My nephew is training for his PPL and mentioned missing a quiz question about a "hot mag check". Apparently his ground school instructor has spoken about this "hot mag check" which according to him is to be performed during FLIGHT (Cessna 172). This idea makes no sense to me! In my mind turning off ignition to either mag during flight is asking for trouble. It should be against AFM procedures, (normal and emergency), as well as some federal regulation (any country) for public endangerment purposes. Have any of you heard of such a procedure? If so where can it be referenced? If it is a violation of procedure or regulation which one? Thanks
grumpy geezer2008-12-05T12:26:34Z
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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.
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.