What are the steps for an emergency shutdown of the APU?

The procedure for an emergency shutdown of the APU involves moving the APU control switch to the OFF position and then confirming that the APU has stopped functioning. This action is crucial because the APU control switch is the primary method of controlling the APU's operation. Placing the switch in the OFF position interrupts the fuel supply, effectively stopping the APU, which is essential in an emergency situation to prevent further issues, such as fire or damage to the aircraft systems.

Once the switch is moved to OFF, monitoring the status of the APU is vital to ensure that it has indeed ceased operations. This step helps to provide confirmation that the emergency shutdown was successful and that no residual operations could pose a risk. Understanding this procedure is critical for maintaining safety and effectively managing potential emergencies involving the APU.

In contrast, while reducing fuel flow, disconnecting the battery, or activating emergency alarms may be parts of broader emergency protocols, they do not specifically address the immediate actions necessary to shut down the APU effectively. Thus, these alternatives do not serve as direct replacements for the critical step of moving the APU control switch to OFF.