INTRODUCTION TO AIRCRAFT SYSTEM
An aeronautical engineer must have a solid foundation in basics of A/C System, the principle of cooling and sound knowledge of the way the principle is applied to various systems used in the A/C. The various systems that exist in aircrafts are as follows 1. Hydr Hydrau auli licc Sys Syste tem m 2. Airc Aircra raft ft Oxy Oxygen gen Syst System em 3. Pneu Pneuma mati ticc Sy System stem 4. Air-condit Air-conditioning ioning and Pressuriz Pressurization ation System System 5. Elec Electr tric ical al Sys Syste tem m 6. Engi Engine ne oil oil & Fue Fuell Sys Syste tem m 7. Aircra Aircraft ft Instru Instrumen mentt Syste System m 8. Ice and rain rain prote protecti ction on sys system tem 9. Fire Fire protec protectio tion n and smoke smoke detect detection ion syste system m 10. Leak and Waste syste system m 11. Aircraft weapon (Rocket, (Rocket, Gun, Missiles, Missiles, Bomb& Ejection system) system) 12. Communicati Communication on and navigation navigation system system 13. Propulsion Propulsion system system Though the systems are used to operate the various counter and components, they require day to day check, repair & examination for smooth and proper function. The purpose to conduct A/C system lab is to familiarize day to day activities required to maintain airworthy condition of A/C. AIRWORTHINESS
The contin continuin uing g capabi capabilit lity y of the A/C to perfor perform m in satisf satisfact actory ory manner manner,, the flight flight operation for which it is designed. INSPECTION
It is the most important form of function of aviation maintenance. As the A/C gives complexity, it becomes more important to detect any possible trouble before it becomes serious. To assist this, aero engineers are provided with detail special check list and the maintenance manual for each type of A/C. The engineer has to go through maintenance manual thoroughly before attempting any kind of activity in aircraft and its components. The operations may be carried out on A/C on daily flying hours and/or cycle basis. MAINTAINENCE
The set of action including inspection, servicing, and determination of condition required to achieve a derived outcome which restore an A/C part and equipment in serviceable condition.
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OVERHAUL
Overhaul means stripping a unit and restoring it to its design performance level after replacing, reworking of parts to a given standard.
SERVICING
It means preparing the A/C for flight, includes providing the A/C with fuel and other fluid and gases but do not include any work that is maintenance. TROUBLE SHOOT
It means to analyses and identify the malfunction. REPAIR
It means to correct the defective condition. MODIFICATION
It is a continuous process to improve its reliability and performance. SERVICING SCHEDULES
Servicing on Hours/Calendar/Cycle basis, which are to be carried out on aircraft at set Hours/Calendar/Cycle basis are mentioned in the manual or A/C servicing schedule. The servicing includes examination, inspection, lubrication and removal of major components such as landing gear jacks, door locks, air-conditioning equipments; aircraft brake units wheels etc. landing gear functional test, flying control range and moment check., A/C rigging procedure, hydraulic fluid contamination test, fuel contamination test & some activities requires replacement of components. Aircraft maintenance checks are periodical checks that have to be done on all aircraft after a certain amount of time usage. Aircrafts usually refer to as one of the following checks. A CHECK
This is performed approximately every month. This is usually done over night. The actual occurrence of this check varies by the type, cycle or number of hours flown since the last check. The occurrence can be delayed by the aircraft if certain predetermine conditions are met. B CHECK
This is performed in approximately 3 months.
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C CHECK
This is performed every 12 to 18 months. This check puts aircraft out of service and requires plenty of space usually at the hanger and maintenance base. Schedule and occurrence has many factors. The component is described and thus varies with the A/C category and type. D CHECK
This is the heaviest check of an A/C. This check is done approximately every 4 to 5 year. This is the check that take the entire A/C apart for inspection. A comprehensive check, analysis Non Destructive Testing (NDT) check and complete health monitoring of the engine has to be recorded. Complete overhauling of the A/C and its components even A/C painting is also required in this process. CONCLUSION
In order to ensure air worthiness condition of an A/C and its associated systems. Various checks/inspections within stipulated time, following the schedule show the A/C and its system are kept in fully serviceable condition at all time and in turn enhance the A/C safety. The time frame of schedules varies from A/C to A/C.
