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I Shut off Engine Ignitions in Flight…

Piper J3

Well Known Member
I’m curious if I’m the only person that does this…. I shut off engine ignitions in flight – :eek:. I started doing this years ago when flying my J-3 Cub. The Cub had a Continental A65-8 with Eisemann Magnetos originally used on farm tractors back in the 1920s. Suffice to say – not a great confidence builder. I often would fly the Cub, and now the RV-12, up to the islands in western Lake Erie. The islands are a couple of miles offshore and so I started a habit of verifying both ignitions were running solidly before acting like Christopher Columbus.

So, to this day, I often will shut off one ignition at a time while in cruise flight to verify RPM drop and compare engine smoothness when running on separate ignitions.

Need to be very careful when doing this so you don’t shut both ignitions off at same time. Things would get quiet really fast.

Anybody else do this? I doubt if this is taught in ground school…
 
I shut down the engine with every student I have so they know what to expect and also how to attempt a restart in flight (if applicable). In flight mag checks are good for diagnosing some issues too. Nothing wrong with it at all IMO.
 
Run-up...

I think most of us do this PRIOR to taking flight. Better to discover a broken P-lead, badly timed magneto, failed plugs, etc. etc. on the ground before committing to flight over hostile terrain.

I think that introducing a failure mode in flight puts unneeded stress on the system(s), including the pilot - if it's gonna fail, it's gonna fail and you should know what the indications are before pressing on...
 
Done it left, right and both as an experiment.

We were doing c/s prop experiments so were over an airport at the time.

Not an issue :D
 
Yep

...and the first question the FAA is going to ask is, “Why did you shut off the ignition (or engine) while in flight?”
 
Be careful that you don't inadvertently shut off BOTH ignitions at the same time and then quickly turn one or both ignitions back on without first adjusting the throttle to a low-power setting -- this could result in an after-fire explosion of unburned fuel/air mixture in the exhaust pipes or muffler = $$$?
 
Has anyone here that runs almost all Mogas, all the time, regardless of ethanol free to E-10, ever fouled a spark plug on a Rotax 912 ULS engine?

If so, how many hours did you run the plugs without inspection, cleaning or regapping the spark plugs? I am running the NGK stock version... DCPR8ES, I believe.
 
Mag Check War Story

Decades ago, a friend told me about the time he was flying his Ryan PT-22. He was in the back seat, a non-pilot buddy in the front. Pilot decided to do an inflight mag check, and since he was a pretty short guy, he naturally ducked down into the cockpit to reach the mag switch mounted well forward of the instrument board. Of course one magneto was bad, very rough and stumbly. He returned the switch to both and the engine ran better. When he got his head back above the cockpit coaming, he saw his passenger’s face up close with eyes like silver dollars, said pax having twisted around when the engine went rough and seen that his pilot was missing.
Seriously, I’ve checked ignitions in flight lots of times. Its not weird, but I DO have an aversion to shutting down an engine that’s functioning normally.
 
I've learned to do in-flight mag checks to really put some stress on the system in order to find anomalies earlier, rather than later. The procedure advocated by Mike Busch is to select a time shortly before your descent into your home base, have the engine leaned (if you can and normally do so) and do a mag check prior to descent. This condition is the most difficult for an ignition system to function correctly. Any rough running suggests an early failure in progress. DHeal's point about ensuring lean/low-power engine controls prior to returning to "Both" is right on the money.

The other times I will shut the ignitions is when I practice engine off landings. (BTW, I have a glider rating and I'm comfortable with power off patterns). The plane flies perfectly well with the prop stopped but does have a significantly better glide than when it's windmilling. You will probably need to aggressively slip if you are expecting the glide angle you normally get w the engine running.

Our 912's have such high compression, that I think that anyone who actually has an engine failure will have a stopped prop, but the 912's are so reliable that I'm not aware of anyone who's actually experienced one!

-dbh
 
Like many things, carefully consider the situation.

Anybody else do this?

You are not alone. It can provide good information.

The only warning is not to do it when the engine is operating in a low detonation margin condition. High MAP, high RPM, hot day, max power mixture, probably not a good idea. But it depends on the engine -blah blah.
 
I stopped my 912ULS for probably 2 dozen engine-off landings in the pattern. My experience in my Flight Design is the prop will windmill unless I pull the nose up pretty well and slow the airspeed down.
I've also restarted it on short final a couple of times for fun.
Once, I took the plane to 10,000 feet and stopped the engine. Glided at best glide to 4,000 feet (about 3,000 AGL). Figured out glide ratio was about 9:1.
I'm also a glider pilot, not that it matters much.
I've previously done the GAMI mag check per George Braly and later Mike Busch in my T210. No big deal.
 
