B777 Landing Gear

7/27/2019 B777 Landing Gear

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B777

Landing GearDO NOT USE FOR FLIGHT



Introduction

The airplane has two main landing gear and a single nose gear. The nose gear is a

conventional steerable two–wheel unit. Each main gear has six wheels in tandem pairs. To improve turning radius, the aft axle of each main gear is steerable.

Hydraulic power for retraction, extension, and steering is supplied by the center

hydraulic system. An alternate extension system is also provided.

[Option – Synoptic Tire Pressure Indication]The normal brake hydraulic system is powered by the right hydraulic system. The

alternate/reserve brake hydraulic system is powered by the center hydraulic

system. Antiskid protection is provided with both systems, but the autobrakesystem is available only through the normal system. A brake temperature monitor

system and tire pressure indication system displays each brake temperature and

tire pressure on the GEAR synoptic display.

Air/Ground Sensing System

In–flight and ground operation of various airplane systems are controlled by the

air/ground sensing system.

The system receives air/ground logic signals from sensors located on each main

landing gear beam. These signals are used to configure the airplane systems to the

appropriate air or ground status.

Landing Gear Operation

The landing gear are normally controlled by the landing gear lever. On the ground,

the lever is held in the DN position by an automatic lever lock. The lever lock can

be manually overridden by pushing and holding the landing gear lever LOCK OVERRIDE switch. In flight, the lever lock is automatically released through

air/ground sensing.

Landing Gear Retraction

When the landing gear lever is moved to UP, the landing gear begins to retract.

The landing gear doors open and the main gear wheels tilt to the retract position.

The EICAS landing gear position indication display changes from a green DOWN

indication to a white crosshatch in–transit indication as the landing gear retractinto the wheel wells. After retraction, the landing gear are held up by uplocks. The

EICAS landing gear position indication changes to UP for 10 seconds and then

blanks. With the landing gear retracted and all doors closed, the landing gear

hydraulic system is automatically depressurized.

Boeing B777 - Systems Summary [Landing Gear]

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If any gear is not up and locked up after the normal transit time, the EICAS caution

message GEAR DISAGREE is displayed. The EICAS gear position indication

changes to the expanded non–normal format, with the affected gear displayed as

in–transit or down, if the gear never unlocked from the down position. The EICASadvisory message GEAR DOOR is displayed if any hydraulically actuated door is

not closed after normal transit time.

Landing Gear Extension

When the landing gear lever is moved to DN, the landing gear doors open, the gear

are unlocked, and the in–transit indication is displayed on the EICAS landing gear

position indication.

The gear free–fall without hydraulic power to the down and locked position. Thedownlocks are powered to the locked position, all hydraulically actuated gear

doors close, and the main gear trucks hydraulically tilt to the flight position. When

all gear are down and locked, the EICAS gear position indication displays

DOWN.

The EICAS caution message GEAR DISAGREE is displayed if any gear is not

locked down (side and drag brace on the same main gear not locked, or nose gear

drag brace not locked) after the normal transit time. The EICAS gear position

indication changes to the expanded non–normal format, with the affected gear displayed as in transit (or UP if the gear never unlocked from the up position).

If only one brace on a main gear is locked (either drag or side brace not locked)

after the normal transit time, the EICAS caution message MAIN GEAR BRACE

L or R is displayed for the affected gear. The EICAS gear position indication

changes to the expanded non–normal format, with the affected gear displayed as

in transit. The EICAS advisory message GEAR DOOR displays if any

hydraulically actuated door is not closed after the normal transit time.

Landing Gear Alternate Extension

The alternate landing gear extension system uses a dedicated DC powered electric

hydraulic pump and center hydraulic system fluid to extend the landing gear.

Selecting DOWN on the ALTERNATE GEAR switch releases all door and gear

uplocks. The landing gear free–fall to the down and locked position. The landing

gear lever position has no effect on landing gear alternate extension.

