Auxiliary Power Unit

Description

The Auxiliary Power Unit (APU) is a small jet engine in the back of the A320neo which supplies the aircraft with pneumatic and electrical power.

Controls the APU operation and its start- and shutdown sequence.

ON:
- Blue ON light.
- APU system is powered (performs a power-up test after set to ON).
- APU Air intake flap opens.
- Fuel valve opens.
- The APU uses fuel from the left wing tank only.
- If both main fuel pumps in the left wing tank are off, the APU Fuel Pump will be automatically activated.
- 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 N = 7 %
FAULT Lt:
- Amber light and ECAM warning message, if an automatic APU shutdown occurs. Possible causes:
  - Air inlet flap closed
  - Clogged oil filter
  - DC power lost (BAT OFF when aircraft on batteries only)
  - ECB failure
  - EGT overtemperature
  - Fire (on ground only)
  - High oil temperature
  - IGV failure
  - Inlet overheat
  - Loss of EGT thermocouples
  - Loss of overspeed protection
  - Low oil pressure
  - No acceleration
  - No flame
  - No speed
  - Oil system shutdown
  - Overcurrent
  - Overspeed
  - Reverse flow
  - Sensor failure
  - Slow start
  - Underspeed

ON:
- Blue ON light.
- Starter is energized when the flap is completely open.
- Ignition activates 1.5 seconds after the starter is energized.
- When N = 55 %. The APU starter is de-energized. The ignition is turned off.
- 2 seconds after N reaches 95 %, or when N is above 99.5 % 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 > 10 s.
AVAIL Lt:
- Green light comes on when N is above 99.5 % or 2 seconds after N reaches 95 %.

Last update: June 28, 2023