Dual Magneto Failure in flight?

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skipone

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skipone
Hi, curious to know if one magneto goes out in flight, could the second follow?

And if both went, would the engine just cut out ( zero sound) and you would just drop?

Could you survive with both out?
 
skipone said:
If just one went out, what are the audible and visual signs - a reduction in power and the plane shaking?
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Yes, but...
depends on how the mag failed. It could fail in the most common failure mode of just not firing in which case it would run like during your mag check - you might not even notice in flight. I could fail in a manner where it fires at the wrong time in which case you would need to cut off the mag to make the motor run smoothly.
 
skipone said:
If just one went out, what are the audible and visual signs - a reduction in power and the plane shaking?
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You do a single mag check on your run-up. there is a 50-100 rpm drop ideally.
 
skipone said:
If just one went out, what are the audible and visual signs - a reduction in power and the plane shaking?
Click to expand...

There would be a reduction in power. If you are flying a fixed-pitch prop, you would notice the RPM drop. If you were flying a constant speed prop plane, you would likely not hear much of a difference, but would hopefully notice the slight reduction in power.

There would likely not be a noticeable vibration.
 
Jeff Oslick said:
There would be a reduction in power. If you are flying a fixed-pitch prop, you would notice the RPM drop.
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My experience with a dead mag was a very modest power loss/rpm drop. I just sensed that the engine wasn't producing quite as much power as it should, flew on to the destination, and did a mag check before shut-down, which identified the dead mag. I didn't want to do an in-flight mag check and spook my passenger.
 
Jeff Oslick said:
There would be a reduction in power. If you are flying a fixed-pitch prop, you would notice the RPM drop. If you were flying a constant speed prop plane, you would likely not hear much of a difference, but would hopefully notice the slight reduction in power.

There would likely not be a noticeable vibration.
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Jeff in the scenario that either one or both went out and you were gliding down in a remote area where you had no choice but to put it down on water... I gather if it had wheels it would be a hell of a rough landing and the tail would likely flip over the nose, and then sink, do you agree with that? And if it had floats, the landing would be fine?
 
With normal maintenance the likelihood of that happening is near zero.

the ignition switch is the item that would be the most likely item to fail.

Mags are maintained better than switches.
 
There are dual mags and then there are dual mags. An older engine like an O200A has two completely independent mags that are mounted in different locations driven by the flywheel. There are some particular engines that were built later with a dual mag arrangement that mounted at the same position with a common gear that meshed to the flywheel, then drove two different mags. That common gear acts as a single point of failure. To make things worse one or more of those gears are plastic. I would NOT purchase an aircraft with that arrangement unless there were a way to upgrade to a two completely independent mag drive arrangement.

Tom can probably comment on the common mag drive arrangement.
 
skipone said:
Hi, curious to know if one magneto goes out in flight, could the second follow?

And if both went, would the engine just cut out ( zero sound) and you would just drop?

Could you survive with both out?
Click to expand...
I can assure that a second mag (in my case the other half of a D3000 Bendix) can fail within seconds of the first. The engine stops making power but the prop keeps windmilling. From 9,000’ a sharp controller found me a strip of asphalt within gliding distance, and all was well.
 
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I lost a mag in flight. Non-event and barely noticeable.

I fly behind a constant speed prop. The only indication that was possible to notice, which I did but did not realize its significance, was the loss of horsepower on the climb out from a gas stop: extremely shallow.

I attributed this loss of horsepower to the heat/humidity of a Louisiana afternoon. I was wrong.

It was only until the next morning during the mag check did I realize there was something wrong; I pray my engine never makes that sound again during the run up.

Took it over to the maintenance shop on the field. The mechanic diagnosed the issue within minutes: a broken gear inside the mag itself.
The second mag (which I'm eying at replacing now!) ran fine all by its lonesome after losing the right neighbor.
 
skipone said:
Jeff in the scenario that either one or both went out and you were gliding down in a remote area where you had no choice but to put it down on water... I gather if it had wheels it would be a hell of a rough landing and the tail would likely flip over the nose, and then sink, do you agree with that? And if it had floats, the landing would be fine?
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Well, were going far afield from the initial question. First, if only one mag goes out, I'm continuing on to an airport. The odds of both mags going out at the same time in my plane (a Cessna 182) are very slim. We overhaul our mags every 500 hours, and we do it on an alternating schedule so it isn't both mags getting overhauled at the same time, in case there is a quality issue with parts, or a technician having a bad day.

