FUEL JETTISON -FUNCTIONAL DESCRIPTION -FUEL FLOW
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FUEL JETTISON -FUNCTIONAL DESCRIPTION -POWER & CONTROL
Power
The left fuel jettison pump receives 115v ac power from the left main bus.
Jettison Pump Control -Ground
When the airplane is on the ground, the ELMS electronics unit turns on the fuel jettison pumps when you put the jettison ARM switch in the ARM position.
The jettison arm switch sends a signal on the systems ARINC 629 buses to the ELMS electronics unit in the left power management panel. Pump logic in the ELMS electronics unit sends a command to an ELCU in the left power panel to turn on the left fuel jettison pump. The pump logic also sends a signal to turn on the right fuel jettison pump. The ELCU closes a contactor to permit power to go from the left main bus to the pump. The ELCU receives power from the left main dc bus.
The pump control logic in the P210 panel can also turn on the left fuel jettison pump.
Jettison Pump Control -Air
When the airplane is in the air, the ELMS electronics unit turns on the fuel jettison pumps, when all of these conditions occur:
*
Jettison arm switch is in the ARM position
*
Left or right jettison nozzle valve is open
*
Fuel quantity is more than the fuel-to-remain value.
Fault Indication
The jettison pump has a pressure switch to check for low pressure at the pump outlet. The jettison pump pressure switch closes when there is low pressure. The ELMS logic sends a signal through OPAS to turn on the fault light in the arm switch. The fault light comes on only when the system is armed.
An EICAS status message tells you which pump is defective.
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FUEL JETTISON -FUNCTIONAL DESCRIPTION -POWER & CONTROL
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FUEL JETTISON -FUNCTIONAL DESCRIPTION -ISOLATION AND NOZZLE VALVE CONTROL
Fuel Jettison Isolation Valve
The left main dc bus supplies power to open and close the left fuel jettison isolation valve. Valve logic in two ELMS electronics units (P110 or P210) controls the left and right jettison isolation valve control relays. The relay energizes to open the isolation valve.
When the airplane is on the ground, the ELMS electronics units open the isolation valves when the jettison arm switch is on.
The ELMS electronics units open the isolation valves in the air when these conditions are met:
*
Jettison arm switch is on
*
Left or right jettison nozzle valve is open
*
Fuel quantity is greater than fuel-to-remain.
Fuel Jettison Nozzle Valve
The left main dc bus supplies power to open and close the nozzle valve. Power goes through an air/ground relay.
The nozzle valve does not open when the airplane is on the ground.
When the airplane is in the air, the nozzle valve opens when the jettison system is armed and you push the nozzle switch.
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FUEL JETTISON -FUNCTIONAL DESCRIPTION -ISOLATION AND NOZZLE VALVE CONTROL
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777 AIRCRAFT MAINTENANCE MANUAL
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FUEL JETTISON -OPERATION
General
You can use the jettison system in the air to dump fuel overboard. The airplane must be in air mode for the jettison nozzle valves to open. If the airplane is in ground mode when you arm the jettison system, the main tank fuel jettison pumps and the jettison isolation valves operate immediately.
Jettison
This is a brief description of jettison system operation when the airplane is in the air mode:
*
Push the ARM switch
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