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Airframe Test > Landing Gear Systems > Flashcards

Landing Gear Systems Flashcards

1
Q

List the steps in servicing shock struts

A
  1. position aircraft so that the shock struts are in
    the normal ground operating position
  2. remove the cap from the air servicing valve
  3. check the swivel nut for tightness
  4. if the servicing valve has a valve core, depress
    it to release any air pressure that may be
    trapped
  5. loosen the swivel nut
    a. for a valve with a valve core - rotate swivel
    nut one turn - depress valve core to release
    all air in the strut
    b. for valve without a valve core - rotate the
    swivel nut enough to allow air to escape
  6. aircraft on jacks may need to have the lower
    strut jacked with an exerciser jack to achieve
    the full compression of the strut
  7. Remove the valve core of an AN6287 valve
    with a valve core removal tool - then remove
    the entire service valve
  8. fill the strut with hydraulic fluid
  9. reinstall the air service valve assembly using a
    new O ring packing
    a. If an AN2687-1 valve, install a new valve
    core
    10 Inflate the strut according to manufacturers
    instructions - inflate slowly to avoid excess
    heating and over inflation
  10. tighten the swivel nut and torque as
    specified
  11. remove the fill hose fitting and finger tighten
    the valve cap of the valve
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2
Q

List the steps to bleeding the shock strut

A
  1. construct and attach bleed hose containing a
    fitting suitable for making an airtight
    connection at shock strut service valve port
  2. jack the aircraft until the shock struts are fully
    extended
  3. release any air pressure in the shock strut
  4. remove the air service valve assembly
  5. fill the strut to the level of the service port
    with approved hydraulic fluid
  6. attach the bleed hose to the service port and
    insert the free end of the hose into a
    container of clean hydraulic fluid
  7. place an exerciser jack under the shock strut
    jacking point. compress and extend the strut
    fully by raising/lowering the jack. continue
    until all air bubbles cease to form
  8. remove the exerciser jack. lower aircraft and
    remove all other jacks
  9. remove bleed hose assembly and fitting from
    service port of the strut
  10. install the air service valve, torque, and inflate
    the shock strut to manufacturers specs
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3
Q

If a skid is not corrected quickly, what can happen?

A
  1. tire blowout
  2. possible damage to aircraft
  3. loss of control of the aircraft
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4
Q

What aircraft require anti skid systems?

A

large aircraft with power brakes

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5
Q

What is the purpose of the anti skid system?

A
  1. detects wheel skid
  2. detects when wheel skid is imminent
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6
Q

How does the anti skid system work?

A

It automatically relieves pressure to the brake pistons of the wheel in question by momentarily connecting the pressurized brake fluid area to the hydraulic system return line

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7
Q

Most anti skid systems contain these 3 main types of components

A
  1. wheel speed sensors
  2. anti skid control valves
  3. control unit
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8
Q

Describe wheel speed sensors

A
  1. wheel speed sensors are transducers
  2. may be alternating current (AC) or direct
    current (DC)
  3. includes a stator, rotor, and lobes
  4. the frequency produced is directly
    proportional to the speed of wheel rotation
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9
Q

What is a control unit in an anti skid system?

A
  1. the brain of the anti skid system
  2. receives signals from the wheel sensors
  3. comparative circuits are used to determine if
    a skid is imminent
  4. common for it to be located in the avionics
    bay of the aircraft
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10
Q

Describe anti skid control valves

A
  1. fast acting, electrically controlled hydraulic
    valves that respond to the input from the anti
    skid control unit
  2. there is one control valve for each brake
    assembly
  3. typically located in the main wheel for close
    access to hydraulic pressure, return
    manifolds, and brake assemblies
  4. they are positioned downstream of the power
    brake control valves and upstream of the
    debooster cylinders, if equipped
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11
Q

What should be checked when completing an On Aircraft Wheel inspection?

