What are common reasons for APU auto shutdown during flight?

• A. Auto shutdown is usually triggered by pilot miscommunication.
• B. Auto shutdown occurs due to landing gear issues.
• C. Auto shutdown due to engine start in flight.
• D. High EGT/overtemperature, low oil pressure or high oil temperature, overspeed, fire detection, or system faults.

Answer: (D)

APU auto shutdown in flight is driven by safety protections that kick in when operating conditions exceed limits or a fault is detected. The APU continuously monitors factors like exhaust gas temperature, oil pressure, oil temperature, rotor speed, and fire-detection signals. If any of these indicators go outside safe ranges or a fault is detected, the control system automatically stops the APU to prevent damage and to protect the aircraft’s systems. That’s why the most common reasons are high EGT/overtemperature, low oil pressure or high oil temperature, overspeed, fire detection, or system faults. Other ideas like pilot miscommunication or landing gear issues aren’t automatic APU shutdown triggers, and starting an engine in flight is not a typical automatic shutoff cause for the APU.