B777
Landing Gear
DO NOT USE FOR FLIGHT
Boeing B777 - Systems Summary [Landing Gear]
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 autobrake
system 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 retract
into 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.
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Boeing B777 - Systems Summary [Landing Gear]
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 EICAS
advisory 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. The
downlocks 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 alternate
extension, 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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Boeing B777 - Systems Summary [Landing Gear]
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 rotation
about 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:
• antiskid protection
• normal brake hydraulic system
• autobrake system
• alternate/reserve brake
hydraulic system
• parking brake.
• brake accumulator
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.
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Boeing B777 - Systems Summary [Landing Gear]
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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Boeing B777 - Systems Summary [Landing Gear]
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 one
axle 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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Boeing B777 - Systems Summary [Landing Gear]
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 the
BRAKE 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 BRAKE
SET 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.
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Boeing B777 - Systems Summary [Landing Gear]
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.
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Boeing B777 - Systems Summary [Landing Gear]
Landing Gear EICAS Messages
The following EICAS messages can be displayed.
Note: Configuration warning messages are covered in Chapter 15, Warning
Systems.
Brakes
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.
Landing Gear
Message
Level
Aural
GEAR DISAGREE Caution
Beeper
GEAR DOOR
Advisory
MAIN GEAR
BRACE L, R
Caution
MAIN GEAR
STEERING
Advisory
Condition
Gear position disagrees with landing gear
lever position.
One or more gear doors are not closed.
Beeper
Affected main gear is down with one brace
unlocked.
Main gear steering is unlocked when
centered.
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Boeing B777 - Systems Summary [Landing Gear]
Tail Skid
[777-300 and 777-300ER]
Message
TAIL SKID
Level
Aural
Advisory
Condition
Tail skid position disagrees with landing
gear lever position.
Tires
[Option]
Message
TIRE PRESS
Level
Advisory
Aural
Condition
One or more tire pressures are not normal.
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Boeing B777 - Systems Summary [Landing Gear]
14.10 Landing Gear-Controls and Indicators
Landing Gear Panel
G/S
GND PROX
FLAP
GEAR
GND
PROX
OVRD
OVRD
G/S INHB
RETRACT
270K-.82M
TERR
OVRD
LOCK
OVRD
UP
OVRD
ALTN
GEAR
NORM
1
4
DN
EXTEND
270K-.82M
DOWN
3
AUTOBRAKE
DISARM
1
2
3
4
MAX
AUTO
OFF
RTO
2
CENTER FORWARD 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.
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Boeing B777 - Systems Summary [Landing Gear]
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
2
LEFT AND RIGHT SIDEWALLS
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.
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Boeing B777 - Systems Summary [Landing Gear]
Brake System
Rudder/Brake Pedals
1
2
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
PARKING
BRAKE
PULL
1
CONTROL STAND
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Boeing B777 - Systems Summary [Landing Gear]
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
BRAKE
SOURCE
1
4 BRAKE
3
2
ACCUM
0
0
PS
I X 10
2
1
LEFT FORWARD PANEL
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
1
DOWN
GEAR
2
DN GEAR DN
EICAS DISPLAY
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Boeing B777 - Systems Summary [Landing Gear]
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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Boeing B777 - Systems Summary [Landing Gear]
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]
160
DOOR
1
7.1
ASKID
3.3
2
160
CLOSED
3.1
160
160 BRAKE
0.0
ASKID
1.7
3.3
160
160 2.4
8.3
2.8
160
160
160
160 2.2
160
160
160
160
4
5
2.8
3
3.4
DOOR
MULTIFUNCTION DISPLAY
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.
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Boeing B777 - Systems Summary [Landing Gear]
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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