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selector valve to the MLG transfer cylinders and MLG downlock
actuators. The transfer cylinders stroke. This delays full
pressurization to the MLG actuators until the downlock
actuators unlock the downlock mechanism. After the
downlocks unlock, pressure increases in the head end of the
MLG actuators and they extend to retract the landing gear.
As the landing gear gets to the up position, the restrictor
decreases the flow of fluid that goes into the head end of the
retract actuators. The roller on the MLG strut touches the uplock
hook and turns the hook and uplock mechanism to the locked
position. This locks the MLG in the retracted position.
The landing gear lever is moved to the OFF position and the
normal landing gear hydraulic system is depressurized.
Extension
This is the extension sequence for the main landing gear:
* Landing gear control lever moved to DOWN
* Uplock actuator retracts
* Uplock mechanism unlocks
* Main landing gear actuator retracts
* Main landing gear extends
* Downlock actuator retracts
* Downlock mechanism locks.
When the landing gear control lever is in the DOWN position,
hydraulic pressure pressurizes the MLG down lines through the
selector valve to the MLG transfer cylinders and MLG downlock
actuators. The transfer cylinders stroke. This delays full
pressurization to the MLG actuators until the uplock actuators
unlock the uplock mechanism. After the uplocks unlock,
pressure increases in the rod-end of the MLG actuators and
they retract. The landing gear extends by actuator force, landing
gear weight, and airloads.
As the landing gear gets to the down position, the restrictor
decreases the flow of fluid that leaves the head-end of the
retract actuators. The downlock actuators and downlock springs
move the downlock mechanism to the locked position to lock
the MLG in the extended position.
When the landing gear lever is in the DOWN position, the
downlock actuators, retract actuators, and transfer cylinders
remain pressurized.
MLG EXTENSION AND RETRACTION - OPERATION
EFFECTIVITY
GUN ALL 32-32-00
Page 4
D633A101-GUN Oct 10/2002
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
32-32-00-002
MLG EXTENSION AND RETRACTION - OPERATION
MLG EXTENSION AND RETRACTION - OPERATION
EFFECTIVITY
GUN ALL 32-32-00
Page 5
D633A101-GUN Feb 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
32-32-00-002
Purpose
The main landing gear actuator with a walking beam applies a
force to the landing gear trunnion to retract and extend the main
landing gear.
Location
The main landing gear actuator is outboard of the main landing
gear shock strut. The head end attaches to a beam hanger and
walking beam pivot on the wing structure outboard of the shock
strut. The rod end attaches to a fitting on the main landing gear
shock strut at the trunnion.
Physical Description
The main landing gear actuator is a double-acting, unbalancedtype
actuator. It contains an internal, variable orifice slide/
sleeve snubber in the head-end to control the rate of the gear.
The hydraulic connections to the actuator are different sizes.
This prevents incorrect connection of the hydraulic hoses when
you remove and replace the actuator.
The actuator weighs 42 pounds (19 kg).
Functional Description
The actuator and walking beam work together to raise and
lower the main landing gear. The walking beam decreases the
force that goes to the structure during actuator operations.
When the main gear retracts, the inboard force from the
actuator rod end is applied directly to the gear. The outboard
reaction force from the cylinder of the actuator is transmitted to
the shock strut through the walking beam. Action and reaction
forces combine together and provide the power to raise the
gear. The reaction force that results rotates the gear aroaund its
trunnion axis. Forces caused by the rotation are transmitted to
the structure through the beam hanger.
During extension, the forces operate in the opposite direction to
extend the gear.
The restrictor on the up pressure port of the actuator decreases
the flow of fluid from the actuator to 8 gpm (30 lpm) during gear
extension. This prevents an uncontrolled main landing gear
extension when a hydraulic hose or tube fails. The check valve
permits full flow into the actuator during landing gear retraction.
Training Information Point
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