Under what condition will the APU turn off automatically?

The automatic shut-off of the Auxiliary Power Unit (APU) under certain conditions is a safety feature designed to protect the aircraft and its systems. In the context of an APU fire, the unit is programmed to shut down automatically to prevent further damage and to mitigate the risk of a fire spreading. This response is crucial for ensuring the safety of the aircraft and its occupants, as an uncontrolled fire can create hazardous conditions.

The other scenarios, such as engine failure or requirements for maintenance, do not necessarily trigger an automatic shutdown. While those situations might require attention, they do not pose an immediate and critical risk in the same way that a fire does. Hence, the APU's design prioritizes shutting down in the event of a fire to maintain safety standards and minimize potential threats during operations.