ATA 32 Hawker 750/800/800XP/850XP/900XP

LANDING G EAR TRAINING MANUAL (B1/B2)

ATA 32
LANDING GEAR

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INTRODUCTION
GENERAL
• The hydraulically actuated landing gear on Hawker 900XP/750/800XP Series Pro Line 21 airplanes is enclosed by hydraulically
and mechanically actuated doors. Gear position and Warning are provided by annunciators and a warning horn.
• The inward retracting main gear and the forward retracting nose gear (Figure 32-1) are actuated by one hydraulic actuator (jack)
attached to each gear. The main gear inboard doors are hydraulically actuated; the outboard doors are mechanically controlled
by gear movement. The nose gear doors are mechanically controlled by movement of the nose gear.
• Landing gear position indication is provided by six annunciators on the centre instrument panel and a mechanical-position-
indicator for the nose gear on the centre pedestal. Standby annunciators for the main; gear are on the right console. In addition,
a warning horn sounds if any of the three gears is not locked down when the lap selector lever is ii the approach position or
beyond, or when either or both throttles are set to less than 60% N1 rpm and airspeed is below 150 KIAS.
• The hydraulically actuated nose wheel steering system, manually controlled by a hand wheel on the left console, provides
directional control] on the ground. A relief valve in the return line functions as a shimmy damper. A mechanically operated:
steering 3 on-off shutoff valve provides hydraulic pressure to the system only when the nose gear is down and locked.
• The hydraulic brake system, controlled from a brake control valve by master cylinder pressure, provides for normal and
emergency braking. Parking brakes are provided from the normal and. emergency brake systems.
• Master cylinders, operated by the brake pedals, provide control pressure to actuate inlet valves in the brake control valve for
normal or emergency operation of the brakes.
• Selection of normal, emergency, or parking brakes is made with the handbrake lever labelled WHEEL BRAKE on the centre
pedestal. Antiskid braking is available only during normal braking.
• Twin Wheels with tubeless tires are installed at each main and nose gear leg assemblies.

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LANDING GEAR
• Main Gear - Description
• Each main gear leg assembly incorporates an oleo-pneumatic shock absorber strut, at the base of which are mounted the
two offset axle tubes (see Figure 32-1).
• The complete leg assembly is supported in trunnion bearings on a fitting extending aft from the wing rear spar, and
stabilized, when in the down position, by a side stay between the leg and the wing structure.
• The side stay folds during retraction and forms the main locking component when the gear is in both the extended and
retracted position. The gear leg is faired in the up position by a fairing which is hinged to the lower wing skin and linked to
the leg by a short strut.
• The wheel well is covered by a faired door which closes after both extension and retraction.
• Components- Side Stay
• The side stay (Figure 32-2) is the locking mechanism for the gear in the up and down position. It is between the gear leg
assembly and wing structure. The stay is the stabilizing component with the gear extended. It is over centre at full
extension or retraction, creating an up lock or down lock condition.

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Leg Assembly
• The main gear leg assembly (Figure 32-4) features a plunger
tube (oleo strut) with an oil- metering orifice plate and flutter
plate to absorb landing and taxiing shock
• The upper part of the leg contains MIL-H-5606E hydraulic fluid;
the lower part is nitrogen-charged through a valve at the
bottom of the leg.
• The complete leg assembly is supported in trunnion bearings on
a fitting extending aft from the wing rear spar.

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Leg Assembly
Seal Replacement
• Seals in the main gear leg assembly can be removed and replaced without removing the leg from the airplane (Figure 32-5). With
the air- plane on jacks, follow the procedures the AMM. Nitrogen servicing and seal replacement is presented in the AMM.

