EAA Webinar, "Those Deadly Switches". What would I have learned?

[Brad W]

A few days back I received an email announcing a webinar. I signed up for it but got busy last night and missed it.

I figured there are some smart aviation minded folks here so I'll ask....
Had I listened in, what would I have learned?

Webinar
Deadly Switches​

Wednesday, December 6, 2023, from 7 - 8:30 p.m. CDT

Presenter: Mike Busch

That ubiquitous key-operated ignition switch in most single-engine piston airplanes is fraught with peril. There are two different designs that have different failure modes and are subject to different airworthiness directives. Yet one critical failure mode is unaddressed by any of these ADs and has resulted in death, serious injury, and costly property damage. Maintenance expert Mike Busch discusses how and why these switches fail and what you can do to protect yourself from the deadly consequences. If you own or fly an aircraft with a key-operated ignition switch, this webinar is a must-see. Qualifies for FAA WINGS and AMT credit.

By clicking the button, you submit your information to the webinar organizer, who will use it to communicate with you regarding EAA Webinars.​

Webinar Registration

pages.eaa.org

 

[bkspero]

Too much to summarize. If you're an AOPA member then you can read his article in the November 2023 AOPA Pilot magazine. Same information.

Some points.

1) Ignition switches can wear and appear to be in the off position when one or more mags are not grounded.
2) Key wear can contribute to the behavior described in #1 (eg. an IA may find no issues with a switch using a like-new key, while the problem shows up with the old worn key that you usually use).

 

[DaleB]

And a few other points. You can still watch it: https://www.eaa.org/videos/webinars

 

[Brad W]

Too much to summarize. If you're an AOPA member then you can read his article in the November 2023 AOPA Pilot magazine. Same information.

Some points.

1) Ignition switches can wear and appear to be in the off position when one or more mags are not grounded.
2) Key wear can contribute to the behavior described in #1 (eg. an IA may find no issues with a switch using a like-new key, while the problem shows up with the old worn key that you usually use).

Thanks! I'll look for that article...it's here in a stack someplace.
Back when I was younger and single, and had much more time on my hands I used to read all my magazines cover to cover so I would have already read it. These days, I flip through a magazine now and then but often a long time after they come...if ever. I'll look for this one!

and update, I found that they posted the webinar replay in a members only access area so I have that pinned to watch too

*

I'm interested in this topic after having learned a little about checking mags for grounding years ago. I got into the habit of checking mags at shutdown by momentarily switching to off prior to pulling mixture, to see if the mags will shut off. One issue for me was that I was renting various aircraft and never really learned in detail about how all this works. Anyway, Fast forward to many years later after a long rusty period, doing a rental checkout, when shutting down, muscle memory had me switch the key to off instead of just pulling the mixture like the checklist said... I immediately hesitated and was uncertain about hwy I even did it so I paused a moment longer....and the CFI freaked out.... He of course was not in the habit of checking mags, and I reckon he didn't even fully understand

After the CFI freaked a bit, and I was still trying to realize what I had done, he was going into a little bit of troubleshooting mode but pretty much dismissed the whole thing

In hind site after all of this came back to me, I realized I had paused with the key OFF longer than I normally would have. The thing was, the engine slowed and stumbled, kind of surging like it was almost going to die but it kept coming back to life. So, I was left with an uneasy feeling about that rental, and the safety of that plane.... But if my understanding is correct it's more complicated and depending on some variable that plane may or may not of actually been dangerous.

all this was doubling down on my "respect" for a prop even when the key is laid up on the glare shield.... and I want to know more.
so I'll be watching that video AND looking for that article this weekend!

 

[Lndwarrior]

It was partially for the known failure of these switches that I went with simple aviation-grade toggle switches in my homebuilt. Also, this was recommended by aviation wiring guru Bob Nuckols. And I never wanted to be stranded, or have to carry, a key for my airplane.

 

[flyingron]

Turning the mags off (do it at idle please) proves NOTHING. I had one of those worn keys/switches and yeah I could turn the switch off and kill the engine, but remove the key while it was off and it would jiggle back to leaving one mag ungrounded. NEVER TRUST A MAG TO BE GROUNDED.

The one thing that I do like about the MVP50 is it has a RPM pick up on both mags. When you do your normal (not the student click-click-click-BANG) check it tells you that the right or left mag was dead (as appropriate). Lets you know that you're really testing BOTH the mags.

 

[Ed Haywood]

It was partially for the known failure of these switches that I went with simple aviation-grade toggle switches in my homebuilt. Also, this was recommended by aviation wiring guru Bob Nuckols. And I never wanted to be stranded, or have to carry, a key for my airplane.

Good call. My certificated aircraft (Decathlon) has that design also. Simple, reliable, robust.

 

[Dan Thomas]

Turning the mags off (do it at idle please) proves NOTHING. I had one of those worn keys/switches and yeah I could turn the switch off and kill the engine, but remove the key while it was off and it would jiggle back to leaving one mag ungrounded.

Two different problems there that you're conflating. Turning the mags to off confirms that the P-leads aren't broken and the mags are grounding in the off position. If the switch moves away from the off position with the key out, that's a separate problem from any P-lead concerns, and the switch should never be allowed to get to that point. Doing the shutdown mag check will catch 99.9% of hot mags due to switch or P-lead problems. Not doing it can introduce a hot prop that kills some unsuspecting, curious person.

NEVER TRUST A MAG TO BE GROUNDED.

That is correct. Never assume that something hasn't failed since you shut it down. For instance, some pilots like to reach in and yank on stuff to make sure everything is secure, but they can move frayed P-leads and break that last couple of strands. Now the mag is hot.


The Bendix AD looks for the engine to continue to run if the key is forced a bit past the off position. It ungrounds one mag. The problem was a poorly-manufactured stop in the switch. The AD did not apply to Bendix switches with a date code on them, or with the white dot signifying a corrective modification, yet I found countless maintenance logs with that AD test done annually for 30 years, but often the airplane did not even have a switch affected by the AD. It would have the modified or date-coded switch, or an ACS switch that has an entirely different AD against it that was overlooked for decades because the mechanic never crawled under the panel, ever, to look at stuff. The ACS AD is 93-05-06, from 1993, 30 years ago. It requires an internal inspection and lubrication of the switch, and a diode across the starter contactor coil to prevent contact burning. Burned contacts can affect mag control.

 

[Magman]

IIRC Bendix Switches HAS a black contact plate and the ACS/ Gerdes was white.

Newer components have changed and some use green.


Note that if you are buying the ACS item you should verify BOTH both keys are working.

If one does not , they may want the whole switch and keys back for warranty.

They will not sells blanks too.