never had a mag quit on me before

[Yooper Rocketman]

I was flying back north from Ashville NC last summer (2014) and while doing my run up, after a fuel stop for cheap fuel in Indiana, I noticed during the mag check one side seemed a bit rough.  I leaned it and it seemed to clean "the suspect plug" so launched for home.  As I was over Lake Michigan (at FL170) I thought I detected some roughness.  I did all the normal stuff, check fuel, tried boost pump, switched tanks, then finally thought let's do a mag check.  Holy crap, the engine quit when I went to the one mag with a hell of a back fire when I went back to both.  I imagine the raw fuel in the exhaust lit off when hot exhaust hit the pipe.  I continued towards home base, as I was never out of glide range of an airport at that altitude and within 15 minutes of my discovery, I was in glide range to my airport as well.

My mechanic gave me 3 options.  He could repair it with replacement of some common parts (but no assurance this would fix it), send it out for repair, or for complete rebuild.  With prices going up by level of repair, ($350, $550, $800) and already over TBO, I elected to send it out for repair.  The mag shop screwed up and rebuilt it so I got a rebuilt mag for repair price.  I did NOT send the second mag out, as I don't know if I will be doing an engine in the next 100 or 300 or ? hours and would rather not dump the extra money in it and possibly return it with an engine core a short time later.

[PTK]

Did you reduce throttle before going back to both mags after engine quit?

[chrisk]

Did you reduce throttle before going back to both mags after engine quit?

I believe you want to set the mixture to idle cut off before restart, so you don't blow up your exhaust.  It's the reason for step #7, although I don't know why they didn't put it before the mag check. 

 

Power Loss in Flight

1. Throttle - FULL FWD
2. Prop - 2700 RPM
3. If ALT. AIR light on, proceed with POWER LOSS - AIR FILTER BLOCKAGE procedure
4. High Boost Pump - ON
5. Fuel Selector - OTHER TANK (FULLEST)
6. Mags - CHECK BOTH
7. If engine does not restart - Mixture - IDLE CUTOFF
8. Alternate Air - PULL OPEN
9. Mixture - ADVANCE SLOWLY TOWARD RICH UNTIL ENGINE STARTS
10. When engine starts retard throttle to desired power setting.
11. High Boost - OFF - If engine fails suspect engine driven fuel pump failure - proceed to ENGINE DRIVEN FUEL PUMP FAILURE procedure.
12. Alternate Air - PUSH CLOSED
13. If engine does not Restart - DESCEND BELOW 12,000' AND REPEAT
14. If engine does not Restart - PROCEED TO POWER OFF LANDING procedure

[PTK]

Thank you Chris. Mixture I meant to say. I mistakenly said throttle.

[jetdriven]

You really should retard both, to prevent an over speeds. Feed the mixture in first and get it relit. Then slowly put the throttle back in to cruise setting.  

[Shadrach]

I was flying back north from Ashville NC last summer (2014) and while doing my run up, after a fuel stop for cheap fuel in Indiana, I noticed during the mag check one side seemed a bit rough.  I leaned it and it seemed to clean "the suspect plug" so launched for home.  As I was over Lake Michigan (at FL170) I thought I detected some roughness.  I did all the normal stuff, check fuel, tried boost pump, switched tanks, then finally thought let's do a mag check.  Holy crap, the engine quit when I went to the one mag with a hell of a back fire when I went back to both.  I imagine the raw fuel in the exhaust lit off when hot exhaust hit the pipe.  I continued towards home base, as I was never out of glide range of an airport at that altitude and within 15 minutes of my discovery, I was in glide range to my airport as well.

My mechanic gave me 3 options.  He could repair it with replacement of some common parts (but no assurance this would fix it), send it out for repair, or for complete rebuild.  With prices going up by level of repair, ($350, $550, $800) and already over TBO, I elected to send it out for repair.  The mag shop screwed up and rebuilt it so I got a rebuilt mag for repair price.  I did NOT send the second mag out, as I don't know if I will be doing an engine in the next 100 or 300 or ? hours and would rather not dump the extra money in it and possibly return it with an engine core a short time later.

I had a similar situation over the Chesapeake with the seats filled.  I felt an ever so slight split second burble in the steady drone of the engine. It was so imperceptible that I thought it might just be the "auto rough" that tends to kick in when over large bodies of water.  A quick look at the EGTs told another story; the lowest was 1580.  I knew a mag had failed, but doing an in flight mag check to determine which one had failed would have scarred the chit out of my passengers. It turned out that the coil was shorting to the case on the right mag. 

Edited October 21, 2015 by Shadrach

[Yooper Rocketman]

Did you reduce throttle before going back to both mags after engine quit?

No, unfortunately, since I was flying over the lake, not expecting that was the problem, and caught totally be surprise, the mag was only off for a fraction of a second.  Yes, I've looked over the exhaust and since the repair have another 100+ hours on it, so really doubt there was any long term issue.  Just won't be doing power mag checks again for a while.  Needed to change my shorts after that flight.

[pinerunner]

I lost a mag just once. I was a student pilot taking off with a J-3 cub from a 2000 ft strip with trees at the end. Instead of clearing them easily I cleared them  not so easily. After taking it around the pattern and landing I did another mag check and I had lost one.  Made me glad I had two mags. I bet during the early years of flying they had a few unfortunate incidents berfore they decided duel, independant, mags were a must. At that same strip the C150 that was considered more "upscale" to rent wasn't able to clear the trees by much with both me and my slightly chubby instructor. Neat thing about that cub was it was the same plane my father had first owned and soloed a couple of decades before.