"I have often said that, if an enemy was shooting at me and I only had time to check two items on a preflight inspection, one of the items I would check would be the propeller.”—Dale De Remer

It is possible that an aircraft structure will have a resonant frequency the same as certain vibrations from the engine, propeller or even the air intake duct. For this reason, aircraft undergo extensive flight and vibration testing to minimize the chances of resonance excitation. Therefore, a propeller should never be used on an aircraft without first determining that it has been tested and certified for use with that particular engine and airframe combination.

A propeller must be capable of withstanding severe stresses, which are greater near the hub, caused by centrifugal force and thrust (the centrifugal force of the blades can amount to as much as 25 tons. The stresses increase in proportion to RPM. The blade face is also subjected to tension from the centrifugal force and additional tension from bending. For these reasons, nicks or scratches on the blade may cause very serious consequences. A two-blade propeller turning at 2700 RPM has a tension load on it of nearly 20 tons—Picture a propeller blade with a locomotive hanging outward from each blade tip! Blade tension loading increases with the square of the tip speed or RPM, so an overspeed of 10%—270 RPM—adds another locomotive to the propeller.

Any rock strike, nick, or irregularity (usually found on the leading edge of the blade) should be examined and treated by a mechanic. Tightness of variable pitch blades should be checked by holding the tip of the blade between the thumb and one forefinger and attempting to move the blade fore and aft, up and down. If the blade moves other than normal bending, consult a mechanic. Also check the prop spinner for security and look for streaks of grease or oil on the propeller blade face and on the leading edge of the cowling. In flight specks of oil on the windshield could indicate leaking propeller seals.

If you must reposition a propeller blade, move it in the opposite direction from normal rotation to keep the magnetos from firing the spark plugs—Always assume that the "gun is loaded. "Park" the propeller in the 10 o'clock / 4 o'clock position.