Lost a Mag in Flight

[201er]

I was going to take a flight up to Blairstown, NJ today but was going to make a stop by my mechanic at Robbinsville. I had flown my entire Canada trip without a single squawk, then when I got back, the tie down ring just clean fell out as I was putting a rope on. Rust was apparent from inside and the remainder of the bolt was lodged up in the wing socket. So the plan was to stop by my mech to have this removed and replaced.

 

 

Taxiied the long way to runway 9 for the mere 3 knot headwind. Did a run up, everything a-ok. In fact I did the long way with the mixture leaned to best power and run up with my JPI in normalize on the EGTs and made sure to get an EGT rise on each mag. Take off was normal but the climb was anemic. I felt like I didn't have the altitude to make the right turn-out I intended, so I hung on and flew an outbound pattern. Coming out of the pattern and on course, I noticed my EGTs around 1350 across the board. I figured it was because I pulled the mixture too much (but really it was only a smidge). I pushed in the mixture and it barely made a difference.

 

At first I thought it was an issue with fuel flow, that the engine was running leaner than desired. Change in mixture continued to show about 100 degrees over normal across the board. Reduction in throttle only made the engine run rougher, more the feeling of flying excessively lean. Then it dawned on me that it was most likely a magneto failure. I kept the power in and climbed to 3000ft (higher than I would have normally done on the quick 20 mile run). I didn't turn back because this was not yet an emergency, I was making power, and there would be repair services available at my destination but not my departure. I kept the altitude all the way to the airport while keeping an eye on fields.

 

I didn't dare reduce power or descend until over the downwind of the airport. Because reducing throttle felt rough every time prior, I wasn't certain that the engine wouldn't quit with a power reduction. I slowly reduced power while circling aggressively to get rid of altitude. I was a bit peeved by a skyhawk taking his sweet time exiting the runway after cutting into the pattern. I announced that I was coming in with possible engine trouble. I kept things a bit high in the pattern and didn't pull throttle idle till on final. I flew the pattern a bit too tight and had to S turn and slip on final. Nonetheless I made a smooth touchdown and was off midway down the runway by the maintenance hangar. On the taxiway, I stopped and did a run up. Two clicks left to the right mag and the engine began to quit. There it was! As predicted, dead mag. I pulled up to the hangar and dropped my bird off with the doctor. Let's wait and see what it was. Boy am I glad I converted my a3b6d to a3b6 with separate mags!

 

[WardHolbrook]

Isn't redundancy a wonderful thing? 

[MooneyBob]

Glad you made it ok.

[PaulB]

How many hours were on your mags?

[PTK]

"...Boy am I glad I converted my a3b6d to a3b6 with separate mags!..."

The Bendix dual setup are perfectly good mags. It has a single drive from the engine but they are two totally independent mags.

There is only one gear train inside the engine to drive the mags anyway. No matter how many mags you have! If these gears fail your mags, any mags, will fail.

Mags fail due to internal components and not the drive coupling to the engine.

There has not been any NTSB reports that I know of that show more frequent failure of the dual mag. All mags are held onto the case by clamps. These clamps are loosened to time the mags then tightened. Sometimes these clamps can loosen on their own when not properly torqued or reused throwing the timing off. This is NOT unique to the dual mag. It can happen to any mag.

Strict adherence to 500 hr inspection and always using new and properly torqued clamps and washers is very important.

[chrisk]

Really glad this turned out well for you.   I can't even imagine the stress this would have caused, had it happened on your Caribbean trip.

[201er]

A few more thoughts. First of all, it's important to keep your cool and not turn into a slightly problematic situation into a real problem. Secondly, my full engine analyzer really helped me diagnose my problem and prioritize. At first I thought it was a fuel or leaning problem until I realized that EGTs were high and CHTs were low! I recalled a discussion on mooneyspace explaining why CHTs are lower during a mag check so that was when I became 90% certain it was a single failed mag.

Without an engine analyzer and perhaps a more distracted pilot, I can see an accident chain beginning. Thinking from the roughness that the engine is on fringe of imminent failure could lead a pilot to make a more rash maneuver than necessary. I am glad I had the information on hand and the ability to use it. I am more convinced than ever that a full engine analyzer is the 2nd best add on gadget a pilot can get after an angle of attack indicator.

