Which statement best describes surge margin?

• A. A larger margin indicates greater compressor stability.
• B. A larger margin indicates less stability.
• C. Margin is unrelated to stability.
• D. Margin only affects fuel flow.

Answer: (A)

Surge margin is the distance, in terms of flow or pressure ratio, between the current operating point and the compressor’s surge limit. It acts as a stability buffer: the larger the margin, the farther you are from the point where surge can begin, so the compressor is more stable during transients or load changes.

A bigger margin means you can absorb disturbances from rapid throttle changes, inlet pressure shifts, or speed variations without slipping toward surge. If the margin shrinks, you’re closer to that surge limit and stability becomes more vulnerable.

The other ideas don’t fit because surge margin is fundamentally a stability measure related to avoiding surge, not an unrelated concept or something that only controls fuel flow.