MD-11 Flight Crew Operations Manual
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Fuel -
Description and Operation
Fuel.10.9
For tanks 1 and 3 there are two scavenge jet pumps, one pumping the low points
of the outboard compartment and the other pumping the low points of the main
compartment. Since the outboard compartment must be maintained full during
most of the flight, a small bleed flow tapped off of the engine fuel supply is
directed to this compartment through the transfer valve control line. The bleed
flow to the compartment is greater than the scavenge flow from the compartment
to ensure that the outboard compartment remains full.
Check valves in the primary flow line of the jet pumps prevent air entry in the
engine supply line during suction feed operation (boost pumps off). A pressure
operated valve in the outboard compartment secondary flow (scavenge flow) line
is opened by boost pump pressure and is used to prevent drainage from the
outboard compartment to the main compartment when the boost pumps are not
operating.
Two scavenge jet pumps are installed in tank 2. One is located in the left
compartment and one in the right. Both are located low in the tank and discharge
scavenged fluids at the inlets of the spar mounted boost pumps.
The upper aux tank contains two identical scavenge systems, one for the left side
and one for the right side. Each system has two jet pumps which receive motive
flow from the respective fuel transfer pump and return the scavenge fluid to the
inlet of the same pump. The lower aux tank contains a bladder cell and does not
have a scavenge system.
The tail tank contains two identical scavenge systems, one for the left side and one
for the right side. Each system has four jet pumps which receive motive flow from
the respective fuel transfer pump and return the scavenge fluid to the inlet of the
same pump. There are two scavenge rakes on each side of the operating bulkhead.
Fuel Quantity Gaging System (FQGS)
The FQGS consists of:
• Probes in the fuel tanks.
• An Standard Electronic Module (SEM).
• A Data Control Unit (DCU) in the cockpit.
• Refueling panel on the right wing.
The probes in the fuel tanks send quantity data to the electronic module. The
electronic module processes this quantity data and sends it to the data control unit
and the refueling panel.
The data control unit sends the fuel quantity data to aircraft components that use
the data. These components include:
•FSC.
• FUEL control panel in the cockpit.
• MCDU through the FMC.
October 02, 2006
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