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JETTISON PUMP
OVERRIDE/
P
P
P
P
P
P
CARDS
A & B
TO
APU
T
A
F
F
D
W
December 01, 1999
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
12.20.6 D6-30151-425
Fuel -
System Description
Center Wing and Horizontal Stabilizer Pump Schematic
Reserve Tank 2 and 3Transfer
Each reserve tank contains two transfer valves. The valves open and fuel gravity
transfers to the inboard main tanks when main tank 2 or 3 fuel quantity decreases
to 18,140 kilograms.
TRANSFER VALVE
VALVE
JETTISON
VALVES
TRANSFER/JETTISON
TRANSFER/JETTISON
NOZZLE VALVE
TO JETTISON
A & B
CARDS
PUMP
CENTER TANK
P P
MANAGEMENT
FUEL
L CTR R
L STAB R
PRESS PRESS
ON ON
PRESS PRESS
ON ON
PUMP
OVERRIDE/JETTISON
L_E_G_E_N_D_
TANK
STABILIZER
HORIZONTAL
P P
December 01, 1999
747 Operations Manual
Fuel -
System Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 12.20.7
Main Tank 1 and 4Transfer
Main tank 1 and 4 each contain one transfer valve. When the valves open, fuel
gravity transfers from the outboard main tanks to the inboard main tanks. Fuel
transfers to approximately 3,200 kilograms remaining in each outboard main tank.
During fuel jettison, the valves open when either main tank 2 or 3 fuel quantity
decreases to 9,072 kilograms. The valves may be opened manually using the Fuel
Transfer Main 1 & 4 switch on the overhead panel.
APU Fuel Feed
APU fuel is normally supplied from main tank 2. When AC power is available,
fuel is supplied by main pump 2 aft. If AC power is not available, a dedicated DC
pump in main tank 2 supplies fuel to the APU.
Fuel System Operation
Fuel system management cards (FSMCs) command fuel valves open or closed and
fuel pumps on or off according to fuel management logic.
Preflight
When fuel pump switches are off before engine start, low pressure lights are
illuminated on the main pump switches and extinguished on the override, CWT,
and stabilizer tank pump switches.
OperationWith Fuel in CenterWing Tank
The FSMCs close crossfeed valves 2 and 3 when flaps extend to takeoff position
on the ground. Override/jettison pumps 2 and 3 are inhibited from operating when
pressure is detected from both CWT override/jettison pumps. The CWT
override/jettison pumps provide fuel to engines 1 and 4 and main pumps 2 and 3
provide fuel to their related engine.
The FSMCs open crossfeed valves 2 and 3 when the flaps are retracted. The CWT
override/jettison pumps provide fuel to all engines.
When CWT fuel quantity decreases to 36,470 kilograms, the FSMCs open the
appropriate valves and activate the transfer/jettison pumps to transfer fuel from the
stabilizer tank to the CWT.
The Stabilizer Tank Pump switches are pushed off when both FUEL PMPSTAB
messages are displayed and fuel quantity indications show the stabilizer tank
empty.
The CWT pump switches are pushed off when either FUEL OVRD CTR message
displays and CWT fuel quantity is less than 900 kilograms.
December 01, 1999
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
12.20.8 D6-30151-425
Fuel -
System Description
An electrical scavenge pump in the CWT activates automatically to pump the
remaining CWT fuel to main tank 2.
Note: With CWT fuel quantity less than 2,700 kilograms, the EICAS message
FUEL OVRD CTR may display due to an uncovered pump inlet. With
CWT fuel quantity between 2,700 and 4,500 kilograms, the EICAS
message FUEL OVRD CTR may display temporarily during taxi, takeoff,
or climb due to fuel movement in the tank. The message no longer displays
after the airplane is level and no longer accelerating.
Note: When CWT quantity drops belowapproximately 2,300 kilograms and total
fuel consumption is greater than 6,800 kilograms per hour, the CWT
override/jettison pumps can no longer provide full override of the outboard
main tank pumps. As a result, a shared flow situation between the CWT
and outboard main tanks is established. During this shared flow situation,
approximately 900 kilograms of fuel are consumed from each outboard
main tank prior to display of the EICAS message FUEL OVRD CTR.
The FMSCs activate override/jettison pumps 2 and 3 when low pressure is
detected from either CWT override/jettison pump. Override/jettison pumps 2
provide fuel to engines 1 and 2 and override/jettison pumps 3 provide fuel to
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