A
  1. all wheel tie bolts and nuts should be in place
    • a missing bolt is grounds for removal
  2. thorough inspection of wheel halves
  3. wheel hub dust cap and anti skid sensor
    should be secure
  4. inboard wheel half should interface with the
    brake rotor with no signs of chafing or
    excessive movement
  5. all brake keys on wheel must be present and
    secure
  6. examine wheels for cracks, flaked paint, and
    any evidence of overheating
  7. inspect thermal plugs - no sign of fusible alloy
    being melted
  8. make sure wheel not abnormally tilted
  9. flanges should not be missing any pieces
  10. check wheel for signs of impact damage
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12
Q

Why is Axle Nut Torque extremely important on an aircraft wheel installation?

A
  1. if the nut is too loose, the bearing and wheel
    assembly may have excessive movement
    a. the bearing cup(s) could loosen and spin
    damaging the wheel
    b. could be impact damage from bearing
    rollers leading to bearing failure
    ** all aircraft axle nuts must be installed and
    torqued in accordance with the airframe
    manufacturer’s maintenance procedures**
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13
Q

When is an Off Aircraft Wheel inspection required?

A
  1. discrepancies found while inspecting a wheel
    mounted on the aircraft may require further
    inspection with the wheel removed from the
    aircraft
  2. other items, such as bearing condition can
    only be performed with the wheel assembly
    removed
  3. a complete inspection requires the tire be
    removed from the wheel rim
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14
Q

Why should you deflate the tire before removing the wheel assembly?

A
  1. wheel assemblies have been known to
    explode while removing the axle nut
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15
Q

What are the steps for removing the wheel assembly?

A
  1. deflate the tire
  2. let aircraft cool (min 3-4 hours)
  3. approach wheel assembly from front or rear
  4. do not stand in the path of the released air
  5. make sure to remove only one tire and wheel
    assembly from a pair at a time - this leaves a
    tire and wheel assembly in place in case
    aircraft falls from jack
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16
Q

What are the steps in an Off Aircraft Wheel Inspection?

A
  1. loosen tire from the wheel rim
  2. disassemble the wheel
  3. clean the wheel assembly
  4. clean the wheel bearings
  5. inspect the wheel bearings
  6. lubricate bearings
  7. inspect wheel halves
  8. inspect wheel tie bolt
  9. inspect key and screws
  10. inspect fusible plug
  11. balance weights
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17
Q

List the things to know when loosening the tire from the wheel base

A
  1. bead must be broken to remove tire - there
    are mechanical and hydraulic presses made
    for this purpose
  2. an arbor press can be used, if above not
    available
  3. never pry a tire off the rim with a screwdriver
    or other device
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18
Q

Disassembly of the wheel - What are some things to know?

A
  1. should take place in a clean area on a flat
    surface, such as a table
  2. remove wheel bearing first - set aside for
    cleaning/inspection
  3. don’t use an impact tool to disassemble the
    tie bolts - aluminum and magnesium alloys
    too soft for repeated hammering
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19
Q

Cleaning the Wheel Assembly - What are some things to know?

A
  1. clean wheel halves with solvent
    recommended by wheel manufacturer
  2. use a soft brush
  3. avoid abrasive techniques, materials, and
    tools, such as scrapers
  4. when wheels clean - dry with compressed air
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20
Q

What is used to clean the wheel assembly?

A

a soft brush and solvent recommended by the wheel manufacturer

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21
Q

What can happen to the wheel if abrasive techniques/materials are used to clean the wheel assembly?

A

corrosion can quickly form and weaken the wheel if the finish is missing in an area

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22
Q

How do you dry the wheels once clean?

A

compressed air

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23
Q

Why shouldn’t you use an impact tool when disassembling tie bolts?

A

aircraft wheels are made of relatively soft aluminum and magnesium alloy - these materials are not designed to receive repeated hammering of an impact tool

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24
Q

Describe the process of cleaning the wheel bearings

A
  1. bearings should be removed from the wheel
  2. clean with manufacturer approved solvent,
    such as Varsol, Naptha, or Stoddard solvent
  3. brush clean with a soft bristle brush
  4. dry with compressed air - never rotate the
    bearing while drying
  5. avoid steam cleaning of the bearings
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25
Q

Why should wheel bearings never be steam cleaned?

A

the surface finish of the metals will be compromised leading to early failure

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26
Q

Why should you never rotate wheel bearings when drying with compressed air?