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Fluid Charging
The upper part of each leg is filled with MIL-H-5606 mineral-based hydraulic fluid through a filler plug at the top of the leg. The lower
part is charged with dry air or nitrogen through a valve at the rear of the leg, between the wheels (Figure 32-6).
• With weight on wheels, service the leg as follows:
1. Install the gear down lock pins. Protect the wheels and tires from fluid.
2. Slowly release air pressure from the leg. Ensure that the leg is fully bottomed, and then remove the air charging valve.
3. Remove the two bleed screws from the top of the leg, and connect in their place a pump adapter and a length of tubing.
4. Pump in fluid until air-free fluid flows from the tubing.
5. Replace the tubing with a bleed screw, and pump fluid into the leg at 200 psi maximum. Cease pumping, and check that
the leg holds this pressure for a minimum of two minutes.
6. Failure to hold pressure could be caused by leakage from the pump unit or the strut leg; however, if that does not
appear to be the case, a probable cause is the separator piston “creeping” to the bottomed position. Continue to pump oil
slowly until a steady pressure is achieved.
7. Release the pressure, remove the pump adapter, and install the bleed screw.
8. Reinstall the air charging valve, using a “new O-ring seal
• Service the leg with dry air or nitrogen through NOTES the charging valve at the bottom of the leg until the pressure extension
limits in Figure 32-7 are obtained. Complete nitrogen and oil servicing instructions are found in the AMM.

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Main Gear Jack

• The main gear jack (Figure 32-8) is a conventional double-acting hydraulic actuator incorporating an integral shuttle valve. It
provides motive force for main gear extension and retraction.
• The eccentric bush allows adjustment to minimize the actuator ram over travel. The flat of the bush has one identification
groove (position 1) which coincides with the minimum wall thickness. The flat with four grooves (position 4) coincides with the
maximum wall thickness.

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Main Gear Doors

• The inboard doors are attached to the wing structure by two hinges. A door jack ram is attached to the forward edge of each
door.
• Jack movement is controlled by the reversing valve operated by the side stay. With the gear locked up or down, the doors are
closed. When the gear is up, hooks are positioned to engage rollers on the doors to mechanically lock the doors (Figures 32-9
and 32-10).
• Clearance between the tip of the door hook and the uplock roller, with the gear locked down and the door closed, is achieved by
adjustment of the spring strut.

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The outboard doors (fairings) are attached to and mechanically positioned by main gear movement. The doors are attached to the
wing structure with hinges and to the side stays by mechanical linkage (Figure 32-11).

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NOSE GEAR
• Description:
• The self-cantering nose leg assembly incorporates an oleo pneumatic shock absorber strut, the base of which carries a
twin live axle. The leg is in bearings attached to fittings on each side of the nose gear bay and is stabilized in the down
position by a drag stay assembly which folds during retraction and forms the main locking component in both the
extended and retracted positions.
• Steer the nose wheels with a hand wheel on the left console in the flight compartment.
• Two hinged doors, mechanically linked to the retraction mechanism, enclose the gear in both the retracted and extended
positions. A rear door attached to the leg completes the enclosure in the retracted position.
Components- Drag Stay
• The drag stay (Figure 32-12) is the folding component between the leg assembly and air- plane structure.
• Preinstallation checks and adjustments of the drag stay are as follows:
• 1. With the drag stay fully locked down, check the clearance between the roller and the end face of the cam on the lower
arm (clearance A), Adjust shims under the stop bolt to obtain the desired clearance.
• 2. With the locking lever held in the fully unlocked position and the locking pin hard against the unlocked end of the slots
in the upper arms, fold the drag stay. Check the clearance between the roller and-the-upper face of the cam on the lower
arm (clearance B). Adjust the short link to obtain the desired clearance.
• 3. Check that short link ends are safe tied and lock wired.

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Leg Assembly
• The nose gear leg assembly (Figure 32-14 and Figure 32-15) features a plunger tube (oleo strut) similar in operation to the main
gear shock strut.
• An oil orifice plate and flutter plate absorb landing/ taxiing shock. The upper part of the strut contains MIL-H-5606 hydraulic
fluid; the lower part is nitrogen-charged through a valve at the bottom of the strut.
• A floating piston separates the oil and nitrogen chambers. The plunger tube features a self-centering cam to center the gear at
retraction.

