APU Operation
The APU starts and operates up to the airplane maximum certified altitude.
The APU supplies bleed air for both air conditioning packs on the ground or
one pack in flight. Both transfer busses can be powered on the ground or in
flight.
APU Fuel Supply
Fuel to start and operate the APU comes from the left side of the fuel manifold
when the AC fuel pumps are operating. A DC operated APU fuel boost pump is
installed to ensure positive fuel pressure to the APU fuel control unit. During
APU start and operation, the pump operates automatically when the APU fuel
control unit senses low fuel pressure. The pump shuts off automatically when
an AC fuel pump pressurizes the fuel manifold. If the AC and DC fuel pumps
are not operating, fuel is suction fed from the No. 1 tank. During APU
operation, fuel is automatically heated to prevent icing.
The APU starts and operates up to the airplane maximum certified altitude.
The APU supplies bleed air for both air conditioning packs on the ground or
one pack in flight. Both transfer busses can be powered on the ground or in
flight.
APU Fuel Supply
Fuel to start and operate the APU comes from the left side of the fuel manifold
when the AC fuel pumps are operating. A DC operated APU fuel boost pump is
installed to ensure positive fuel pressure to the APU fuel control unit. During
APU start and operation, the pump operates automatically when the APU fuel
control unit senses low fuel pressure. The pump shuts off automatically when
an AC fuel pump pressurizes the fuel manifold. If the AC and DC fuel pumps
are not operating, fuel is suction fed from the No. 1 tank. During APU
operation, fuel is automatically heated to prevent icing.