A

the high speed metal to metal contact of the bearing rollers with the race causes heat that damages the metal surfaces

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27
Q

List the common conditions of a bearing that are cause for rejection

A
  1. Galling
  2. Spalling
  3. Overheating
  4. Brinelling
  5. False Brinelling
  6. Staining and Surface Marks
  7. Etching and Corrosion
  8. Bruising
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28
Q

What is Galling?

A
  1. reason for bearing rejection
  2. caused by rubbing of mating surfaces
  3. the metal gets so hot it welds
  4. the surface metal is destroyed as the motion
    pulls the metal apart in the direction of
    motion
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29
Q

What is Spalling?

A
  1. reason for bearing rejection
  2. a chipped away portion of the hardened
    surfaced of a bearing roller or race
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30
Q

What is Overheating?

A
  1. reason for a bearing rejection
  2. caused by lack of sufficient lubrication
  3. results in a bluish tint to the metal surface
  4. bearing cup raceway is usually discolored as
    well
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31
Q

What is Brinelling?

A
  1. reason for a bearing rejection
  2. caused by excessive impact
  3. appears as indentations in the bearing cup
    raceways
  4. any static overload or severe impact can
    cause true brinelling which leads to vibration
    and premature bearing failure
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32
Q

What is False Brinelling?

A
  1. reason for a bearing rejection
  2. caused by vibration of the bearing while in a
    static state
  3. identified by a rusty coloring of the lubricant
  4. also known as frictional corrosion
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33
Q

Describe Staining and Surface Marks on bearings

A
  1. reason for a bearing rejection
  2. located on the bearing cup
  3. appears as grayish black streaks with the
    same spacing as the rollers
  4. caused by water that has gotten into the
    bearing
  5. it is the first stage of deeper corrosion that
    follows
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34
Q

Describe Etching and Corrosion

A
  1. reason for a bearing rejection
  2. caused when water and the damage caused
    by water penetrates the surface treatment of
    the bearing element
  3. appears as a reddish/brownish discoloration
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35
Q

Define Bruising

A
  1. reason for a bearing rejection
  2. caused by fine particle contamination -
    possibly from a bad seal or improper
    maintenance of bearing cleanliness
  3. leaves less than smooth surface on the
    bearing cup
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36
Q

What causing galling on a bearing?

A
  1. rubbing of mating materials
  2. metal gets hot - melds - destroys surface
    metal
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37
Q

How does overheating appear on a bearing?

A

a bluish tint on the metal surface

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38
Q

How does brinelling appear on a bearing?

A

appears as indentations in the bearing cup raceways

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39
Q

How can false brinelling be identified?

A

a rusty coloring of the lubricant

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40
Q

How does bruising appear on a bearing?

A

it leaves a less than smooth surface on the bearing cup

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41
Q

Describe the process of Bearing Handling and Lubrication

A
  1. avoid conditions where contamination,
    moisture, and vibration can occur
  2. install and torque bearings according to
    manufacturers instructions
  3. lubricate with lubricant recommended by
    manufacturer
  4. use of a pressure bearing packing tool or
    adapter is recommended
42
Q

Describe the process of inspecting the wheel halves

A

A thorough visual inspection should be
conducted - use of magnifying glass
recommended
Corrosion -
1. check for corrosion carefully - check locations
where moisture is trapped closely
2. it is possible to dress out some corrosion
according to manufacturers instructions - use
an approved protective surface treatment and
finish
3. corrosion beyond stated limits is cause for
rejection of the wheel
Cracks - cracks in certain areas are common
1. Bead Seat Area - check using Eddy current
3. Wheel Brake Disc - check using dye penetrant
test - no corrosion permitted in this area

43
Q

How do you check for cracks in the bead seat area?

A

check using an Eddy current

44
Q

How do you check for cracks in the wheel brake disc?

A

check using dye penetrant test

45
Q

Name two areas where cracks are commonly found during inspection of the wheel assembly

A
  1. Bead Seat Area
  2. Wheel Brake Disc
46
Q

Wheel Tie Bolt Inspection - things to know

A
  1. tie bolts stretch and change dimension at the
    threads and under the bolt head
  2. most cracks are found in this area
  3. magnetic particle inspection can be used
47
Q

What inspection technique is used to check for cracks in wheel tie bolts?

