Overheat / Fire Protection Panel
APU Fire Warning Switch

Illuminated –

Note: Master FIRE WARN lights illuminate, fire warning bell
sounds, and in the main wheel well the APU fire warning
horn sounds (on the ground only), and the APU fire warning
light flashes.

Down – Normal position. Mechanically locked down if there
is no fire signal.
Up –

  • Arms the APU extinguisher circuit.
  • Closes the fuel shutoff valve, APU bleed air valve, and
    APU inlet door.
  • Trips the APU generator control relay and breaker.
  • Allows the APU fire warning switch to rotate.

Rotate (left or right) –

  • Discharges the APU fire bottle.

  • Indicates a fire in the APU
  • Unlocks the APU fire warning switch.