A320 APU CONTROL PANEL

MASTER SW pb

• Controls the APU operation and its starting and shutdown sequences.
• OFF: APU is off, or APU is in manual shutdown sequence:
  • ON light on the MASTER SW pb-sw, and the AVAIL light on the START pb go out.
  • If the aircraft was using APU bleed air, the APU keeps running for a cooling period of 60 to 120 s.
  • At 7 % the air inlet flap closes.
• ON: APU is in operation, or APU is in starting sequence:
  • Electric power goes to the APU system; the ECB performs a power-up test.
  • APU air intake flap opens.
  • APU fuel isolation valve opens.
  • If no fuel tank pump is running, the APU fuel pump operates
  • If the aircraft has ground power or main generator power, the APU page appears on the ECAM display.
• FAULT: Amber light and ECAM warning, if an automatic shutdown of the APU can happen in case of:
  • Fire (on ground only)
  • Air inlet flap closed
  • Overspeed
  • No acceleration
  • Slow start
  • EGT overtemperature
  • No flame
  • Reverse flow
  • Low oil pressure
  • High oil temperature
  • DC power lost (BAT OFF when aircraft on batteries only)
  • Overcurrent
  • Sensor failure
  • IGV failure
  • ECB failure
  • No speed
  • Underspeed
  • Loss of overspeed protection
  • Oil system shutdown
  • Inlet overheat
  • Clogged oil filter
  • Loss of EGT thermocouples

START pb

• OFF: APU is off.
• ON: APU start sequence is in progress –
  • When the flap is completely open, the APU starter is energized
  • 1.5 s after the starter is energized, the ignition turns ON
  • When N = 60 %, the APU starter is de-energized, and the ignition turns OFF
  • 2 s after N reaches 95 %, or when N is above 99.5 % the ON light on the START pb goes out
  • 10 s later, the APU page disappears from the ECAM display
• AVAIL: APU is started, and can supply bleed air and electrical power to the aircraft systems. The AVAIL light comes on when N is above 95 %.