APU Fire Extinguishing
The APU fire extinguisher system consists of one APU fire extinguisher bottle, an
APU fire warning switch, an APU BOTTLE DISCHARGE light, and an EXT
TEST switch. The APU ground control panel located in the right main wheel well
also contains an APU fire warning light, an APU BOTTLE DISCHARGE switch,
an APU fire control handle and APU HORN CUTOUT switch.
The APU fire warning switch is normally locked down to prevent inadvertent
shutdown of the APU. Illumination of the APU fire warning switch unlocks the
switch. The switch may also be unlocked manually.
Pulling the APU Fire Warning switch up:
Rotating the APU fire warning switch in either direction electrically “fires” the
squib discharging the extinguishing agent into the APU. The APU BOTTLE
DISCHARGE light illuminates after a few seconds, indicating the bottle has
discharged.
Main Wheel Well Fire Protection
Main wheel well fire protection consists of fire detection powered by the No. 1 AC
transfer bus.
Note: The main wheel well has no fire extinguishing system. The nose wheel
well does not have a fire detection system.
The APU fire extinguisher system consists of one APU fire extinguisher bottle, an
APU fire warning switch, an APU BOTTLE DISCHARGE light, and an EXT
TEST switch. The APU ground control panel located in the right main wheel well
also contains an APU fire warning light, an APU BOTTLE DISCHARGE switch,
an APU fire control handle and APU HORN CUTOUT switch.
The APU fire warning switch is normally locked down to prevent inadvertent
shutdown of the APU. Illumination of the APU fire warning switch unlocks the
switch. The switch may also be unlocked manually.
Pulling the APU Fire Warning switch up:
- Provides backup for the automatic shutdown feature.
- Deactivates the fuel solenoid and closes the APU fuel shutoff valve.
- Closes the APU bleed air valve.
- Closes the APU air inlet door.
- Trips the APU generator control relay and breaker.
- Allows the APU fire warning switch to be rotated for discharge.
- Arms the APU fire extinguisher bottle squib.
Rotating the APU fire warning switch in either direction electrically “fires” the
squib discharging the extinguishing agent into the APU. The APU BOTTLE
DISCHARGE light illuminates after a few seconds, indicating the bottle has
discharged.
Main Wheel Well Fire Protection
Main wheel well fire protection consists of fire detection powered by the No. 1 AC
transfer bus.
Note: The main wheel well has no fire extinguishing system. The nose wheel
well does not have a fire detection system.
