"Jim Fisher" wrote in message ...
So, either the mag failed during my flight back from the beach and I didn't
notice or it failed during the last crank . . . Or perhaps gremlins sneaked
in the hangar overnight. It was a little unnerving to think it might have
failed during flight and I didn't notice.

So, yeah, just 'cause you had no run-up problems during the previous flight
doesn't mean you won't have them on the next.

I just had a Cherokee fail a runup a couple weeks ago with a student.
I showed him how to clear the plugs but the mag was clearly dead. My
concern was that he was going to switch back to the other mag before
pulling the throttle down. If you get next to nothing on a mag during
runup, don't switch back to the good mag or you may blow out your
exhaust. Let the engine die or pull the power back to idle before you
switch back to a working mag.

-Robert