As far landing in a remote area on water, I *very* rarely fly out of gliding distance of land, and when I do, my "out of gliding range" exposure is only a few minutes. Each type of airplane has a particular ditching profile in the operating handbook (or equivalent, for older planes), and you follow that procedure. Generally, in fixed-gear planes, when ditching you slow as much as possible and ditch without flaring, so the gear all hit the water at the same time with a moderate sink rate, to help prevent a nose-over. Unfortunately, this is a procedure that is essentially impossible to practice, so you have to "fly the numbers" and do what your training tells you do. You crack the door(s) open before ditching so you aren't fighting the water pressure to open the door(s).

Why do I have a feeling you're an author hunting down details for a story?
 
Does LOP operation change things with a constant speed prop? I’m thinking some rough engine operation would result in LOP with one mag out.

Obviously I’ve not done an inflight mag check running LOP. Will have to try that.


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MBDiagMan said:
There are dual mags and then there are dual mags. An older engine like an O200A has two completely independent mags that are mounted in different locations driven by the flywheel. There are some particular engines that were built later with a dual mag arrangement that mounted at the same position with a common gear that meshed to the flywheel, then drove two different mags. That common gear acts as a single point of failure. To make things worse one or more of those gears are plastic. I would NOT purchase an aircraft with that arrangement unless there were a way to upgrade to a two completely independent mag drive arrangement.

Tom can probably comment on the common mag drive arrangement.
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the dual mag found on the Lycomings has more than one point of failure, It has a impulse coupling, shaft and gear. all other parts are duplicating in each part of the unit.

I steer my customers away from the 172 s with the the H2AD engines.
to change from the dual mag requires a engine change to an engine with 2 mags.
 
Tom-D said:
the dual mag found on the Lycomings has more than one point of failure, It has a impulse coupling, shaft and gear. all other parts are duplicating in each part of the unit.

I steer my customers away from the 172 s with the the H2AD engines.
to change from the dual mag requires a engine change to an engine with 2 mags.
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Dual mag vs two mags?
 
MBDiagMan said:
There are dual mags and then there are dual mags. An older engine like an O200A has two completely independent mags that are mounted in different locations driven by the flywheel. There are some particular engines that were built later with a dual mag arrangement that mounted at the same position with a common gear that meshed to the flywheel, then drove two different mags. That common gear acts as a single point of failure. To make things worse one or more of those gears are plastic. I would NOT purchase an aircraft with that arrangement unless there were a way to upgrade to a two completely independent mag drive arrangement.
Click to expand...

As a student pilot on a solo flight in a 172 to pick up my instructor, I had that gear fail which caused both mags to fail. I was on very short final and made the runway. Pushed the plane the rest of the way to parking. I was shocked they made such a non redundant system.
 
Kent Wien said:
As a student pilot on a solo flight in a 172 to pick up my instructor, I had that gear fail which caused both mags to fail. I was on very short final and made the runway. Pushed the plane the rest of the way to parking. I was shocked they made such a non redundant system.
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What did it sound like as it went out and when it was out? Did the propeller keep windmilling?
 
MBDiagMan said:
There are dual mags and then there are dual mags.

Tom can probably comment on the common mag drive arrangement.
Click to expand...

Lance F said:
I can assure that a second mag (in my case the other half of a D3000 Bendix) can fail within seconds of the first. The engine stops making power but the prop keeps windmilling. From 9,000’ a sharp controller found me a strip of asphalt within gliding distance, and all was well.
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Hence when at reman time back in January of '19 we went with a Lycoming factory overhaul exchange. We traded the A3B6D for an A3B6, gaining two independent mags driven by separate gears and shafts. We also went to roller tappets, but the main thing was increased safety due to the mags.
 
skipone said:
What did it sound like as it went out and when it was out? Did the propeller keep windmilling?
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It was was 31 years ago, but as I remember, when I added power it just wasn’t there. Prop windmilled until touchdown.
 
My mags had cooling problems and yes, they both failed at the same time. The scenario would go like this, go fly for an hour and take a break. Come back to the plane, do a run up and check the mags. All fine. Takeoff and not long afterward things started misfiring. I was always able to limp it back to the field but it is scary.
 
skipone said:
Jeff in the scenario that either one or both went out and you were gliding down in a remote area where you had no choice but to put it down on water... I gather if it had wheels it would be a hell of a rough landing and the tail would likely flip over the nose, and then sink, do you agree with that? And if it had floats, the landing would be fine?
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http://www.equipped.com/ditchingmyths.htm

Sent from my SM-G965U using Tapatalk
 
Although there are a couple possible common points of failure on the Bendix dual mag none of those caused my failures. The points/contacts on both sides wore to the point they didn’t open at the same time. This was a maintenance issue and could have happened with two independent mags. Nothing wrong with a properly maintained dual Bendix mag.
There are LOTS of possible single points of failure on single engine airplanes.
 
