787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Fuel -
System Description
Copyright © The Boeing Company. See title page for details.
D615Z003-TBC 12.20.3
The dissolved air in the fuel tank eventually depletes after reaching cruise altitude.
The depletion time is dependent upon airplane altitude, fuel temperature, and type
of fuel. Once the dissolved air is depleted, the engine should effectively operate
on suction feed.
Fuel pressure can be provided from a main tank with operating fuel pumps to both
engines by opening the fuel crossfeed valve. Continued crossfeed use results in a
progressive fuel imbalance.
Fuel Crossfeed
The fuel manifolds are arranged so that any fuel tank pump can supply either
engine. The crossfeed valve is closed during normal operations. The closed
crossfeed valve isolates the left and right systems. The valve can be opened to feed
an engine from the opposite fuel tank. If the valve position does not agree with the
switch position, the CROSSFEED switch VALVE light illuminates and the
EICAS advisory message FUEL CROSSFEED displays.
Fuel Balance System
Fuel can be transferred from main tank to main tank using the fuel balance system.
Fuel transfer is initiated by pushing the fuel balance switch ON. Fuel from the
higher quantity main tank is transferred through its defuel/jettison valve to the
lower quantity main tank through its inboard refuel valve. Transfer stops
automatically when fuel is balanced.
Anytime the fuel balance system is selected ON and balance is not achieved, the
balance system shuts down, the BALANCE switch FAULT light illuminates, and
the EICAS advisory message FUEL BALANCE SYS is displayed. This occurs if
there is a system failure or if the system is functional but inhibited.
Fuel balance operation is inhibited for the following reasons:
• refueling, defueling and ground transfer of fuel (using the refueling control
panel)
• airplane is on the ground with one or two engines running, or the APU is
off
• one or both center pumps are operating
• fuel jettison.
Fuel Imbalance
When the fuel quantity in left and right main tanks differ by a predetermined
quantity, the EICAS alert message FUEL IMBALANCE displays.
Fuel balancing is accomplished by using either the fuel balance system or the
manual crossfeed.
February 15, 2010
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