Definition
An engine that is operating unevenly, producing irregular power, vibration, or audible roughness rather than the smooth, steady output expected in normal operation. Causes can include fouled spark plugs, a faulty magneto, improper fuel mixture, induction system icing, contaminated fuel, or a mechanical problem inside the engine.
Plain English
The engine is running, but not smoothly. It feels shaky, sounds uneven, or seems to be working harder than it should — a sign that something is wrong and needs attention.
Context Anchor
A pilot may notice a rough-running engine during the pre-takeoff engine check, after changing power, during cruise, or while troubleshooting an engine problem in flight.
Why Pilots Care
A rough-running engine signals a problem that can reduce available power, increase pilot workload, or progress to complete engine failure if left unresolved.
Intuition Check
Do not confuse a rough-running engine with rough air. Rough air shakes the airplane from outside; a rough-running engine is the engine itself operating unevenly.
Example Sentence 1
During the run-up, the pilot noticed a rough-running engine on the left magneto and taxied back to have the spark plugs inspected.
Example Sentence 2
After leaning for cruise, the engine began running rough until the pilot enriched the mixture slightly to restore smooth operation.