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.