F.
Alternate Uplock Release Actuator (Fig. 5 and 6)
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SEE A
MAIN LANDING GEAR WHEEL WELLS (OUTBOARD WALL)
ALTERNATE UPLOCK RELEASE ACTUATOR
INBD
A
Main Landing Gear Alternate Uplock Release Actuator Figure 5
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(1)
The alternate uplock release actuator is a piston-type actuator that operates hydraulically in one direction. The piston is spring-loaded to go back to the normally retracted position when hydraulic pressure is removed. The main landing gear actuator supplies the force to move the uplock hook to release the landing gear from the up and locked position. The nose landing gear actuator supplies the force to move the lock links from the overcenter position. This releases the nose landing gear from the up and locked position.
(2)
There is one alternate uplock release actuator for each landing gear. Each main landing gear actuator is installed on the uplock assembly. The uplock assembly is found on the outboard fairing of the wheel well for the main landing gear. The nose landing gear actuator is installed on the ceiling of the wheel well for the nose landing gear above the landing gear trunnion.
SEE A
FWD
NOSE LANDING GEAR WHEEL WELL (AFT WALL) RELEASE ACTUATOR ALTERNATE UPLOCK
A
Nose Landing Gear Alternate Uplock Release Actuator
Figure 6
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G. Alternate Extension Hydraulic Shuttle Valve (Fig. 6A)
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(1)
The alternate-extension-hydraulic-shuttle valve (Fig. 6A) is a two-position shuttle valve. It is installed in the landing gear "up" line between the landing gear selector valve and the normal extension system mechanisms. The valve position during normal system operation permits the flow of fluid in the landing gear retraction "up" line. When alternate extension is started, hydraulic pressure for alternate extension changes the position of the shuttle valve. This the sends normal system "up" line fluid to return. This permits alternate extension to occur without the hydraulic system pressure removed. This condition occurs when the position of the landing gear selector valve cannot be changed from the "up to the "down" position. When the position of the valve is changed the higher (3,000) psig normal system up pressure is removed from the normal system uplock mechanisms. This permits the lower (2250) psig alternate extension pressure to operate the landing gear doors and landing gear through the alternate extension release mechanism.
H.
Hydraulic Pressure Switch (Fig. 7)
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(1)
A pressure switch is installed in the hydraulic line for the alternate extension system. The switch is used to control the time of operation for the power pack in the alternate extension system. After hydraulic pressure has extended the door lock release and the alternate uplock release actuators, the landing gear and doors are released. When this occurs the pressure in the system starts to increase. When the pressure switch receives an input of 1700-2200 psi, the switch operates to remove electrical power from the power pack. If the system does not stop in 30 seconds, a LDG GEAR MONITOR message will show on EICAS.
(2)
The pressure switch is installed on a bracket at the top of the wheel well for the nose landing gear.
I.
Door Closed and Locked Switches (Fig. 8 and 9)
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(1) The door closed switch is a mechanical plunger-type switch. It is used to supply an input when the landing gear door is open. The switch operates directly by movement of the door. When the door opens, the plunger extends and the switch turns on a red door not safe light. This light is used to tell persons that the door is not in a safe condition. There is one switch for each landing gear door. The door switch for the main landing gear is installed near the forward end of the outboard wall of the wheel well for the main landing gear. The door switch for the nose landing gear is installed on the forward wall of the wheel well for the nose landing gear.
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SEEA 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：757 AMM 飞机维护手册 起落架 CHAPTER 32 - LANDING GEAR 2(91)
