Which statement about APU auto-shutdown protections is true?

Which statement about APU auto-shutdown protections is true?

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

Answer: (B)

Auto-shutdown protections are there to stop the APU immediately when conditions could cause damage or danger. The set that directly triggers an automatic shutdown consists of fire detection, overspeed, and low oil pressure. Fire protection kicks the APU offline the moment a fire is detected, preventing spread and hazards. Overspeed protection shuts the unit down when the RPM goes beyond safe limits, protecting the turbine and bearings from excessive speed. Low oil pressure signals that lubrication is failing, and continuing operation would quickly cause severe damage; shutting down prevents catastrophic failure. Other potential issues like high oil temperature, electrical overload, or fuel leaks are important safety concerns, but they aren’t the standard automatic shutdown trio used in many APU designs. The combination of fire, overspeed, and low oil pressure is the most fundamental automatic protection set.

Auto-shutdown protections are there to stop the APU immediately when conditions could cause damage or danger. The set that directly triggers an automatic shutdown consists of fire detection, overspeed, and low oil pressure.

Fire protection kicks the APU offline the moment a fire is detected, preventing spread and hazards. Overspeed protection shuts the unit down when the RPM goes beyond safe limits, protecting the turbine and bearings from excessive speed. Low oil pressure signals that lubrication is failing, and continuing operation would quickly cause severe damage; shutting down prevents catastrophic failure.

Other potential issues like high oil temperature, electrical overload, or fuel leaks are important safety concerns, but they aren’t the standard automatic shutdown trio used in many APU designs. The combination of fire, overspeed, and low oil pressure is the most fundamental automatic protection set.