What is the minimum time interval between attempts to start the APU?

The minimum time interval between attempts to start the Auxiliary Power Unit (APU) is 2 minutes. This requirement is in place to prevent overheating and excessive wear on the APU's starting components. When an APU fails to start, allowing a cooldown period of at least 2 minutes helps to ensure that the internal temperatures stabilize, which can reduce the risk of damage and increase the chances of a successful restart.

This cooldown period is crucial because rapid successive attempts to start the APU can lead to operational failures or even component failures due to the high heat generated during the starting process. The 2-minute interval also aligns with maintenance protocols that aim to extend the life of the APU and ensure reliable performance for aircraft operations.