You are not alone. It can provide good information.

The only warning is not to do it when the engine is operating in a low detonation margin condition. High MAP, high RPM, hot day, max power mixture, probably not a good idea. But it depends on the engine -blah blah.

Bill, I thought the same at one time. However, George Braly said nope, he had tried it with GAMI's 540K, and single ignition was not pro-detonation. On one plug, pressure rise was slow, so the peak was low and more distant from TDC.

Some years ago here, Vic reported doing single ignition checks at full power in climb. Quite a few posters expressed concern, but there was no ill effect.

Consider certification, and the fact that ignitions do go AWOL in the real world. If our engines habitually detonated at WOT because one ignition dropped out, I think we would flying some different arrangement.
 
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I would never do this

I would never turn off a mag in flight. If the mags check out ok during run up, it is highly unlikely one will fail during flight. And if one mag failed during flight, then a mag check creates an instant emergency.
But the most important reason I would not check in flight is that electrical and mechanical things tend to fail during turn on or turn off. Just like a light bulb usually burns out when it is turned on.

Now I can understand maybe a check right before a long overwater portion, but that is a tough call.

Personally, I think this is asking for trouble. Do you check if your marriage is sound by flirty with the waitress?
 
I would never turn off a mag in flight. If the mags check out ok during run up, it is highly unlikely one will fail during flight.
...
Now I can understand maybe a check right before a long overwater portion...

Does your aircraft, or your magneto, have any idea what it's flying over?

Does the fact that you're about to cross a body of water increase the chances that one or both magnetos will fail during flight?
 
Exactly

Does your aircraft, or your magneto, have any idea what it's flying over?

Does the fact that you're about to cross a body of water increase the chances that one or both magnetos will fail during flight?

This is the reliability dilemma that we face in complex systems. Do you verify back up systems would work if needed, at the risk of breaking something, or discovering a problem.

Before asking the question, one should decide if they really want to know the answer.
 
I would never turn off a mag in flight. If the mags check out ok during run up, it is highly unlikely one will fail during flight. And if one mag failed during flight, then a mag check creates an instant emergency.
But the most important reason I would not check in flight is that electrical and mechanical things tend to fail during turn on or turn off. Just like a light bulb usually burns out when it is turned on.

You must really hate switching tanks ;)

Personally, I think this is asking for trouble. Do you check if your marriage is sound by flirty with the waitress?

If enough to break a marriage, the analogy would be poor fabrication and poor component choice.
 
Before asking the question, one should decide if they really want to know the answer.
I asked the questions because I wanted to know your answers. You said you would never check them in flight, but would understand checking them before a water crossing. Why?

The only reason I can surmise is that there is something special about flying over water as opposed to flying over land, that makes mags more reliable just before you cross the water, and hence safer to check.
 
I would never turn off a mag in flight. If the mags check out ok during run up, it is highly unlikely one will fail during flight. And if one mag failed during flight, then a mag check creates an instant emergency.
But the most important reason I would not check in flight is that electrical and mechanical things tend to fail during turn on or turn off. Just like a light bulb usually burns out when it is turned on.

Now I can understand maybe a check right before a long overwater portion, but that is a tough call.

Personally, I think this is asking for trouble. Do you check if your marriage is sound by flirty with the waitress?

You need to better understand how a mag works. The P lead, when switched OFF (according to your switch), simply grounds the primary winding. Same thing happens twice per engine revolution (points are closed for 340-350 degrees of revolution and closed points also ground the primary). Only difference is that when the mag is switched on, the ground is removed by the points for a short period, also twice per revolution. The P lead just maintains a constant ground regardless of the points, so that even when the points open, the ground is still there and the secondary winding cannot produce energy.

There are no electronics in a mag.

Larry
 
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You need to better understand how a mag works. The P lead, when switched OFF (according to your switch), simply grounds the primary winding. ------

There are no electronics in a mag.

Larry

Methinks perhaps you need to reread the first post of this thread. Many if not most of the responses are talking about mags. And the kind of failures that mag systems have.

The OP appears to be asking about his Rotax, and posted the thread in the RV 12 forum.

The Rotax ignition in the RV 12 is electronic not a mag. Each of the ignitions has a dedicated coil in the dynamo, and has its own electronic module and coil.

rotax-912-wiring-diagram-epubpdf.jpg
 
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Ignition off in flight

LR172 provides a very informative point about magneto function, thanks.