A

Magnetic Particle Inspection

48
Q

Where are cracks in tie bolts usually found?

A

At the threads and under the bolt head

49
Q

Key and Key Screw Inspection - things to know

A
  1. drive keys are subject to extreme forces when
    brakes are applied
  2. bolts should be inspected for security
  3. keys should be inspected for cracks
  4. there is a limitation on how worn keys can be -
    too much wear allows excessive movement
  5. wheel manufacturers maintenance
    instructions should be used to perform the
    inspection
50
Q

How are fusible plugs or thermal plugs inspected?

A
  1. fusible plugs or thermal plugs are inspected
    visually
51
Q

Fusible plug inspection - things to know

A
  1. inspected visually
  2. check for deformation due to high
    temperatures
  3. if detected, all thermal plugs in the wheel
    should be replaced with new plugs
52
Q

Inspecting Balance Weights - things to know

A
  1. when manufactured - each wheel set is
    statically balance
  2. weights are added to balance, if needed
  3. weights are permanent part of the wheel
  4. balance weights are bolted to the wheel
    halves
  5. balance weights can be removed when
    cleaning/inspecting the wheel
  6. must be re-fastened in their original position
53
Q

What does Pascal’s Law state?

A

states that pressure applied to any part of a confined liquid is transmitted with undiminished intensity to every other part

this means that if a number of passages exist in a system, pressure can be distributed through all of them by means of the liquid

54
Q

What properties and characteristics must be considered when choosing the best liquid for a particular hydraulic system?

A
  1. Viscosity
  2. Chemical Stability
  3. Flash Point
  4. Fire Point
55
Q

Define Viscosity

A
  1. viscosity is internal resistance to flow
  2. most important properties of any hydraulic
    fluid
  3. most hydraulic fluids are low viscosity
56
Q

What instruments are used to measure viscosity?

A
  1. viscometers or viscosimeters
57
Q

Define chemical stability

A
  1. very important property in choosing hydraulic
    fluid
  2. it is the liquid’s ability to resist oxidation and
    deterioration for long periods
58
Q

Define flash point

A
  1. the temperature at which a liquid gives off
    vapor in sufficient quantity to ignite
    momentarily or flash when a flame is applied
  2. a high flash point is desirable for hydraulic
    liquids - it indicates good resistance to
    combustion and low degree of evaporation at
    normal temperatures
59
Q

Define fire point

A
  1. the temperature at which a substance gives
    off vapor in sufficient quantity and continue to
    burn when exposed to a spark or flame.
  2. a high fire point is required of desirable
    hydraulic fluid
60
Q

What are the 3 principal categories of hydraulic fluid?

A
  1. minerals
  2. polyalphaolefins
  3. phosphate esters
61
Q

Where do you find the correct hydraulic fluid to use in a system?

A

aircraft manufacturers maintenance manual or the instruction plate affixed to the reservoir of unit being serviced

62
Q

Describe Mineral Based Fluids

A
  1. oldest hydraulic fluid from the 1940’s
  2. used in many systems where the fire hazard is
    low
  3. suppliers generally ship components with MIL-
    H-6803
  4. processed from petroleum
  5. odor similar to penetrating oil and is dyed red
    • some are dyed purple or green
63
Q

What is Phosphate Ester-Based Fluid?

A
  1. used in most commercial transport category
    aircraft
  2. Skydrol & Hyjet are examples
  3. Today types IV and V fluids are used
64
Q

Name 2 general contaminants of hydraulic fluid

A
  1. abrasives, including core sand, weld spatter,
    machining chips, and rust
  2. nonabrasives, including those resulting from
    oil oxidation and soft particles worn or
    shredded from seals and other organic
    components.
65
Q

Checking the Hydraulic System for contamination - things to know

A
  1. to determine which component is defective,
    liquid samples should be taken from the
    reservoir and various other locations in the
    system
  2. samples are taken according to
    manufacturers instructions
  3. some systems are equipped with permanently
    installed bleed valves for taking liquid
    samples - in other systems the lines must be
    disconnected
66
Q

