Have you heard of a "hot" magneto check?

If done in the air, it's no violation of any regulation per se, just plain dumb, and serves no useful purpose.

If a mag goes bad inflight, you're gonna switch from both to whichever one is firing. This ends up as a trial and error type of thing.

The hot mag check is done on the ground prior to shutdown. The idea is that when the mag switch is in the OFF position, the mags are indeed off and not susceptible to firing inadvertently. If the engine fails the check; that is if the the engine doesn't momentarily skip when you switch to the OFF position, then one of the leads to one (or both) magnetos is broken and must be repaired or replaced.

The procedure is also known as a grounded mag check. You won't find it in any Cessna handbook. Many instructors these days haven't done one because their instructors haven't ever heard of it.

How To Check A Magneto

I vaguely remember my instructor doing it in flight in an early flight lesson to demonstrate that an engine failure is nothing to panic about, the airplane glides just fine with a dead engine, the prop continues to turn (and the engine immediately restarts when the mags are turned back on). This was done with the engine at idle and near the airport. That was almost 50 years ago and I haven't done it since. Of course that wasn't to check for a hot mag. Perhaps there are regulations against it today. After all spin recoveries are no longer required either.

I have never heard of such a thing. I know I have heard of mag checks on the ground where you momentarily turn the ignition to the off position as to make sure both mags are being disengaged appropriately. But as far as an in flight check, that doesn't sound like anything but dangerous to me.If you are in the air you do not care if a mag will not disengage, you want both of them to be running so why does it matter? And if you are checking to make sure they are both operating correctly, and one is not, the engine will shut down for at least as long as the ignition switch is turned to the bad mag. This is very interesting to me...

A hot mag check is performed on the ground, immediately before shutting down. It is performed by momentarily turning the ignition to off and ensuring that the engine does not continue to run. If the engine continues to run with the ignition off, it indicates that one or both of the mags are improperly grounded (a broken "p-lead"). After checking, immediately turn the ignition back to both, so that the engine continues to run and can be shut down using the mixture control.

Not a good idea to do it in flight, the engine is developing full power and you suddenly take away the spark and then add it back, that causes a sudden rotational change to the engine which is not healthy for the crankshaft, accessories like alternator and vacuum pumps, gears in engine, etc. Do your hot mag checks at idle on the ground, that way if the switch fails you just walk away.

You do it by placing a finger on the end on the magneto hi tension wire and asking somebody to turn on the ignition. If you get shocked the magneto is working properly.

Grumpy and Chris have given you the correct gouge.

Was thinking to ask this question too