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On the bottom of the plunger tube is an axle assembly which houses a live axle (Figure 32- 16) that rotates on a pair of tapered roller
bearings. The left cover plate is shimmed to allow axle bearing preload adjustment. The axle barrel must be separated from the
plunger tube before the axle can be removed; otherwise, damage could occur.

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Nose Gear Jack

• The nose gear jack (Figure 32-17) is a conventional double-acting hydraulic actuator with an integral shuttle valve. It
provides extension/retraction power for the nose gear.
Nose Gear Doors
• The nose gear doors (Figure 32-17), attached to the airplane structure with hinges, are mechanically actuated through
linkage from the drag stay. The doors are normally closed, opening momentarily during extension and retraction,

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Nose Gear Doors Quick – Release Strut

• The nose gear forward doors, closed with the gear extended, can be manually opened with a lever attached to the door quick-
release strut (Figure 32-18).
• The doors are to be manually opened only when the nose gear is locked down. The doors must be closed and the quick-release
strut latched prior to retraction.
• On production airplanes SNs 8041 and subsequent, Mod 3030 incorporates a micro switch on the nose gear door quick-release
strut. If the strut is not closed and latched, the red N. GEAR annunciator illuminates with the green N GEAR annunciator. This-
modification is optional for airplanes SNs 8001 through 8040.

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Landing Gear Controls and Indications

• Lever Locking Installation
• A locking solenoid! (Figure 32-19) in the selector lever-assembly, controlled: by a:microswitch on the left, main gear leg,
prevents upward movement of the selector lever with the airplane on the ground:
• The circuit-to the solenoid is opened, permitting the mechanism to spring-load to the locked position. Lever- locking is
accomplished by a cam engaging a pawl to prevent lever movement. With weight off the wheels, the micro switch closes
to complete a circuit to the solenoid, removing the pawl from the cam and releasing the lever for gear retraction
• Lifting the override lever mechanically disengages the lock, allowing upward movement of the selector lever, if required.
The override lever has been replaced by a GEAR OVRD button.
• Lever Lock
• The selector lever is formed with a cam segment which engages with a pawl when the lever lock is applied. The pawl is
connected to a solenoid attached to the selector lever mounting. On the torque link on the left hand main gear is a micro
switch which is in circuit with the lever lock solenoid. The-electrical supplies are taken from bar PS1)
• With the main gear leg extended (airplane in flight or on jacks), the leg micro switch is closed and the locking solenoid
energized to with- draw the paw] clear of the cam segment. The selector lever is now free to move between the landing
gear up and down selections.
• When the main gear leg is compressed (airplane on ground) the leg micro switch is opened, breaking the power supply to
the locking solenoid. If an up selection is now at- tempted, the end face of the selector lever cam segment contacts the
pawl and further selector lever movement is prevented.

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• Selector and Dump Valve

• The selector valve and dump valve are incorporated in one unit. The selector valve is mechanically actuated by movement
of the seléctor lever on the center instrument panel.

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Landing Gear Operation

• Down lock provisions
• In addition to down lock mechanisms within the nose gear drag stay and the main gear side stay, landing gear lockping are
provided for on- the-ground-safe tying of the landing gear (Figure 32-20).
• The pins should be installed as soon as possible after landing and remain in position until immediately prior to engine start
for the next flight. When not in use, the pins may be stowed in a pouch in the vestibule or under the second step in the
main entrance door.
• Normal Retraction
• With the landing gear locked down, the wheel doors are closed but not locked. When the landing gear is selected up,
hydraulic pressure is supplied to extend the door jacks (Figure 32- 21), which in turn operate the sequence valves to allow
pressure to the main gear jacks.
• When the gear locks up, reversing valves are operated, causing the door jacks to be retracted. This final movement locks
the door up.

