Question about magnetos leading to crash

[azpilot]

I have been engaging in one of my favorites hobbies today, which is pursuing the NTSB accident database and reading reports. (by the way, I am very fun at parties)

This particular crash caught my attention.

https://data.ntsb.gov/Docket?ProjectID=100307

I am very happy to report that all four occupants walked away, and were not injured. The following wording is taken directly from the NTSB report.

"Examination of the engine and accessories revealed that the left magneto fired on only 3 of its 6 terminals. The airplane was equipped an electronic ignition system that was coupled to the magnetos. The system created multiple sparks over a longer duration and synchronized timing between the two magnetos. This synchronization was accomplished by using the left magneto as a trigger for the complete system. When the electronic ignition was operating, it relied solely on the left magneto points to fire both magnetos with an enhanced multi-spark. If the left magneto failed or deteriorated, then the complete ignition cycle would be compromised. The degraded functionality of the left magneto was likely the cause of the partial engine power loss."

Here's the question. Wouldn't a mag check prior to takeoff show that something was wrong here? If I understand this correctly, the right magnetos were running based on the left magnetos. So if you shut the left mags off, the engine should not be able to run. I must be missing something...

The NTSB didn't say anything about the runup before takeoff. The root cause was determined to be partial loss of engine power due to faulty wiring.

 

[Kenny Phillips]

I have been engaging in one of my favorites hobbies today, which is pursuing the NTSB accident database and reading reports. (by the way, I am very fun at parties)

This particular crash caught my attention.

https://data.ntsb.gov/Docket?ProjectID=100307

I am very happy to report that all four occupants walked away, and were not injured. The following wording is taken directly from the NTSB report.

Stuff ...

Certainly one could fire two or a hundred systems from a single set of points; the fact that the points operated [not the mag on that side] may be all that's needed for the electronic setup to trigger.

 

[dtuuri]

Wouldn't a mag check prior to takeoff show that something was wrong here?

No. I had a similar mag failure right after takeoff with a student in a Piper Colt. I elected to do a crop duster turn and return, landing successfully probably because the engine still was making some power. I didn't know how long it would continue to run, so I landed ASAP and did my trouble shooting on the ground. One of the mags lost the distributer portion and that threw spark willy-nilly to the cylinders causing power reduction.

 

[Rgbeard]

...... (by the way, I am very fun at parties)

That's it - not inviting you to any of our parties! LOL!

 

[Checkout_my_Six]

Hmmm....sounds like a single point failure mode. Not a nice thing.

 

[Bell206]

Wouldn't a mag check prior to takeoff show that something was wrong here?

Considering he stated he had been flying for some time before the loss of power the previous mag check probably was okay. The interesting part is he didn't mention turning off the G3i switch as stated in the manual when experiencing loss of engine power in flight. Whether that would have made a difference don't know. But to lose 3 out of 6 is somewhat interesting as well.

 

[Plano Pilot]

Considering he stated he had been flying for some time before the loss of power the previous mag check probably was okay. The interesting part is he didn't mention turning off the G3i switch as stated in the manual when experiencing loss of engine power in flight. Whether that would have made a difference don't know. But to lose 3 out of 6 is somewhat interesting as well.

I found this on the Vanairforce page: G3i Experience [Archive] - VAF Forums (vansairforce.net)

"Also, the G3 unit does not automatically switch back to MAG mode when there is a failure. This is a misconception. You have to realize there is a problem and turn the G3i system off with the toggle switch. VERY IMPORTANT to understand this. Especially during takeoff.[/B If you have a rough running engine in flight, the system should be switched off immediately from my experience."

 

[Dan Thomas]

This was in an RV-10, and almost anything goes in an E-AB. There have been numerous accidents due to systems that didn't perform properly because they were poorly designed or poorly assembled or because they demanded too much of the pilot. The latter seems to be in play here.

Magnetos can fail anytime, particularly if they're not maintained properly. They can run fine in the runup, but fail in flight. They're going to fail sometime, and the airplane usually spends most of its running time in flight. Mags need periodic inspections, but the vast majority, in my experience, don't get them. The attitude of owners seems to be "it's running ok. Been running ok for a long time. Nothing wrong with it. Normal mag drops. Why should I spend money on something that ain't broke?"

 

[Dan Thomas]

No. I had a similar mag failure right after takeoff with a student in a Piper Colt. I elected to do a crop duster turn and return, landing successfully probably because the engine still was making some power. I didn't know how long it would continue to run, so I landed ASAP and did my trouble shooting on the ground. One of the mags lost the distributer portion and that threw spark willy-nilly to the cylinders causing power reduction.

You didn't have much time to troubleshoot it, but if you had, you'd have found that fooling with the mag switch would have fixed it, mostly. When the distributor gears slip (worn out!) the willy-nilly sparking happens, and when a cylinder that's on its intake stroke gets a spark, the resulting flame sets off the entire induction system via the still-open intake valve. That makes for a really rough-running and nearly dead engine.

Most pilots think the mag switch is only for testing the mags in the runup. Nope. It's also for shutting off a rogue mag. Can save your life.