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engines 3 and 4.
The FSMCs open the reserve transfer valves when main tank 2 or 3 fuel quantity
decreases to 18,140 kilograms. Fuel transfers from reserve tanks 2 and 3 to the
related main tank.
The electrical CWT scavenge pump is automatically activated. Each activation
terminates after 120 minutes, or no pressure, whichever occurs first.
The EICAS message FUEL TANK/ENG displays when main tank 2 quantity is
equal to or less than main tank 1 quantity, or when main tank 3 quantity is equal
or less than main tank 4 quantity. The override pump switches and crossfeed valve
switches 1 and 4 are pushed off after confirming tank quantities. Main pumps
provide fuel to their related engine until engine shutdown.
Note: On the ground, the FUEL TANK/ENG message can be displayed with as
much as 500 kilogramsmore fuel in an inboardmain tank than the adjacent
outboard main tank.
OperationWith No Fuel in Center Wing Tank
With no fuel in center wing tank, the FSMCs activate override/jettison pumps 2
and 3. The FSMCs close crossfeed valves 2 and 3 when the flaps extend to takeoff
position on the ground. Override/jettisons pumps 2 provide fuel to engine 1 and
override/jettison pumps 3 provide fuel to engine 4. Main pumps 2 and 3 provide
fuel to their related engine.
April 01, 2001
747 Operations Manual
Fuel -
System Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 12.20.9
The FSMCs open crossfeed valves 2 and 3 when the flaps are retracted.
Override/jettison pumps 2 provide fuel to engines 1 and 2 and override/jettison
pumps 3 provide fuel to engines 3 and 4. Reserve fuel transfer and tank-to-engine
configuration are identical to operating with fuel in the CWT.
Note: On the ground, the FUEL TANK/ENG message can display with as much
as 500 kilograms more fuel in an inboard main tank than the adjacent
outboard main tank.
Fuel Jettison
The fuel jettison system allows jettison from all fuel tanks. Override/jettison
pumps in main tanks 2 and 3 and the center wing tank pump fuel overboard
through the jettison nozzle valves.
Fuel jettison is initiated by rotating the fuel jettison selector to A or B. When a
jettison control system is selected, the fuel temperature indication on EICAS is
replaced with the fuel to remain quantity indication. The jettison manifold and
jettison time display on the fuel synoptic.
Rotating the Fuel To Remain selector decreases or increases the fuel to remain
quantity.
Pushing either fuel jettison nozzle valve switch ON activates all override/jettison
and transfer/jettison pumps in the tanks containing fuel (pump switches must be
ON) and opens the required jettison and transfer/jettison valves. The related
jettison nozzle valve also opens. The jettison time is initially estimated using
preprogrammed rates. The system begins updating the estimate based on actual
fuel quantity rate of change ninety seconds after jettison begins.
If override/jettison pumps 2 and 3 are providing fuel to the engines when jettison
begins, the EICAS message FUEL OVRD may be displayed due to reduced
pressure caused by the jettison nozzles valves opening. Jettison is verified by
observing decreasing tank quantities.
The jettison control system controls fuel balancing between main tanks 2 and 3 as
fuel is jettisoned. If fuel balancing is necessary, the override/jettison pumps in the
low tank deactivate until the tanks are balanced.
The FSMCs open the reserve transfer valves when main tank 2 or 3 fuel quantity
decreases to 18,140 kilograms. Fuel transfers from reserve tanks 2 and 3 to the
related main tank.
When either main tank 2 or 3 fuel quantity decreases to 9,072 kilograms during
jettison, both main tank 1 and 4 transfer valves open.
December 01, 1999
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
12.20.10 D6-30151-425
Fuel -
System Description
Jettison terminates when total fuel quantity decreases to the fuel to remain
quantity. The fuel to remain quantity indication changes color from magenta to
white and flashes for five seconds. The jettison control system deactivates all
operating override/jettison and transfer/jettison pumps. The related FUELOVRD
pump EICAS messages display until the Fuel Jettison selector is OFF.
Fuel Jettison Schematic
OVERRIDE/JETTISON PUMP
ìJettison Time
NOTE: RIGHT WING SIMILAR
SECONDARY EICAS DISPLAY PRIMARY EICAS DISPLAY
TRANSFER/JETTISON PUMP
CENTER
MAIN PUMP
SIGNALS
PUMP/VALVE
A & B
CONTROL CARDS
FUEL JETTISON
ìFuel To Remain
FUEL TO REMAIN
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