The EICAS landing gear position indication displays the expanded gear position

indication when the alternate extension system is used. During alternateextension, the EICAS message GEAR DOOR is displayed because all the

hydraulically powered gear doors remain open.

Following an alternate extension, the landing gear can be retracted by the normal

system, if it is operating. Select DN then UP to retract the landing gear using the

normal system.


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Semi-Levered Gear

The semi-levered gear consists of an additional hydraulic actuator that connects

the forward end of each main gear truck to the shock strut. During takeoff, the

actuator locks to restrict rotation of the main gear truck and allow takeoff rotationabout the aft wheel axle, thereby improving airplane performance capability.

During landing, the actuator is unlocked to permit rotation of the main gear truck

and provide additional damping.

Nose Wheel and Main Gear Aft Axle Steering

The airplane is equipped with nose wheel steering and main gear aft axle steering.

Nose wheel steering is powered by the center/reserve hydraulic system. Main gear aft axle steering is powered by the center hydraulic system.

Primary steering control is provided by a nose wheel steering tiller for each pilot.

Limited steering control is available through the rudder pedals. The tillers can turn

the nose wheels up to 70 degrees in either direction. A pointer on the tiller

assembly shows tiller position relative to the neutral setting. The rudder pedals can

be used to turn the nose wheels up to 7 degrees in either direction. Tiller inputs

override rudder pedal inputs.

Main gear aft axle steering automatically operates when the nose wheel steering

angle exceeds 13 degrees to reduce tire scrubbing.

The EICAS warning message CONFIG GEAR STEERING, accompanied by the

takeoff configuration aural alert, is displayed if the main gear aft axles are not

centered and locked when takeoff thrust is applied. The EICAS advisory message

MAIN GEAR STEERING is displayed if the main gear steering actuators are not

locked in the centered position when commanded to the center position.

Brake System

Each main gear wheel has a multiple disc carbon brake. The nose wheels have no

brakes. The brake system includes:

Normal Brake Hydraulic System

The normal brake hydraulic system is powered by the right hydraulic system. The

brake pedals provide independent control of the left and right brakes.

• normal brake hydraulic system

• alternate/reserve brakehydraulic system

• brake accumulator

• antiskid protection

• autobrake system

• parking brake.


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Alternate/Reserve Brake Hydraulic System

Alternate/reserve brake hydraulic system selection is automatic. If the right

hydraulic system pressure is low, the center/reserve hydraulic system

automatically supplies pressure to the alternate/reserve brake hydraulic system.Pushing a brake pedal then sends hydraulic pressure through the alternate antiskid

valves to the brakes. If center hydraulic system fluid quantity is low, the C1

primary pump is isolated from the center hydraulic system to provide a reserve

braking pressure source.

Loss of the right and center/reserve hydraulic systems causes the BRAKE

SOURCE light to illuminate and the EICAS advisory message BRAKE SOURCE

to display.

Brake Accumulator

The brake accumulator is located in the normal brake hydraulic system. If right

and center/reserve brake hydraulic power is lost, the brake accumulator can

provide several braking applications or parking brake application.

Antiskid Protection

Antiskid protection is provided in the normal and alternate/reserve brake

hydraulic systems. Antiskid protection is also provided when the brake system is being supplied pressure only from the brake accumulator.

The normal brake hydraulic system provides each main gear wheel with

individual antiskid protection. When a wheel speed sensor detects a skid, the

associated antiskid valve reduces brake pressure until skidding stops.

The alternate/reserve brake hydraulic system provides antiskid protection to

tandem wheel pairs for the forward and middle axle wheels. The aft axle wheels

remain individually controlled.

Touchdown and hydroplaning protection is provided using airplane inertial

ground speed. Locked wheel protection is provided using a comparison with other

wheel speeds.

The EICAS advisory message ANTISKID is displayed if an antiskid fault

affecting the brake hydraulic system in use is detected, or if the parking brake

valve is not fully open with the parking brake released, or if the system is

completely inoperative.

