Why should responders not move or stop a propeller?

• A. Moving it can restart the engine immediately.
• B. Propellers are safe to touch when stationary.
• C. Moving it can turn the magneto, create sparks, ignite unspent fuel, or restart the engine.
• D. There is no risk in moving a propeller.

Answer: (C)

Moving a propeller is dangerous because it can energize the engine’s ignition system and cause ignition of fuel vapors or even restart the engine. The propeller drives the magnetos and spark plugs; if you spin it, you can generate sparks and ignite any unburned fuel or vapors in the engine or induction system. If the engine isn’t fully shut down, turning the crank can also cause the engine to restart. Beyond ignition risks, a moving propeller can injury nearby responders. So the correct caution is to avoid touching or moving the propeller and rely on proper shutdown procedures and barriers until trained personnel can secure the aircraft.