APU Control Panel

APU Master Switch

ON - When the APU MASTER switch is selected to ON:

  • APU ON light illuminates blue
  • Electronic Control Box (ECB) power-up test is initiated
  • APU air inlet flap opens
  • APU fuel isolation valve opens
  • APU fuel pump runs (if fuel pressure is low)
  • ECAM APU page is displayed when AC busses are powered

OFF - When OFF is selected:

  • After the APU bleed air switch is closed the APU continues to run for 120 seconds to cool down the APU
  • After the APU cool down, the ON light extinguishes, the APU shuts down, and the APU air inlet flap closes at 7% N.

APU Master SwitchFAULT - The FAULT light illuminates amber when an automatic APU shut down occurs.

The APU shuts down automatically for the following:

  • APU fire (ground only)
  • APU air inlet flap not open
  • APU over speed or under speed
  • Abnormal start (e.g., slow, no flame, no acceleration)
  • Over-temperature
  • Low oil pressure
  • High oil temperature
  • DC power loss (BATs OFF when airplane on batteries only)
  • ECB failure
  • Loss of over speed protection
  • Reverse air flow