What is the first step in shutting down the C-5 APU?

The first step in shutting down the C-5 APU is to turn off the APU control switch. This action is crucial because it directly initiates the shutdown process of the APU. Once the control switch is turned off, the APU begins to safely cease operations, leading to the cessation of fuel and power generation.

It is essential to follow this procedure first to ensure that the APU can transition safely to the shutdown state. Other actions, such as turning off the fuel supply or checking oil levels, are important components of the overall shutdown process but should occur after the initial command to turn off the APU has been executed. Cooling down the APU is also a necessary follow-up step once it has been turned off, ensuring that the unit can be safely managed post-operation.