MD-11 Flight Crew Operations Manual
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Fuel -
Description and Operation
Fuel.10.6
Electrically controlled fire shutoff valves are mounted on the front spar for the
wing mounted engines. There are two cable controlled fire shutoff valves for the
aft engine, one on the rear spar and one in the aft fuselage. The two shutoff valves
for the aft engine are operated from the same fire extinguishing handle in the
cockpit.
The APU fuel system consists of a dc start pump and two solenoid operated fire
shutoff valves. The system is controlled from the APU control panel. The start
pump, controlled by the Miscellaneous System Controller (MSC), is used to
supply fuel to the APU for start and ground operation.
When the APU START/STOP switch or the APU PWR ON switch is pushed, the
MSC opens both valves. One solenoid valve is located at the rear spar and one is
located in the aft fuselage near the inlet to the APU. The solenoid valves are
normally closed and require electrical power to open them. A pressure sensor at
the APU inlet provides the MSC with APU inlet fuel pressure information.
When the fuel system is in auto mode, the FSC will recognize when the APU is
operating and will turn on a tank 2 boost pump. After a 90 second time delay,
when the tank 2 boost pump is operating and providing adequate fuel pressure, the
FSC will interrupt start pump operation. Fuel then continues to be supplied to the
APU through the aft engine feed line.
With the FSC in manual mode, APU start pump operation will not be interrupted,
even if tank 2 boost pumps are operated. Fuel feed to the APU, whether from a
tank 2 boost pump or the dc start pump, is continued for 90 seconds after a
shutdown has been commanded. This prevents possible damage to the APU.
Fuel Transfer and Crossfeed
For fuel transfer from the center wing auxiliary tank (assuming fuel in both upper
and lower tanks) the FSC commands both the left and right center aux tank
transfer pumps on and energizes the three main tank (tanks 1, 2, and 3) fill valve
solenoids.
With the left and right transfer pumps commanded on, the upper and lower pumps
are energized along with the upper fill valve solenoid. When the fill valve
solenoids are energized, flow through the valve is controlled by the mechanical fill
pilot valves. These valves contain floats which sense the level of fuel present in
the tank. The three main tank and upper aux tank fill valves cycle open and closed
automatically to maintain the tanks full.
October 02, 2006
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