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How common are magneto failures as a cause of accidents?

mturnerb

Well Known Member
Given the recent discussion of electronic ignition issues, and concerns on some folks' parts about reliability of either EI or magnetos, I decided to do a little personal research.

I reviewed the NTSB accident database, using the keywords "Magneto failure". Over a 30 year period, 27 accidents had this term. In a significant portion (maybe 1/3) of those a pilot or mechanic theorized that magneto failure had occurred but magneto failure was ruled out (magnetos were functioning correctly), or the cause of the accident was undetermined. In the vast majority of the magneto-failure related accidents since about 2000, failure was ascribed to either non-compliance with required or recommended maintenance (in one case more than 2500 hours since last magneto service/inspection - engine had close to 3000 hours SMOH) or magneto damage due to engine overspeed or backfires. Most of the accidents where magneto failure was a primary cause, with no mention of maintenance or inspection non-compliance, occurred before 2000. Many of these were ag planes (no idea why).

Using the term "magneto" for the search is not practical for this project - most of the references are simply to the pre-flight magneto check (based on a quick sample) and there are too many (>3000) for me to review in detail.

I didn't do any charts or spreadsheets, just scanned the reports and looked at probable causes.

I also tried the term "ignition failure" which returned a total of 6 results: most of these were electronic ignition (one magneto), including Rotax. Given the much smaller number of aircraft flying with electronic ignitions, this is significant but the small "n" makes it hard to draw any meaningful conclusions. None of these accidents were fatal - which makes me suspect that electronic ignition failures in fatal accidents may be very hard to detect, assuming there is more significant damage to engine/airframe/components.

I'm guessing there are a significant number of accidents where magneto failure occurred but damage to the aircraft made determination impossible, however since a majority of engine failure accidents are non-fatal (or forced landing still allows examination of engine even in a fatal accident) I doubt the number is a significant multiple of the known cases. All conjecture on my part, don't rely on my opinions.

Am I being naive or missing the bigger picture?
 
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With 2 mags, it would be highly unlikely that both would fail on the same flight so you probably would find few, if any accidents caused by double mag failures.
 
With 2 mags, it would be highly unlikely that both would fail on the same flight so you probably would find few, if any accidents caused by double mag failures.

That's how I would see it with the only exception if one magneto broke and threw parts into the engine and then that engine failure takes you down.
 
It seems likely to me that the vast majority of mag failures don't result in an accident, so that data isn't captured in the NTSB database.

I think that for the most part the opportunity for a mag failure to cause an engine failure would be limited to one physically coming apart and throwing parts into the accessory case, or maybe somebody who's been flying around on one because they haven't been doing a run-up and the other one fails in flight.
 
I've had one mag failure in over 53 years of flying, and that happened on the ground. (LOE RV Fly-In in Las Cruces)

In hindsight, the engine had been getting harder to start for several weeks prior.
 
Continuing on the idea of one breaking up into the engine, is it the one with the impulse coupler that breaks or can it be one without it?
 
Continuing on the idea of one breaking up into the engine, is it the one with the impulse coupler that breaks or can it be one without it?

Slick SB 1-19: "There have been limited reports in which impulse coupling stop pins have moved relative to the factory placement within the magneto frame of Slick magnetos. There has been one report of a liberated stop pin. A liberated stop pin could potentially enter the gear train of the engine, resulting in damage to the gear train, damage to engine accessories and could ultimately cause catastrophic engine failure."
 
continuing on the idea of one breaking up into the engine, is it the one with the impulse coupler that breaks
Yes it is. The impulse spring breaks or the flyweights on the coupling can get caught on the stop pins and break or the riveted type flyweight attachment fails and everything falls into the accessory drive gears and lunch's them putting the other magneto out of business as well.:eek: If you have a Lycoming with the single drive dual magneto (D-2000/D-3000) and the impulse spring breaks, the mag will go so far retarded the engine will not run at all or will have very little power. It doesn't matter about the broken bits on them :eek:
 
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Mags

I?ve been interested in the mag reliability question for a long time and scan accident data often. This is just my experiences & observations starting from the mid 70?s when I finished A&P school. I only know of 2 aircraft that were unable to stay airborne solely because of mag failure. 1 was a Tomahawk with dual Slicks (limited info) & the other a Mooney with D-3000 dual mag(oil seal failure mag full of oil). Another dual mag Mooney in New Orleans landed in the city after the mag came off the engine (mag was good, improper gasket used on install). When I ran a shop 85-90 with 200+ active customers and a busy flight school & charter dept we might have had 10 ?mag failures?. Usual report was mag found dead on pre takeoff run up, which could mean it was dead on last landing. The guys that listen when the plane is trying to tell them something and come in for maintenance likely prevent outright failures. We found and fixed lots of mag issues during inspections and did a lot of mag AD work in those years. I?ve always heard impulse couplings can come apart and cause engine damage but never saw anything like that myself. I have changed out a number of impulse couplings due to wear and strongly recommend adherence to the the manufacturer?s inspection interval(or more often). My 9 will have 1 impulse Slick and 1 ElectroAir.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
question?

