What are common indicators of compressor stall or surge during operation?

• A. Steady, smooth RPM and temperature.
• B. Constant power output.
• C. Loud rumble or flutter, fluctuating RPM, erratic engine indications, and loss of surge margin.
• D. Decreased fuel consumption.

Answer: (C)

When a compressor starts to stall or surge, the most telltale signs are an audible loud rumble or flutter, along with fluctuating rotor speed and unstable engine indications, including a drop in surge margin. This happens because the airflow through the compressor becomes unsteady and may even reverse momentarily, causing large, rapid pressure and flow variations. Those flow instabilities translate into visible and audible symptoms: the engine RPM can bounce or oscillate, instrument readings become erratic, and the available headroom before surge—the surge margin—reduces.

In stable operation, you wouldn’t see those chaotic indicators. Steady, smooth RPM and temperature point to a non-surging state. Constant power output suggests the engine is maintaining a steady operating condition. Decreased fuel consumption is not a sign of surge; it indicates better efficiency and isn’t related to surge behavior.