Poor Mixture Control = Fire? I Think So

[Desert185]

While attending a fly-in this weekend, a number of us witnessed a Piper Warrior taxi out, do a rather long runup (with some backfiring during the mag check by selecting OFF). Whether it was a bad mag or leaded/fouled plugs, I don't know, but I suspect fouled plugs.

Rather than takeoff, the pilot, with instructor in the right seat, taxies back, shuts down and confers with someone rather experienced to determine what to do. The pilot and instructor re-enter the Warrior and attempt a hot start (Lycoming, carbureted four-banger). A fire in the cowling ensues after repeated cranking. Even though I am 100 yds away, I am the first to arrive with a fire extinguisher and successfully extinguish the fire after running by zombie on lookers.

You can imagine all the why's and how's like me, but I feel it all started by taxiing out with mixture full rich, causing the plugs to foul, which resulted in the excessive mag drop and the taxi back. The CFI didn't know to lean during taxi, how to clear the plugs during the runup, nor how to do a successful hot start. :mad: shame all around. :ugh:

Learn from this...and carry a fire extinguisher.

FYI...

[mad_jock]

I would say they didn't follow the hot start procedure.

Over Primed it and managed to get fuel into the air filter.

More than likely 5 squirts with full mixture then waggle the throttle while cranking it.

The initial taxi will have been other issues.

But your right clueless instructor that doesn't have a clue what they are teaching or how to operate the aircraft. The won't be an airline op for starting a piston engine any more.

[huv]

Exactly what is the link between mixture control and the engine fire that seems to be caused by overpriming? Other than that both can be classified as some sort of engine mismanagement?

So the pilot did not try to stop the fire by simply keep on cranking to pull the carb-fire back into the engine (with the throttle fully open and the fuel cut off)? That is the procedure for all carburetted PA-28s I know.

[grafity]

Even though I am 100 yds away, I am the first to arrive with a fire extinguisher and successfully extinguish the fire after running by zombie on lookers.

Was this playing in the back of your mind as you ran to save the day?

OBwS66EBUcY

Fair play to you for stepping up to the mark, but do you really have to come on here and snipe at the misgivings of the CFI? I'm pretty sure you were that experience level at one stage.

Thanks for sharing the incident, as we can all learn from it I'm sure, but a little more modesty would make you a much more like hero. :ok:

[mad_jock]

It does show the lack of understanding of operating the machinery which is quite common out there.

[cockney steve]

Well, they say "Ignorance is bliss" ! I'd expect ANY person professing to be a tutor, to have a PROFESSIONAL level of understanding of their subject.

Unfortunately, it seems too easy ,nowadays , for some halfwit to jump through a few hoops and become "qualified"

I'm buggered if I'd trust my life to someone who didn't understand the fundamentals of operating an internal-combustion engine on which our continued good health depended.

[ShyTorque]

Seems to me that the aviation industry is all back to front.

The folks with the knowledge won't teach because the pay is rubbish.

Those with no experience are more or less obliged to teach because it's just about the only way to build their own experience.

So when something like this happens it's easy to say "Ah, but they should have known!"

But they obviously don't and in many cases it's hardly their fault. Why did no-one else teach them?

But in any case, "Lessons will have been learned", no doubt.

[Unusual Attitude]

From what I'm seeing nowadays its pretty much as you've already observed.

Little Johnny gets his PPL then CPL/ IR and comes out with just over 200hrs having spent all his flying life in a supervised 'school' environment. If an aircraft has an issue, he signs it tech and goes off and flys another.

Unable to get an airline job, he then goes on and gets an FI ticket to build hours out of necessity rather than a deisre to instruct. He then starts teaching the next 'Little Johnny' still having never left the supervised school environment himself and so the cycle continues.

I personally learned a heck of a lot about 'operating' an aircraft from the older more experienced members when I first joined a group and flew with them. Some of these chaps had 30years+ flying with well over 1000 GA hours behind them and knew all sorts of practical tips and tricks you'll never get from a 200hr FI.