Autobrake System

The autobrake system provides automatic braking at preselected deceleration rates

for landing and full pressure for rejected takeoff. The system operates only when

the normal brake system is functioning. Antiskid system protection is provided

during autobrake operation.


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EICAS memo messages display the selected autobrake settings:

• AUTOBRAKE 1 through 4

• AUTOBRAKE MAX

• AUTOBRAKE RTO.

The EICAS advisory message AUTOBRAKE is displayed if the autobrake system

is disarmed or inoperative, or autobrake solenoid valve pressure is high when not

commanded on.

Rejected Takeoff

Selecting RTO (rejected takeoff) prior to takeoff arms the autobrake system. The

RTO mode can be selected only on the ground. The RTO autobrake setting

commands maximum braking pressure if:• the airplane is on the ground

• groundspeed is above 85 knots, and

• both thrust levers are retarded to idle.

Maximum braking is obtained in this mode. If an RTO is initiated below 85 knots,

the RTO autobrake function does not operate.

Taxi Brake Release

During each taxi brake application, the antiskid system releases the brakes of oneaxle pair of each main landing gear (if wheel speeds are less than 45 knots). The

system sequences through the axle pairs at each brake application, thereby

reducing the number of brake applications by each brake. This extends service life

and reduces brake sensitivity during taxi.

All active brakes are applied for a heavy brake application, landing rollout, RTO,

or when setting the parking brake.

The taxi brake release system operates only with the normal brake hydraulic

system.

Landing

Five levels of deceleration can be selected for landing. However, on dry runways,

the maximum autobrake deceleration rate in the landing mode is less than that

produced by full pedal braking.

After landing, autobrake application begins when:

• both thrust levers are retarded to idle, and• the wheels have spun up.

Autobrake application occurs slightly after main gear touchdown. If MAX AUTO

is selected, deceleration is limited to the AUTOBRAKE 4 level until pitch angle

is less than one degree, then deceleration is increased to the MAX AUTO level.

The deceleration level can be changed (without disarming the system) by rotating

the selector.


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To maintain the selected airplane deceleration rate, autobrake pressure is reduced

as other controls, such as thrust reversers and spoilers, contribute to total

deceleration. The system provides braking to a complete stop or until it is

disarmed.Autobrake – Disarm

The autobrake system disarms and the EICAS advisory message AUTOBRAKE

is displayed if any of the following occur:

• pedal braking applied

• either thrust lever advanced after landing

• speedbrake lever is moved to the DOWN detent after the speedbrakes

have deployed on the ground• DISARM or OFF position selected on the AUTOBRAKE selector

• autobrake fault

• normal antiskid system fault

• loss of inertial data from the ADIRU

• autobrakes are applied after loss of normal brake hydraulic pressure.

When the autobrake system disarms after landing, the AUTOBRAKE selector

automatically moves to the DISARM position, and removes power from the

autobrake system.

When the autobrake system disarms during takeoff, the autobrake selector

remains in the RTO position, but automatically moves to OFF after takeoff.

Parking Brake

The parking brake can be set with the normal or alternate brake hydraulic system

pressurized. If the normal and alternate brake systems are not pressurized, parking

brake pressure is maintained by the brake accumulator. The brake accumulator is

pressurized by the right hydraulic system. Accumulator pressure is shown on theBRAKE ACCUMULATOR PRESSURE indicator.

The parking brake is set by fully depressing both brake pedals, pulling the parking

brake lever up, then releasing the pedals. This mechanically latches the pedals in

the depressed position and commands the parking brake valve to close.

The parking brake is released by depressing the pedals until the parking brake

lever releases.

When the parking brake is set, the EICAS memo message PARKING BRAKESET is displayed. If the parking brake is set and either engine is set to takeoff

thrust, the takeoff configuration aural alert sounds and the EICAS warning

message CONFIG PARKING BRAKE is displayed.


