Which statement about compressor stall is true?

• A. Rise in exhaust temperature or rpm fluctuation is observed when stall occurs.
• B. A decrease in fuel flow indicates stall.
• C. Stall is indicated by improved fuel efficiency.
• D. Stall cannot be detected by readings.

Answer: (A)

Compressor stall is a disruption in the airflow through the compressor, causing instability that leads to a surge and fluctuating pressure in the engine. That instability shows up in engine readings, especially as rises in exhaust gas temperature and noticeable RPM fluctuations. The turbine and compressor are no longer operating in steady, matched fashion, so the exhaust temperature can spike and the rotor speed can jump around as the system tries to regain stability. These indicators are classic signs pilots watch for stall.

Decreases in fuel flow aren’t a reliable indicator of stall, because fuel metering can be altered by protective systems or throttle behavior independent of the airflow condition. Improved fuel efficiency would not accompany a stall, since stall means inefficient, unstable operation. And readings can indeed reveal stall, so the statement that they can’t is incorrect.