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  #1  
Old 06-01-2020, 04:37 AM
mturnerb mturnerb is offline
 
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Location: Ponte Vedra, FL
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Default How common are magneto failures as a cause of accidents?

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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Last edited by mturnerb : 06-01-2020 at 04:44 AM.
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  #2  
Old 06-01-2020, 05:46 AM
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rv6ejguy rv6ejguy is offline
 
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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.
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  #3  
Old 06-01-2020, 06:24 AM
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Pilot135pd Pilot135pd is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
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.
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Old 06-01-2020, 06:57 AM
Desert Rat Desert Rat is offline
 
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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.
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Old 06-01-2020, 07:06 AM
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Mel Mel is offline
 
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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.
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Old 06-01-2020, 08:01 AM
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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?
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  #7  
Old 06-01-2020, 08:19 AM
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N804RV N804RV is offline
 
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Quote:
Originally Posted by Pilot135pd View Post
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."
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  #8  
Old 06-01-2020, 08:29 AM
airtractor8 airtractor8 is online now
 
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Location: Dardanup. Western Australia
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Default

Quote:
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. 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

Last edited by airtractor8 : 06-01-2020 at 09:31 AM.
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  #9  
Old 06-01-2020, 08:33 AM
cajunwings cajunwings is offline
 
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Default 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.

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  #10  
Old 06-01-2020, 08:45 AM
RV7ForMe RV7ForMe is offline
 
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Default 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.
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