Definition
A system on multiengine airplanes that automatically matches the rotational speed (RPM) of one propeller to the other so both turn at exactly the same rate. The system uses a small electric or electronic control to fine-tune one engine's propeller governor to follow a designated master engine, eliminating the slow throbbing sound and vibration that occurs when the two propellers turn at slightly different speeds.
Plain English
A switch the pilot can turn on that makes both propellers spin at exactly the same speed, so the airplane stops making that wah-wah-wah pulsing noise and feels smoother.
Context Anchor
Seen in multiengine airplane operations when setting propeller speed in cruise or other normal flight conditions where the airplane’s checklist allows the system to be used.
Derivation
“Prop” is a short form of “propeller.” “Sync” is short for “synchronization,” from words meaning “together” and “time.” That fits the aviation meaning: the system keeps the propellers operating together in speed.
Why Pilots Care
Unsynchronized propellers create a fatiguing drone and increase airframe stress; engaging prop sync improves comfort and reduces crew workload on long flights.
Analogy
It is like two household fans running at almost, but not quite, the same speed. When their speeds match, the uneven pulsing sound becomes much smoother.
Intuition Check
Prop sync does not mean the system controls engine power for you. It only helps match propeller speed after the pilot has set the controls properly.
Example Sentence 1
After leveling off in cruise, the pilot adjusted both prop levers to 2300 RPM and then switched on prop sync to smooth out the cabin vibration.
Example Sentence 2
With prop sync engaged the airplane maintained smooth, quiet operation throughout the three-hour cross-country flight.