Page 6



Brake Temperature Indication

Wheel brake temperatures are displayed on the GEAR synoptic display.

Numerical values related to wheel brake temperature are displayed adjacent to

each wheel/brake symbol. These values range from 0.0 to 9.9 in increments of 0.1.The values tend to increase after the brakes are used.

Normal range values of 0 to 4.9 are white. For values of 3.0 to 4.9, the brake

symbol for the hottest brake becomes solid white. Values of 5.0 and above are

amber. For values of 5.0 and above, the EICAS advisory message BRAKE TEMP

is displayed.

Tire Pressure Indication

[Option]

Individual tire pressures, from 0 to 400 PSI, are displayed inside the individual

wheel symbols on the GEAR synoptic display.

The EICAS advisory message TIRE PRESS is displayed if any tire pressure is

above or below the normal range, or there is an excessive pressure difference

between two tires on the same axle.

Tail Skid[777-300 and 777-300ER]

The airplane is equipped with a tail skid system. The tail skid extends for takeoff

and landing and retracts during flight. It helps protect the pressurized part of the

airplane from contact with the runway. The tail skid uses the main landing gear

actuation system.

The EICAS advisory message TAIL SKID is displayed when the tail skid is not in

the correct position.


Page 7



Landing Gear EICAS Messages

The following EICAS messages can be displayed.

Note: Configuration warning messages are covered in Chapter 15, Warning

Systems.

Brakes

Landing Gear

Message Level Aural Condition

ANTISKID Advisory A fault is detected in the antiskid system.

AUTOBRAKE Advisory Autobrake is disarmed or inoperative.

AUTOBRAKE 1,2, 3, 4, MAX, RTO Memo Indicates selected autobrake level.

BRAKE SOURCE Advisory Normal, alternate, and reserve brakes are

not available.

BRAKE TEMP Advisory Temperature of one or more brakes is

excessive.

PARKING

BRAKE SET

Memo The parking brake lever is up and the

parking brake valve is closed

RESERVE

BRAKES/STRG

Advisory Reserve brakes, normal nose gear

extension, and nose wheel steering may

not be available.


GEAR DISAGREE Caution Beeper Gear position disagrees with landing gear

lever position.

GEAR DOOR Advisory One or more gear doors are not closed.

MAIN GEAR

BRACE L, R

Caution Beeper Affected main gear is down with one brace

unlocked.

MAIN GEAR

STEERING

Advisory Main gear steering is unlocked when

centered.


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Tail Skid

[777-300 and 777-300ER]

Tires

[Option]

Message Level Aural ConditionTAIL SKID Advisory Tail skid position disagrees with landing

gear lever position.


TIRE PRESS Advisory One or more tire pressures are not normal.


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14.10 Landing Gear-Controls and IndicatorsLanding Gear Panel

1 Landing Gear Lever

UP – the landing gear retracts.

DN – the landing gear extends.

2 AUTOBRAKE Selector

OFF – deactivates and resets the autobrake system.

DISARM –

• disengages the autobrake system

• releases brake pressure.

1, 2, 3, 4, MAX AUTO – selects the desired deceleration rate.

RTO – automatically applies maximum brake pressure when the thrust levers are

retarded to idle above 85 knots.

GND PROX

G/S FLAP GEAR

G/S INHB

GND

PROX

OVRD OVRD

RETRACT

270K-.82M

UP

DN

ALTN

GEAR

NORM

DOWN

EXTEND

270K-.82M

LOCK

OVRD

12

3

4

MAX

AUTO

DISARM

OFF

RTO

AUTOBRAKE

OVRD

TERR

OVRD

CENTER FORWARD PANEL

1

2

3

4


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3 Alternate Gear (ALTN GEAR) Switch

NORM – the landing gear lever operates normally.

DOWN – the landing gear extends by the alternate extension system.