I sequentially OFF my Pmags in flight ( one at a time) to optimize leaning. My EGT readings were all over the place with my carb 320. Identifying first cyl to peak was a little sketchy. So I lean until one Pmag runs noticeably a little rough, then richen back til both are equally smooth when OFF'd.
 
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Just me

I asked the questions because I wanted to know your answers. You said you would never check them in flight, but would understand checking them before a water crossing. Why?

The only reason I can surmise is that there is something special about flying over water as opposed to flying over land, that makes mags more reliable just before you cross the water, and hence safer to check.
Before I head overwater, I want to know my true odds of making it. In this case, stress the system to verify margin exists.
But I see your point, and it is a good one. Gotta think more about that.

And the others are right, I used the term “mag” in my discussion, but the OP was talking about electronic ignition modules. And my reasoning is more geared towards complex electronic things. For mags, as other people point out, turning on or off the mag is a simple switch with very little change to the operating
circuits.

Each person has to make their own decision. For me with electronic modules, I would never turn off in flight. For true mags, I would probably check to see if they are both working before heading over water. But the best option is to have an independent way of verifying the ignition is working. Like is the egt and cht behavior different on one ignition verse two?
 
breakin things

Thanks guys for the laughs this cold grey morning here in Washington state.
Having been a mechanic all my knowing life it cracks me up. Why does my shoulder hurt today? It didn't yesterday!
Stuff breaks when it wants to not when you think it is gonna break. My wife is a constant for my life. She goes "Well it worked yesterday" why doesn't it work now to no matter what ever breaks or leaks or ????
Yes I have run my plane out of gas on purpose and landed as a glider, flown higher than God should have allowed me to so I got goofy and blue lipped etc etc
But I don't do it all the time to tempt fate.
Still laughing.
Keep it coming I'll keep reading.
Thanks Art
 
I ALWAYS check both ignitions in flight on every aircraft I fly, especially if it is not mine. Under high power settings, ignition problems will manifest themselves in ways that won't show up on a run-up. I do a check at the beginning and end of every flight while airborne.

As an example, most runups are performed at 50% or LESS power. Peak cylinder pressures are obtained much higher than that. Sometimes the spark will jump elsewhere besides at the spark plug electrode if there are problems elsewhere in the system, such as broken shields, bad rotors in mags, poor connections, etc.

Just last week this practice helped discover a problem. NO names, locations, or anything else to embarrass anyone. I was asked if I would like to fly a certain model RV that had been recently purchased. Of course, I would! Great friends, and they take care of their airplanes. I was briefed by the owners (every airplane is different, right?), and run up and ground control was all normal.

Takeoff was wonderful, and as usual, I checked the ignitions on the crosswind prior to leaving the airport. When running on one particular mag, the engine was so rough I thought it was going to come out of the mounts. I reduced power and tried it again to see if I could figure out if it was just a plug or two. Nope. It was clearly a mag issue as ALL cylinders reacted the same on the EGT's.

Truth be told, it wasn't as smooth as I thought it should be when BOTH were selected, and now I understood why. So, stayed within gliding distance of airport, but did get a roll or two in, and some control checks. Very sweet flying airplane. I was very thrilled to get to fly it!

They have since replaced the mag with a PMAG, and it is now super smooth and all is well.


A long time ago, when I was flying the KLM engine in my very first Kitfox, the same thing happened. Runup was fine, and after takeoff while still in the pattern, an ignition check was made. That time the engine completely quit when one ignition was turned off, as one of the electronic ignitions had failed completely since the runup.

This is my procedure, and it has served me well over the years.

BTW, for those of you who have a feel for engines, and have 2 mags, you will be able to tell when the timing is different between the mags by checking the ignitions in flight. It won't quite be as smooth when BOTH are selected. :)

Vic
 
When I started this thread, I had no idea it would stimulate so much constructive conversation. I was just trying to see if I was a lone wolf in the aviation community. Some very good thoughts discussed here.

Correct that 912ULS has dual Capacitive Discharge Ignition (CDI). The ignition is a waste-spark system where plugs fire on both compression and exhaust strokes. Still, a lot of stuff can go wrong.

My main reason for cycling the ignitions in-flight is to ascertain engine health. I’m not 100% certain, but I think each ignition fires two top and two bottom plugs on opposite sides of engine to make everything symmetrical. At 5500 RPM cruise flight I see about 75 RPM drop on each ignition and noticeably smother running when both ignitions are functioning.

