What action occurs on the ground when the APU detects and annunciates a fire?

• A. Auto shuts down, auto discharge of the fire bottle
• B. Auto restarts after manual discharge
• C. Auto shuts down and manual discharge
• D. No automatic action is taken

Answer: (A)

When the APU fire detection triggers on the ground, the protection system responds automatically. The APU is shut down to stop fuel and airflow, and the fire bottle is discharged automatically into the APU compartment to suppress the fire. This automatic sequence provides immediate protection without relying on crew input, which is crucial for rapid and effective fire suppression.

Auto restart after manual discharge isn’t how the system operates—restarting would risk re-ignition or fueling a continuing fire. Auto shutdown with manual discharge would delay the extinguishing agent release, and no automatic action isn’t correct because the system is designed to respond automatically to detected fires.