In most aircraft, there are two separate mags in the ignition system, attached at different locations on the engine. For almost all mag failure modes, the failure of one magneto is not likely to affect the other. The failure of one magneto will result in a slight loss of power, unless you have a failing spark plug on the remaining good magneto ignition harness, in which case you might also experience engine vibration from the missing cylinder. But typically it is just a slight reduction in rpm.

I've had two in-flight magneto failures in 35 years, both shortly after takeoff. The tipoff was a lower than expected Vy climb rpm, and diminished climb rate. A quick in-flight magneto check revealed the silence on one mag. In both cases, a return to the departure airport was warranted to repair or replace the offending magneto. Hey, that's why we have two magnetos. Failure of one means the other can be used to uneventfully fly to a precautionary landing for repairs.

If both magnetos fail, it's just a basic engine failure mode. You glide to an emergency landing, using your emergency checklist and training skills. This is something every pilot trains for during primary instruction. I've had one of those, too, but it was likely carburetor ice, not a dual magneto failure. A dual mag failure has to be a pretty rare event in general aviation for aircraft with independent magnetos.
 
Maintenance. And training. Both are essential to safely operating magnetos. Magnetos are failure-prone, which is the biggest reason we have two of them. We have one carb or fuel injection system, which tells you something about the most common cause of engine performance hassles: electrical, 90% of the time.

Maintenance: These things suffer wear, corrosion, and damage due to age and heat. If the owner makes a lot of short flights, or just ground-runs it and puts it away sometimes, moisture builds up in the case and corrosion takes over. If that impulse spring corrodes it can break, and if it breaks the timing on that mag goes to around TDC and the spark from it is useless. On the Bendix D-series mag, if that spring breaks BOTH magnetos go to TDC, no advance, and you are going to land whether you like it or not.

I once removed a mag from a 170 that was acting up. I found that the ball bearing in the front had corroded so much that the balls were coming out. If that mag had continued like that it would likely have broken its shaft or gear and the result could easily be accessory case gear failure, and the engine would be dead. That mag likely hadn't been off in 30 years. It required an expensive new mag, where regular inspections and maintenance would have had it still airworthy.

Points and rubbing blocks wear out. Condensers can fail. Plastic gears wear out, sometimes rapidly. If the distributor's plastic gears wear enough they can lose their timing positions and start sending sparks to the wrong plugs, causing all sorts of backfiring and power loss. That's where training comes in. Do you know why we have a mag switch that can shut off a magneto? For times like this. Check the mags and leave the switch in the position that the engine runs smoothly, and head for a runway. Don't fight the silly thing as it burps and barks and surges. Shut off the rogue mag.

Like Tom said, that mag switch gets ignored. There are two common mag switches, the Bendix and the ACS. I have found 20 and 30 years of log entries showing that the Bendix switch AD test has been carried out annually. I crawl under the panel and find that the airplane has an ACS switch, and it has its own AD that is far different from the Bendix, and the airplane has been legally unairworthy since 1993. https://rgl.faa.gov/Regulatory_and_...B8ABD56539B4684886256A3E00759DBF?OpenDocument

The Bendix AD requires testing of switches that do not have the four-digit date code, or the white dot indication modification. I have found that AD test done for years on switches with the date code. https://rgl.faa.gov/Regulatory_and_...C14960A415D956BD86256E520053A53E?OpenDocument

Do some mechanics never crawl under the panel to get a look at stuff??? I guess not. Vacuum filters crumbling and falling apart. Holes in aluminum vacuum lines. Wiring and plumbing getting chomped by control system movements. Worn cables. Burned terminals on landing light switches. Altimeters, especially, with outstanding ADs on them.
 
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I once saw a pilot that thought a 0 - 0 mag drop was a good thing. until he was shown the engine would not shut down by turning the key off.
ADs ..... What?
 
skipone said:
What did it sound like as it went out and when it was out? Did the propeller keep windmilling?
Click to expand...

Jeff Oslick said:
Why do I have a feeling you're an author hunting down details for a story?
Click to expand...

I agree with Jeff. Your questions are oddly specific and yet unusual. If you let us know the context of why you're asking, we can probably give you a better answer. And if it is a book you're writing, that's cool too! We'll be happy to give you way more advice than you probably want!
 
Question for the OP:

this is a very specific and rare issue you’re bringing up. Any special reason?

edit: Darnit I posted this without reading the above, which asks the same question.
 
Bear in mind that a mag can "fail" by slipping its timing...which may cause severe roughness, even if the other mag is good. Use the mag switch to isolate. Happened to a friend of mine in an RV-7 on takeoff. Engine went rough, he checked the mags, and flew out normally on the good mag.

