater than 10 metres. harles’ Law The volume of a fixed mass of gas is directly proportional to its absolute temperature provided the pressure remains constant. General Gas Law
(P V ) P = Pressure
= (P V )
V = Volume
T = Temperature
Flick’s Law The rate of gas transfer is proportional to the area of the tissue and the difference between the partial pressures of the gas on the two sides, and inversely proportional to the thickness of the tissue. Respiratory and Circulatory Systems
- Components of the Respiratory and Circulatory Systems
Respiratory System Primary function is the intake of O₂ which enters through the respiratory system and transported in the body through the circulatory system. All body cells require O₂ to metabolise food. Respiration: Process of breathing in O₂ rich air and breathing out O₂ poor air. Components of the Respiratory System Oral-Nasal Passage: Includes mouth/nasal cavities. Mucous membrane hairs filter air as it enters. Pharynx: The back of the throat connected to oral/nasal cavities. Humidifies and warms air entering. Trachea: Windpipe which moves air into the bronchi. Air moves into smaller ducts entering alveoli. Alveoli: Surrounded by capillaries (joining arteries/veins) allowing RBCs to move through allowing gaseous exchange within. CO₂ and O₂ move in/out of the alveoli due to pressure differentials. As the blood travels through the capillaries, the O₂ flows from high pressure (alveoli) to low (in the blood). CO₂ diffuses from the blood to the alveoli in the same way. The amount of O₂/CO₂ transferred depends on the pressures of the alveoli and arteries which decreases as altitude increases (O₂ saturation in the blood decreases leading to hypoxia). Carbon Dioxide Removal A by-product of the metabolic process. It is dissolved in blood plasma from tissues to the lungs. Autoregulation Receptor cells in the brain and sensitive to the level of CO₂ and acids in the blood, control the rate and volume of breathing. Too high levels trigger and increase in breathing (greater volume) until levels are normal. Other body receptors monitor the levels of O₂ and CO₂ leaving the lungs. When O₂ partial pressure falls it triggers an increase in breathing. Low O₂ levels by themselves may not increase breathing rate until a dangerously low O₂ partial pressure has been reached. Body Heat Balance Body temperature must be maintained around 36.9°C (98.4°F). Body Chemical Balance (O₂ and CO₂) Normal body pH level is 7.4 (slightly alkaline). Any shift from the narrow limits is sensed by the brain and chemical receptors trigger the respiratory system to return the pH to normal limits.
Composition of Air in the Lungs Tidal Volume: Adult breathes in/out 12-15 times a minute (0.35-0.65 litres of air each breath). Tracheal Air: Inhaled air becomes saturated with water vapour and warmed to body temperature. Alveolar Air: Enters the lungs (delivers O₂/receives CO₂). Known as external respiration. Lung Volumes Tidal: The amount of air that moves into the lungs with each inspiration (or out – expiration). Inspiratory Reserve: Air inspired with a maximal effort in excess of tidal volume. Expiratory Reserve: Volume expelled by an active respiratory effort after passive expiration. Residual: Air left in the lungs after maximal expiratory effort. Respiratory Dead Space: Space in the conducting zone of airways not exchanging in the alveoli. Vital Capacity: Largest amount of air that can be expired after a maximal inspiratory effort. Maximal Breathing Capacity: Largest volume of gas moved into/out of the lungs in 1 minute. Circulatory System Primary function is to maintain equilibrium of fluids in the body. It also regulates body chemical balance and provides cell nutrition, body excretion, and body heat exchange. Components of the Circulatory System Heart: Made up of 4 chambers; Atria (left/right) and Ventricles (left/right). Right-side: Pumps O₂ poor blood (cells→lungs). Left-side: Receives O₂ rich blood (lungs→cells). Arteries: Vessels which move blood from the heart to the tissues. Aorta: Conveys O₂ rich blood from the left ventricle to the body. Pulmonary Artery: Conveys blood from the right ventricle to the lungs. Veins: Vessels which return blood to the heart. Capillaries: Connect arteries to veins. Transfer O₂, CO₂, nutrients and waste between cells and blood. Baroreceptors: Stretch receptors monitoring/maintaining blood pressure when alterations occur. Factors Affecting Heart Rate Accelerated: Inspiration, hypoxia, painful stimuli, fever, increased activity, thyroid hormones. Decelerated: Expiration, fear, grief, increase in intracranial pressure. Blood Pressure The heart beats around 70x/min at rest which produces an arterial pulse causing a pressure increase (peak = systolic pressure). The pressure then falls (minimum = diastolic pressure) as the heart relaxes (allows blood to flow into heart). Measured in mmHg. Normal reading: 120/80 (120 = systolic/80 = diastolic). Regulated automatically by carotid/aortic sinus pressoreceptors which detect pressure changes. Hypertension (High Blood Pressure) Symptoms: Headache and distorted vision but often symptomless until organ damage occurs. Causes: Being male, positive family history, smoking, diabetes, alcohol, obesity. Treatment: Antihypertensive medications (if diastolic pressure >100 on at least 3 readings). Hypotension (Low Blood Pressure)/Circulatory Shock Symptoms: Dizziness, blurred vision, weakness/fatigue/nausea, cognitive impairment, neck ache. Causes: Heart failure, bleeding, fluid loss, allergic reactions, infections, heat exposure, certain drugs.
Coronary Artery Disease/Angina Narrowing of coronary arteries. Angina is a symptom of reduced O₂ supply to the heart. Makes an individual susceptible to myocardial infarction and cardiac arrest. Symptoms: Crushing chest pain (may radiate to jaw, neck, one/both arm(s) after exertion/stress). Causes: Positive family history, smoking, hypertension, high cholesterol, lack of exercise, diabetes. Myocardial Infarction Blockage of the coronary artery by a thrombus (clot) usually in an already compromised vessel. May or may not be painful but will cause damage to the heart muscle. Cardiac Arrest Sudden inability of the heart to function. Causes: Myocardial infarction, pulmonary embolism, trauma, shock, hypoxia, hypothermia. Anaemia Causes: Inadequate delivery of O₂ to body tissues from abnormal reduction of haemoglobin. Symptoms: Low energy, dizziness, shortness of breath, pallor, digestive disorders. Stroke Occurs when blood supply to a certain part of the brain is cut off. Hypertension is a risk factor. Victim may experience memory loss or be unable to walk (depending on affected part of brain). Causes: Haemorrhagic – Ruptured blood vessels (placing pressure on the brain). Ischemic – Blocked arteries (starving areas of the brain controlling sight, speech, movement) Components and Functions of Blood Red Blood Cells: Transport O₂ in haemoglobin. Cells produced in bone marrow. White Blood Cells: Fight inflammation/infection. Small size enables movement through capillaries. Platelets: Aid in coagulating blood and maintaining the circulatory system. Plasma: Transports CO₂, nutrients and hormones. Composed of water, protein and salts. Hy oxia (Insufficient ₂ in the bloodstream) – usually occurs +10,000ft Hypoxic Hypoxia Insufficient O₂ in breathed air or when conditions prevent diffusion of O₂ from the lungs to the bloodstream. Most likely encountered at high altitudes. Prevented by ensuring sufficient O₂ is available (limiting time at altitude, pressurisation, O₂ masks). Anaemic Hypoxia Reduction in the O₂ carrying capacity of the blood. Anaemia/blood loss are the most common causes. Carbon monoxide, nitrites and sulpha drugs also cause hypoxia by reducing haemoglobin. Stagnant Hypoxia O₂ carrying capacity of the blood is adequate but there is inadequate circulation. Heart failure, arterial spasm, occlusion of a blood vessel and venous pooling (during +G manoeuvres) cause this. Histotoxic Hypoxia Interference with the use of O₂ by body tissues. Alcohol, narcotics and certain poisons (cyanide) interfere with the cells’ ability to use an adequate supply of O₂.