Now a few questions for veteran pilots. What is the best way to run an engine on a single remaining mag? I didn't want to change anything because the engine was working and it would get rougher if I reduced throttle or RPM. I wanted to lean the mixture some but already seeing high EGTs, I did not want to make them higher in that configuration. I wonder if the mixture was ezcessively rich from lacking the second spark and if some leaning would have been better? Any other thoughts in case someone is ever caught out on a single mag with a long way to go? Whats the best way to fly on it without making it any worse?

[PTK]

Perceptible roughness and all EGT's elevated is normal when running on one mag.

If mag doesn't totally go offline but something fails to throw timing off such as distributor gear failure, then turn off the bad mag and fly to your destination or next runway.

The most common mag failure is distributor gear failure. The mag keeps on firing but randomly all over the place.

Things become hairy when the pilot doesn't recognize it and makes it worse than it has to be.

Just shut off the bad mag and fly. Redundancy is indeed a beautiful thing.

[Andy95W]

There has not been any NTSB reports that I know of that show more frequent failure of the dual mag. All mags are held onto the case by clamps. These clamps are loosened to time the mags then tightened. Sometimes these clamps can loosen on their own when not properly torqued or reused throwing the timing off. This is NOT unique to the dual mag. It can happen to any mag.

I agree it can happen to any magneto. But if it happens to me, I suffer the loss of a magneto; if it happens to you, you lose the engine.

[PTK]

I agree it can happen to any magneto. But if it happens to me, I suffer the loss of a magneto; if it happens to you, you lose the engine.

If the dual mag is maintained properly according to set requirements I'll stick my neck out and say it's as reliable as any.

The fact is that our Lycomings have only one gear on the crankshaft driving the gears in the accessory housing.

All mags are driven off of this one crankshaft gear.

[yvesg]

Mike, did you check your maintenance logs and find out when was the last time the mags were inspected? The recommendation is every 500 hours.

Yves

[Cris]

Mike Very well done! Safety first through out the process. Kudo's to you

[Piloto]

The failure could have been caused by a magneto switch or P-lead chaffing with ground. I agree with others that there is no difference between single or dual mags. The gear that drives the mags is not under any stress to cause it to fail.

 

José

[jnisley]

Nice job staying safe by staying cool!

Several years ago a mag quit on me on during a two hour cross country, what alerted me that something was wrong was higher then normal EGTs and slight to moderate engine roughness (I didn't realize I had lost a mag until I did my preshut down mag check) the problem ended up being in the ignition switch.

[jetdriven]

Well there is a few caveats, one the magneto hold-down system. The dual mag is held down with two clamps and studs which have star lockwashers and nuts.  4 times now I have seen a loose mag because someone loosened the mag to reset the timing, then tightened it back up. One of those resulted in the Slick mag (2 mag O-320) sitting on the engine mount, fell right out of the case.  Check for yourself, remind your mechanic, and always ask if the mag nuts were loosened, those star washers are not reusable. Mark them with torque seal and if it is ever broken, replace the star washers. If you're not sure, replace them anyways.  At least on a two-mag engine you have two chances to get home on this, with the Bendix dual mag, you get only one.

 

The other is the breaker point cam.  The points for both sides of the dual mag share this lobe.  If your mechanic or shop sets the E-gap they must loosen this screw to adjust the cam, but its a special screw with made-on loctite and it is NOT reusable. If its reused,  will then loosen on the next flight, the engine power will roll back to idle or it stops, and you are landing off-field.

 

the third single-point failure is the impulse coupling. If it fails, the mag drops to zero timing and the engine may not shut down, but it wont make enough power to sustain flight.

