Learn what 'clear prop' means, when pilots call it, what the safety check covers, and why it happens before engine start—not on the runway.
‘Clear prop’ is a warning shouted immediately before starting a propeller-driven aircraft’s engine. It tells anyone near the aircraft that the propeller is about to turn and they must move clear. The pilot must also look outside and confirm the propeller area is actually clear; the call alone is not a safety check.
When do pilots say ‘clear prop’?
In real-world aviation, pilots normally call ‘clear prop’ immediately before engaging the starter, while the aircraft is still parked. It is not a runway call, a take-off command or a substitute for take-off clearance.
The aircraft may not take off until several minutes later, after engine checks, taxi and the pre-take-off checklist. If the engine is shut down and restarted, the propeller area must be checked and the warning given again. Our Cessna 172 start-to-landing walkthrough shows where the call fits into a typical light-aircraft sequence.
The shouted warning is most closely associated with light piston aircraft. Larger turboprops may use ground crew, hand signals or interphone communication instead, but the principle is the same: nobody starts an engine until its propeller area is confirmed clear.
What should the pilot check before starting?
The pilot must check the propeller’s swept area, nearby blind spots and the space affected by propeller wash. People, baggage, tie-downs, ground leads, tow bars and other loose equipment can all create a serious hazard.
- Secure the aircraft: apply the approved brake or chocking procedure and set the engine controls according to the aircraft checklist.
- Scan outside: inspect the full propeller area and look for anyone approaching from either side.
- Give the warning: call ‘clear prop’ loudly enough for people nearby to hear.
- Pause and check again: allow time for someone to move or signal, then verify that the area remains clear.
- Engage the starter: start only when it is safe, while continuing to watch for anyone entering the area.
The aircraft’s pilot operating handbook and operator procedures govern the exact sequence. A common mistake we see reproduced in simulation is treating the spoken call as permission to start without making the visual check.
What should you do when you hear ‘clear prop’?
Move well away from the propeller’s swept disc and do not approach the aircraft until the engine is shut down and the pilot or ground crew indicates that it is safe. Never duck beneath, step over or pass through the arc of a propeller, even when its blades appear stationary.
Anyone who has not cleared the area should signal the pilot clearly without entering the propeller arc. Hearing protection, cockpit glazing and apron noise can prevent the warning from being heard, which is why the pilot cannot rely on shouting alone.
Is a stopped propeller safe to touch?
A stopped propeller must still be treated as potentially live. Piston-aircraft magnetos can produce ignition independently of the aircraft’s electrical master switch, and an ignition-system fault can leave a magneto live even when the cockpit switch indicates off.
Moving the propeller by hand could then cause the engine to fire under the wrong conditions. Propeller handling and hand-starting require specific training; ‘clear prop’ does not make a stopped propeller safe to move.
Do you need to say ‘clear prop’ in a flight simulator?
Most flight simulators do not require the spoken call and will start the engine regardless, but including it preserves the correct operating habit. During a cold-and-dark simulator start sequence, pause at the starter step, check the virtual ramp and then make the call.
For a common training aircraft, our practical Cessna 172 simulator checklist places the propeller-area check within the wider engine-start flow. Multiplayer traffic, animated ground staff and pushback equipment make the visual check useful for realism even though the simulator may not model the physical danger.