SAFETY PRECAUTIONS WHILE HANDLING AIRCRAFT SYSTEMS AND ITS COMPONENTS AIM
To prevent incident, accident and damage to man and material. OCCASIONS
Whenever required to handle the A/C and its system components and ground equipments. AIRCRAFT
Before carring out any work on the A/C, the respective maintenance manual is to be referred for further instructions. The necessary safety precautions are to be strictly followed. 1. Before entering the cock pit of a fighter A/C, ensure that the ejection seat is in safe and all armament operating switches are in safe position and all the safely pins are in position.
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2. Before switching on the master battery switch ensure that the under carriage selector lever is in down position and latched and all the armament store door switches are in safe condition. 3. Ensure that the wheel chocks are engaged. 4. Before operating the control surface, ensure that the control locks are removed. 5. Before starting the engine. a. b. c. d.
Chocks are to be kept in front of the wheel. A/C brake system in servicable. A serviceable fire extinguisher is available. Never tow an aircraft without a person inside the cockpit before towing the A/C, check the brake pressure. e. While towing the A/C never exceed the walking speed. f. Never drop any tool while working. g. While working inside the A/C, collect all the tools and space on completion of the job and ensure no items are left behind.
HYDRAULIC SYSTEM
1. Always release the system pressure before removing a component from the A/C 2. Never does any maintenance work on airplane with any other specified oil other than the recommended one. 3. Carry out the patch test on the system to prevent the contamination of oil. This can be carried out using Millipore patch test kit. 4. Never mix different grade of hydraulic oil to service the A/C. 5. Blank all the ports of the removed components and the A/C pipe ends to avoid the entry of dust, dirt and foreign particles. 6. Follow the necessary precautions to dismantle the hydraulic components. 7. Avoid spilling of hydraulic fluid on the A/C and in and around from the A/C. If spilled it should be cleaned immediately to avoid slipping. 8. Before fitting a new hydraulic component, it should be unblanked, degreased, washed and flushed. 9. While fitting the non return valve and restrictors, ensure that the marked arrows are in the desired direction.
PNEUMATIC SYSTEM
1. 2. 3. 4.
Release the system pressure before attempting a job. Clean all the vents of the aircraft On removal of components, blank all the parts of the component and the respective pipes. While carrying out the pressure test never exceed the given limitation
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5. While charging the pneumatic pressure always use the pressure regulator and safety valve. Drain the oil and water separator. 6. Never handle any bottle or cylinder from its charging nozzle. Always use protective cover.
OXYGEN SYSTEM
1. Smoking, open flames or smokes should not be permitted while working on the oxygen system. 2. Do not carry matches while handling the O2 system 3. A/C must be grounded and all electrical power must be switched off. 4. Keep working area and equipment free of oil, grease or any other flammable material. 5. Keep the tools and clothing free of oil and grease. 6. Object should not come in contact with grease or solvents as this will cause spontaneous explosions. 7. Never lubricate the O2 system components except on approved compatible lubricant. 8. Hand should be clean and free from oil. Do not use greasing gloves. 9. A spark is not necessary to cause a fire or explosion but the chemical reaction of fuel, gas and oil combined with O2 is sufficient to develop instant combustion and cause fire and explosion. 10. Never permit O2 cylinder to come in contact with electrical welding circuits and apparatus. 11. Never use oxygen from cylinder without reducing the pressure through a reducing regulator and safety valves. 12. Never mix other gas or compressed air is an O2 cylinder. 13. Never test for pipe line leaks or flow pipe line with oxygen unless the lines are specifically made for that.
SAFETY PRECAUTIONS DEFUELLING
TO
BE
FOLLOWED
DURING
FUELLING
AND
1. Do not operate radio, radar or any other electrical and electronic equipment except those specified. 2. Ground the fuel supply unit and aircraft. 3. Make sure the fuelling source contain the proper fuel grade as specified by the manufacture. 4. No smoking, open flame is permitted in and around the A/C. 5. It is not permitted to drop any tool while the operation is on. 6. The operation should be carried out in an open or fully ventilated space. 7. Do not carry out oxygen related work.
