MD-11 Flight Crew Operations Manual
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Fuel -
Description and Operation
Fuel.10.3
The center wing auxiliary tanks consist of an upper tank and a lower tank. The
upper tank has upper (overwing) and wing box compartments which are
interconnected for gravity flow. The lower tank fuel is transferred to the wing box
by two transfer pumps through a fill valve. This fill valve controls the transfer
flow to maintain a specified fuel level band in the wing box tank. The fill valve
also prevents overfilling.
Fuel from the upper tank is transferred to the main tanks through the fill/crossfeed
manifold by two transfer pumps. The fuel quantity for the upper and lower tanks
is shown on one quantity readout as the total for the auxiliary tank.
There is one sump drain valve in each outboard compartment and four spar
mounted drain valves for the main tanks. One drain valve is located in each tank
1 and 3 main compartment and two are located in tank 2, one on each side of the
fuselage. Two sump drain valves are located in the center wing upper auxiliary
tank. The lower auxiliary tank has a sump drain in the bottom of the tank.
The tail tank is located in the horizontal stabilizer and is divided into three
compartments by the operating bulkheads. These structural members contain the
stabilizer pivots (aft) and are connected to the jack screws which control stabilizer
pitch attitude (forward). The operating bulkheads also serve as check valve
bulkheads allowing fuel flow into the center (constant) section but inhibiting flow
into the outboard compartments.
The tail tank functions as part of the aircraft Center Of Gravity (CG) management
system. Fuel is transferred to and from the tail tank as necessary maintain a fuel
efficient CG. Fuel is transferred from the tail tank by two transfer pumps.
In case of transfer pump failure, tail tank fuel quantity may be reduced by feeding
the tail engine directly from a dedicated alternate pump. During operation in auto
mode, the forward boost pump in tank 2 remains on during this procedure to
provide uninterrupted fuel flow to the aft engine when tail tank fuel is depleted.
All tail tank pumps and valves are mounted on the front spar of the constant
section. The tail tank has four front spar mounted sump drain valves. Two drain
the center section and one drains each of the two outboard sections.
October 02, 2006
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