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Filters
• Four line filters are in the main gear hydraulic system and one line filter in the nose gear steering jack pressure line; these are
additional to the line filters protecting the main gear restrictor valves
• Three of the main gear filters are in the area below the left overwing fairing and the other in the right main gear wheel well area
(Figure 32- 24). The nose gear filter is in the nose gear bay.
• The unit comprises a hollow cylindrical housing threaded externally at both ends. A filter element fits inside the housing and is
retained in position by an end connection which screws onto the housing. A seal prevents leakage from the end connection and
filter housing joint faces.
• Fluid entering the filter percolates through the finely spaced windings on the outer surface into the center of the element and
then passes through the end connection to the hydraulic service.
• To ensure the correct filtration, when installed, an arrow is embossed on the housing to indicate hydraulic flow direction. The
arrow indicates that the filter end connection is facing downstream.

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Reversing Valve
• The reversing valve (Figure 32-25) operates in conjunction with the main gear to ensure that the inboard doors are closed when
the gears are locked up or down and that the doors are open when the gears are in transit. The reversing valve plunger is
connected by a rod and linkage to the side stay.
• Plunger position is controlled by the side stay. The valve operates through three positions in conjunction with four stages of
movement as follows:
• * Main gear locked down—valve plunger in
• Main gear locked up—valve plunger out
• * Main gear in transit—valve plunger in middle position
• One of the two landing gear down lines to the reversing valve incorporate a non return valve which is effective only when the
gear is retracting. On extension the valve opens, allowing fluid return to the reservoir. A flow restrictor in the return line controls
the main gear rate of extension.
• On initial installation of the reversing valve, adjust the connecting rod to obtain a gap of 0.050 inch or less between the plunger
flange and the valve body.
• With the gear locked up, ensure that the total extension of the plunger flange and the valve body does not exceed 0.87 inch.
Refer to the AMM for more details.

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Sequence Valve
• The sequence valves (Figure 32-27), mechanically actuated by the inboard doors, prevent the main gears unlocking from the
down position until the doors are opened.
• When the doors are fully open, the sequence valves direct pressure to the main gear jacks for retraction. For more details of the
installation adjustment sequence of the valve, see
Figure 32-25.
• To ensure the inboard doors are locked open while
working in the wheel wells, install a clamp over the
door jack ram, or disconnect the doors. If the doors
are disconnected, the sequence valves must also be
disconnected.

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Emergency Gear Extension

• Emergency extension of the gear is accomplished with the auxiliary hydraulic system hand pump (Figure 32-28).
• Pulling the AUX HYD SYSTEM PULL handle on the left side of the center radio console:
• * Removes a baulk to allow hand pump operation
• * Closes an on-off valve to allow pressure buildup
• * Positions a dump valve to block main system pressure
• * Connects the normal gear up and down lines to reservoir return
• Operation of the hand pump handle draws fluid from the auxiliary tank and delivers pressure via a check valve and shuttle valves
to the down side of the main and nose gear jacks, al- lowing the jacks to unlock the gears and doors. The main gear doors are
pushed open by the extending.main gears and will remain open. Continued pumping fully extends and locks the gears in the
down position. The AUX HYD LO LEVEL annunciator comes on during emergency extension when a half pint of fluid has been
removed from the auxiliary tank.

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Figure 32-28 Emergency Landing gear Extention

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MECHANICAL INDICATING SYSTEM

• Description
• This system is associated with the nose gear only. The white nose gear mechanical indicator, at the top left side of the
control (centre) pedestal, protrudes above the top surface of the pedestal when the gear is locked down, and by a lesser
amount with the gear in any other position (Figure 32-29).
• The indicator consists of the plain portion of one end of a Teleflex cable, the other end is se- cured to a lever attached to a
shaft at the top of the nose gear wheel well. A forked lever, at the opposite end of this shaft, is rotated by a pin on a lever
connected to the locking pin of the gear locking mechanism during locking and unlocking action of the nose gear.
• The forked lever is also rod-connected to the steering on- off valve, the internal spring of which loads the indicator to the
unlocked position.

