During an APU fire protection activation in flight, what happens to the APU?

• A. The fire bottle will discharge
• B. The APU will continue to run
• C. The APU will shut down
• D. Electrical power will fail

Answer: (C)

When APU fire protection is activated, the system immediately restricts the APU to prevent the fire from feeding on fuel. The APU is shut down to cut off fuel and stop the generation of heat and power, which helps contain the fire and protect the aircraft systems. At the same time, a fire-suppression bottle is discharged into the APU bay to suppress the flame. So the primary effect on the APU is that it will shut down, even though the fire bottle discharge is also part of the protective response. In flight, this shutdown helps isolate the fire and maintain safety while the airplane continues with other power sources.