Note: Alternate extension may be selected with the landing gear lever in any

position.

4 Landing Gear Lever Lock Override (LOCK OVRD) Switch

Push – releases the landing gear lever lock.

Nose Wheel Steering Tiller

1 Nose Wheel Steering Tiller

Rotate –

• turns the nose wheels up to 70 degrees in either direction

• overrides rudder pedal steering

• main gear aft axle steering is slaved to nose wheel steering.

2 Tiller Position Indicator

Shows tiller displacement from the straight–ahead, neutral position.

LEFT AND RIGHT SIDEWALLS

1

2


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Brake System

Rudder/Brake Pedals

1 Rudder Pedal Adjust Crank

Adjusts the rudder pedals forward or aft.

Note: To avoid inadvertent rudder pedal movement, the crank handle should be

stowed when not in use.

2 Rudder/Brake Pedals

Push the full pedal –

• turns the nose wheel up to 7 degrees in either direction

• does not activate main gear steering.

Push the top of the pedals – actuates the wheel brakes. Parking Brake Lever

1

2

PULL

BRAKE

PARKING

CONTROL STAND

1


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1 Parking Brake Lever

Pull – sets the parking brake when both brake pedals are simultaneously

depressed.

Release – simultaneously depress both brake pedals.

Brake Accumulator Pressure Indicator

1 BRAKE SOURCE Light

Illuminated (amber) – both active brake hydraulic sources (right and

center/reserve hydraulic systems) have low pressure.

2 BRAKE ACCUMULATOR PRESSURE Indicator

Indicates brake accumulator pressure.

Landing Gear System Indications

Landing Gear Position Indications

SOURCE

BRAKE

3

2 1

0

4 BRAKEACCUM

PSI X

00

1

LEFT FORWARD PANEL

1

2

DOWN

GEAR

GEAR DNDN

EICAS DISPLAY

1

2


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1 Gear Position Indication (Normal Display)

DOWN (green) – all landing gear are down and locked.

Crosshatched (white) – one or more landing gear are in transit.

UP (white) – all landing gear are up and locked (blanks after 10 seconds).

Empty box (white) – all landing gear position indicators are inoperative.

2 Expanded Gear Position Indication (Non–Normal Display)

DN (green) – the associated landing gear is down and locked.

Crosshatched (white) – the associated landing gear is in transit.

UP (white) – the associated landing gear is up and locked.Empty box(es) (white) – the associated landing gear position indicators are

inoperative.


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Gear Synoptic Display

The landing gear synoptic is displayed by pushing the GEAR synoptic display

switch on the display select panel. Display select panel operation is described in

Chapter 10, Flight Instruments, Displays.

[Option – Tire Pressure Indication]

1 Brake Temperature

Indicates a relative value of wheel brake temperature:

• values range from 0.0 to 9.9

• white – normal range

• amber – high range.

2 Brake Symbol

Blank box indicates any brake less than 3.0.

Solid white box indicates hottest brake on each main gear within range of 3.0 to

4.9.

Solid amber box indicates brake overheat condition on each wheel within range of

5.0 to 9.9.

3 Gear Door Status

Crosshatched – the door is not closed.

CLOSED (white) – the door is closed.

CLOSEDDOOR

160 160

160160

160160

160 160

160160

160160

BRAKE0.0

2.4

3.4

3.1

3.3

2.8

2.2

ASKID

1.7

8.3

7.1

ASKID

3.3

2.8

DOOR

160 160

MULTIFUNCTION DISPLAY

1

2

3

4

5


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Empty box(es) (white) – the associated landing gear door position indicators are

inoperative.

4 Fault Indication (amber)BRAKE – indicates brake deactivation on the associated wheel.

ASKID – indicates antiskid fault on the associated wheel.

5 Tire Pressure Indication

Displays individual tire pressures:

• white – normal range

• amber – abnormal high or low range.


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B777 Landing Gear

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