What is the Hydraulic Sampling Schedule

A
  1. Routine Sampling - each system should be
    sampled
    a) at least once a year
    b) every 3000 flight hours or
    c) whenever airframe manufacturer suggests
  2. Unscheduled Maintenance - when
    malfunctions may have a fluid related cause
  3. Suspicion of Contamination - fluids should be
    drained and replaced, with samples taken
    before and after the maintenance procedure
67
Q

Describe the hydraulic fluid sampling procedure

A
  1. Pressurize and operate hydraulic system for
    10-15 minutes - operate various flight controls
    to activate valves
  2. Shut down and depressurize the system
  3. Wipe off sampling port or tube with a lint free
    cloth
  4. Place a waste container under the reservoir
    drain valve and open valve so a steady stream
    flows
  5. Allow 1 pint of fluid to drain
  6. Insert precleaned sample bottle under the
    fluid stream and fill - leave an air space at top
  7. Close drain valve
  8. Fill out sample id label
  9. Service system reservoirs to replace the fluid
    that was removed
  10. submit samples for analysis to laboratory
68
Q

What information is included on a hydraulic fluid sample id label?

A
  1. customer name
  2. aircraft type
  3. aircraft tail number
  4. hydraulic system sampled
  5. date sampled
  6. indicate if a routine sample or taken due to a
    suspected problem
69
Q

What procedures should be followed to control contamination?

A
  1. Keep tools and work area clean and dirt free
  2. a suitable container should always be used to
    receive the drained hydraulic fluid
  3. clean affected area with dry cleaning solvent
    before disconnecting hydraulic lines or fittings
  4. all hydraulic lines and fittings should be
    capped or plugged immediately after
    disconnecting
  5. wash all parts with a dry cleaning solvent
    before assembly of any hydraulic components
  6. dry parts thoroughly and lubricate them with
    recommended preservative or hydraulic fluid
  7. all seals and gaskets should be replaced
    during the reassembly procedure
  8. connect all parts carefully to avoid stripping
    metal slivers from threaded areas / all fittings
    and lines installed and torqued
  9. all hydraulic servicing equipment should be
    kept clean and in good operating condition
70
Q

Hydraulic system filters - things to know

A
  1. a screening or straining device used to clean
    the hydraulic fluid, preventing foreign
    particles and contaminating substances from
    entering
  2. filter rating given in microns, which is the
    smallest particle size that is filtered out
  3. replacement interval of filters is established
    by the manufacturer and included in the
    maintenance manual
  4. can be located in reservoir, pressure line, etc
71
Q

What is the recommended service life of filter elements?

A
  1. Pressure filters - 3000 hours
  2. Return filters - 1500 hours
  3. Case drain filters - 600 hours
72
Q

How often should pressure filters be replaced?

A

every 3000 hours

73
Q

How often should return filters be replaced?

A

every 1500 hours

74
Q

How often should case drain filters be replaced?

A

every 600 hours

75
Q

Describe the procedure for flushing the hydraulic system?

A
  1. Connect a ground hydraulic test stand to the
    inlet and outlet test ports of the system.
    Verify the ground unit fluid is clean and
    contains the same fluid as the aircraft
  2. Change the system filters
  3. Pump clean, filtered fluid through the system
    and operate all subsystems until no obvious
    signs of contamination are found. Dispose of
    contaminated fluid and filter
  4. Disconnect the test stand and cap the ports
  5. Ensure the reservoir is filled to the full line or
    proper service level
76
Q

How are hydraulic filters rated?

A

in microns

77
Q

What are the 3 main classes of seals?

A
  1. packings
  2. gaskets
  3. wipers
78
Q

Describe V Ring packings(AN6225)

A
  1. one way seals
  2. always installed with open end of V facing the
    pressure
  3. must have a male and female adapter to hold
    them in place
  4. torque seal retainer to manufacturer
    specifications
79
Q

Describe U-Ring packings

A
  1. U ring packings and U cup packings are used
    in brake assemblies and brake master
    cylinders
  2. lip of packings must face toward the pressure
  3. U ring packings are primarily low pressure
    packings to be used with pressures less than
    1000psi
80
Q

O Ring Color Coding - what information is provided by color coding?