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AIRCRAFT JACKING PROCEDURE THEORY
For maintenance activities such as rigging, leveling, retraction test, wheel brake assembly change and major component change the A/C must be jacked up properly. The jacking up can be done by single point lifting by bottle jack or three point lifting by tripod jack. The jacks may be hydraulic or screw type as supplied by the manufacturer apart from this required the additional tail jacks or trestles may be used in accordance with the maintenance manual or the type of activities. PREFERENCE
It is always recommended to refer the respective A/C maintenance manual before attempting to perform jacking up operation. AIM
To lift the A/C by using jacks. REQUIREMENT
1. Man hours 2. Man power 3. Document 4. Equipment
-3 - 3+1 - A/C maintenance manual - bottle jack, wheel chocks, A/C ladder
PRECAUTIONS
1. Refer A/C manual before jacking up the A/C to know the correct method/procedure, sequence of operation and requirement of equipments. 2. Ensure the lifting capacity of the jack and the jacks are fully serviceable. 3. If necessary fit the jack pads on the A/C structure. 4. Avoid A/C jacking up operation in open area. 5. Find out the weather status from the ATC/MET department. 6. Select the hard & level ground. 7. If required keep trestles ready for use. Do not jack up the A/C before ensuring that the C.G and Gross weight are within safety limits. 8. Do not attempt to jack up the A/c by the main gear shock strut. 9. Ensure that the nose landing gear upper & lower torque links are connected prior to jacking. 10. Maintain the communication between the crews. 11. Ensure all ground support units are clear of the A/C. 12. Place caution boards/sign boards on the ground near the nose, wing tip and tail of the A/C. 13. Keep safety lines around the A/C.
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PROCEDURE
The procedure offers as per the type of A/C and as per the manufacture instruction. 1. 2. 3. 4. 5. 6.
Ensure that the ground is hard & level without slipping Remove the Chocks from the wheels Place the trestles wherever it is applicable Place all jacks at specified jacking points. Deploy one person at each jacking point, ensure that the jacks are properly placed Raise the jack slowly till the contact of the A/C jacking pod is at the correct place slightly way out the jack and align it. 7. First raise the nose slightly then simultaneously all the jacks till the wheels are clear by one inch from the ground 8. Engage the lock mechanism and lock the jack to prevent the sudden collapse due to hydraulic leakage of jacks. 9. If the A/C is likely to be jacked more than 24 hours or over night, it is recommended to adjust the trestles at all specified stations to support the A/C weight. 10. Place a display board (“A/C ON JACKS”) in front of A/C 11. While lowering the A/C from the jack, ensure the parking brakes are in off position. 12. No loose items are available in and around the A/C while lowering the A/C and abstraction if any to be cleared before lowering. RESULT
A/C jacked up safely without any damage to men, material and equipments.
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AIRCRAFT LEVELING PROCEDURE AIM
To place the A/C level with the ground by using strain gauge and spirit level method. (A/C type light wt) THEORY
Leveling of an A/C is the procedure of placing an A/C in its rigging position by means of lifting the A/C by hydraulic jacks so as to enable the rigging check on newly assembled A/C or replacement/renewal of any major component of the A/C in order to ensure the correct fitting and alignment of A/C. The rigging position is the position of the A/C at which longitudinal and lateral axis are parallel to the ground (Straight level position). It can be done by three different methods on the A/C type as follows. 1. Strain gauge and spirit level method (Light A/C) 2. Plumb ball method (Large wide body) 3. Engineers steeper method for super sonic A/C NOTE
As the procedure differs always, therefore always refer the instruction specified by manufacturer for the correct procedure for rigging and instructions required.
OCCASSIONS
1. 2. 3. 4.
On replacement/renewal of major components. During rigging check During symmetry check As required by manufactures and competant authority
REQUIREMENT
1. Man hours - 3 2. Manpower - 3+1
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3. Document - A/C Maintenance manual, A/C forms, A/C rigging charts 4. Equipment - Tripod jack (hydraulic/screw), A/C ladder, leveling board, spirit level, tail trestles PRECAUTIONS
1. Observe all the precautions while jacking up the A/C 2. Check accuracy of spirit level PROCEDURE
1. 2. 3. 4. 5. 6. 7. 8.
Ensure that the A/C is jacked up properly and place the trestles wherever it is required Place the longitudinal leveling board at port side Place the spirit level over the longitudinal board. Adjust the tail trestle till the bouble of the spirit level in brought in center Repeat the same operation Place the Spirit level after checking the accuracy Adjust the main jacks till the double of the spirit level in brought to the center Recheck the lateral level as well as longitudinal level
CAUTION
Always finish the leveling procedure by checking the longitudinal level without any adjustment RESULT
The A/C is level and ready for further checks
CHECKING OF WING INCIDENCE ANGLE AIM
To ensure correct alignment of using, wing fitment in order to achieve the correct design parameters.
