HOT MAG

[AHassell]

While working on a costumers Cessna 182 1986 model , I found the left mag was hot . I checked the Plead connection and every thing checked out. I did a continuity check with the switch . I had an open to the left mag the right mag was working correctly in all switch positions. So I removed the switch ( being careful to mark all the wires)Thinking I had a bad mag switch. I did a continuity check to the left Plead still no continuity.

I was really dreading running a new Plead when I took a look at the factory installed connector on the Plead it looked terrible . I removed the factory connector and checked continuity. I had continuity ! Installed a new connection from the Plead wire to the mag and the shielding to ground. every thing worked normally.

Everyone should be suspicious of the new connector to the Plead.

 

[bnt83]

While working on a costumers Cessna 182 1986 model , I found the left mag was hot . I checked the Plead connection and every thing checked out. I did a continuity check with the switch . I had an open to the left mag the right mag was working correctly in all switch positions. So I removed the switch ( being careful to mark all the wires)Thinking I had a bad mag switch. I did a continuity check to the left Plead still no continuity.

I was really dreading running a new Plead when I took a look at the factory installed connector on the Plead it looked terrible . I removed the factory connector and checked continuity. I had continuity ! Installed a new connection from the Plead wire to the mag and the shielding to ground. every thing worked normally.

Everyone should be suspicious of the new connector to the Plead.

Its not particularly quick and easy to rewire the firewall forward so generally the wiring up front on these old airplanes looks like dog ****, especially p leads.

I completely rewired my dad's airplane, a 1968 177 with 1400 hours total time as the wiring up front was terrible.

http://www.pilotsofamerica.com/forum/showthread.php?t=59403&highlight=cessna+177

 

[Silvaire]

The whole idea behind the magneto is that it is completely autonomous and has to be purposely disabled by shorting it to ground. So ANY broken or disconnected p-lead ends up in a hot mag condition. This is one of the reasons we have the idle cut-off on most carburetors and fuel injection systems.

But really, the bottom line is that you should always treat an airplane propeller like a loaded gun and not take anything for granted.

 

[flyingron]

Mine was often hot because of a balky ignition switch. Always check that. The failure more on mine was such that I aways tell everybody NEVER TRUST A MAG TO BE GROUNDED. People come here and whine "but I do a hot mag check on every shutdown" ... bullhockey. You could turn mine to off and yes the engine would die, but remove the key and one of the mags would go hot again.

 

[Pedals2Paddles]

The hot mag check on shutdown certainly verifies it works properly at that time. 20 minutes later, the wire could fall off. So ya, don't turn the prop with your head next to it.

 

[Dan Thomas]

Watched an idiot instructor last weekend showing a female student how to pull the propeller through during a preflight. In the direction of usual rotation, yet. She was pushing down on the blade, leaning right over it, just asking (without knowing it) to be beheaded. They were some distance away, too far to yell at them. Don't know who they were; was just visiting the museum at that airport. And I don't know why anyone would need to do that maneuver, anyway.

Dan

 

[Skip Miller]

The hot mag check on shutdown certainly verifies it works properly at that time. 20 minutes later, the wire could fall off. So ya, don't turn the prop with your head next to it.

Negative. It depends on how you do the mag check.

I had been in the habit of turning the key to the off position and leaving my hand on the key. I realize that my hand pressure was still in the counter-clockwise direction; i.e. I was trying to turn the key "more off". When released, the key would move to the off detent position and in that position the mags (or at least one of them) were live.

I am now in the habit of removing my hand from the key during the mag check. (And I haven't had that problem since....)

 

[Dan Thomas]

Negative. It depends on how you do the mag check.

I had been in the habit of turning the key to the off position and leaving my hand on the key. I realize that my hand pressure was still in the counter-clockwise direction; i.e. I was trying to turn the key "more off". When released, the key would move to the off detent position and in that position the mags (or at least one of them) were live.

I am now in the habit of removing my hand from the key during the mag check. (And I haven't had that problem since....)

See this AD: http://rgl.faa.gov/Regulatory_and_G...C14960A415D956BD86256E520053A53E?OpenDocument

It addresses a problem similar to yours, and you might want to have a look to see if that affected switch is installed. It's one of those much-overlooked ADs, and at least half of the Bendix switches I check fail the test. They can be deadly, especially once they get old and sludged up a bit.

Dan

 

[Skip Miller]

See this AD: http://rgl.faa.gov/Regulatory_and_G...C14960A415D956BD86256E520053A53E?OpenDocument

It addresses a problem similar to yours, and you might want to have a look to see if that affected switch is installed. It's one of those much-overlooked ADs, and at least half of the Bendix switches I check fail the test. They can be deadly, especially once they get old and sludged up a bit.

Dan

Dan, the AD addresses a different problem. In my plane, with the switch off and the key out of the lock, the mags were hot. However, with key in the too-far left position, the mags were off giving the false result that the mags were safely off. No, let go of the key and they were live.... -Skip

 

[flyingron]

The hot mag check on shutdown certainly verifies it works properly at that time. 20 minutes later, the wire could fall off. So ya, don't turn the prop with your head next to it.

NO, it doesn't even do that...read my test.

 

[Pedals2Paddles]

Yes, it does exactly what I said. It tests exactly what you test, nothing more, nothing less. My whole point is you have no idea what happens 10 seconds or 10 minutes later so you must treat it accordingly.