- Possible signs and symptoms of hypoxia Individual Susceptibility Factors Smoking and alcohol increase the physiological altitude of the body. Also greatly influenced by; metabolic rate (increased by temperature extremes), diet, physical fitness (greater condition = higher tolerance) nutrition, and emotions. These determine whether hypoxia develops at a lower/higher altitude than usual. Exposure Duration The longer the duration of exposure, the more detrimental the effect of hypoxia. However, the higher the altitude, the shorter the exposure before hypoxia symptoms occur. Effects of Hypoxia Nerve tissue has a heavy requirement for O₂ and brain tissue is the first to be affected by any deficiency. If this is prolonged/severe, brain death occurs and the cells can never regenerate. Time of Useful Consciousness (TUC) The time a crew member has from the interruption of the O₂ supply to the time when the ability to take corrective action is lost. Varies with rate of decompression and altitude in pressurised aircraft. Altitude (ft) 20,000 25,000 30,000 35,000 43,000
TUC 5 – 12 minutes 3 – 5 minutes 1 – 2 minutes 30 – 60 seconds 9 – 12 seconds
Stages of Hypoxia Indifferent: Night vision deteriorates at about 4,000ft due to darkness and loss of visual acuity. Compensatory: Circulatory/respiratory systems provide defence. Can compensate up to 12,000ft. Above 12,000ft the effects on the nervous system become apparent (10-15 mins). Drowsiness and judgement errors begin to be made. Co-ordination becomes difficult Disturbance: Physiological responses can no longer compensate for O₂ deficiency. Crew members can lose consciousness. Fatigue, sleepiness, headaches, dizziness, breathlessness, and euphoria are reported Peripheral and central vision impaired. Weakness/loss of muscle co-ordination. Thinking is slow (early sign), short-term memory is poor as well as reaction time. Aggressiveness, overconfidence, or depression can occur. Stammering and writing illegibly are typical at this stage. Skin becomes bluish in colour (O₂ molecules fail to attach to haemoglobin). Critical: Within 3 to 5 minutes, incapacitation and unconsciousness occur. Limitations of Time at Altitude Aircraft not O₂ equipped should not fly above 10,000ft for extended periods of time. 14,000ft must never be exceeded in an unpressurised aircraft without supplemental O₂.
Altitude 0 – 10,000ft 10,000 – 33,700ft 33,700 – 40,000ft + 40,000ft
Required ₂ Delivery to Lungs Ambient Air Increasing O₂ concentration 100% O₂ 100% O₂ under positive pressure
Treatment of Hypoxia Must be treated immediately with 100% O₂ through a mask. If no mask available, descent to below 10,000ft is mandatory. Carbon Monoxide (CO) CO has an attraction for haemoglobin 200x greater than O₂ meaning RBCs cannot carry O₂ until all the CO is expelled. CO prevents O₂ being used by the body and can harm the central nervous system. Is the result of incomplete combustion of fuels and is colourless, tasteless, and odourless. The effects are cumulative and can take several days for the body to completely recover. Symptoms: Headaches, dizziness, weakness, nausea, rapid heartbeat, seizures, cardiac arrest, loss of hearing, blurred vision, vomiting, disorientation, loss of consciousness, death. Hyperventilation – usually occurs <10,000ft Excessive rate and depth of respiration leading to an abnormal loss of CO₂ from the blood. Causes: Emotions – Fear, anxiety, or stress causing the individual to consciously control breathing. Pressure Breathing - O₂ forced into lungs under pressure, breathing out against pressure. Pauses between exhaling/inhaling can maintain normal CO₂ levels. Hypoxia – Respiratory system triggers an increase in breathing rate.
Symptoms: Dizziness, visual impairment, muscle spasms, tingling/cold/hot sensations, unconsciousness. Treatment: Voluntary reduction in respiration rate. Breathing into a paper bag to re-establish correct CO₂/O₂ balance. Heat Strain Physiological: - Profuse sweating leading to dehydration. - Peripheral vasodilation (blood vessels dilate). - Reduction in tolerance to sustained acceleration by around 1G. - Decrement of vision. Psychological - Affects memory registration and recall. - Attention and vigilance reduced. - Reasoning and decision making takes longer. - Manual dexterity reduced. Hyperthermia: - Body sweats to try to reduce temperature (up to 2 litres for brief periods). - Dehydration and salt depletion unless water and salt intake are increased. - Heat stroke may result if body temperature not reduced. Hypothermia: - Body metabolism increased to generate heat (shivering). - Extra O₂ required to prevent onset of hypoxia. - Body eventually closes down to conserve heat in vital areas (organs, torso). Vitamins:
- Regulate metabolism of digested food. - Assist in formation of hormones, blood cells, genetic material.
Fat Soluble Vitamins
- Stored in body fat. - Do not need consuming every day. A: Derived from carotene (eggs, butter, cheese, carrots, green vegetables). Affects; vision, skin maintenance, bones, teeth, mucous membranes. Important for night vision (rod cells). D: Sunshine vitamin. Necessary for bone formation and retention of calcium. E: Plays a part in forming RBCs and muscle. K: Necessary for blood clotting. Water Soluble Vitamins - Cannot be stored in the body. - Must be consumed frequently. B: 8B’s (complex). Affects; metabolism, skin, muscle tone, immune and nervous systems. C: Important in formation of collagen. Enhances absorption of iron from vegetables.
