- The APU consists of a 2-stage compressor and a turbine.
- APU fuel is suction fed from the LH Fuel Manifold and is automatically heated to prevent icing.
- During start-up, the fuel solenoid valve is opened by an oil pressure switch.
- APU Starting limits:
- 2 starts/hr : in-flight
- 4 starts/hr : on the ground (all starts after the 2nd start to be monitored by ground personnel in the event of a fire).
- 0-10,000 ft: Pneumatics & Electrics
- 10,000 – 17,000 ft: Either Pneumatics or Electrics
- 17,000 – 35,000 ft: Only Electrics.
- 35,000 ft: Max altitude for APU start-up
- APU max air demand: 90 lbs/min on the ground (restricted by APU bleed valve).
80 lbs/min in the air.
- APU fuel consumption: 90 kg/hr (no load)
115 kg/hr (under load)
- APU bleed valve is an electro-pneumatically operated solenoid valve.
- When electrical load and bleed air extraction combine to raise the EGT above acceptable levels, the bleed air valve will modulate towards the closed position. In the event of an EGT overtemp, the bleed air valve will close rapidly but the APU will continue to run.
- APU turbine speed: @ 100% RPM: 41,800 RPM
@ 110% RPM: 46,000 RPM (overspeed shutdown)
- APU generator speed @ 100% RPM: 6,000 RPM
- APU generator’s rating: 40 KVA in-flight (can only supply one of the Gen Buses)
45 KVA on the ground.
- APU will automatically shut down for:
- Low oil pressure
- High oil temp (157°C)
- Overspeed (110% or 46,000 RPM)
- Fire indication
- Battery switched OFF.
- APU oil tank capacity: 1.5 US Gal.
- APU low oil quantity light illuminates @ 1.5 US Qts
- APU max EGT constant running: 710°C
- APU max EGT: 760°C
- Max APU generator load – ground: 125 amps
- Max APU generator load – air: 111 amps
- Engine starting requirement: 30 psi @ SL reducing @ ½ psi per 1,000 ft.