A
  1. system fluid or vapor compatibility
  2. not a reliable source of identification
81
Q

Describe O Rings

A
  1. most packings and gaskets used in aircraft are
    in the form of O rings
  2. the O ring packing seals most effectively in
    both directions
  3. the sealing is done by distortion of its elastic
    compound
82
Q

What is a Backup Ring?

A
  1. made of Teflon
  2. don’t deteriorate with age
  3. unaffected by any system fluid or vapor
  4. can tolerate extreme temperatures
  5. their dash numbers indicate their size and the
    number of the O ring it is suited for
  6. installed downstream of the O ring
83
Q

What is a Gasket?

A
  1. used as static (stationary) seals between two
    flat surfaces
  2. commonly made from asbestos, copper, cork
    and rubber
  3. asbestos sheeting is used for exhaust system
    gaskets
84
Q

What are seals made of?

A
  1. most seals are made from synthetic materials
    that are compatible with hydraulic fluid
85
Q

Seal Compatibility - what you should know

A
  1. Seals used for MIL-H-5606 hydraulic fluid are
    not compatible with phosphate ester-based
    fluids
  2. Seals used for MIL-H-5606 are made of
    neoprene or Buna-N
  3. Seals for phosphate ester-based fluids are
    made from butyl rubber or ethylene-
    propylene elastomer
86
Q

What is a pressure control valve?

A
  1. some are an escape for excess pressure
  2. some only reduce the pressure to a lower
    pressure system
  3. some keep the pressure in a system within
    the required range
87
Q

What is a pressure relief valve?

A
  1. used to limit the amount of pressure being
    exerted on a confined liquid
  2. necessary to prevent the failure of
    components or rupture hydraulic lines under
    excessive pressure
88
Q

What are the most common types of pressure relieve valves?

A
  1. Ball type
  2. Sleeve type
  3. Poppet type
89
Q

Pressure relief valves may be used as what?

A
  1. System relief valve
  2. Thermal relief valve
90
Q

How is a pressure relief valve used as a thermal relief valve?

A

used to relieve excessive pressures that may exist due to thermal expansion of the fluid

91
Q

What is a Pressure Regulator

A
  1. a device used in hydraulic systems that are
    pressurized by constant delivery type pump
92
Q

What are the 2 purposes of the pressure regulator?

A
  1. to manage the output of the pump to
    maintain system operating pressure within a
    predetermined range
  2. to permit the pump to turn without resistance
    (unloading the pump) at times when pressure
    in the system is within normal operating range
93
Q

What is a Pressure Reducer?

A

Pressure reducing valves are used in hydraulic systems where is is necessary to lower the normal system operating pressure by a specified amount

94
Q

What does a pressure reducer do?

A
  1. provide a steady pressure into a system that
    operates at a lower pressure than the supply
    system
  2. can be set for any desire downstream
    pressure
95
Q

What is a Shuttle Valve?

A

the main purpose of the shuttle valve is to isolate the normal system from an alternate or emergency system

96
Q

The housing of the shuttle valve contains what 3 ports?

A
  1. normal system inlet
  2. alternate or emergency system
  3. outlet
97
Q

Name the four types of shuttles

A
  1. sliding plunge
  2. spring-loaded piston
  3. spring-loaded ball
  4. spring-loaded poppet
98
Q

What is a Shutoff Valve?

A
  1. used to shut off the flow of fluid to a
    particular system or component
  2. generally electrically powered
  3. also used to create a priority in a hydraulic
    system and controlled by pressure switches
99
Q

What is an Accumulator?

A
  1. a steel sphere divided into 2 chambers by a
    synthetic rubber diaphragm
100
Q

What is the function of an Accumulator?

A
  1. dampen pressure surges
  2. aid or supplement the power pump when
    several units operating at once
  3. Store power for the limited operation of a
    hydraulic unit when the pump isn’t operating
  4. supply fluid under to pressure to compensate
    for small internal or external leaks
101
Q

What are the 2 types of accumulators normally used in aircraft hydraulic systems?

A
  1. Spherical
  2. Cylindrical

Airframe Test (11 decks)

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