High Altitude Environment Radiation The Earth’s magnetic field deflects many charged particles (solar/cosmic) and is most effective at the geomagnetic equator. This reduces with increasing latitude, disappearing over the geomagnetic poles. Death from cancer is the principle health concern associated with occupational exposure to radiation. ICAO Annex 6, Part I – Radiation Monitoring All aeroplanes intended to be operated above 49,000ft shall carry equipment to measure and indicate continuously the dose of total cosmic radiation being received and the cumulative dose on each flight. The display unit shall be readily visible to a flight crew member. Ozone Is classified as a highly toxic gas and excessive levels can significantly impact respiratory functions. Stratospheric ozone is found in varying quantities (peak: 115,000ft, negligible: ≤40,000ft). Sensory Systems Cognition: Attention, perception, memory, reasoning, judgement, imagining, thinking, speech. Central Nervous System (CNS) Takes care of the reception of stimuli, the transmission of nerve impulses and the activation of muscle mechanisms. The conducting elements of the CNS are neurones (can be slow/generalised or highly efficient/rapid). There exists a sensory threshold, below which stimuli may not be detected by receptors even when within the detectable frequency range. Habituation: If the stimulus is continuous/repetitive the receptor may change in sensitivity (displays a diminishing response to that stimulus). Can have flight safety implications e.g. reduced visual sensitivity due to an unchanging visual scene at high altitude. Peripheral Nervous System (PNS) Controls vital functions over which the individual has no conscious control (respiration, circulation, intestinal movement, sweating). Also controls reactions to painful stimuli (reflexes). Connects CNS to the rest of the body: - Sensory (provides input from body to CNS). - Motor (carries signals to muscles and glands). Somatic Nervous System Includes all nerves controlling muscular system/external sensory receptors. Reflex arc is an automatic involuntary reaction to a stimulus. Autonomic Nervous System Consists of motor neurons that control internal organs (heart, intestine, bladder). Sympathetic Nervous System: Fight or Flight. Parasympathetic Nervous System: Relaxation to maintain homeostasis. Homeostasis: Maintenance of metabolic equilibrium. Brain Receives information from the Central and Peripheral Nervous Systems. It then acts as control centre
for vital activity. Biological control systems are neuro-hormonal processes. Contains three distinct parts: - Cerebrum (two hemispheres forming largest part of the brain). - Cerebellum (essential to the control of the human body). - Brain Stem (all structures between the cerebrum and spinal cord). Sensory Receptors Mechanoreceptors: Hearing, balance, stretching (most adaptable = hair). Photoreceptors: Light. Chemoreceptors: Smell, taste (also internal sensors in digestive/circulatory systems). Thermoreceptors: Temperature changes. Electroreceptors: Electrical currents. Orientation in Flight Eyes: Both peripheral and central vision. Most important sense for orientation. Inner Ear: Vestibular (semi-circular canals and otoliths). Kinesthesis A variety of sensory endings (mechanoreceptors) in the skin, joints, muscles and deeper supporting structures are influenced by forces acting on the body. Proprioceptive sense: Uses mechanoreceptors to provide spatial relationships between body parts. Visual System Flight crew rely more on sight than any other sense to orientate themselves in flight. Contributing factors: - Depth perception (for safe landings). - Visual acuity (to identify terrain features/obstacles in the flight path). Anatomy/Physiology of the Eye Cornea: The clear portion of the eye. Light from an object enters and 70% of refraction takes place. Pupil: The black area of the eye. After light refracts through the cornea it passes through the pupil. Iris: Coloured portion of the eye. Controls the diameter of the pupil/amount of light entering eye. Lens: Located behind the pupil and focuses light onto the retina. Ciliary Muscle: Alters the curvature of the lens changing the refraction of light entering the eye. (Accommodation). Retina: Composed of many photosensitive cells (rods/cones). Visual Cortex: Part of the brain where information from the eyes is interpreted.
Rod and Cone Cells Rods: - Peripheral vision and most concentrated outside the foveal region. - Achromatically sensitive to low intensity light and to movement. - Used for night vision (greatest sensitivity after 30-45 minutes in darkness). Cones: - Central vision most concentrated in the foveal region directly opposite the lens. - Most sensitive to bright light and distinguish form and colour. - Each cell contains one of three different pigments (absorptions): blue/green/yellow.
Visual Field Eye’s sensitivity is able to adapt to ambient levels of illumination. Dark adaptation takes several minutes. Light adaptation occurs mostly within a few seconds (complete after 2 – 3 minutes). The visual field is the locus of all points on a surface in front of and concentric with the stationary eye from which a visual signal can be stimulated. Acuity: The ability of the eye to see detail. 6/6 vision = you can see at 6m, what normal people can see at 6m.
Day blind spot: Area of Optic Disk. No photosensitive cells on the retinal nerves. Evident when the eye is fixated centrally forward as an object is brought inside the visual field. Night blind spot: Area of Fovea. Central area of the retina lacks rod cells. Dim lighted objects are most noticed in peripheral vision. Deliberate use of eccentric vision is important for night flying. Empty-field Myopia: Absence of visual stimulus (clear sky), muscles in eye relax preventing lens focus. Hinders effective search and detection. Problem minimised by focusing on an object further than 1 – 2 metres away (wing tip). Scanning It is not possible to voluntarily make a continuous scan of featureless space. A scanning technique should employ regularly spaced eye movements (each covering an overlapping sector of 10°). At night the scan should be executed more slowly to enable peripheral vision to detect objects. Sunlight and its Effects on the Eyes Visible light consists of a small portion of the spectrum (380 nanometres – violet to 760 nanometres – red). Blue light is very energetic and long term exposure may cause cumulative damage to the retina. Prolonged exposure to UV wave lengths can also cause damage (absorbed by the lens). UV light produces a painful swelling with sensitivity to light (snow blindness) after prolonged exposure to
high-intensity sunlight (e.g. reflected by snow, water or desert). UV burns do not produce permanent damage and usually filtered by cockpit transparency. Sunglasses Coloured Filters: Permit different amounts of light of different wavelengths to pass. Neutral Filters: Absorb approximately equal amounts of all wavelengths of light. Polarising: Limited in usefulness. Pilots may see dark bands when sky scanning. Neutral-grey lens with 15% transmission is most suitable for the level of brightness when flying. Distance Estimation and Depth Perception Distance can be estimated by using individual or a variety of cues. Pilots normally use subconscious factors to determine distance. Stereoscopic Vision: Focusing both eyes on a single object. Each eye sees the object at a slightly different angle. The images are merged together producing a three-dimensional image. Binocular Cues: Depend on the slightly different view each eye has on an object. Only of value when the object is close enough to make a perceptible difference in the viewing angle of both eyes. Geometric Perspective: An object appears to have a different shape when viewed at varying distances and angles. - Linear Perspective: Parallel lines (railroad tracks), tend to converge as distance increases. - Apparent Foreshortening: Objects appear higher on the horizon than those closer. Motion Parallax: The apparent, relative motion of stationary objects as an observer moves. Near – move fast/opposite the path of motion. Far – Move slow in the direction of movement/fixed. Known Size of Objects The nearer an object to an observer, the larger it’s retinal image. By experience, the brain learns to estimate the distance of familiar objects. To use this cue, the observer must know the actual size of the object and have prior visual experience of it. Interposition of Objects Lights disappearing/flickering in the landing area should be treated as barriers and the flight path adjusted accordingly. Visual Deficiencies Myopia (Near-sightedness) Error in refraction whereby the lens of the eye does not focus an image directly on the retina. Distant objects are not seen clearly; only nearby objects are in focus. – Eyeball too long.
Hypermetropia (Far-sightedness) Error in refraction as in myopia. However, nearby objects are not seen clearly. – Eyeball too short.
Astigmatism Caused by unequal curvature if the cornea or lens. Is the inability to focus different meridians simultaneously. Presbyopia Part of the aging process which causes the lens to harden. Individuals gradually lose the ability to accommodate for and focus on nearby objects. Retinal Rivalry If one eye is viewing one image while the other eye is viewing another, there may be a problem in total perception. The dominant eye will override the non-dominant eye image. Radial Keratotomy Surgical procedure that creates multiple radial incisions in the cornea to produce better visual acuity. Glare sensitivity is the most common complication of the procedure. Colour Blindness Permanent condition that affects males more than females. Individuals who are colour blind are usually unable to distinguish between red and green. (Anomaly: weakness, Anopia: blindness). Hypoglycaemia Low sugar levels may result in hunger pains, distraction, breakdown in habit patterns, shortened attention span. Missing/postponing meals can cause low blood sugar levels. Cataracts Lens opacity and changes the lens refractive index producing blurred vision. Scattering of light may lead to glare sensitivity. Risk factors; old age, positive family history, diabetes, smoking. Glaucoma Occurs mainly in middle-later life due to elevated intraocular blood pressure (due to blockage). Symptoms; blurred vision, haloes around bright lights, pain, vomiting, circumcorneal redness. Dry Eyes Low relative humidity in aircraft can lead to drying of the eye surface. Dryness causes discomfort and may expose the individual to infection.
