MTV: first plane, 7AC 46 Champ lost plastic gear in mag- C65 when we were learning 1981. No commercial flying: 4 Cessna and 6 tandem TWs since (5000+hrs): have not lost a mag. C65 through TSIO520: 520 was 200 past TBO and still strong when sold last year. Normal 500 hr maintenance.
YMMV

Several years ago, I purchased a Rockwell Commander 114 that has the IO-540 with dual-mag. Before the closed the deal, I was getting a pre-purchase inspection from a former Commander dealer very familiar with the plane. That mechanic suggested that we pull the mag to check it more closely, as it looked like it "hasn't been touched in years" (his words, not mine). The owner had flown it to the shop, and thought we were being ridiculous, but agreed.

When the IA pulled the mag, the plastic gear that drives BOTH of the "dual" mags was completely stripped - only small "nubs" of the gear teeth remained. I have no idea how those mags maintained their timing, since you could literally turn either drive gear without the plastic gear turning, thus the other mag didn't move at all. We had the mags rebuilt, and they were fine after that...

But you can bet I was pretty religious about doing mag checks on that plane before every takeoff for the entire time I owned it!

Happy 2023 fellas!

What a passionate bunch we are It's almost a prerequisite. I mean with all the hoops to jump through, just to earn a ppl, and the exponential hoops to continue to climb the career ladder, it is a given that the further advanced a pilot is, the more likely he is a passionate individual. It took drive and motivation to get him there. But that doesn't negate the next guys passion, and more than likely his experiences will not carbon copy yours...

This thread has great reminders, although I *think* some are getting buried in the banter. And although IMHO Squash summed up the entire scenario elegantly, I'd like to expand on why I agree with it.

Moto, you were presented with an opportunity to continue learning. Don't take the 'knee jerk' approach. That angle typically sells you short. Your engine has been talking to you for the last five flights. That means you knew by your own admission, that something was amiss. Adding a 'mag check' buys you nothing there, heck adding one every 5 minutes after the initial moment of discovery adds nothing. You already had the knowledge that there was a problem. The failure in your routine was not the lack of redundant 'mag checks' the failure in your routine was the lack of action upon the discovery of a deficiency. I'm not casting aspersions, we all are guilty of this at times, I'm just suggesting your antidote could be better.

This is just like 'contact flying' Do something... don't like it? do something else, like that better? good... if you just sit there and enjoy the sights when you've made a negative discovery you are a passenger... Pilot up

Mags and mag checks....

Let's talk about that. What are you checking on a mag check? I for one will admit that I have never completed a 'mag check' with the intention of 'checking' for the catastrophic failure of a bearing. Which is what happened here.

For me, a 'mag check' is an archaic ignition system test. If you are flying a 1929 Travelaire , it probably should be a mandatory part of each departure. A 1943 J3? Ditto... as we advance in to more sophisticated aircraft, we hopefully have advanced our 'flight deck' and while a 'mag check' should still be a 'quick and easy' 'down and dirty' part of your run up on any recip powered aircraft, it is really not the holy grail of diagnoses. If you have a >$50K engine, you really need to take advantage of the modern day instrumentation available to you and educate yourself on how to use it. It will give you infinitely more detailed information about the health of your entire engine, than simply grounding a mag.

What am I looking for on a cursory mag check? Or more accurately what am I going to suspect if one indicates a more thorough look is in order?

#1 thing.... fouled or bad plug. You really could call this a 'plug check' as probably 95% of all bad mag drops are plug related
2) bad plug wire. I don't know why recip aviation lags in engine technology, but that is just the way it is. Your plug wires will be crap long before your mag is.
3) broke P-lead. This is the mag check that had no drop. We all know this. but this is the third most common 'bad mag check'
4) poor timing or capacitor health... this is the most common excessive drop in my experience outside of plugs and wires. I would not call this a catastrophic failure (which is probably where MTV and 93K are getting stuck on stupid) I would call this a maintenance issue... as in someone needs to pay more attention to their 70 y/o mags...

So no where in my career, which is shorter and less diverse than many comm pilots here, and certainly longer than some will ever see, would the thought occur to me that a poor 'mag check' should yield any information as to the structural health of a magneto. And although I have wore plumb through several sets of mags, on flat and round engines alike, like Mike I have never had one catastrophically fail. I am absolutely certain it does happen, but if you are a Bendix fan (and I am) then you must by default recognize that these things are built such that a well maintained set can and does last almost infinitely. Make them both impulse coupled. KISS... and because redundancy is not redundancy if you're only going halfway on the second mag.

