In flight, what does the APU automatic fire protection do?

• A. Will shut down the APU but will not discharge the fire bottle
• B. Will discharge the fire bottle
• C. Will isolate the APU from the electrical system
• D. Will switch to an internal power source

Answer: (A)

When the APU fire protection system detects a fire in flight, its immediate job is to shut the APU down to stop fuel flow and rotation, reducing the risk and spread of fire. The extinguishing bottle is a separate capability and, in this configuration, is not discharged automatically by the protection system during flight; it requires the crew to activate it if needed. So the automatic protection focuses on stopping the APU, not on releasing the fire suppressant. The other options describe actions that aren’t the automatic response of this system in flight.