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ELECTRICAL INDICATING SYSTEM

• Gear Position Indicating System
• Position indication for the gear is provided by annunciators on the center instrument panel (Figure 32-30).
• A standby electrical system duplicates the green locked-down indication for the main gear only. These annunciators are
under a hinged cover on the right console.
• The power supply for the annunciators on the center instrument panel is from the PE bus; the power supply for the
standby system is bus PS2. An electrical diagram shows gear standby conditions in Figure 32-31. Figure 32-32 shows
indicator light displays

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STANDBY INDICATING SYSTEM

• This system is associated with the main gear only and consists of one microswitch on each gear, located above the attachment
point of the side stay to wing structure and adjacent to the normal system microswitch (Figure 32-33).
• The light unit, under the hinged panel on the right console, consists of two sections, one for each gear. The indication will be
either green or no light, depending on main gear position.

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Instrument Panel Light Unit

• The instrument panel light unit contains three red sections in the upper half and three green sections in the lower half (Figure
32-34). Each section is illuminated, as appropriate, by two filaments. Pressing the end of the pivoted light section permits access
to the filaments, which are press-fitted into the section. Electrical dimming is provided.
• An electrical schematic of the landing gear indication and warning system is shown in Figure 32-34,
• Microswitches associated with this light unit operate as follows.

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• Main Gear
• Two microswitches are provided in each main wheel well area to indicate position. One, above the attachment point of
the side stay to the wing structure (see Figure 32-2), is operated by the lever assembly to give either a green (locked-
down) or red (unlocked) indication.
• The second microswitch, located above the door hook, when operated by the door roller engaging the hook, cancels the
red annunciator to give a no-light (locked-up) indication (Figure 32-34).
• Nose Gear
• A downlock microswitch on the upper arm of the drag stay (see Figure 32-12) is actuated by the locking lever to give an
appropriate green or red indication.
• A changeover microswitch (see Figure 32-17) is at the top rear of the nose gear bay; when operated by the pick-up forging,
it prevents the green indication when the gear locks up.

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Gear Warning System

• A warning horn sounds steadily if the landing gear is not locked down and either of the following conditions exists:
• The flaps are selected to the approach position or beyond.
• Either or both throttles are retarded to less than 60% N, rpm with airspeed below 150 + 3 KIAS.
• Cancel the horn operation initiated by throttle position by pressing the HORN ISOLATE switch forward of the No, 1 throttle, The
horn is isolated until the throttles are advanced above 60% N; rpm and the airspeed increases to above 150 +3 KIAS, or until the
landing gear is locked down.
•
• Refer to Figure 32-35 for schematics on the landing gear aural warning system.

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Weight on Wheels Switch Interface

A switch is mounted to each torque link of the main gear. These switches indicate to the airplane systems when the airplane is in the
air or on the ground. Figure 32-36 shows the system and how some systems receive a 28 VDC signal in flight while others receive this
signal in the air. Some systems receive a ground signal instead of voltage.

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Nose Wheel Steering System

The nose wheel steering system provides a

steering angle of 45° in either direction (Figure 32-
37). The manually controlled system, powered by
the main hydraulic system, can be disconnected
for towing.

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Component
• Steering Hand wheel
• The hand wheel (Figure 32-38) is on the pilot left console. A sprocket in the hand wheel housing is rotated by the hand
wheel through a bevel gear and pinion. Through an endless chain, the sprocket drives a double sprocket assembly below
the housing. Control cables leading to the steering system are attached to the double sprocket by a short length of chain.
• On-off Valve
• An on-off valve, actuated to the closed position by the nose gear drag stay when the nose gear unlocks for retraction,
ensures there is no hydraulic pressure available for steering with the gear retracted.
• Spring strut
• A spring strut in the control linkage to the selector valve on the steering jack absorbs motion of the hand wheel, and
provides rotation in the steering system during retraction and extension of gear.

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• The ram of the hydraulically powered steering jack is secured to a bracket on the strut; the jack body is attached to pivot levers
and a short lever which are connected to the steering sleeve around the strut. Since the ram is attached to a fixed point,
hydraulic pressure, when applied, moves the body of the jack to transmit steering motion. A selector valve is attached to the
jack. (Figure 32-39).
• Nose wheel steering operation
• Rotation of the hand wheel is transmitted by mechanical linkage to provide movement of the selector valve on the
steering jack. Main hydraulic pressure is applied to the selected side of the steering jack.
• Movement of the jack also moves the selector valve body, bringing it to the neutral position when the selected position
has been attained. A relief valve in the jack re- turn line functions as a shimmy damper by retaining low pressure in the
steering jack.
• Nose wheel steering adjustment
• Refer to the AMM for details on nose wheel steering system adjustment.