PilotjohnS - As far as flirting with waitress - can of worms there. My wife has no problem calling out bad behavior on my part - actual or perceived…
 
I ALWAYS check both ignitions in flight on every aircraft I fly, especially if it is not mine. Under high power settings, ignition problems will manifest themselves in ways that won't show up on a run-up. I do a check at the beginning and end of every flight while airborne.

As an example, most runups are performed at 50% or LESS power. Peak cylinder pressures are obtained much higher than that. Sometimes the spark will jump elsewhere besides at the spark plug electrode if there are problems elsewhere in the system, such as broken shields, bad rotors in mags, poor connections, etc.

Just last week this practice helped discover a problem. NO names, locations, or anything else to embarrass anyone. I was asked if I would like to fly a certain model RV that had been recently purchased. Of course, I would! Great friends, and they take care of their airplanes. I was briefed by the owners (every airplane is different, right?), and run up and ground control was all normal.

Takeoff was wonderful, and as usual, I checked the ignitions on the crosswind prior to leaving the airport. When running on one particular mag, the engine was so rough I thought it was going to come out of the mounts. I reduced power and tried it again to see if I could figure out if it was just a plug or two. Nope. It was clearly a mag issue as ALL cylinders reacted the same on the EGT's.

Truth be told, it wasn't as smooth as I thought it should be when BOTH were selected, and now I understood why. So, stayed within gliding distance of airport, but did get a roll or two in, and some control checks. Very sweet flying airplane. I was very thrilled to get to fly it!

They have since replaced the mag with a PMAG, and it is now super smooth and all is well.


A long time ago, when I was flying the KLM engine in my very first Kitfox, the same thing happened. Runup was fine, and after takeoff while still in the pattern, an ignition check was made. That time the engine completely quit when one ignition was turned off, as one of the electronic ignitions had failed completely since the runup.

This is my procedure, and it has served me well over the years.

BTW, for those of you who have a feel for engines, and have 2 mags, you will be able to tell when the timing is different between the mags by checking the ignitions in flight. It won't quite be as smooth when BOTH are selected. :)

Vic

+1

I routinely do Ignition checks in the air. Like Vic, I find that small variances can more easily be spotted by doing this. The risk of a failure due solely to an ON OFF ON cycle is WAY less than the risk of not noticing slight changes that very often appear in advance of complete failures.

Larry
 
Does your aircraft, or your magneto, have any idea what it's flying over?

Does the fact that you're about to cross a body of water increase the chances that one or both magnetos will fail during flight?

It is not that the probability changes. It is that the consequences change.
 
I ALWAYS check both ignitions in flight on every aircraft I fly, especially if it is not mine. Under high power settings, ignition problems will manifest themselves in ways that won't show up on a run-up. I do a check at the beginning and end of every flight while airborne.

As an example, most runups are performed at 50% or LESS power. Peak cylinder pressures are obtained much higher than that. Sometimes the spark will jump elsewhere besides at the spark plug electrode if there are problems elsewhere in the system, such as broken shields, bad rotors in mags, poor connections, etc.

Vic

I was going to say what Vic said. A mag check (or any ignition check) at lean 75% power condition is quite different than a run-up, and will reveal weak plugs, leads, coils.

If you really want an eye-opener, do a mag check while 70F LOP! I have one Lightspeed EI and one Slick mag. Running LOP with the spark advance of the Lightspeed is very smooth. Turn that ignition off and Holy &%$#! Shows the importance of spark advance for very lean operations.
 
This is an interesting thread. I never considered doing a mag check in the air. After reading the replies so far... hmmm.. I feel like.. Lets say I'm crossing a Great Lake.... I think its better to actively look for reasons why you shouldn't do the crossing while you're still over land. If your systems are in that bad of shape that doing a mag check is going to kill your engine and prevent a restart.. then.. geez.. I'd rather have the engine die over land (maybe with the possibility of a beach or airport landing) than to go out over water with a system that's on the brink of failure.

There was some saying about the unknown risk is riskier than the known risk? The unknown risk of going out over water with an untested system.. the known risk is intentionally doing a check before going out? IF you have a failure, at least you how how to undo what you just did in a hurry.

Hope to read more comments on this.
 
Well Rob you won't have to worry about that with your 912iS. If one ignition fails the other lane (ECU) will take over for it. And you will get a warning light to tell you. :)
 
Just going by the 912iS Operators Manual.

