777 AIRCRAFT MAINTENANCE MANUAL
PFCS -AUTOPILOT -FUNCTIONAL DESCRIPTION
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PFCS -FLIGHT CONTROL SHUTOFF VALVES -LOCATION
Purpose
The flight control shutoff valves (SOV) permit the maintenance technicians to stop hydraulic power to the primary flight control actuators.
When 28v dc power is available, the flight control SOVs for the left and right systems can operate in the air or on the ground. The flight control SOVs for the center system can operate only on the ground.
Location
The flight control SOVs for the left hydraulic system are on the left wing, aft of the rear spar, and inboard of the left flaperon. The wing SOV is outboard of the tail SOV.
The flight control SOVs for the center hydraulic system are on the aft bulkhead of the left landing gear wheel well. The tail SOV is the top one, the wing SOV is the bottom one.
The wing shutoff valve for the right hydraulic system is on the right wing, aft of the rear spar, and inboard of the right flaperon.
The tail shutoff valve for the right hydraulic system is on the ceiling of the right landing gear wheel well, near the aft bulkhead.
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PFCS -FLIGHT CONTROL SHUTOFF VALVES -LOCATION
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PFCS -FLIGHT CONTROL SHUTOFF VALVES -PHYSICAL DESCRIPTION
Physical Description
There are six identical valves on the airplane.
Each valve is a two position, two way, ball valve operated by a 28v dc electric motor. The valve has a lever that shows the position of the valve. The maintenance crew may move the lever to operate the valve by hand.
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PFCS -FLIGHT CONTROL SHUTOFF VALVES -PHYSICAL DESCRIPTION
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PFCS -FLIGHT CONTROL SHUTOFF VALVES -CONTROLS AND DISPLAYS
Controls
The control switches for the flight control SOVs are on the P61 overhead maintenance panel.
There are six guarded toggle switches. Three are for the tail SOVs and three are for the wing SOVs.
Each toggle switch has two positions, NORM and SHUTOFF. In the NORM position, the switch commands the valve to open. In the SHUTOFF position, the switch commands the valve to close.
Displays
Below each toggle switch, there is an amber VALVE CLOSED light. The light shows when the valve is not open.
An advisory message FLT CONTROL VALVE shows on the EICAS display when one or more flight control shutoff valves are not open.
Training Information Point
After the third tail flight control SOV is closed during maintenance operations, there can be an uncommanded movement of the rudder and/or elevator until the residual hydraulic pressure trapped between the SOVs and the power control units (PCUs) bleeds down.
If a command is made to move the rudder or elevator while the residual hydraulic pressure is high, the related control surface can move rapidly.
For any maintenance action that requires closure of the tail flight control SOVs, do at least one of these:
*
Keep all personnel and equipment clear of the rudder and elevator sweep areas for at least one minute after the third tail flight control SOV closes to let the surface move and stop
*
Depressurize all the hydraulic systems before you close the tail flight control SOVs to prevent control surface movement.
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PFCS -FLIGHT CONTROL SHUTOFF VALVES -CONTROLS AND DISPLAYS
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PFCS -FLIGHT CONTROL SHUTOFF VALVES -FUNCTIONAL DESCRIPTION
General
This description is for the tail flight control SOV for the center system. The other flight control SOVs operate in a similar manner. This does not include the left and right SOVs which do not use air/ground signals.
The 28v dc left and right main buses supply power to the flight control SOVs.
Functional Description
The valve has two positions: open and closed. A 28v dc electric motor opens and closes the valve. Two limit switches stop power to the motor at the end of the valve movement. A position indicating switch sends a signal to the HYDIM cards when the valve leaves the open position. This switch stops the signal to the HYDIM cards when the valve is fully open. 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 飞行操纵 Flight Controls 1(13)
