Fire Protection - APU

APU Fire Protection

APU Fire Protection consists of these systems:

APU Fire Detection

There are dual fire detector loops in the APU compartment. There is no APU overheat detection.

In normal operation, both loops must sense the fire to activate the fire warning. The APU fire loops are continuously for faults. When a fault is detected in one of the loops, the systems reconfigures itself for single loop operation. When the good loop senses a fire condition, the fire warning activates. If both loops indicate a fault, a fire warning is activated.

The SYSTEM FAIL light illuminates and the EICAS advisory message FIRE/OVHT SYS displays to indicate failure of the APU fire detection system. An EICAS status message indicates the inoperative loop. The SYSTEM FAIL light and advisory message can be reset to allow monitoring of the remaining systems.

APU Fire Warning

APU Fire Warning

The indications of an APU fire warning are:

Nose Gear Strut APU Ground Control Panel APU Fire Light APU Ground [Fire] Shutdown Switch APU Bottle Discharge Switch

In addition to the above APU fire warnings, if the airplane is on the ground:

The fire warning lights remain illuminated as long as the fire signal exists. The fire bell (and horn if the APU fire is on the ground) may be silenced by any of the following actions:

The fire warning bell rings intermittently for 2 seconds on, then 3 seconds off.

APU Fire Extinguishing

There is one APU Fire Extinguisher bottle. When the APU fire switch is pulled out:

Rotating the switch in either direction discharges the extinguisher bottle into the APU compartment. When the bottle is discharged or has low pressure:

APU Automatic Fire Extinguishing

An APU fire on the ground with both engines shutdown is automatically extinguished. The fire signal causes discharge of the APU fire extinguisher system a few seconds after automatic shutdown.

APU Fire and Override Switch

Fire and Override switch. The APU fire switch is mechanically locked in the down position. When a fire is detected the switch is electrically unlocked and may then be pulled out. Manual unlocking of the switch is accomplished by pushing the fire override switch located beneath the fire switch.

Wheel Well