Flash Blindness (from lightning) Protection: - Increase cockpit lighting to max intensity. - Lower seats/ cockpit sun visors. - Look in as much as possible. Near Vision Correction When only near-vision requires correcting, pilots should never use full-lens spectacles whilst flying (requires frequent changes from near/distant vision). Half-moon spectacles MUST be used. Near and Distant Vision Correction When both are required, bifocal lenses are essential and pilots are advised to with an AME/optician the shape and size most suitable for each segment. Varifocal Lenses Alternate to bifocal/multifocal lenses. There is no clear demarcation between upper distance vision and near vision correction of the lower portion of the lens (gradual merging). Not generally advised for flying. Spectacles Restrict Peripheral Vision All spectacles restrict peripheral vision and thick frames should be avoided. Spectacle wearers have to increase their head movements in scanning. Photosensitive lenses should not be used. Contact Lenses An ophthalmic report from an optician is required to confirm contact lenses will provide a satisfactory field of vision and that they have been worn for 8hrs a day over 1 month. A pair of ordinary spectacles should be carried at all times. Visual Clues on Landing 1) Assessment of Glideslope:
2) Maintaining Glideslope: 3) Ground Prox. Judgements:
- Lights: VASIs/PAPIs. - To fly 3° Approach must ensure angle between eye/impact point is 3° below horizon. - Visual texture flows away from the impact point = APP GOOD. - Apparent speed of ground. - Texture of surface. - Size, relationship and clarity of objects.
Vestibular System The inner ear contains the vestibular system, which is the motion and gravity detecting sense organ. This system is located in the temporal bone on each side of the head.
Otolith Organs Sense changes in linear acceleration or gravity and located in the vestibule. Changes in head position relative to the gravitational force cause the otolithic membrane to shift position on the macula. The sensory hairs bend, signalling a change in head position. When the head is upright, a “resting” frequency of nerve impulses is generated by the hair cells. When the head is tilted, the “resting” frequency is altered. The body cannot distinguish between the inertial forces from linear accelerations and force of gravity (forward acceleration can create illusion of backward tilt).
Semicircular Canals Sense changes in angular accelerations (yaw, pitch, roll attitude). Are situated in 3 perpendicular planes to each other and filled with fluid (endolymph). Initial torque from angular acceleration puts the fluid in motion moving hair stimulating the vestibular nerve. No acceleration means the hair cells are upright. During a clockwise acceleration a counter-clockwise movement of fluid in the canal is created. The hairs cells bend in the direction of fluid movement. The canal wall and body move in the opposite direction. The brain interprets the hair movement to be a turn in the same direction as the canal wall. If continued for several seconds the fluid motion no longer lags (hairs no longer bend) and brain receives false information a turn has stopped. When the aircraft rotation stops, it may be falsely interpreted as body movement in the opposite direction. Proprioceptive System Reacts to sensations resulting from pressures on joints, muscles, and skin. Forces act upon the seated crew member in flight. With training and experience, the crew member can easily distinguish the most distinct movement of the aircraft by the pressures of the seat against the body.
Illusions A false impression/misconception with respect to actual conditions or reality. Somatogyral (Vestibular) Caused when angular acceleration stimulates the semicircular canals. Occur in IMC/marginal VMC. Leans: Most common form of spatial disorientation. Occurs when a crew member fails to perceive some angular motions (during a slow roll, crew member feels the aircraft is still straight and level). Pilot should trust attitude indicator and lean body in the original direction of roll until sensation leaves. Graveyard Spin: Usually occurs in fixed-wing aircraft when entering a spin for several seconds. Semicircular canals reach equilibrium (no motion perceived). When recovered from the spin the sense is a spin in the opposite direction. Graveyard Spiral: Observed loss of altitude during a co-ordinated constant-rate turn that ceases stimulating the motion sensing system. Creates the illusion of being in a descent with wings level. Coriolis Illusion: Most dangerous of all vestibular illusions causing overwhelming disorientation. Can take place whenever a climbing/descending turn is initiated. When making a head movement in a geometrical plane other than that of the turn creates the feeling the aircraft is rolling, pitching and yawing at the same time. Vertigo The illusion of movement (often rotary), of the individual or of their surroundings. Causes: Disorders of the vestibular system, accelerations during steep turns (no horizon). Symptoms: Difficulty in walking/standing, nausea, vomiting, pallor and sweating. Alternobaric (Pressure) Vertigo Causes: Blockage of the Eustachian tube. Can occur during ascent or descent. Symptoms: Blurring of vision, apparent movement of the visual scene. Short-lived (10-15 seconds). Most likely experienced when flying with a cold/similar infection. Flicker Vertigo Causes: Flashing light from flickering sunlight on rotor/propeller blades. Strobe light cloud reflection. Symptoms: Irritation/distraction, disorientation of angular motion in opposite direction of shadow. Wearing sunglasses or removing the individual from the lit area may relieve symptoms. Somatogravic Caused from changes in linear acceleration/gravity that stimulate the otolith organs. Oculogravic Illusion: Occurs when an aircraft accelerates forward. Causes a sense of a nose-high attitude. Does not occur if adequate outside references are available. Cross-check instruments. Elevator Illusion: Occurs during upward acceleration. Due to inertia, the pilot’s eyes track downwards, causing a sense of aircraft nose rising. Common when encountering updraughts. Oculoagravic Illusion: Exact opposite of Elevator illusion resulting from downward motion. Proprioceptive Illusions Rarely occur alone. Closely associated to the vestibular and visual systems. Proprioceptive inputs to the brain may lead to a false perception of the true vertical.
Prevention of Spatial Disorientation - Never fly without visual reference points (natural or artificial horizon). - Trust your instruments. - Never stare at lights. - Allow eyes to adapt to the dark before night flying. - Avoid fatigue, smoking, hypoglycaemia, hypoxia, and anxiety (aggravates illusions). Treatment of Spatial Disorientation - Refer to instruments and develop a good cross-check. - Never try to fly VMC and IMC at the same time. - Delay intuitive actions long enough to check both visual and instrument references. - Transfer control to the other crew member (if two crew). Visual Illusions on Approach Runway Slope Upslope Downslope
Think TOO HIGH Think TOO LOW
Up to Runway Down to Runway
Think TOO HIGH Think TOO LOW
If Bright If Dim
Think CLOSE TO RUNWAY Think FAR AWAY FROM RUNWAY
If Wide If Narrow
Think TOO LOW Think TOO HIGH
Terrain Slope
Lights
Runway Width
Shallow Fog Layer
Think PITCH UP
Black hole Approach Occurs when approaching a runway on a dark night where the only lights visible are runway lights. Tendency to think you are higher than you are resulting in a fly-down urge. ILS, VSI, VSIs/PAPIs can assist in reducing this tendency. Can also occur in white-out conditions (light carries depth perception messages to the brain in the form of; colour, glare, shadows). Atmospheric Illusions Rain on Windscreen Atmospheric Haze Fog Penetration
Illusion of greater height Illusion of greater distance from runway Illusion of pitch up
False Horizon A sloping cloud formation, an obscured dark horizon spread with ground lights and stars, and certain geometric patterns of ground light. Can create the illusion of not being aligned with the horizon.