I then learned a whole load more once I went on to own my own aircaft and had to start maintaining it myself!

In principle I think LAA pilot coaches could have a lot to offer a freshly qualified PPL but with only 2 in the whole of Scotland I'm not surprised not many people use their services!

Regards

UA

[Desert185]

Quote:
Originally Posted by Desert185
Even though I am 100 yds away, I am the first to arrive with a fire extinguisher and successfully extinguish the fire after running by zombie on lookers.
Was this playing in the back of your mind as you ran to save the day?

Since you ask...I was thinking why are all those pilots just standing around doing nothing? Why doesn't someone grab an extinguisher? Something had to be done and no one was doing anything.


Fair play to you for stepping up to the mark, but do you really have to come on here and snipe at the misgivings of the CFI? I'm pretty sure you were that experience level at one stage.

How else would you describe the incident? By not mentioning the CFI in the airplane? I published this as a learning experience for those on this forum who might not now have the knowledge and might have a CFI who needs a bit more vetting before being paid to do his job...and I get criticized for doing it. :ugh:

An interesting side story is that another CFI ground-looped her aircraft, which is why she was in a Warrior at this fly-in.

BTW, I never had that experience as a CFI or as a small aircraft operator. Must have had good instruction and paid attention. Now that we have computers and the internet, the acquisition of knowledge should be easier...provided one isn't concerned about criticism for contributing to that knowledge. [/quote]



Thanks for sharing the incident, as we can all learn from it I'm sure, but a little more modesty would make you a much more like hero.

Hero status is overrated and over-applied these days. I'm no hero. It was just part of relaying the story, and the point is that no one was doing anything. Do people have to be taught to be resourceful and assist others these days, or do people just not want to lend assistance for whatever reason?

[Desert185]

Exactly what is the link between mixture control and the engine fire that seems to be caused by overpriming? Other than that both can be classified as some sort of engine mismanagement?

Perhaps I should have outlined the details more clearly.

They apparently taxi with the mixture full rich causing the plugs to foul (mixture error one). During the runup there was the resulting out of limit mag drop. The pilot and CFI, also apparently, didn't know how to clear the plugs by leaning the mixture at a higher RPM (mixture error two). It was a 2100' MSL airport, but leaning during taxi should also be done at sea level.

One could argue that if they had adjusted the mixture properly during the taxi out, they wouldn't have had to do a hot start, which resulted in an unresolved induction fire.

So the pilot did not try to stop the fire by simply keep on cranking to pull the carb-fire back into the engine (with the throttle fully open and the fuel cut off)? That is the procedure for all carburetted PA-28s I know.

No.

Control of mixture during hot start (mixture error three). No induction fire resolution attempt (mixture error four).

[Cows getting bigger]

If the instructor had worked for me I would have fired him for wasting fuel. :8

[172driver]

grafity, you have just been added to my 'ignore' list.

Desert185, thanks for sharing. I does show stunning ignorance on the part of the CFI.

[Desert185]

Every place I worked as a CFI in the early days of my career, I can't remember when the Chief Flight Instructor would sit down with new CFI's and talk shop on how to manage engines and airplanes. I did learn a lot from a crusty, old airplane salesman who took me under his wing. I was a CFI and he wasn't, but thankfully I was smart enough to listen and absorb his experience and wisdom. He was my go-to guy.

RIP, John. You did good.

[BackPacker]

They apparently taxi with the mixture full rich causing the plugs to foul (mixture error one).

I just checked. There is no recommendation or instruction to lean the mixture during taxi in the 1988 PA28-161 Cadet POH. The only thing regarding this is "avoid prolonged idling at low RPM to prevent plug fouling".

The pilot and CFI, also apparently, didn't know how to clear the plugs by leaning the mixture at a higher RPM (mixture error two).

Again not a procedure that's listed in the POH.

Control of mixture during hot start (mixture error three).