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BRAKES
• Description
• Normal and emergency brakes each provide differential braking and parking brakes. Antiskid is provided only in the
normal system. Movement of the handbrake lever progressively applies pressure to the brakes for parking.
• Components : Master Cylinders
• Four master cylinders (Figure 32-40), one connected to each brake pedal, supply pressure to operate the inlet valves in the
brake control valve. The spring strut provides feel and absorbs master cylinder movement when back pressure from the
brakes closes the inlet valves in the brake control valve.

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BRAKE CONTROL VALVE

• The brake control valve (Figure 32-42) controls normal and emergency braking. The valve meters pressure to the brakes in direct
proportion to the amount of master cylinder pressure applied. When the pedals are released, return fluid from the brakes
reverse-flows through exhaust valves to reservoir return.

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• Main Reducing Valve

• The main reducing valve reduces main hydraulic system pressure to 1,750 to 1,900 +50 psi before entering the brake
control valve.
• Emergency Reducing Valve
• The emergency reducing valve (Figure 32-43) reduces emergency brake accumulator pressure to 1,750 to 1,900 psi = 50
psi before entering the emergency section of the brake control valve. The reducing valve closes during normal brake
operation and opens for operation by mechanical connection from the handbrake lever.

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MODULAR UNIT
• The modulator unit (Figure 32-44) ensures unrestricted flow of fluid pressure to match the capacity of the brakes on initial
application and ensures restricted flow as brake pedal force is increased. The reduced flow conserves main system pressure and
enables the brake unit pressure to fully exhaust to return when the Maxaret unit actuates (Figure 32-45).

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• Main Gear Wheel

• The center of each wheel hub is counter bored to accommodate a tapered roller bearing. Drive blocks on the inner
periphery of one half engage the tenons of the brake unit rotors. The other half has four tapped holes for mounting the
Maxaret drive plate.
• Brake Unit
• The multi piston, disc-type brake unit (Figure32-46) consists of a heat pack (pressure plate, stators, rotors, and thrust
plate) and a cylinder block. Friction pads are riveted to the inner faces of the pressure and thrust plates and to both faces
of the stators. Each rotor is a series of segments interlocked to form a ring. Tenons on the rotors are engaged into drive
blocks in the wheel to provide rotation. Hydraulic movement of the pistons presses the stators and rotors together against
the thrust plate to achieve braking action.
• Automatic adjuster assemblies maintain running clearance as the brake unit wears. The unit is installed by bolting the
cylinder block to the axle flange and can be installed on either axle.

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• Wear Indicator – Mod 7688A

• The wear indicator consists of two indicator pins which are in retainers riveted to the pressure plate and secured by a cotter key.
The pins protrude through holes in indicator brackets attached to the cylinder block assembly. Wear is measured by the amount
of pin protrusion from the face of the indicator bracket with the brake pressurized.
• A brake is considered to be in a fully worn condition when the end face of either indicator pin is flush with face B (Figure 32-47)
of the indicator bracket with the brake pressurized.
• Handbrake Lever
• The handbrake lever, labelled WHEEL BRAKE (Figure 32-48), on the center pedestal controls the selection of normal, emergency,
or parking brake operation.

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• The EMER and the PARK BRAKE positions are placard in red. The spring-loaded paw] engages in the forward notch of a rack when
emergency brakes are selected.
• Full parking brake pressure is applied when the pawl is engaged in the aft notch, The pawl is disengaged by pressing a release
button on the lever. The lever is connected by rods and levers to the brake control valve and the emergency reducing valve
(Figure 32-49)
• A differential lever and a spring strut ensure that the valves are operated in the correct sequence according to lever position.
The spring strut preloads the handbrake lever to the forward position. When removing the strut, use a compression tool in
accordance with procedures in detailed in the AMM.
• OPERATION
• Normal Brake Operation
• The main hydraulic system provides pressure to actuate the brake units, one in each main gear wheel. Master cylinders,
operated by mechanical linkage from the brake pedals (Figure 32-50), provide control pressure for brake operation.