Autokinesis A distant light (star/aircraft tail-light) seen in the dark will appear to move about when stared at for a time. Apparent movement increases if the light source becomes the prime focus of attention. To avoid effects, shift gaze so as not to stare at a single light source. Motion Sickness Motion sickness is caused by continued stimulation of the inner ear. The symptoms are progressive. First, the desire for food is lost. Then saliva collects in the mouth and the person begins to perspire freely. Eventually, the person becomes nauseated and disorientated. The head aches and there may be a tendency to vomit. If the air sickness becomes severe enough, the crew member may become completely incapacitated. Prevention of Motion Sickness - Susceptible individuals should not take the preventative drugs (cause drowsiness). - Open up air vents and loosen clothing. - Use supplemental oxygen. - Keep the eyes on a point outside the aircraft and avoid unnecessary head movements. Acceleration The rate of change of velocity and occurs when the speed or direction of a body changes. The magnitude (G) of acceleration is expressed in multiples of the acceleration due to gravity (weight). The body’s capacity to tolerate G depends on the intensity, duration and direction. Long Duration (+1 second) Headwards (+Gz) - Reduction of hydrostatic blood pressure above the heart, increase below. +2.5Gz (loss of mobility – difficult to stand up). +3.5Gz (loss of peripheral vision & loss of colour vision ‘grey out’). +4.5Gz (‘black out’ – hearing and mental functions unaffected at onset). >+4.5Gz (unconsciousness ‘G-LOC’). Footwards (-Gz)
- More uncomfortable/dangerous than +Gz. - Inertial forces increase vascular pressure in the upper thorax, head, neck. - Symptoms: bursting of small vessels (eyes), pushing up of lower eyelid. -3Gz (maximum tolerable level – for short periods).
Short Duration (-1 second) Mainly due to impact following a crash. Can withstand maximums of +45Gx and +25Gz. Noise The human range of hearing is 20 to 20,000Hz (most sensitive 200 to 6,800Hz). Sound Measurement Frequency: Physical characteristic that gives sound the quality of pitch. The number of oscillations or cycles per second is measured in hertz. Intensity: A measure that correlates sound pressure to volume. Measured in decibels (dB) which express the relative intensity of sounds on a scale from zero to about 140. For every 20dB increase in volume, sound pressure increases by a factor of 10. Duration: The length of time an individual is exposed to a noise.
Steady-state Noise: Continuous noise encountered around aircraft. High intensity (wide frequency). Direct link between duration of exposure and intensity (louder sound = shorter time hearing loss). Impulse Noise: Characterised by an explosive sound (high intensity). Most detrimental although short duration (intensity usually exceeds 140dB). Outer Ear: Middle Ear: Inner Ear:
- Auricle (picks up sound waves) → External canal → Ear drum. - Ossicles (3 small bones) transfers sound waves from ear drum to inner ear. - Cochlea (composed of fluid-filled chambers with hair-like receptors). Converts vibration to nerve impulses but loud noise may fatigue hair cells.
Hearing Loss Conductive Occurs when there is a defect/impediment of sound transmission from external to inner ear. Effects al frequencies and can be treated medically (hearing aid) – inner ear still capable of sound detection. Sensorineural Occurs when the hair cells of the cochlea are damaged. Most frequently produced by noise exposure (NIHL) be can be caused by disease/aging. Occurs first in the higher frequencies. No known medical treatment. Presbycusis Hearing loss caused by aging. Can be conductive or sensorineural in nature (or both). Noise Exposure Criteria Frequency: Narrow-bands/pure-tone more damaging (turbine engine whine). Intensity: Louder = greater possibility of damage. >85dB can damage hearing. Duration: For every 5dB increase above 85dB, safe time limit for exposure is reduced by half. Vibration Symptoms are determined by resonance effects according to frequency and amplitude of vibration. 1 – 4Hz 4 – 10Hz 8 – 12 Hz 10 – 20Hz 25 – 40Hz 60 – 90Hz
Interference with breathing Chest/Abdominal pains Backache Headaches, eyestrain, throat pains, speech disturbance, fatigue Visual impairment (skull resonance) Visual impairment (eyeball resonance)
Sudden or Gradual Hearing Damage Acoustic Trauma Usually sudden resulting from intense impulse noise (+140dB). Most damage results in eardrum injury. Repeated exposure damages the cochlea. Often manifested as a ringing sensation in ear. Noise-induced Hearing Loss (NIHL) Onset is much slower than acoustic trauma. Results from repeated exposure to steady-state noise (such as that experienced at airports/in aircraft). Individuals rarely notice NIHL as it does not initially affect the speech frequency range. A more subtle effect is the change in phonetic content of speech (mumbling), only vowels (lower frequencies are heard). Early stages, communication difficult with background noise. Later stages, speech recognition impossible. Temporary Threshold Shift (TTS) Temporary loss of hearing from overexposure to noise. Results from exposure for a short period of time to intense noise levels (>78-84dB). NIHL occurs first as TTS (fatigue of cochlea cells). TTS can become permanent. 85dB is regarded as the max permissible sound level for continuous exposure to steady-state noise. TTS may last from a few minutes/hours to days (depending on duration/intensity of exposure). Individuals mostly recover to near-normal hearing limits unless overexposed. Permanent Threshold Shift (PTS) Hearing loss present when the nerve fibres of the cochlea are destroyed (hair cell destruction is permanent). May develop before an individual recognises that it is happening. Hearing Protection Crew members and ground-crew should wear hearing protection at all times. Virtually all NIHL is preventable if these devices fit properly and are worn on all flights. Protective measures include: - Designing “quiet aircraft” - Enclosing the cabin areas with soundproofing Earplugs: Most common type of protection. Have a tendency to work loose. Protection: 30-35dB. Earmuffs: Tend to give slightly more high-frequency protection (less low) than earplugs. Headsets: Provide some protection against high-frequency sound. Need to be properly maintained. Decibels Effect on Listeners 0 65 85 90 120 140 160
Threshold of hearing Average male conversation Damage risk noise limit Speech interference at 1ft Threshold of discomfort Threshold of pain Eardrum rupture
Drugs and Self Medication Drugs Considered Incompatible with Flying Antibiotics: May have short-term/delayed side effects. Indication implies an infection is present. Antidepressants/Sedatives: Degrade a pilot’s ability to react. Stimulants: May cause dangerous overconfidence, headaches and dizziness. Antihistamines: Widely available to allergy sufferers. Drowsiness is a common side effect. Antihypertensives: Treat high blood pressure. Can change cardiovascular reflex and impair intellect. Anaesthetics: Time elapse before flight: Local – 12 hours. General – 48 hours. Analgesics: May significantly degrade a pilot’s performance. Indication implies significant pain. Alcohol Hypnotic drug which degrades a crew member’s judgement and ability to perform skilled tasks. Consumption measured in units (1 unit = a standard glass of wine/half a pint of beer). Maximum blood alcohol limit for pilots of 20 milligrams per 100 millilitres. Pilots are advised not to fly for at least 8 hours after ingesting small amounts of alcohol. Alcohol wears off at a rate of approximately 1 unit (15mg per 100ml) per hour. Damaging alcohol consumption levels: - Men: 6 units/day or 30 units/week. - Women: 4 units/day or 20 units/week. Nicotine/Tobacco Nicotine is a highly addictive drug. Smoking tobacco is a major risk factor in lung cancer and cardiovascular disease. Smoking exacerbates hypoxia. Reduces tolerance to G-forces and degrades night vision. Caffeine Weak stimulant found in tea, coffee, soft drinks and some pain relieving medications. May cause headaches in excessive doses. Donors Blood: Pilots should not fly within 24 hours. Bone Marrow: Pilots should not fly within 48 hours. Obesity A weight to height ratio that exceeds a prescribed value. May be precipitated by genetic and physiological factors (rarely by disease). Will reduce the body’s tolerances to G-forces, hypoxia and decompression sickness. Diabetes Very common metabolic disorder that changes the way a body breaks down sugars (glucose) and starches. Insulin helps to change glucose into energy that can be stored or instantly used. Non-insulin-dependent: Pancreas produces insulin but body unable to use it effectively. Insulin-dependent: Less common. Insulin injections given because of lack of insulin production. Coronary Problems Obesity contributes to congestive heart failure. Can also increase cholesterol, blood sugar levels and blood pressure.