Why a Bendix fan? Because the mandatory parts changes in a set of Slicks cost more than a new set, and because as others have noted, there are Bendix mags and parts at any and every grass roots shop in the world. Consequently, Bendix fit my mission (of getting away from people) better than even the E-stuff which has an incredibly better reliability and performance advantage. When the reliability can say there is a zero chance of failure, I will go that route, but for now, some chance of failure is a place I'd prefer not to visit with a part that isn't hiding under every rock... YMMV

Take care, Rob

Josh
The issue with doing a mag check on every start up is dependent on where you are. Trying to do a brake lock 1800 RPM run up on a small rock covered gravel pad or sandbar or dirt strip can cause damage over time. Straight skis on ice or short strip may also be an issue. If you want to do it at proper place and time, just put it in your normal flow just like flaps. Do it every time unless you have a good reason not to or modify it to a rolling mag check for off field flying if possible.

For everyone that has that ACS switch there is a SB out on it .https://acsproducts.co/wp-content/uploa ... B92-01.pdf Note it also lists a SB for the switches made by Cessna.

DENNY

Here’s a related but different check for you all: How many verify P-Lead continuity prior to every shutdown?

MTV

mtv wrote:Here’s a related but different check for you all: How many verify P-Lead continuity prior to every shutdown?

MTV

Probably far more valuable than adding random mag checks considering that most props get touched, turned or pushed on at virtually every flight.

You can get a gimpy airplane back on the ground, but it's infinitely harder without arms.

Take care, Rob

Probability of a dual mag failure is 2.7 per million flight hours. Hell, I'll take those odds, I mean y'all comfortable with ETOPS over the North Pole with a 777?

Early on I had a mag quit on a Beaver in an isolated inlet on the west coast. Being a Boy Scout I parked the aircraft and called for an engineer, who chartered out to me on another plane and balanced on a couple planks thrown over the floats, pulled the cowling and replaced a mag in the rain. Never again, when a mag quits now I'll fly it several hours back to the hangar.

My tach tells me if a mag has failed, mag checks are done downwind before I land.

Stats don't lie.
https://repository.lib.fit.edu/bitstrea ... sAllowed=y

Public service announcement to check mags IN THE AIR (over an airport) once in awhile. Couple months ago had a slightly rough sounding IO-520D but making plenty of power. Everything seemed fine on the ground including plugs and mag check at 2300rpm. Checked in the air at 5000 feet, bam, bad left mag. Replaced with overhauled problem resolved. Surely someone here can explain what happens to them at altitude and why turbos need pressurized mags.

mtv wrote:Here’s a related but different check for you all: How many verify P-Lead continuity prior to every shutdown?

MTV

What’s the cleanest way to do that? Look for mag drop as you switch between L and R? Just barely touch the OFF position to see if it stumbles? Then kill with mixture?

Zzz wrote:

mtv wrote:Here’s a related but different check for you all: How many verify P-Lead continuity prior to every shutdown?

MTV

What’s the cleanest way to do that? Look for mag drop as you switch between L and R? Just barely touch the OFF position to see if it stumbles? Then kill with mixture?

Yep, quick switch to “off” and back on. Just prior to shutdown. Better to find out BEFORE you want to fly again.

MTV

Zzz wrote:

mtv wrote:Here’s a related but different check for you all: How many verify P-Lead continuity prior to every shutdown?

MTV

What’s the cleanest way to do that? Look for mag drop as you switch between L and R? Just barely touch the OFF position to see if it stumbles? Then kill with mixture?

It's a quick switch to OFF and back on. If the engine acts like its quitting, the p-leads are grounded. If engine runs normally when doing that, your P-leads are ungrounded. Shut down with mixture to idle.

mtv wrote:

Zzz wrote:

mtv wrote:Here’s a related but different check for you all: How many verify P-Lead continuity prior to every shutdown?

MTV

What’s the cleanest way to do that? Look for mag drop as you switch between L and R? Just barely touch the OFF position to see if it stumbles? Then kill with mixture?

Yep, quick switch to “off” and back on. Just prior to shutdown. Better to find out BEFORE you want to fly again.

MTV

QUICK DRAW MTV!

Squash wrote:

mtv wrote:

Zzz wrote:

mtv wrote:Here’s a related but different check for you all: How many verify P-Lead continuity prior to every shutdown?

MTV

What’s the cleanest way to do that? Look for mag drop as you switch between L and R? Just barely touch the OFF position to see if it stumbles? Then kill with mixture?

