ENGINE FUEL FEED -FUNCTIONAL DESCRIPTION -CROSSFEED VALVE CONTROL
Control
The crossfeed valve switches on the P5 directly control the crossfeed valves. A 28v dc bus supplies power to the crossfeed valve actuator. When you push the switch, you supply power through the limit switches to the actuator. The actuator moves the valve to the commanded position. When the valve is in the commanded position, the limit switches remove power from the actuator and send power to the ELMS valve agree status logic.
Fault Indications
The VALVE light comes on to show the related valve is in transit, or a valve disagree fault exists. The light comes on when the valve position disagrees with the switch position. The ELMS controls the light. An EEU sends a valve disagree message to the OPAS to cause the OPAS to turn on the light.
If the valve disagree condition exists for more than 10 seconds, the ELMS sends a fault signal to the AIMS. The AIMS shows the related EICAS advisory and status messages.
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ENGINE FUEL FEED -OPERATION
Fuel Panel
The fuel panel is on the P5 overhead panel. It has alternate-action switches that control the fuel pumps and the crossfeed valves.
Each fuel pump switch has two indication lights. The ON light is on when the switch is on. The pressure light comes on when there is low pressure at the pump outlet.
Crossfeed Valve Switches
Each crossfeed valve switch has two indication lights. The flowbar light is on when the switch is on. The VALVE light comes on when there is disagreement between switch and valve positions.
Normal Operation
Normally all pump switches are on at the beginning of a flight. The center tank supplies fuel to the engines. When the center tank is empty, you turn off the override/jettison pumps.
Crossfeed
You supply fuel to an engine from the opposite tank through the crossfeed valve(s) to correct an imbalance between the main tanks. You open a crossfeed valve and turn off the boost pumps in the tank that has less fuel.
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ENGINE FUEL FEED -OPERATION
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ENGINE FUEL FEED -INDICATIONS
Fuel Synoptic Display
The fuel synoptic display is a simplified schematic of the fuel system. It shows the system configuration for these components:
*
Override/jettison pumps
*
Boost pumps
*
Spar valves
*
Crossfeed valves
The fuel synoptic display also shows fuel quantity.
The configuration in the fuel synoptic display below shows the center tank empty and the boost pumps feeding the engines from the main tanks. The crossfeed valves are closed and the spar valves are open.
Fuel Management Maintenance Page
The fuel management maintenance page shows the commanded and actual status for the fuel system components.
Training Information Point
The ENG S/O VLV data tell you about the spar valves. The AC PUMP data tell you about the left forward boost pump. The VLV 1 data tell you about the forward crossfeed valve. The VLV 2 data tell you about the aft crossfeed valve.
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BOEING PROPRIETARY -Copyright # -Unpublished Work -See title page for details.
APU FUEL FEED -INTRODUCTION
Purpose
The APU fuel feed system normally supplies fuel to the APU. It can also supply fuel to the left engine when there is no pressure in the left engine feed manifold and the left engine is not operating.
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APU FUEL FEED -GENERAL DESCRIPTION
General
The APU fuel feed system supplies fuel to the APU during APU operation. Fuel comes from the fuel pumps (not shown) or the APU dc fuel pump. Power and control come from the ELMS.
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