Gout Genetic disorder in which the body produces an excessive amount of uric acid or the kidneys are unable to eliminate the uric acid. The accumulating uric acid deposits in tissues and joints causing inflammation, swelling and severe pain (gouty arthritis). Arthritis Inflammation and stiffening of the joints often causing great pain. Is a lifelong illness that can progressively disable and handicap an individual. Extra weight from obesity puts extra stress on joints. Body Mass Index (BMI)
ei ht (k ) Hei ht (m) Underweight Normal Range Overweight Obese
<18.5 18.5 – 25 25 – 30 >30
Diet Carbohydrates: Absorbed rapidly, chief and most important energy source for the body. Fats: Provide most concentrated source of heat energy, can be stored in large quantities. Proteins: Needed for building/repair of body tissues, composed of smaller units (amino acids). Fibre: Complex mixture of indigestible plant substances. Essential for digestive/bowel process. Tropical Diseases Diseases/conditions similar to, prevalent or commonly encountered in areas characterised by a climate with high temperature and humidity usually located within a region between the North/South 23rd degree parallels of latitude. Water Contaminated drinking water is one of the most frequent sources of intestinal infection. Unless one is assured that centrally distributed water is constantly safe, it should not be used for human consumption, for ice cubes or brushing teeth unless it has been purified. Safest purification procedure is to boil water for 3 – 5 minutes and thereafter keep it in the same vessel until used. If unable to boil, treat with a chlorination tablet. Food There is an old tropical food maxim not to eat raw any fruit or vegetable that does not have an unbroken skin, and which has not been well washed and peeled/skinned by oneself immediately prior to eating. Fruit salad should be avoided. In other cases, boiling/baking will render food safe. Milk is safe only if boiled or as canned evaporated milk, condensed milk, or powdered milk (ice cream is likely to be as contaminated as milk). Avoid cold pastries, custard, soft-type cheese and other delicacies. Food poisoning does occasionally occur on board aircraft or during flight. It is recommended that crew members should not consume food from the same source prior to or during flight.
Diarrhoea of Undetermined ri in ( raveller’s Diarrhoea) Acute diarrhoea onset characterised by frequent watery stools, acute gastro-enteritis, nausea, vomiting, abdominal cramps, chills, myalgia and profound malaise. Rapid dehydration may occur. May occur sporadically or in groups of travellers of all ages. Origin mostly not clearly established. Cholera Acute enteric infection caused by Vibrio Cholera. Causes: Spread by the ingestion of water/foods contaminated by excrement of infected persons. Prevention: Main method of control by purification of water supplies, proper disposal of excrement and effective quarantine methods. Cholera vaccine provides varying degrees of protection for 6 months. Modern treatment greatly reduces mortality (untreated exceeds 50%). Amoebic Dysentery (Amoebiasis) May be encountered anywhere in the world. Causes: Cysts from faeces of infected persons (transmitted: hand-mouth, polluted water, flies). Symptoms: Liver, lung and brain abscesses (long latent period). Malaria Spread by mosquitos. Incubation period 8 – 9 days. Symptoms: Chills, fever, sweating, intra-erythrocytic parasites, splenomegaly. Prevention: Prophylactics, using anti-mosquito sprays/creams, wearing long sleeves. Immunisations Immunisation of flight crew differs according to country. The only worldwide compulsory immunisation is against smallpox. Toxic Materials Aviation Gasoline (AVGAS) AVGAS fumes are an upper respiratory irritant and produce tearing, choking, coughing and excess salivation. It may also cause CNS hyperactivity, confusion, seizure or death. It can also cause chemical skin burns. Jet Fuels (AVTUR) If inhaled in high concentrations, they may cause headaches, nausea, confusion, drowsiness, convulsions, coma, and finally death. Prolonged skin exposure can lead to second degree burns. Ethylene Glycol (Anitfreeze/Hydraulic Fluid) Not an inhalation hazard unless heated. In cases of fatal poisonings, symptoms include those of typical alcohol intoxication followed by coma and death. Methyl Alcohol (De-icing Fluid) Absorbed by ingestion producing disturbances of vision, headaches, vertigo, unsteady gait, weakness, nausea and vomiting. Blindness is a common symptom. Chlorobromo Methane (CBM) Used in fire extinguishers to remove the oxygen from combustion. Considered safe for crew members due to rapid dissipation and distance from extinguisher (engine).
Halon Gas is a CNS depressant which can lead to cardiac arrhythmia but is harmless if breathed for only a few minutes. Incapacitation Most are caused by gastrointestinal upsets. Obvious Incapacitation Those immediately apparent to the remaining crew members. They can occur suddenly and are usually prolonged resulting in a complete loss of function. It may be silent and occur without any warning. Detection may only be indirect (not taking anticipated action). Insidious Incapacitation Can be harder to identify and more subtle in its onset (therefore more dangerous). Can be an even greater problem when a drug will be used over a period of several days or longer. Incapacitation Detection Flight crew members should have a high index of suspicion of a ‘subtle’ incapacitation any time a crew member does not respond appropriately to two verbal communications. A basic monitoring requirement is that all crew must know what should be happening with and to the aircraft at all times (following SOPs). Information Processing and Memory Perception The process of information extraction from the environment through experiences and sensed by the five senses. The information is passed to the brain and interpreted, then memorised. Bottom-up Processing: Uses sensory information to start building a mental model. Top-down Processing: Uses previous knowledge to modify the mental model. Physiological Sensing Errors Caused by medical deficiencies (impaired vision/hearing) or hypoxia which reduces body oxygen levels. Complacency Not paying attention or not using the senses properly is a problem during routine operations. Typical problem for experienced crew members. Processing Errors Crew can also experience errors during the processing of the information in the brain. Previous experience with the information enables processing to be much easier. Pre-determined Opinions Receiving information that we have a pre-determined opinion about (tendency to see/hear what we expect). Microphone clipping, speaking too quietly and fast, background noise enhances the risk.
Memory The final part of the sensing and processing sequence. Selective attention requires information to be stored in the sensory register. The working memory governs the information storing process. Ultra-short Term: - Sensory register retains all sensory impressions up to about 1 second. - Material is processed very quickly according to current importance. - Iconic (stores visually ≈ 0.5 seconds) Echoic (stores auditory ≈ 8 seconds). Short Term: - Working memory (focus of consciousness) holds material for ≈ 20 seconds. - Capacity is limited - maximum items for rehearsal is 7 (±2). Long Term: - Semantic: Based upon facts/skills. Info successfully entered is never lost. - Episodic: Based upon memories/experiences, can be influenced. - Procedural: Based upon motor memory, performed automatically.
Situational Awareness Maintaining an accurate mental model of knowing:
- Where the aircraft is. - Where it has been. - Where it is going.
Gestalt Psychology A system of thought that regards all mental phenomena as being arranged in patterns/structures (gestalts) perceived as a whole and not merely as the sum of their parts. Gestalt Laws Perception: Elements that are closer together tend to be seen as a group as do similar elements. Organisation: Distinction between what is seen as the figure/object and what is seen as background.