Yep, quick switch to “off” and back on. Just prior to shutdown. Better to find out BEFORE you want to fly again.

MTV

QUICK DRAW MTV!

Fastest finger in the west……Happy New Year!

MTV

Had a brand new mag fail in 10 hours once.

DENNY wrote:.....For everyone that has that ACS switch there is a SB out on it .https://acsproducts.co/wp-content/uploa ... B92-01.pdf Note it also lists a SB for the switches made by Cessna. DENNY

FWIW there is an old recurring AD on Bendix mag switches.
Annual compliance via function testing required.
AD 76-07-12

https://drs.faa.gov/search?modalOpened=true

Coyote wrote:Had a brand new mag fail in 10 hours once.

When it comes to airplane components, in general, I’ll trust something that’s been in service for 1000 hours waaaay before I trust one that’s brand new.

MTV

Rob wrote:Happy 2023 fellas!

What a passionate bunch we are It's almost a prerequisite. I mean with all the hoops to jump through, just to earn a ppl, and the exponential hoops to continue to climb the career ladder, it is a given that the further advanced a pilot is, the more likely he is a passionate individual. It took drive and motivation to get him there. But that doesn't negate the next guys passion, and more than likely his experiences will not carbon copy yours...

This thread has great reminders, although I *think* some are getting buried in the banter. And although IMHO Squash summed up the entire scenario elegantly, I'd like to expand on why I agree with it.

Moto, you were presented with an opportunity to continue learning. Don't take the 'knee jerk' approach. That angle typically sells you short. Your engine has been talking to you for the last five flights. That means you knew by your own admission, that something was amiss. Adding a 'mag check' buys you nothing there, heck adding one every 5 minutes after the initial moment of discovery adds nothing. You already had the knowledge that there was a problem. The failure in your routine was not the lack of redundant 'mag checks' the failure in your routine was the lack of action upon the discovery of a deficiency. I'm not casting aspersions, we all are guilty of this at times, I'm just suggesting your antidote could be better.

This is just like 'contact flying' Do something... don't like it? do something else, like that better? good... if you just sit there and enjoy the sights when you've made a negative discovery you are a passenger... Pilot up

Mags and mag checks....

Let's talk about that. What are you checking on a mag check? I for one will admit that I have never completed a 'mag check' with the intention of 'checking' for the catastrophic failure of a bearing. Which is what happened here.

For me, a 'mag check' is an archaic ignition system test. If you are flying a 1929 Travelaire , it probably should be a mandatory part of each departure. A 1943 J3? Ditto... as we advance in to more sophisticated aircraft, we hopefully have advanced our 'flight deck' and while a 'mag check' should still be a 'quick and easy' 'down and dirty' part of your run up on any recip powered aircraft, it is really not the holy grail of diagnoses. If you have a >$50K engine, you really need to take advantage of the modern day instrumentation available to you and educate yourself on how to use it. It will give you infinitely more detailed information about the health of your entire engine, than simply grounding a mag.

What am I looking for on a cursory mag check? Or more accurately what am I going to suspect if one indicates a more thorough look is in order?

#1 thing.... fouled or bad plug. You really could call this a 'plug check' as probably 95% of all bad mag drops are plug related
2) bad plug wire. I don't know why recip aviation lags in engine technology, but that is just the way it is. Your plug wires will be crap long before your mag is.
3) broke P-lead. This is the mag check that had no drop. We all know this. but this is the third most common 'bad mag check'
4) poor timing or capacitor health... this is the most common excessive drop in my experience outside of plugs and wires. I would not call this a catastrophic failure (which is probably where MTV and 93K are getting stuck on stupid) I would call this a maintenance issue... as in someone needs to pay more attention to their 70 y/o mags...

So no where in my career, which is shorter and less diverse than many comm pilots here, and certainly longer than some will ever see, would the thought occur to me that a poor 'mag check' should yield any information as to the structural health of a magneto. And although I have wore plumb through several sets of mags, on flat and round engines alike, like Mike I have never had one catastrophically fail. I am absolutely certain it does happen, but if you are a Bendix fan (and I am) then you must by default recognize that these things are built such that a well maintained set can and does last almost infinitely. Make them both impulse coupled. KISS... and because redundancy is not redundancy if you're only going halfway on the second mag.

