A pilot reports a loud bang and a momentary flash of flame from the engine inlet during a rapid throttle advance, accompanied by a sudden drop in EPR and a brief rise in EGT. A mechanic explains this event is a compressor 'surge' rather than a localized 'stall.' What distinguishes a surge from a stall?
- AA surge occurs only at idle power, while a stall occurs only at high power
- BA surge is caused by fuel starvation, while a stall is caused by excess fuel flow
- CA surge is a complete breakdown and momentary reversal of airflow through the entire compressor producing a violent pressure pulse, while a stall is localized airflow separation on individual blade rows
- DA surge only affects a single compressor blade row, while a stall affects the entire compressor
Show answer & explanationAnswer & explanation
Correct answer: C. A surge is a complete breakdown and momentary reversal of airflow through the entire compressor producing a violent pressure pulse, while a stall is localized airflow separation on individual blade rows
A compressor stall is a localized aerodynamic breakdown (flow separation) on one or more blade rows, often manageable and self-clearing. A surge is a more severe, engine-wide instability in which the entire compressor's airflow momentarily reverses or breaks down, producing a loud bang, vibration, and a pressure/temperature pulse, often requiring a throttle reduction to recover normal operation.
Why the other options are wrong
- A. Both stall and surge can occur across various power settings, not restricted to idle or high power only.
- B. Both conditions relate to aerodynamic flow instability, not simply fuel scheduling errors.
- D. This reverses the actual definitions — stall is localized, surge is engine-wide.
Compressor Surge
A severe, whole-compressor aerodynamic instability causing momentary airflow reversal and a violent pressure pulse, distinct from a localized compressor stall affecting individual blade rows.
- Often accompanied by a loud bang and visible flame from inlet or exhaust
- Can cause EGT spike and EPR/N1 fluctuation
- More severe and engine-wide compared to localized stall
Memory trick: Stall is a local hiccup; surge is the whole compressor throwing up.