AIRPLANE
OPERATIONS
MANUAL
LANDING GEAR AND
BRAKES
REVISION 38
2-12-05
Page
3
Code
01
AOM-145/1114
LANDING GEAR OPERATION
Landing gear retraction and extension are powered by the hydraulic
system 1. An accumulator prevents pressure fluctuations and assists
gear retraction after takeoff. The main landing gear legs retract
inboard, while the nose landing gear retracts forward. Each main gear
leg is mechanically linked to its respective door, which remains open
when the gear is down. The doors close automatically when the main
landing gear is retracted. The nose landing gear doors are
hydraulically actuated and operate in sequence with the nose gear.
Gear retraction and extension are electrically commanded. If normal
extension fails, the landing gear can be extended through an electrical
override system. If the electrical override is not available, a free-fall
system allows gear extension. Gear position is indicated on the EICAS
display.
LANDING GEAR RETRACTION
Landing gear retraction is commanded through the Landing Gear
Lever, installed on the main panel. Positioning the lever to the UP
position signals the LGEU to command the Nose Gear Door Solenoid
Valve and the Landing Gear Electrovalve. This allows pressure from
the hydraulic system 1 to simultaneously reach landing gear and down
unlock actuators. All gear legs are then retracted into their respective
wheel wells.
The LGEU logic only allows the nose gear doors to close after the
nose landing gear is locked in the UP position. When the uplock boxes
are actuated, the proximity switches signal the LGEU that the gear is
up and locked and that the Landing Gear Electrovalve may be
deenergized. Nose landing gear door actuators are kept pressurized,
but the gear actuator lines are connected to the return.
To preclude an inadvertent retraction command while on the ground,
the air/ground system provides a signal to a solenoid inside the
Landing Gear Lever. This locks the lever and prevents movement
towards the UP position. For emergency purposes only, a lock release
button is provided beside the lever, allowing this protection to be
overriden.
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