Why a Bendix fan? Because the mandatory parts changes in a set of Slicks cost more than a new set, and because as others have noted, there are Bendix mags and parts at any and every grass roots shop in the world. Consequently, Bendix fit my mission (of getting away from people) better than even the E-stuff which has an incredibly better reliability and performance advantage. When the reliability can say there is a zero chance of failure, I will go that route, but for now, some chance of failure is a place I'd prefer not to visit with a part that isn't hiding under every rock... YMMV

Take care, Rob

It was a drop of 180 rpms instead of the maximum 150, I called the mechanic and he said most likely bad timing, and it could be flown like this, not an emergency.
Plenty of power and engine running smooth until the last flight, if you did not do a mag check you could not see it.

motoadve wrote:

Rob wrote:Happy 2023 fellas!

What a passionate bunch we are It's almost a prerequisite. I mean with all the hoops to jump through, just to earn a ppl, and the exponential hoops to continue to climb the career ladder, it is a given that the further advanced a pilot is, the more likely he is a passionate individual. It took drive and motivation to get him there. But that doesn't negate the next guys passion, and more than likely his experiences will not carbon copy yours...

This thread has great reminders, although I *think* some are getting buried in the banter. And although IMHO Squash summed up the entire scenario elegantly, I'd like to expand on why I agree with it.

Moto, you were presented with an opportunity to continue learning. Don't take the 'knee jerk' approach. That angle typically sells you short. Your engine has been talking to you for the last five flights. That means you knew by your own admission, that something was amiss. Adding a 'mag check' buys you nothing there, heck adding one every 5 minutes after the initial moment of discovery adds nothing. You already had the knowledge that there was a problem. The failure in your routine was not the lack of redundant 'mag checks' the failure in your routine was the lack of action upon the discovery of a deficiency. I'm not casting aspersions, we all are guilty of this at times, I'm just suggesting your antidote could be better.

This is just like 'contact flying' Do something... don't like it? do something else, like that better? good... if you just sit there and enjoy the sights when you've made a negative discovery you are a passenger... Pilot up

Mags and mag checks....

Let's talk about that. What are you checking on a mag check? I for one will admit that I have never completed a 'mag check' with the intention of 'checking' for the catastrophic failure of a bearing. Which is what happened here.

For me, a 'mag check' is an archaic ignition system test. If you are flying a 1929 Travelaire , it probably should be a mandatory part of each departure. A 1943 J3? Ditto... as we advance in to more sophisticated aircraft, we hopefully have advanced our 'flight deck' and while a 'mag check' should still be a 'quick and easy' 'down and dirty' part of your run up on any recip powered aircraft, it is really not the holy grail of diagnoses. If you have a >$50K engine, you really need to take advantage of the modern day instrumentation available to you and educate yourself on how to use it. It will give you infinitely more detailed information about the health of your entire engine, than simply grounding a mag.

What am I looking for on a cursory mag check? Or more accurately what am I going to suspect if one indicates a more thorough look is in order?

#1 thing.... fouled or bad plug. You really could call this a 'plug check' as probably 95% of all bad mag drops are plug related
2) bad plug wire. I don't know why recip aviation lags in engine technology, but that is just the way it is. Your plug wires will be crap long before your mag is.
3) broke P-lead. This is the mag check that had no drop. We all know this. but this is the third most common 'bad mag check'
4) poor timing or capacitor health... this is the most common excessive drop in my experience outside of plugs and wires. I would not call this a catastrophic failure (which is probably where MTV and 93K are getting stuck on stupid) I would call this a maintenance issue... as in someone needs to pay more attention to their 70 y/o mags...

So no where in my career, which is shorter and less diverse than many comm pilots here, and certainly longer than some will ever see, would the thought occur to me that a poor 'mag check' should yield any information as to the structural health of a magneto. And although I have wore plumb through several sets of mags, on flat and round engines alike, like Mike I have never had one catastrophically fail. I am absolutely certain it does happen, but if you are a Bendix fan (and I am) then you must by default recognize that these things are built such that a well maintained set can and does last almost infinitely. Make them both impulse coupled. KISS... and because redundancy is not redundancy if you're only going halfway on the second mag.

Why a Bendix fan? Because the mandatory parts changes in a set of Slicks cost more than a new set, and because as others have noted, there are Bendix mags and parts at any and every grass roots shop in the world. Consequently, Bendix fit my mission (of getting away from people) better than even the E-stuff which has an incredibly better reliability and performance advantage. When the reliability can say there is a zero chance of failure, I will go that route, but for now, some chance of failure is a place I'd prefer not to visit with a part that isn't hiding under every rock... YMMV

Take care, Rob

It was a drop of 180 rpms instead of the maximum 150, I called the mechanic and he said most likely bad timing, and it could be flown like this, not an emergency.
Plenty of power and engine running smooth until the last flight, if you did not do a mag check you could not see it.

