What happens when the APU fire push button is activated?

When the APU fire push button is activated, the correct action is to shut down the Auxiliary Power Unit (APU). This procedure is critical during abnormal situations, such as an onboard fire, as it reduces the potential hazards associated with a potential APU fire or further complications that could arise from continued operation. Shutting down the APU helps to mitigate risk and protect the aircraft and crew.

While it may seem intuitive that activating such a button could start or modify the operation of the APU, in the case of a fire emergency, the priority is to eliminate any sources of ignition and prevent further damage or risk. Therefore, the immediate and appropriate response is to initiate a shutdown of the APU.