What is the initial step for an APU emergency shutdown?

Setting the APU Emergency Shutdown Switch to the shutdown position is the critical first step during an APU emergency shutdown. This action immediately initiates the shutdown process for the Auxiliary Power Unit (APU), ceasing its operations and preventing further fuel usage or potential hazards. The emergency shutdown switch is specifically designed to safely disable the APU in emergency situations, allowing for rapid and effective mitigation of risks associated with malfunctions or other emergencies.

By executing this step first, personnel can effectively stop the APU before addressing any additional safety measures, such as disconnecting electrical cables or pulling circuit breakers, which may follow depending on the specifics of the situation. Timely action with the emergency shutdown switch is essential in maintaining safety protocols and responding appropriately to emergencies on the aircraft.