LANDING GEAR ALTERNATE EXTENSION SYSTEM -LG DOOR UNSAFE LIGHTS -FUNCTIONAL DESCRIPTION
General
The landing gear door unsafe lights come on when a landing gear door is open and the safety valve in the landing gear door release/safety valve module is in the NORMAL position.
Inputs
The 28v dc hot battery bus supplies power for operation of the landing gear door unsafe lights.
The safety latch position sensing switch in the door release/ safety valve modules supply safety valve position inputs.
The door closed switches supply landing gear door position inputs.
Press-To-Test
The nose landing gear press-to-test switch lets you do a test of the nose landing gear unsafe light when the nose gear door is open and the safety valve is SAFE.
The main landing gear press-to-test switch lets you do a test of both main landing gear unsafe lights when the main landing gear doors are open and the safety valves are SAFE.
Training Information Point
During normal operation of the landing gear extension-retraction system, the safety valves in the door release/safety valve modules are in the NORMAL positions. The LG door unsafe lights turn on while the LG doors are open during normal landing gear extension and retraction.
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LANDING GEAR ALTERNATE EXTENSION SYSTEM -FUNCTIONAL DESCRIPTION -ELECTRICAL
General
A switch on the P2 center instrument panel or switches on the wheel well electrical service panel (P56) start alternate extend power pack operation.
Alternate Extension System Operation
The alternate gear switch is a two position (NORM and DOWN) guarded toggle switch. It is a momentary switch and is spring-loaded to NORM.
When you push the alternate gear switch, the alternate extend control relays in ELMS energize. These relays have a latching circuit which keep them energized after you release the alternate gear switch.
The relays permit power from the hot battery bus to go to the alternate extend power pack.
The alternate extend power pack comes on and supplies hydraulic pressure for alternate extend operation.
After all doors and gear are unlocked, the alternate extend hydraulic pressure increases. At 2100 psi, the alternate extend hydraulic pressure switch opens and removes electrical power in the latching circuits for both alternate extend control relays. This removes electrical power from the alternate extend power pack.
EFFECTIVITY
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Ground Door Operation
Ground door operation is almost the same as operation with the alternate gear switch.
The only difference is that you use the switches on the P56 panel to power the alternate extend control relays.
Indications
The PSEUs monitor the alternate extend control relays.
When you operate the alternate extend switch or the ground door release switches, the gear display on the EICAS expands to the multi-symbol display. The multi-symbol display shows the position of each gear. The display remains expanded until all landing gear doors are closed.
The position of each door shows on the landing gear synoptic display. The GEAR DOOR advisory message shows on the EICAS when the alternate extension system is energized. The GEAR DOOR advisory message stays displayed until all of the doors close.
If either or both relays are energized for more than 60 seconds, the ALTN GEAR EXTEND message shows on the status display. Since the normal alternate extension cycle is less than 60 seconds, this indicates a system fault.
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LANDING GEAR ALTERNATE EXTENSION SYSTEM -FUNCTIONAL DESCRIPTION -ELECTRICAL
Training Information Point
To manually remove power from the alternate extension system, you pull the LDG GR ALTN EXT MOT circuit breaker on the P11 panel. This circuit breaker controls the LDG GR ALTN EXT MOT REMOTE circuit breaker on the P310 standby power management panel.
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LANDING GEAR ALTERNATE EXTENSION SYSTEM -FUNCTIONAL DESCRIPTION -HYDRAULIC 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：777 AMM 飞机维护手册 起落架 Landing Gear(27)