Stress A heightened state of arousal caused by stressors (events that induces stress) in the environment. In moderation, it is a key factor in the achievement of peak performance. Too much = Loss of ability to reason/function. Too little = Complacency. Types of Stress Physical: Environmental conditions, noise, vibration, stages of hypoxia. Physiological: Fatigue, lack of physical fitness, improper eating habits. Emotional: Related to social and intellectual activities. Categories of Stress Chronic: Result of long term demands of lifestyle or personal situations (health, relationships, job). Most dangerous, can exaggerate effects of acute stress. Can threaten health. Acute: Result of demands placed on the body by a current issue (time constraints, bad weather). Adrenaline enters bloodstream, body is charged into a “fight or flight” mode. Effects of Stress:
- Eroded judgement. - Compromised or accepting of lower performance levels. - Loss of vigilance and alertness. - Loss of situational awareness.
Stress Coping Strategies Coping is the process in which the individual either adjusts to the perceived demands of a situation or changes the situation itself. Action: Used to reduce the stress by removing the problem/altering situation. Cognitive: Used when situation cannot be changed. Rationalisation/detachment from situation. System Direct: Removing stress symptoms with stress management (relaxation, counselling). Fatigue Considered to be one of the most treacherous hazards to flight safety. Crew members routinely experience fatigue throughout their aviation careers. The Danger of Fatigue Individuals cannot readily feel the onset of fatigue (insidious) and may not be aware of its gradual and cumulative effects (performance degradation). Short Term (Acute): Normal in everyday life (tiredness after long periods of physical/mental strain). Prevented by adequate rest/sleep, regular exercise and proper nutrition. Long Term (Chronic): Not enough time for full recovery between episodes of acute fatigue. Recovery requires a prolonged period of rest. Causes of Fatigue:
- Disturbance of circadian rhythms. - Continuous wakefulness. - Cumulative sleep loss.
Symptoms of Fatigue: - Slowed reaction time (physically and mentally). - Increased errors despite increases effort. - Underestimation of performance degradation.
- Impaired judgement and decision making. - Fixation on a single source of information. Stages of Sleep Determined from:
- Electroencephalogram (EEG) measuring brain activity. - Electrooculogram (EOG) measuring eye movement. - Electromyogram (EMG) measuring chin muscle activity.
When awake, the EEG shows two activity patterns:
- Alpha (Resting) - Bravo (Alert)
Stage 1:
- 10 minutes long - Transitional stage between waking and sleeping. - Alpha → small, rapid irregular waves. EOG = rolling eye movements.
Stages 2 – 4:
- Stage 2 = 15 minutes (50% of sleep). Stage 3 = 15 minutes. Stage 4 = Early in night. - Delta activity within deeper sleep stages (3 & 4) – larger amounts. - Stages 3 & 4 = slow wave sleep.
Rapid Eye Movement (REM)
- Begins after 90 minutes. - Then in 90 minute cycles (REM increases). Typically 4 – 5 cycles. - EEG irregular, EOG rapid eye movements, EMG silent (relaxed).
Non-REM (Orthodox) Sleep: Revitalises the body after physical activity. REM (Paradoxical) Sleep: Restores the brain after mental activity. Circadian rhythms Rhythms having a period of about a day are called circadian rhythms. When the body receives no clues from the environment these rhythms free-run around 25 hours. Core body temperature averages 36.9°C with a circadian fluctuation of ±0.3°C and with the lowest temperature occurring around 05:00. Peak performance occurs with rising or high body temperature. Zeitgebers: From the German ‘time giver’. Cues that serve to synchronise the internal biorhythms. Sleep Cycles 1 hour of high quality sleep = 2 hours of activity. Around 8 hours may be an upper limit to the number of sleep hours credit that can be accumulated. When credit is exhausted the individual becomes lethargic and will require further sleep. Sleep deficit reduces performance and is cumulative.
Microsleeps Uncontrolled, spontaneous episodes of sleep that could last for seconds or minutes. The chances of microsleep increase during night-time hours and relative to the number of hours worked. Sleep Disorders Insomnia: Difficulty in falling asleep/frequent awakening. Hypersomnia: Excessively long/deep sleep. Only awakened by vigorous stimulation. Narcolepsy: Involuntary attacks of sleep lasting around 15 minutes at any time of day. Jet Lag: Mismatch between body clock and actual times. Westbound flights easier than Eastbound. Personality Emphasis is placed on the value of maintaining a friendly, relaxed, and supportive tone in the cockpit and aircraft cabin. Behavioural Styles Relationship Orientated: First consideration – Feelings of others (caring/nurturing style). Task Orientated: First consideration – Task completion (aggressive style of behaviour). Assertive Behaviour High relationship and task orientated:
- To put into words positively and with conviction. - To defend/insist on the recognition of one’s own rights. - To state to be true. Body Language: 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. In the cockpit, you have the right to ensure that your life will not be compromised by any action/inaction, miscommunication or misunderstanding. Assertive behaviour in the cockpit does not challenge authority; it clarifies position, understanding or intent enhancing safe operation. Attitudes Anti-authority: Found in people who do not like anyone telling them what to do. Impulsivity: Those who frequently feel the need to do something, anything, immediately. Invulnerability: Many people feel that accidents happen to others but never to themselves. Macho: Those who are always trying to prove that they are better than anyone else. Resignation: Those who do not see themselves as making a great deal of difference.
Interactive Style G = Goal Orientated
P = Person Orientated
Leadership Not a one-way process since it requires both leader actions and effective crew responses/feedback. A leader’s behaviour is less effective without complementary follower behaviour. Primary Functions:
- Regulation of the flow of information. - Directing and co-ordinating crew activities. - Motivation of crew members. - Decision making.
Effective Leadership Characteristics Competence: Technical and piloting skills should be good to inspire confidence in the crew. Communication: Clear and concise with good listening skills. Personal emotion kept out. Decision Making: Based on the situation at that time. All information used to find solution. Perseverance: Sticks to the task regardless. Always confident a solution can be found. Emotional Stability: Self-control maintained, personal emotions never cloud decision making. Enthusiasm: When the leader is committed then the follower will usually give their best. Ethics: Highest standard of professional conduct is expected at all times. Recognition: Acknowledgement is given to the help of others. Sensitivity: Stress/fatigue recognised in self and others to ensure overload does not develop.
Flexibility: Adaptation of styles to the problem must be possible. No 2 emergencies the same. Humour: Well direct humour is an effective tool, badly directed can be hurtful. Delegation A good leader will bring out the best in their team through trust and delegation of certain duties. In the cockpit, the Commander and crew should make their own mental plan and discuss the outcome in order to reach the ultimate conclusion and reduce chances for error. Delegation of duties should not be done to the level where the combined workload becomes too high. Rasmussen’s Skill-Rule-Knowledge Framework Skill Based Behaviour: Performance governed by stored patterns of pre-programmed instructions and motor programmes learnt by practice/repetition. May be executed without conscious thought. Rule Based Behaviour: Deals with familiar problems for which solutions are governed by rules stored in long-term memory/checklists/SOPs. Conscious decision must be made to apply them. Knowledge Based Behaviour: Comes into play in novel situations for which actions must be planned using conscious, analytical processes and stored knowledge. Errors arise from resource limitations. Maslow’s Hierarchy of Needs
Groups Synergy: The working together of two items to produce an effect greater than the sum of their individual efforts. Group Cohesion: Refers to the extent individual group members are attracted to each other and the group as a whole. Important for group performance. Group-think (Risky Shift): Occurs when a highly cohesive group striving for unanimity of opinion rather than a realistic appraisal of the situation. Decision more risky than that made by individual.
