What action should be taken if the automatic fire extinguishing system fails during an APU or AMAD fire?

Injecting the extinguishing agent into the intake exhaust or APU bay is the correct course of action when the automatic fire extinguishing system fails during an Auxiliary Power Unit (APU) or Airframe Mounted Accessory Drive (AMAD) fire. This method is proactive and enables the crew to directly apply fire suppression materials to the source of the fire, enhancing the chances of extinguishing the fire more effectively.

Fire in the vicinity of the APU or AMAD can escalate quickly, and relying solely on the automatic system or waiting for the fire to extinguish naturally can be extremely hazardous. Injecting the agent allows for a quicker response to a critical situation and helps mitigate damage, ensure safety for personnel, and possibly salvage equipment.

While shutting down the system and closing all doors may seem logical in an attempt to contain the fire, it does not address the immediate need for fire suppression. Similarly, calling for additional fire support is crucial; however, it should not delay the immediate action of combating the fire directly.