Larry,

You didn't do anything dangerous or stupid there, and I'm pretty sure Rob wasn't intending to suggest that you did. Sometimes you just need to make a common sense decision, rather than call out the Mounties. Sounds like that's what you did. Good for you.

MTV

Not casting aspersions, and certainly not calling anyone stupid... As for my observation on Mike and 93K's banter, around here we say 'getting stuck on stupid' here when we have something of little significance blocking our thought process... Kind of like when you can't remember you best friends name... Neither could be any farther from stupid in my books, they are both professionals, in the real deal, wholly invested with nothing to prove, and are here sharing of their own volition. I'd call that pretty wonderful.

Again, you found a deficiency on your very first flight, and unless I'm misunderstanding you, you elected to fly another 4 flights. That's your choice, to the best of your knowledge at the time, the aircraft was safe and airworthy, and given your level of experience, I concur with that thought process, just not how you handled that knowledge moving forward. A double mag failure is only a double mag failure when it happens. Not six months after the first mag failed. Ferrying a gimpy ship out of the bush, is a different animal than continued pleasure flights with a discrepancy. Contact's case... I have nothing for you there In my observation, what you learned from this scenario is how to hit the mute button when someone offers an idea outside of what you want to hear. I could say kudos to you, good on you for discovering a problem, high fives all around... Which would be spineless, because it misses the real learning opportunity, I could point out what I may have done differently, which would have been to try and find out why I have an exceedance. That would be unpopular, and I don't really give a rip. Because I care more about not putting an airplane or pilot in harms way, than I do about making them feel warm and fuzzy with BS....

Your mechanic didn't have his ass in the seat, nor did he have any confirmed direct knowledge as to what was going on. He understood you had an exceedance, and made a judgement call. Obviously a poor one in hindsight, but again, he didn't have that mag sitting right in front of him. Maybe he would have suggested a different course of action if he did?

I had an FCU fail on a GE engine on take off with a full load. After aborting the take off (which was a handful) I confirmed the FCU failure with an expert in the industry, and he reminded me that if I engaged the isolation mode on the FCU, I could fly that load off utilizing the fuel condition lever as a throttle. For those inexperienced with GE or Walter engines, the isolation valve takes the FCU out of the picture completely, and allows you to 100% manually meter fuel. This switch is usually labeled 'emergency fuel' or some such. My response to the mechanic was that 'I am safe on the ground, and the load could be pumped off to be put on a 100% functional airplane, why would I deliberately take off on a circuit designed for use in an 'emergency''. We don't need to look for ways to create our own emergency. The mechanic later apologized, realizing what it truly was he was suggesting. He is a really great mechanic, he just let his mouth out run his brain for a few seconds. Possible, yes it would have been, prudent? not in my mind.

When you operate the same ship for hundreds or thousands of hours, you develop a sense of where needles 'should fall', lights 'should illuminate to', how sights should align, smells should be, and sounds should elevate to. You don't even need true numerical values, you just need to see, smell, taste, hear the same condition that carried you through the last 1000 hrs. Don't look for a reason to confirm or deny those sensations, look for the reason they are not presenting themselves as they have 1000's of times before. This is the same as the difference between flying by feel in a total vfr zen world, or utilizing all the whizzbang dials and indicators to try and guide you... Your mind knew there was an issue, it was right, it did not need more confirmation, it needed a course of action, and it did not have the 'lag' of indicators or tests, trust it...

Anyways.... I've repeated myself enough, and preached a plenty. Want to add mag checks? add mag checks I obviously thought you did a fine job finding a deficiency on the very first one. Better than your mechanic from the get go.

Take care, Rob

What Rob is telling you, Larry, is spot on. I spent many years and many flight hours behind two kinds of airplanes: tired and all used up. That was because I couldn't afford better to own and I needed the work in other peoples airplanes. Given my weakness in this these two areas, I had many actual complete engine failures. But what Rob explained about our experience and feelings about how things are going still applies. With experience and iterations come useful diagnosis ability. While I may tout my fine pilot technique, I actually had fair personal expectations about the health of my hot running engines. They were going to fail relatively soon. That gave me a bit of an edge concerning rapid reaction to those failures.

All that said, your situation is quite different concerning means of prevention. Still, when you have feelings about performance you are continually getting more accurate. Use those iterations. Bank that knowledge. And spend the money you have to stay safe.