MD-11 Flight Crew Operations Manual
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Fuel -
Description and Operation
Fuel.10.8
Gravity and Jet Pump Transfer System
To relieve bending stresses caused by the generation of lift by the wings, the tank
1 and 3 outboard compartments are maintained full until the inboard fuel level
decreases to about 2,268 kilograms.
There are two transfer systems controlled by fuel level in the inboard
compartment. These systems will allow fuel to transfer from the outboard
compartment to the inboard compartment maintaining the inboard compartment
fuel quantity at about 2,268 kilograms. The total amount of wing tank fuel will be
about 4,990 kilograms when the transfer begins.
One fuel transfer system utilizes a transfer valve and transfer float valve. The other
transfer system, a jet pump system, transfers fuel accumulations in the aft portion
of tank 1 and 3 on both sides of the vent box. The jet pump system is the primary
system at aircraft attitudes in excess of six degrees nose-up.
The two compartments of tanks 1 and 3 contain float switches which provide the
FSC with fuel schedule information. One float switch is located high in the
outboard tank and two float switches are located low in the main tank. The FSC
compares the condition of the three float switches in each tank with fuel quantity
information, checking for possible failures.
If outboard compartment leakage has occurred and the fuel schedule condition is
identified with tank total quantity above 5,216 kilograms, the FSC will refill the
outboard compartment by opening the fill valve and using either the transfer pump
or the boost pumps through a crossfeed valve. The manifold drain/outboard fill
solenoid valve can also be used to fill the outboard compartment if the FSC senses
that the fill valve is failed closed. If fuel schedule condition is identified with total
tank quantity below 3,850 kilograms, the FSC assumes a failure in fuel transfer
from outboard to inboard compartment and an alert will be displayed to warn the
crew that the tank fuel quantity is low and that a tip fuel trapped condition exists.
In this condition, approximately 2,495 kilograms of fuel will not be available to
engines.
Continuous Scavenge System
A continuous scavenge system is installed to prevent water accumulations within
the tanks. This is accomplished by pumping fuel/water from the low points to the
fuel pump inlets. The system consists of jet pumps, pressure actuated shut-off
valves, check valves and scavenge rakes.
Jet pumps are used to scavenge the fuel tank low points where the tank bottom is
too flat for gravity draining. The primary flow of these pumps is obtained from the
boost pump manifolds in each tank. The outlets of the jet pumps are located so that
the discharge is directed toward an aft pump inlet. The jet pumps are in operation
whenever the pumps are working.
October 02, 2006
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