When will the APU fire protection system automatically shut down the APU?

The APU fire protection system is designed to enhance safety by automatically shutting down the APU in specific conditions that indicate a potential fire. This automatic shutdown feature is primarily intended to protect the aircraft and crew from the dangers of fire when the aircraft is on the ground. When the APU detects a fire, the system is programmed to engage and facilitate an automatic shutdown to prevent the risk of an uncontrolled fire situation.

While the APU operates in both flight and on the ground, the automatic shutdown response is particularly critical when on the ground due to the higher risk of fire if there is a failure. Situations like engine operation or external power connectivity do not directly influence the APU's capacity to shut down due to fire detection; those are secondary considerations typically focused on operational procedures rather than safety system responses. Thus, the conditions under which the APU fire protection system will automatically shut down are best represented by its operational context on the ground.