"Engine Management System
The Engine Management System has following main
functionality
• Ignition control
• Fuel injection control
• Fault detection
• (Internal-) Generator management

Parts Parts of the Engine Management System are Sensors, Actuators, the ECU and the wiring harness. The core of the EMS is
the engine control unit (ECU), which consists of two modules.
These modules will be denoted by Lane A and Lane B, each
one capable of taking over control, regulation and monitoring of
the engine. In error-free engine operation, both Lanes are
turned ON.
During engine control by Lane A, Lane B ensures that the engine
operation can be maintained even after a failure or reduced
functionality of Lane A."

Obviously a lot different than a magneto system or even the 912ULS.
 
Just going by the 912iS Operators Manual.

Obviously a lot different than a magneto system or even the 912ULS.

I'd agree that the 912iS has better "smarts" than a 912ULS, or traditional aircraft engine. But I think the extra smarts are there to provide redundancy to the extra electronics they put into the 912iS. Example.. they needed to have a second internal alternator .. its not any safer than the 912ULS, but since an electrical failure in 912iS has more implications.. the 2nd alternator is there to ensure the 912iS is as reliable as the ULS.

There are still spark plugs and coil packs that can go bad. There is still an ignition switch, wiring, connectors, and now, Lane A/Lane B rocker switches that could go wonky or chafe over time.

Whether the 912iS system would detect fouled or shorted plugs? I don't think it does, but I haven't done a deep dive into the engine manual yet.
 
It is not that the probability changes. It is that the consequences change.
Exactly! Which makes it no more or less safe to check the mags (or electronic ignition, whatever) before crossing water or before leaving the circuit. Deciding that it's okay to check them before a water crossing and not while flying over land is simply an example of why humans generally do a poor job of evaluating risk.
 
I heard old timers (kinda like I am now) talking about “automatic rough” when you cross the shore outbound over a large expanse of water and immediately hear every little quirky engine noise you never noticed before. Only felt that way twice. Once flying night IMC over Lake Erie and once in daylight IMC headed back to West Palm Beach from the Bahamas. I decided it’s best to not overthink stuff once you’re committed!😁
 
I have a friend who had 150 hrs in gliders and went to get his powered private license. On an early lesson on downwind the young instructor said ok now we will do a simulated engine failure. Apparently they had both made incorrect assumptions about each other’s understanding of the procedure. Every landing my friend had ever done was without an engine, so he thought it was entirely normal, so he shut off the engine. I guess the instructor had never seen or heard of a glider and assumed that actually landing without an engine had a very low probability of success because he lunged at the controls in a panic and proceeded to do a very ropey landing, in a state if abject terror. He was so rattled that it didn’t even occur to him to turn the mag switch back on. Whereas his student was completely calm and actually quite amused. Talk about different perceptions of risk. I believe words were exchanged in the cockpit on landing.

“The most dangerous aspect of communication is the mistaken belief that it has occurred”
 
I have a friend who had 150 hrs in gliders and went to get his powered private license. On an early lesson on downwind the young instructor said ok now we will do a simulated engine failure. Apparently they had both made incorrect assumptions about each other’s understanding of the procedure. Every landing my friend had ever done was without an engine, so he thought it was entirely normal, so he shut off the engine. I guess the instructor had never seen or heard of a glider and assumed that actually landing without an engine had a very low probability of success because he lunged at the controls in a panic and proceeded to do a very ropey landing, in a state if abject terror. He was so rattled that it didn’t even occur to him to turn the mag switch back on. Whereas his student was completely calm and actually quite amused. Talk about different perceptions of risk. I believe words were exchanged in the cockpit on landing.

“The most dangerous aspect of communication is the mistaken belief that it has occurred”

Hmmm, wonder which one of these guys are most likely to survive an off airport emergency landing?
 
I had an engine quit with a student when we were doing stalls. He looked at me with saucer eyes and asked, “What do we do!” I said, “Well start it.” He did and it all worked out. We were over the Ford test track, and I really didn’t want to make the papers sitting on the race track standing next to an airplane.😁
 
I had an engine quit with a student when we were doing stalls. He looked at me with saucer eyes and asked, “What do we do!” I said, “Well start it.” He did and it all worked out.

Kind of disappointing that he couldn't work that out for himself.
 
Can’t blame him. As a 16 year old student the first time my CFI pulled the mixture when I wasn’t looking would have ripped out the yoke and handed it to him if I could have!😝
 
I nearly always do a mag check while flying, sometimes at full power but at a good height. That way you are going to expose any shortcomings in the ignition system.
Do it for a second or two and you will hear the change in engine note.
 
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