Flight Deck Leadership A generally democratic approach to problems is desirable, provided: 1. It is directed towards achieving the operational goal. 2. There is time. In emergencies a more autocratic approach necessary (based upon good pre-planning). Whatever style – it must be consistent. Attention Vigilance: The task of constantly monitoring without lapses in attention. Hypovigilance: An extremely agitated state of panic/near panic. Arousal The preparedness for performing any task. A certain level of arousal is a positive influence on performance. An extremely aroused pilot will underperform than an optimally aroused one. - The Yerkes-Dodson curve Situational Awareness Knowing what is going on and being prepared for the unexpected. Maintaining an accurate mental model of knowing: - Where the aircraft is. - Where it has been. - Where it is going. SA Level 1: Monitor Focus on a broad region – keep the big picture. Focus on a narrow region – pay attention to detail. Focus on the right information – do not get side-tracked or distracted. SA Level 2: Evaluate Using all sources of information you have available and then assessing them to give SA for the current state. SA Level 3: Anticipate Ensures crew have the same awareness of a problem and can both work to the same goal. Playing the ‘what if’ game has an advantage in SA. Guidance for Situational Awareness - Do not make up mental model from first sets of information (gather as much evidence) before decision making. - Do not hurry. - Try to structure information so that logical conclusions can be reached. - When decision made, check back to see if it still fits the facts.
- Situational Awareness Model Sterile Cockpit The purpose is to reduce self-induced distractions during typically high-risk, high-workload phases of flight. Communication Information, thoughts and feelings are exchanged in a readily and clearly understood manner. 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. To ensure it has been correctly received a check of understanding must be carried out. The Message Whenever possible, and especially during high workloads, use short common words. Short and simple commands prevent misunderstandings. Keep it short, keep it simple. The process of establishing trust, good working conditions and a pleasant atmosphere should be initiated during the pre-flight briefing. Good Transmitter - Clear and easy to understand message. - Good timing of transmission. - Challenging understanding/feedback.
Good Receiver - Pays attention. - Notifies if unable to pay attention. - Acknowledges receipt and understanding.
Listening The active listener attends to the words and projects their mind into that of the speaker, so that they can align their thoughts and feelings more closely to those of the speaker.
Closed Questions (for short answers): - Restricts the range of possible responses. - Useful in getting specific information quickly. - Improper use can feel like an interrogation. ‘How long are your shifts?’ Open Questions (for long answers):
- Allows the person a lot of freedom of response. - Useful for identifying attitudes and beliefs. ‘What do you think about the approach into Heathrow?’
Probe Questions (for more information):- Ask the person to clarify or elaborate. - Can be verbal or non-verbal. ‘Tell me more about that.’ Paraphrasing: To show understanding and encouragement by putting the other person’s ideas/feelings into your own words. Active Listening:
- The genuine desire to understand another person’s perception. - Listening and expressing understanding of what the other person said. - Sensitivity to another’s thoughts and feelings.
Discipline on-board It is the Commander’s responsibility to maintain the necessary discipline. The Commander sets the tone and working atmosphere. If not, crew discipline can deteriorate rapidly. Metacommunication: Communication about communication itself. Decision Making Operational Pitfalls Peer Pressure: Based upon emotional response to peers rather than objectively evaluating. Mind Set: The inability to recognise and cope with changes in the situation that may not be planned. Get-there-“itis”: Causes a fixation on the original goal combined with disregard for alternatives. Duck-under: Tendency to try to maintain visual contact with terrain while avoiding contact with it. Confirmation Bias: Tendency to stay with decision ignoring evidence suggesting it was wrong. Decision Making Process - Recognise or identify the problem. - Gather the information to assess the situation. - The information required and where that information is located needs to be established. - Identify and evaluate alternative solutions (risks, advantages, disadvantage) – select optimum. - Implement the decision. - Review the consequences by use of feedback. Evaluation and revision may be necessary. Reaction to Decision Making - Fly the aircraft (do not lose SA of the basic flying/confirm who is PF). - Never assume that you do not have time (remain calm, think first, then act – keep crew in loop). - Identify the problem. - Assess the situation using all resources. - Select and carry out the correct procedure (keep it simple).
- Continue evaluating the situation. - Inform the cabin crew (crucial for cabin preparation and evacuation). - Inform the passengers (seriousness of problem/cockpit workload determines how to brief). Judgement: The process of recognising and analysing all available information about oneself/crew/aircraft/flying environment followed by the rational evaluation of alternatives to implement a timely decision which maximises safety. DODAR : Diagnosis – Options – Decide – Assign – Review Human Error A failure on the part of the human to perform a prescribed act (or the performance of a prohibited act) within specified limits of accuracy, sequence or time, which could result in damage to equipment and property or disruption of scheduled operations. Attributed as the main cause factor in 65-75% of all aviation accidents. Error Categories Commission: Those in which pilots carried out some element of their task incorrectly/not required. Omission: Those in which the pilot neglected to carry out some element of a required task. The Error Chain Most aircraft accidents result from a combination of circumstances rather than from a single cause. These involve a variety of pilot-aircraft-environment factors and occurring as a series of errors in judgement. Links in the Error Chain (presence of one or more symptoms means chain in progress) - Ambiguity (exists any time two or more independent sources of information do not agree). - Distraction/preoccupation (where all attention is given to one problem at the expense of others). - Departure from safe procedures (intentional or not). - Fatigue or stress. - Poor communication (leading to misunderstandings). - Over reliance in automatic systems. - Confusion (leading questions and need for confirmation must come to the fore). - Failure to meet goals that are set. Breaking the Error Chain - Identify the problem. - Communicate what the problem is. - Achieve agreement as to what the problem is. - Decide on an action to solve the problem and break the chain of events. - Evaluate the action to ensure that the problem does not reappear.
Learning Knowledge gained by study, instruction or scholarship. A change in behaviour as a result of experience. Motivation One of the most important factors in:
- Learning. - Performance. - Attention.
Learning Styles - Activist: Person who enjoys things as they happen, rushes into things. - Reflector: Person who takes a cautious, thoughtful approach to learning. - Theorist: Learns by rules. Vertical learner with little lateral thinking. - Pragmatist: Happy putting ideas into practice and learns from life’s experiences.
- Kolb cycle redesigned to produce a model of learning styles. Automation The introduction of advanced automated systems has increased efficiency, precision and safety. Current glass cockpit aircraft are easier to operate than their immediate predecessors. Operations can however become very confusing if the expected response does not occur or in case of malfunction. Automation provides the pilot with:
Advantages of Automation:
- Alternate methods of accomplishing tasks. - Having more capacity to spare for the job in hand.
- Reduction in pilot workload. - High accuracy and reliability. - Cost effective. - MFDs allow increased sophistication and situational awareness.
Disadvantages of Automation: - Programming and monitoring can increase workload. - During cruise, workload may fall to low levels causing boredom. - Can reduce job satisfaction due to reduced vigilance. - Maintenance of manual /cognitive flying skills degraded.
System Opacity: Increases with technology and gives poor mental representation of underlying function. ‘Need to know principle’. System Autonomy: The greater the technology, the more the system is able to adapt to a given situation without operator commands. System Protection: Built-in function to prevent errors from system malfunction. Can lead to SOP deviation. Automation Complacency Passive Monitoring: Inherent belief in the system’s infallibility leads the pilot simply to watch rather than analysing and actively question its performance. Blinkered Concentration: Multifunctional capability of the system can lead to a narrowing of concentration (breakdown of monitoring the whole system). Main contributory factors in automated aircraft accidents: - Pilots who have insufficient knowledge of the systems they are using. - Confusion involved when not knowing the mode of flight. - Liveware – Software design mismatches. - Systems behaviour when modes are changed (what information is being shown). - Over reliance on the computer. - Non-SOP operations.
