Under which condition will the APU automatically shut down if an APU fire is detected?

Under which condition will the APU automatically shut down if an APU fire is detected?

• A. In flight
• B. On the ground
• C. Only when the aircraft is landed
• D. In maintenance

Answer: (B)

The important idea here is how the APU fire protection system operates with respect to the aircraft’s operating phase. When the APU detects a fire, the safety logic is designed to shut the APU down to stop fuel flow and isolate the APU from the aircraft systems to prevent fire spread. On the A320, this automatic shutdown behavior is configured to occur during ground operations, where the APU is typically providing essential electrical power and bleed air for ground systems. In flight, the engines normally supply the primary power and bleed sources, and the APU’s fire protection logic is handled in a way that does not automatically shut the APU down as part of routine flight operations; fire handling in flight is managed by crew procedures and, if needed, manual action via the APU fire switch. Therefore, the condition under which the APU will automatically shut down if an APU fire is detected is when the aircraft is on the ground.

The important idea here is how the APU fire protection system operates with respect to the aircraft’s operating phase. When the APU detects a fire, the safety logic is designed to shut the APU down to stop fuel flow and isolate the APU from the aircraft systems to prevent fire spread. On the A320, this automatic shutdown behavior is configured to occur during ground operations, where the APU is typically providing essential electrical power and bleed air for ground systems. In flight, the engines normally supply the primary power and bleed sources, and the APU’s fire protection logic is handled in a way that does not automatically shut the APU down as part of routine flight operations; fire handling in flight is managed by crew procedures and, if needed, manual action via the APU fire switch. Therefore, the condition under which the APU will automatically shut down if an APU fire is detected is when the aircraft is on the ground.