Auxiliary Power Unit
Usage
MASTER SW
Controls the APU operation and its start- and shutdown sequence.
- ON:
- Blue ON light comes.
- APU system is powered and performs a power-up test is done.
- APU Air intake flap opens.
- Fuel valve opens.
- APU fuel pump operates if fuel pumps are not in operation.
- ECAM shows APU page
- OFF:
- Manual shutdown sequence.
- ON light and the AVAIL light on the START pushbutton, go off.
- The APU keeps running for a cooling period of 60 seconds, if the aircraft was using APU bleed air.
- Air inlet flap closes at 7 %
- FAULT Lt:
- Amber light and ECAM warning message, if an automatic APU shutdown occurs. Possible causes:
- Fire (on ground only)
- Reverse flow
- Air inlet flap not open
- Low oil pressure
- Overspeed
- High oil temperature
- No acceleration
- No speed
- DC power loss. (BAT OFF when aircraft on batteries only)
- EGT over-temperature
- ECB failure
- No flame
- Loss of overspeed protection
- Under-speed
- Oil system shutdown
- Inlet overheat
- Clogged oil filter
- Loss of EGT thermocouples
- Amber light and ECAM warning message, if an automatic APU shutdown occurs. Possible causes:
START
- ON:
- Blue ON light.
- Starter is energized when the flap is completely open.
- Ignition activates 1.5 second after the starter is energized.
- When N = 60 %. The APU starter is de-energized. The ignition is turned off.
- 2 seconds after N reached 95%, or when N is above 99.5% the the ON light on START button goes out. The APU can now supply bleed air and electrical power to the aircraft.
- APU page disappears from the ECAM display after >10sec.
- AVAIL Lt:
- Green light comes on when N is above 99.5 % or 2 seconds after N reaches 95%.
Last update: August 23, 2021