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Emergency break operation

• When main hydraulic system failure occurs, emergency brake pressure is available by selecting the handbrake lever to the EMER
position, mechanically opening the emergency brake reducing valve (Figure 32-51).
• Emergency brake accumulator pressure is reduced and applied to the emergency inlet valves in the brake control valve. As in
normal operation, pressure on the brake pedals produces master cylinder pressure to operate the brake control valve
• . Braking pressure, in proportion to pedal force, is directed through shuttle valves to the brake units, bypassing the modulators
and Maxaret units.
• The WHEEL BRAKE EMER L and R annunciators on the pilot instrument panel illuminate as braking pressure in the respective
gear brake assemblies reaches 1,000 psi. Relieving braking pressure on the pedals releases the brakes in the normal manner. As
the brakes release, the WHEEL BRAKE EMER L and R annunciators extinguish.
• Reduction of emergency brake accumulator pressure to and below 2,300 psi is indicated by Illumination of the EMER BRK LO
PRESS annunciator.

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Parking break operation

• With pressure available from both the main and emergency brake accumulators, both brake systems are available for setting the
parking brake (see Figure 32-49). Set the parking brake by depressing the button on top of the hand- brake lever and moving it
into the PARK BRAKE position (Figures 32-52).
• The emergency reducing valve and the brake control valves are mechanically opened. Reducing pressure is directed through the
control valves to the brake units. As the handbrake lever is moved aft, progressively increased pressure is applied as indicated by
the BRAKES pointer of the pressure indicator and illumination of the L and R annunciators.
• To release the brakes from the fully parked position, press the release button on top of the handbrake lever to release the latch.
Moving the lever forward closes the emergency reducing valve and relaxes the brake control valve. Pressure within the brake
units is re- leased to flow through the brake control valve to return, releasing the parking brakes.

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DIAGNOSTICS
• Master Cylinder
• 1. Adjust the rudder pedals to the minimum leg length position. Remove the master cylinder filler cap and fill to the
bottom of the filler neck. Pump the associated brake pedal a few times, and recheck the fluid level before replacing the
filler plug.
• 2. Ensure that the master cylinder reservoir is filled before, during, and after bleeding.
• 3. Open the appropriate bleed screw on the brake control valve (Figure 32-53) and pump the brake pedal until air-free
fluid is obtained. Tighten the bleed screw during pressure strokes.
• 4. Repeat steps | through 3 for the remaining master cylinders.
• Normal Brake System
• 1. Keep the handbrake lever fully forward, the reservoir full, and the sys- tem pressurized during bleeding.
• 2. Open the bleed screws at the brake units, hold the brake pedals depressed until air-free fluid flow is obtained, and
tighten the bleed screws.
• 3. Release main system pressure and service the reservoir as necessary
• Emergency Brake System
• 1. Release main system pressure. Ensure that the emergency system is pressurized during the emergency system bleeding.
• 2. Select the handbrake lever to the EMER position.

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• 3. Apply the brake pedals and open the bleed screws until air-free fluid flow is obtained. Tighten the bleed screws.
• Maxarets
• 1. Remove the flexible drive assembly, pressurize the main system, and fully depress the respective brake pedal.
• 2. Using a special hand key, rotate the Maxaret input shaft in the direction indicated by the arrow, and then quickly stop.
Repeat several times. Any trapped air returns to the reservoir.
• 3. Refit the flexible drive assembly
• Adjustment/Test of the Brake
• System
• Adjustment and testing the brake system includes the following:
• 1. Adjust brake pressure
• 2. Test normal brake system operation
• 3. Test normal brake system operation
• Brake System Inspection/Check
• Inspecting or checking the brake system includes the following:
• 1. Check operating pressures at brake units
• 2. Normal brake drag check
• 3.Emergency brake drag check
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Wheels and Tires

