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system. This stops wheel rotation during main landing gear
retraction.
See the Wheels and Brakes section for more information about
the gear retract brake system. (SECTION 32-41)
MLG EXTENSION AND RETRACTION - FUNCTIONAL DESCRIPTION
EFFECTIVITY
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MLG EXTENSION AND RETRACTION - FUNCTIONAL DESCRIPTION
MLG EXTENSION AND RETRACTION - FUNCTIONAL DESCRIPTION
EFFECTIVITY
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General
Hydraulic system A usually supplies pressure to extend and
retract the nose landing gear. Hydraulic system B supplies
alternate pressure for retraction only. The landing gear transfer
valve controls the pressure source of hydraulic system A or
hydraulic system B to supply the nose landing gear.
The landing gear selector valve supplies down or up pressure
to extend or retract the nose landing gear. The landing gear
control lever operates the landing gear selector valve.
WARNING: MAKE SURE ALL PERSONS AND EQUIPMENT ARE
CLEAR OF THE NOSE LANDING GEAR. FAST
MOVEMENT OF THE NOSE LANDING GEAR CAN
CAUSE INJURY TO PERSONS AND DAMAGE TO
EQUIPMENT.
CAUTION: DO NOT TURN THE STEERING WHEEL WHEN THE
SHOCK STRUT OF THE NOSE LANDING GEAR IS
FULLY EXTENDED. YOU CAN CAUSE DAMAGE TO
THE CENTERING CAMS IN THE SHOCK STRUT IF
YOU DO THIS.
Pressure also goes to the nose wheel steering system. This
allows for nose wheel steering rotation.
See the Nose Wheel Steering section for more information
about nose wheel steering. (SECTION 32-51)
Components
These are the components of the nose landing gear extension
and retraction system:
* Nose landing gear actuator
* Lock actuator
* Lock mechanism
* Bungee spring
* Valve manifold
* Transfer cylinder
* Fuse (2).
NLG Actuator
The nose landing gear actuator supplies the force to retract and
extend the nose landing gear.
Lock Mechanism and Lock Actuator
The NLG lock mechanism locks the NLG in the extended or the
retracted position. Two bungee springs keep the lock links in
this positions.
The lock actuator unlocks and locks the gear during extension
and retraction.
Valve Manifold
The valve manifold controls extension and retraction hydraulic
fluid to the lock actuator.
NLG EXTENSION AND RETRACTION - GENERAL DESCRIPTION
EFFECTIVITY
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Transfer Cylinder
The transfer cylinder gives a time delay to let the nose landing
gear unlock before the nose gear actuator moves the gear.
NLG EXTENSION AND RETRACTION - GENERAL DESCRIPTION
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
32-33-00-001
NLG EXTENSION AND RETRACTION - GENERAL DESCRIPTION
NLG EXTENSION AND RETRACTION - GENERAL DESCRIPTION
EFFECTIVITY
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32-33-00-001
Retraction
This is the retraction sequence for the nose landing gear:
* Landing gear control lever moved to UP
* Lock actuator retracts
* Lock mechanism unlocks
* Nose landing gear actuator extends
* Nose landing gear retracts
* Lock actuator continues to retract
* Lock mechanism locks
* Landing gear control lever moved to OFF.
When the landing gear control lever is in the UP position,
hydraulic pressure pressurizes the NLG up lines through the
selector valve to the NLG transfer cylinder and NLG lock
actuator. The transfer cylinder stroke delays full pressurization
to the NLG actuator until the lock actuator unlocks the NLG lock
links. After the lock links are unlocked, pressure increases in
the head-end of the NLG actuator and it extends. This retracts
the NLG landing gear.
As the NLG landing gear gets the up position, the restrictor
decreases the flow of fluid that goes to the head-end of the NLG
　
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