(6)
The override/jettison pumps produce a higher fuel outlet pressure than the main tank boost pumps. When a fuel crossfeed valve is opened, fuel from the center wing tank overrides the fuel supplied by the boost pumps and is delivered to the engines.
(7)
Crossfeed valve positions are monitored by valve position logic cards, which send valve-open or valve-closed signals to EICAS through the FSEIC. Valve symbols on the EICAS fuel synoptic change position to indicate that the valves are open.
(a)
If the position of a fuel crossfeed valve disagrees with its commanded position, a FUEL X FEED advisory message is displayed on the EICAS main screen and a status message is recorded.
(8)
The No. 1 and 4 engine crossfeed valves are opened before a flight by switches on the fuel managment panel, P5. The No. 1 and 4 crossfeed valves are controlled by the flight compartment switches only. These valves are not controlled automatically.
(a)
During flight, the EICAS advisory message, >FUEL TANK/ENG, will show when the center wing tank and reserve tanks are empty and the main tanks have equal fuel quanities. This message advises the flight crew to close the crossfeed valves.
(b)
If the No. 1 and 4 valves are closed and the main tank fuel quantities are not equal, the EICAS advisory message >X FEED CONFIG will show.
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A
747-400
MAINTENANCE MANUAL
(9)
The No. 2 and 3 engine crossfeed valves are opened before a flight by switches on the fuel management panel, P5. The No. 2 and 3 crossfeed valves are either manually or automatically controlled. Manual operation is controlled by the flight compartment crossfeed valve switch. Automatic operation controls the valves once the valves are opened manually. Because the No. 2 and 3 crossfeed valves are not manually closed during a flight, the switches have a plastic guard cover over them.
(a)
Manual Control
______________ When the airplane is on the ground and the flaps are not in the takeoff position the fuel crossfeed switch on the fuel management panel, P154, controls the operation of the crossfeed valve.
NOTE: The flap control lever in the flight compartment has
____
several flap position detents.
The flaps extended for takeoff positions are: 10 or 20 (> 7.5 and < 22.5 units).
The flaps not extended for takeoff positions are: UP, 1, 5, 25, or 30 (0-7.5 or 22.5-30 units).
(b)
Automatic Control
_________________ After the No. 2 and 3 crossfeed valves are manually opened, the open/close function of the valves are controlled by the fuel system management cards (FSMC). The FSMC uses flap position and air/ground inputs to supply the logic for the crossfeed close command. When the logic for the crossfeed close command is satisfied, power is supplied to the crossfeed valve auto control relays. The engerized auto control relays cause the No. 2 and 3 crossfeed valves to close. When the crossfeed close command is not active, the power is removed from the auto control relays, and the valves open.
(c)
No. 2 and 3 Crossfeed Valve Operation
_____________________________________
1) On the ground, the No. 2 and 3 crossfeed valves are manually opened. With the flaps not in the takeoff position, (0 to 7.5 units or 22.5 to 30 units) the crossfeed valves remain open.
2) Before takeoff, the flaps are put in the takeoff position. With the flaps in the takeoff position, the logic for the crossfeed close command is satisfied. The No. 2 and 3 crossfeed valves are commanded closed. This is done to seperate the fuel-feed supplies to each engine during the critical, high fuel flow, takeoff section of the flight.
3) After takeoff, a software latch keeps the No. 2 and 3 crossfeed valves closed until the flaps are retracted. When the flaps are retracted, the crossfeed valves are commanded open.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
28-22-00
ALL ú ú 01 Page 18 ú Jun 10/95
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本文链接地址：747-400 AMM 飞机维护手册 燃油 FUEL 2(68)