 

The fourth is the mag clamps themselves. They redesigned them and this is detailed in Lycoming SI 1508C.  I recommend checking if you have these clamps and the SI has been complied with before further flight. I did mine, and the top clamp was fine. The bottom clamp was not reaching the flat holding surface, it was cocked and clamped on the magneto shaft housing which causes it to break. The old style clamp tab was too long to fit between the stud and the shaft housing.  Since the lower clamp was not flat, the lock washer was not clamped up and the nut was loose.

http://www.lycoming.com/Portals/0/techpublications/serviceinstructions/SI%201508C%20%2802-10-2011%29/Dual%20Magneto%20Attachment.pdf

 

I used to fly behind the dual mag and trusted it just the same as I do my 2 Bendix mags today. However, Lycoming and Bendix claim that a properly conforming dual mag engine is just as safe as two separate magnetos. Just be sure your mags and engine are conforming. Not everyone knows these single-point failures.

[ArtVandelay]

Well there is a few caveats, one the magneto hold-down system. The dual mag is held down with two clamps and studs which have star lockwashers and nuts.  4 times now I have seen a loose mag because someone loosened the mag to reset the timing, then tightened it back up. One of those resulted in the Slick mag (2 mag O-320) sitting on the engine mount, fell right out of the case.

This happen to my plane (long before I bought it) 80 hrs after a new engine was installed, fortunately they upgraded to 2 mags.

[201er]

I should point out that the mags were new/overhauled less than 400 hours prior, more like 300. I'm getting the failed mag removed, repaired, and 500 inspected while they're at it.

[jetdriven]

open the cover and see if the points open. If not you can adjust them. The crappy Kelly points have much to be desired and I'd almost bet thats your cause. Mine did. The 1200s go on for hundreds of hours, no need to drop 500$ on a R/R and 500hr.

[Sabremech]

Strict adherence to 500 hr inspection and always using new and properly torqued clamps and washers is very important.

[N601RX]

I have my mags staggered in time. One has about 100 hrs since new, the other one is a little over 500. I check them inflight and will address the high time one when it's performance starts dropping. There were some issues a few years ago where some bad parts got into the supply chain and new cams and brushes were failing within a few hrs of being installed. It was fine at run up and you had a dead mag an hr latter.

[flyboy0681]

Maybe I missed it, but did you switch mags while trying to diagnose the problem? I've heard of similar situations before and cutting off the bad mag resulted in smoother performance because the bad one is upsetting the timing so much.

 

Just curious.

[201er]

Maybe I missed it, but did you switch mags while trying to diagnose the problem? I've heard of similar situations before and cutting off the bad mag resulted in smoother performance because the bad one is upsetting the timing so much.

 

Just curious.

Interesting question. I did specifically look at the ignition switch and possible even flick it clockwise to ensure it was on both and wasn't forgotten in a single mag accidentally from mag check. However, with the engine continuing to run the way it was, I did not want to mess with anything. I did not want to start changing anything until over an airport and my mechanic's airport was the closest anyway. So by the time I was in a reasonable position to change anything, I did not need to cause I was ready to land. I decided to just play it safe and go with what was working and not fiddle with anything till on the ground. Sure enough right mag would shut the engine entirely on the ground.

I guess you gotta be there to understand the reluctance to change anything when what you have is working although not ideally.

Given that the right mag wasn't even providing partial power, would shutting it make any difference at all?

[jetdriven]

you know the devil you got, you dont know the devil you might get.

 

 

I think flyboy is talking about when a mag jumps time. It starts the ignition event at the wrong time, perhaps 40d BTDC which will cause an engine to severely lose power and the CHTs get hot enough to melt down stuff in a minute or less.  In case of a really rough-running or overheating one, the L-R-both procedure has merit.

[Piloto]

David

 

You have a good point about the 500hrs inspection which leads to the question:

Which one is more reliable? A 500hr mag that has never failed or a 10hr overhauled mag. I have seen the same with engines and other equipment. My experience has told me: "if it is working fine leave it alone and don't mess with it".

 

José

[ArtVandelay]

David

You have a good point about the 500hrs inspection which leads to the question:

Which one is more reliable? A 500hr mag that has never failed or a 10hr overhauled mag. I have seen the same with engines and other equipment. My experience has told me: "if it is working fine leave it alone and don't mess with it".

José

My slick mags haven't been changed in 1200 hrs, I was going have them either serviced or replaced in upcoming annual, how far would you push it?

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