Is it possible that a mag goes into a failure mode in witch the timing is off by an amount that it would make the engine break by firing at the wrong time? And I mean get into this on its own? Sorry for the "dumb" question. I have limited knowledge on the subject but it seems that timing does a world of difference in temperatures.
 
I?ve been interested in the mag reliability question for a long time and scan accident data often. This is just my experiences & observations starting from the mid 70?s when I finished A&P school. I only know of 2 aircraft that were unable to stay airborne solely because of mag failure. 1 was a Tomahawk with dual Slicks (limited info) & the other a Mooney with D-3000 dual mag(oil seal failure mag full of oil). Another dual mag Mooney in New Orleans landed in the city after the mag came off the engine (mag was good, improper gasket used on install). When I ran a shop 85-90 with 200+ active customers and a busy flight school & charter dept we might have had 10 ?mag failures?. Usual report was mag found dead on pre takeoff run up, which could mean it was dead on last landing. The guys that listen when the plane is trying to tell them something and come in for maintenance likely prevent outright failures. We found and fixed lots of mag issues during inspections and did a lot of mag AD work in those years. I?ve always heard impulse couplings can come apart and cause engine damage but never saw anything like that myself. I have changed out a number of impulse couplings due to wear and strongly recommend adherence to the the manufacturer?s inspection interval(or more often). My 9 will have 1 impulse Slick and 1 ElectroAir.

Don Broussard
RV9 Rebuild in Progress
57 Pacer

Those dual mags (assuming you mean two mags in one case) are notorious. Your experience is very consistent with what I saw in reading the NTSB reports.
 
There have been reports of mag bearings and gears fragging and the pieces fall into the rest of the gear sets and destroy everything in the accessory case. This often isn't a magneto issue directly but the drive system failure can cause a complete engine power loss.

A 540 in Australia had a mag bearing/ gear disintegrate on short final and it seized up the engine. Made it to the runway as I recall.
 
FWIW I have a hangar at KFIN which is the home of a large magneto overhaul compay and I personally know the owner and employees there. They have told me many times that just about every magnetos they receive for a 500hr overhaul is in real bad condition.

IOW, there is a reason the FAA has the 500hr overhaul requirement for mags.

:cool:
 
Dual mags

I don?t think Notorious is a fair assessment of the single drive 2 mags in 1 housing (D-2000/3000 series). I don?t particularly like them and they are harder to work on and more expensive to service, but properly maintained they are not unreliable. I wouldn?t pass up a good buy on a RV with a dual mag, but would probably convert to electronic ign at mag O/H time.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
Cirrus Failure(s)

There have been reports of mag bearings and gears fragging and the pieces fall into the rest of the gear sets and destroy everything in the accessory case. This often isn't a magneto issue directly but the drive system failure can cause a complete engine power loss.

A 540 in Australia had a mag bearing/ gear disintegrate on short final and it seized up the engine. Made it to the runway as I recall.

I've heard that some Cirrus SR22's with air conditioning installed have in some cases seen destruction of both flexible mag drive couplings due to a suspected harmonics issue. I seem to recall reading of a double drive failure in at least one case, but I can't currently find the source.

I also know of a banner-tow Pawnee at my home airport that experienced a total power loss (from mag shut-down) due to a rather interesting reason. The exhaust system (or muffler) burned through and promptly burned through the insulation on both p-leads causing them to short to ground. The pilot was on approach and, after jettisoning the banner, was able to glide to a safe landing on the runway.

I'm personally aware of 1 Glasair III that experienced a double failure of Electroair timing units that fit into the mag holes. This, however, was a case of the owner being aware of 1 failed unit and continuing to fly the aircraft and the other unit failed. It didn't result in total loss of power but he did experience significant power loss and roughness and was able to make it to a safe landing at an airport.

Just for fairness, I'm also know of 3 "all electric" aircraft that had failures due to less than expected capacity of electrical back-up systems (or delayed recognition of alternator failure). 1 resulted in a precautionary off-airport landing before engine failure, 1 resulted in a safe on-airport full dead stick, and the 3rd resulted in a full dead stick gear up landing on a runway that the pilot walked away from but the aircraft was essentially totaled.

I personally fly behind slick mags. The key to mag reliability is inspection and maintenance. It is essential to keep them clean inside, keep the points properly timed, and regularly inspect the impulse couplings if equipped. in 900 hours, I have had 100% dispatch reliability of my ignition system. At ~800 hours, I discovered a badly wearing impulse coupling during an annual condition inspection and I promptly replaced it. I typically pull my mags at every annual and inspect, clean, and re-time them.

Skylor
 
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I don?t think Notorious is a fair assessment of the single drive 2 mags in 1 housing (D-2000/3000 series). I don?t particularly like them and they are harder to work on and more expensive to service, but properly maintained they are not unreliable. I wouldn?t pass up a good buy on a RV with a dual mag, but would probably convert to electronic ign at mag O/H time.

Don Broussard
RV9 Rebuild in Progress
57 Pacer

Fair enough - I think I used the wrong word. My understanding of the bad rep was due to difficulty in servicing as you describe.
 
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