INCIDENCE ANGLE
It is the angle between the chord line of main plane and the tail plane and the horizontal line when the A/C is in rigging position. THEORY
The wing incidence angle can be defined on the angle made by the chord line and the elective wing, when the A/C is in rigging position or straight level flights condition. It provides least drag, minimum power requirement extra for long endurance of the A/C. The checking procedure differs as per the A/C type
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and follow the instruction given by the A/C manufacture for a correct procedure. In this experiment the general procedure has been followed.
OCCASIONS
1. 2. 3. 4.
On replacement or renewal of wings Initial illustrations of the aircraft/transportation Followed by erosive ‘G’ loads/heavy loading As and when required by the manufacture and compact authority.
REQUIREMENT
1. Man hours 2. Manpower 3. Document 4. Equipment
-3 - 3+1 - Aircraft Maintenance manual, Aircraft rigging charts - Tripod jack (hydraulic/screw type), aircraft ladder, Adjustable board for leveling adjustable spirit level, trestles, using incedeure board
PREPERATION
1. Jack up the A/C as per the procedure by taking all the safety precautions 2. Level the A/C as per the procedure 3. Check the accuracy of Spirit levels PROCEDURE
1. Place the wing incidence board at the top of the wing. (the lib number is reframed in the respective A/C maintenance manual) 2. Place the adjustable spirit level over the wing procedure board 3. If the bubble is in the center the subjected incident angle is correct 4. If the bubble is away from the center the incident angle in member less than the specified dispending upon the position of the bubble. 5. If the incidence angle is not correct the mounting point of the wing fuselage is to be checked for its correct fitment crackers, losers, distortion. 6. The necessary repair/replacement work may be initiated as per the maintenance manual RESULT
The wing alignment is ensured to be corrected and the wing incidence angle is found to be zero degree.
CHECKING OF WING DIHEDRAL ANGLE
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THEORY
The upwind inclinatron of the wing to the fund age given to provide the derived lateral stability during rout of the A/C. when the A/C with dihedral angle is banked the tilted lift vector through its horizontal component set up a grade slipping velocity to wend the lower using tip. The effect of the dihedral angle into toss to meet the lower using at the allowed angle of check than that of higher wing there by allowing moment in lift on the lower and sets up a restoring moment to correct the position of the A/C. AIM
To check the given dihedral angle of the aircraft OCCASIONS
1. 2. 3. 4. 5. 6.
Followed by heavy landing report Followed by flight through turbulence During electron of new airplane On removal or revilement of wings Any major work or repair carried on the wing As and when required by the regulator delay
REQUIREMENT
1. Man hours 2. Manpower 3. Document 4. Equipment
-3 - 3+1 - A/C manual, Maintenance chart - Jack, leveling port, Adjustable spirit level, Adjustable trestles, Dihedral board
PROCEDURE
1. Jack up the A/C by taking up all the precautions 2. Level the A/C and check the accuracy with the help of adjustable sprit levels 3. Place the wing dihedral board at the specified station along the span between the labs (The Lib and statren number is mentioned in the manual) no 1 to 4 in the front spam 4. Place the spirit level in the dinehedral board 5. Check for the bubble, if necessary adjust it if the bubble it is center the angle is considered to be correct RESULT The dihedral angle of 20 of the pushpak A/C is measured and found correct
CHECKING OF WING SWEEP ANGLE
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THEORY
Wing sweep back in the angular setback given to the A/C lateral axis along the longitudinal axis to improve the A/C speed by reducing from the drag. It is misty done by on high speed A/C to improve flight characteristics. When an A/C with a sweep back form in banked by a disturbance, the change in dynatron of the airflow over rewiring passing over a short effect chord with a greater effective camber than that of the reused wing. As the A/C with dihedral the upper wing may also suffer, through begging shielded. The final result in before a relatively greater amount of left from lower wing which affect the lateral level. The stability effect also themes due to higher aspect retro of lower wing. AIM
To measure the wing sweep back angle and to ensure the retention of dared flight characteristic
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