• Description
• Two wheels with tubeless tires are on each main and nose leg assembly. The main wheels use tapered roller bearings. The
nose wheels are splined to a live axle. The main wheels use 12- ply rating 23 x 7.00— 12 tires. The nose wheel uses 6-ply
rating 18 x 4.25—10 tubeless chained tires.
• Main Wheels
• Main wheels (Figure 32-54) are hub and flange-type, bolted together with an O-ring between hub halves. The center of
the hub is counter bored to accommodate tapered roller bearings that are protected at one end by seal housing and at the
other end by an excluder.
• Drive blocks dovetailed into the inner periphery of the hub are secured by lock plates. The center of the hub is tapped in
four places for installation of the Maxaret drive plate. Three gold-coloured fusible plugs are pressed into the wheel hub. A
fusible insert in each plug melts if excessive heating occurs. The insert melts at 199°C, releasing tire pressure to prevent
the tire from exploding.
• Nose Wheel
• The nose wheel, which uses a tubeless chained tire, consists of hub halves bolted together and sealed by an O-ring. The
hub center of the in- board hub half incorporates a pressed-in bore, which, together with the bore of the outboard half,
forms a stepped bore for a splined sleeve.
• The nose wheel, which uses a tubeless chained tire, consists of hub halves bolted together and sealed by an O-ring. The
hub center of the in- board hub half incorporates a pressed-in bore, which, together with the bore of the outboard half,
forms a stepped bore for a splined sleeve.
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• On production airplanes SNs 258091 and subsequent, two nose wheel brake friction pads (see Figure 32-17) are in the
nose wheel ] well. These pads decelerate and stop wheel rotation as the gear retracts at takeoff. The pads can be installed
on earlier 800 series airplanes (refer to SB 32-224).

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Tires
• TIRE
• All tires have the tire size imprinted on the sidewall. Nose tires are chained to deflect water on the runway away from
engine intakes. A red spot on the sidewall marks the light spot of the tire; ply ratings (PR) imprinted on the sidewall are
complete words or are abbreviated and followed by a number.
• Each tire is vented during the manufacturing process by piercing the outer rubber covering with a 1/16-inch awl at several
places around the tire. These vents are identified with 1/4- inch spots of green Litho ink. The vents pro- vide a means of
releasing air from the tire casing caused by normal permeation through the inner lining. The air may result in tread
separation if not relieved.
• Details of the tire construction are shown in Figure 32-55. Complete information on tires, including inspection for damage
and abnormal wear, is found in the AMM.

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Maintenance Considerations
• Inspections
• Inspections are to be performed in accordance with the manufacturer maintenance schedule.
• On-off Valve
• The landing gear functional check is found in the AMM. It must be accomplished following replacement of specified
components. The check requires that the airplane must be on Jacks with external electrical and hydraulic power applied.
• Functional checks of various landing gear, nose- wheel steering, and brake system components are not listed as such;
however, procedures under the heading “Adjustment/Test” are often equivalent to functional checks.
• FAULT ANALYSIS
• Isolation of a fault or malfunction can be accomplished by a systematic analysis of the trouble. Table 32-1 is a
reproduction of a troubleshooting chart from the AMM.
• Brakes
• Brake units are measured by the amount of pin protrusion from the face of the indicator bracket with the brake
pressurized. A brake is considered to be in a fully worn condition when the end face of either indicator pin is flush with
face B (see Figure 34-48) of the indicator bracket with the brake pressurized.
• Crack limitations in brake unit rotor segments must not exceed specified limitations. Cracks shown in Figure 32-56 not
exceeding 3/8 inch in length are permitted in the central area provided they cover only a limited area. Cracks less than 3/8
inch in length are unacceptable if within 3/8 inch of a slot or the edge of the segment. Complete information on
limitations on this and other brake unit components is presented in the AMM.
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