Which conditions are included in the APU auto-shutdown protection?

• A. Fire, overspeed, and low oil pressure
• B. High oil temperature
• C. Electrical overload
• D. Excessive vibration

Answer: (A)

APU auto-shutdown protection is the set of conditions that cause the unit to stop automatically to prevent damage. The most fundamental triggers are fire detection in the APU compartment, an overspeed condition where the RPM exceeds the safe limit, and low oil pressure which means lubrication is insufficient to protect bearings. If any of these occur, the control system shuts the APU down immediately.

High oil temperature, electrical overload, and excessive vibration are serious fault indicators and may prompt warnings or other protective actions, but they are not the predefined auto-shutdown triggers in this protection scheme. Thus, fire, overspeed, and low oil pressure are the conditions included in APU auto-shutdown protection.