In flight, when the APU automatic fire protection is engaged, which action occurs?

• A. Automatic discharge of the fire bottle
• B. Automatic shutdown of the APU, but not automatic discharge of the fire bottle
• C. Automatic shutdown of the entire electrical system
• D. No automatic action

Answer: (B)

The key idea is how APU fire protection operates: its primary automatic response is to stop the APU to isolate the fire source—cutting fuel and power and shutting the unit down. The extinguishing agent, however, is not automatically discharged by this protection in flight in this scenario; releasing the fire bottle is typically a separate action that requires a crew command (or a different automatic path depending on the system). So, when automatic protection engages, the automatic action you see immediately is the APU shutdown, not an automatic discharge of the fire bottle. That’s why this option is the correct one.