Ron Wanttaja
 
When one mag fails, bear in mind that a graphic engine monitor will likely catch your eye as all EGT’s will climb due to delayed flame front, secondary to one of the two plugs/cylinder going offline.


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skipone said:
no choice but to put it down on water... I gather if it had wheels it would be a hell of a rough landing and the tail would likely flip over the nose, and then sink, do you agree with that?
Click to expand...

The DHC1 Chipmunk (fixed gear taildragger) Pilots Notes say something like:-

"Do not ditch.

If ditching is inevitable the aircraft will invert on ditching. Open and lock back the canopy in advance of ditching ... and pray."

OK. I made up that last bit.

The reason I remember that bit from so long ago may be related to a single magneto drive failure at 500 ft after take off. Engine ran rough but kept going. I was a student flying with an instructor who made all the decisions.

At low altitude the rough running drill is to leave the switches well alone because if the wrong one is turned off the engine may stop and there may not be enough time to restart it. The aircraft was maintaining altitude and we landed on a runway.
 
erkmann said:
When one mag fails, bear in mind that a graphic engine monitor will likely catch your eye as all EGT’s will climb due to delayed flame front, secondary to one of the two plugs/cylinder going offline.
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Mine will also note if the thing isn't firing.

I'll take some issues with the assumptions (not yours Erk but others):

The reason you have two mags isn't so much that the concern is that a mag will fail. Mags are fairly reliable, however, plugs can foul and mags are crappy spark sources (compared to other ignition types). The point of dual mags is that it also comes with dual plugs.

While it's possible a mag can break independently that doesn't mean that dual failure is unlikely. A statement was made that (other than the dual mag) that they are connected in different spots on the engine. Well, different drive, but they're usually within inches of each other. They're subject to the same environmental factors usually. Like I said, I cooked a few coils on Bendix mags until I figured out what was going on and it would tend to manifest itself as both mags dying near simultaneously. They share the same accessory case and in many cases the same cheapo ignition switch, which can again make them not entirely independent systems.
 
Tom-D said:
the dual mag found on the Lycomings ... has an impulse coupling, shaft and gear. all other parts are duplicated in each part of the unit.
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Not exactly, Tom... there's only one lobe to actuate the points for the two mags... and it's held in place by a one-use-only screw and washer. Folks have been known to reuse that screw, and the lobe comes loose. That ends up in both mags firing at the wrong time, or not firing at all... the more annoying failure is when one of those nylon gears throws a tooth, or two, and the thrown teeth end up making their way to the OTHER mag, destroying its function.

I've never heard of an engine with two separate mags having an internal mag failure propagate to the other magneto. It's been observed many times inside D2000 or D3000 mags.

All that said, the dual mag can be fairly reliable, but you want a shop working on them that does LOTS of D mags; it's not amateur night. And you want to be proactive about replacing those nylon gears, etc.
 
Tom-D said:
to change from the dual mag requires a engine change to an engine with 2 mags.
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Hopefully, that won't be true much longer. ElectroAir says (!) they're just a month or two from approval of their dual electronic system. They've been working on it about six years, and went down some rabbit trails. But... they've now returned to the configuration they first proposed six years ago (and rejected the two other configurations they wasted a bunch of time and money on in the meantime).

There's one ElectroAir system triggered by a missing-tooth gear attached to the crankshaft just forward of the crankshaft seal, aft of the starter ring gear. There's a second ElectroAir system triggered by their conventional missing-tooth gear in a timing-sensing unit attached in place of the original (dual) magneto. In order to operate TWO electronic ignition systems, the FAA requires either two alternators or two batteries. If the airplane doesn't have such a configuration, ElectroAir expects that TCW's recently certified second battery system will be acceptable.

Stay tuned!
 
Many Cirrus owners are hoping for dual electronic ignition from SureFly. Cirrus planes all come with dual alternators and two batteries, giving it separated redundant electrical power supply.



Wayne
 
RussR said:
I agree with Jeff. Your questions are oddly specific and yet unusual. If you let us know the context of why you're asking, we can probably give you a better answer. And if it is a book you're writing, that's cool too! We'll be happy to give you way more advice than you probably want!
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His threads paint a picture that he's writing a story about a bush pilot who crashes in the wilderness.
 
skipone said:
And if both went, would the engine just cut out ( zero sound) and you would just drop?

Could you survive with both out?
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Shutting off both mags on purpose. Being able to gain altitude like this is not typical, but you can see how the airplane responds. He had to slow down for a moment to stop the prop - normally they keep spinning, but you get better performance with it stopped.

Just for the fun of it - two engines shut down
 
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