What is the 15-ft propeller rule?

• A. Remain at least 15 ft from propellers; even quiet propellers can be lethal.
• B. Remain at least 30 ft from propellers; propellers are never lethal when quiet.
• C. Remain at least 25 ft from propellers; quiet propellers are harmless.
• D. Remain at least 20 ft from propellers; only loud propellers are dangerous.

Answer: (D)

Keep a safe distance from propellers when they are turning, because the danger isn’t just the blade itself but the whole area the blade can sweep and the suction and debris a propeller can pull into its arc. The 15-ft rule is a common reminder, but many training guidelines use a conservative minimum of 20 ft to account for different propeller sizes, engine power, and rotor wash. That extra buffer helps ensure you’re outside the blade path and far enough away to avoid sudden blade movement, vibration effects, or objects being whipped into the air. Noise level isn’t a reliable gauge of danger—propellers can injure even when they sound quiet—so treating any active propeller as hazardous and keeping the 20 ft distance is a prudent safety practice. The other statements either imply a smaller clearance or suggest danger is tied to loudness, which doesn’t hold up to the reality that any propeller in motion can be dangerous. So, maintaining at least 20 ft from propellers provides a safer, more universally applicable guideline.