rikur_ wrote:The worse mag fault I've come across was a rental aircraft where the key could be removed in any position. Somewhat defeats the check of keys in pocket before touching the prop.
The worst fault I've come across was on my T67M where the magnetos were grounded the the key in the Off position, but both became live again when the key was removed...! Even our dead cut check (or is it live cut?) couldn't have detected this. This dangerous condition existed unknown for several weeks and was eventually found during the annual check.
Thanks to all for your thoughts - lots of valid views, but the consensus seems to be that the only potential harm is a backfire, and my experience over ten years of operating my shaeroplane is that it NEVER backfires during the check if the throttle is at idle, so I'm inclined to carry on as I have been.