Care for an airplane’s ignition switch is often overlooked. If there are too many keys (weight) on the ring, hanging from the switch through hours and hours of vibration, the switch can be worn and damaged. The inner workings may be worn in such a way as to allow key removal in a position other than OFF. This is bad.

Even though the pilot diligently tested the grounding out function of the ignition switch before each shutdown (at idle power with avionics off, turning the key momentarily to OFF to verify the engine begins to die, returning the key to BOTH before the engine quits), if the switch is badly worn and the key can be removed while in, say, R (right), you have a hot engine. It may have been shut down normally with the mixture control, but now if the prop is moved forward, it may fire due to residual fuel in one or more cylinders. At least one pilot has been killed when the switch allowed the key to be removed in other than off, the mag was still hot, and he (unaware) moved the prop forward. The engine doesn’t actually start running, but can abruptly fire, moving the prop violently.

-Every leg: Verify the switch works to shut off the mags and then shut down the engine with the mixture.

-Once or twice a year: make sure the key will only come out in the OFF position.

-Always move the prop BACKWARDS, if you must move it (to accommodate the towbar, for instance).

photos:

Bad news, way too many keys and weight.

Okay, only 3.