POH has a hot start procedure. All it specifies is "mixture full rich".

I agree with Mad Jock that the cause is most likely overpriming, NOT incorrect use of the mixture - at least not "incorrect" according to the POH. Furthermore you don't give sufficient evidence that they executed the "induction fire" emergency procedure incorrectly. So I wouldn't be so quick to pile all the blame on the CFI or the education system that he/she grew up in. I'd rather wait for the results of a formal investigation of this incident - one that gives the CFI and the pilot a chance to comment as well, and incorporates the results of a technical survey of the aircraft.

[Cows getting bigger]

Desert, agreed. That's why I would have fired him for wasting fuel despite being taught how not to! :p I suppose there is a possibility that a fuel line let go resulting in the incident but my betting is on the over priming theory.

I also had an instructor who managed to flatten three batteries in a week, again not learning despite extended briefings and demonstrations. I don't believe he instructs any more.

[Desert185]

As you expand your experience, you will realize there is more to flying than what is described in the POH.

It wasn't a fuel line and there will be no formal investigation.

It is accepted practice to lean during taxi to prevent plug fouling, particularly at high density altitudes in the mountains. There is more to life than flying from sea level airports, and pilot-induced plug fouling is avoidable...sea level or otherwise.

Live by the POH; die by the POH.

[grafity]

The CFI didn't know to lean during taxi, how to clear the plugs during the runup, nor how to do a successful hot start. :mad: shame all around. :ugh:

This is the quote that made me want to write the post I wrote. The point I was getting at, is that you could have easily discussed the event without heaping "shame" on the individual.

I agree with a previous poster, the whole flight school industry is back to front. I also find it irritating when those with decades of experience seem to revel in newbies screwing up. This is neither the first, nor last instructor, to not have a clue about the workings of an engine. With that many of them out there, it's not the individuals fault, but a problem with the system.

I do respect the fact that you helped in the situation, the song was only meant as a joke. Sorry if you took it to heart, but your whole post came across to me as; I'm a hero and I share the world with idiots.


Every place I worked as a CFI in the early days of my career, I can't remember when the Chief Flight Instructor would sit down with new CFI's and talk shop on how to manage engines and airplanes. I did learn a lot from a crusty, old airplane salesman who took me under his wing. I was a CFI and he wasn't, but thankfully I was smart enough to listen and absorb his experience and wisdom. He was my go-to guy.

RIP, John. You did good.

So you understand exactly the situation this young CFI was in then? Do you think it was possible that this could have happened to you, just as easily, before John took you under his wing?

Maybe a better way you could have remembered his legacy, would have been to pull the CFI aside and try to impart some of your experience and knowledge on them, as he did for you. Rather than assume them an idiot, due to their lack of experience.

Sorry to hear that 172driver. Have a nice life none the less. :ok:

[BackPacker]

As you expand your experience, you will realize there is more to flying than what is described in the POH.

Absolutely. But you seem to think that instructors are supposed to teach the students all there is to know about flying, in any kind of condition or airplane, well above and beyond the POH. I simply don't agree with that. And in fact, if you don't fly the airplane in accordance with the approved flight manual, you might even fail your exam.

It is accepted practice to lean during taxi to prevent plug fouling, particularly at high density altitudes in the mountains.

Well, I don't exactly call 2100' MSL an altiport, so I would personally not apply "high density altitude" procedures to a take-off from there. If the engine doesn't run rough with full power, I would take off with full rich mixture. Which is - not coincidentally - what's described in the POH about these situations.

The same applies to taxi. Depending on the length of the taxi, the ambient temperature, the altitude, the RPM required to taxi and a few other factors, I might or I might not lean the mixture. And if I do, how much I lean is done purely by gut feeling - it's usually about 1/4 to 1/5th of the full mixture travel. At the very least what you call "accepted practice" is ambiguous (how much do you lean in the first place?) and not universally applicable. And not prescribed in this particular POH.

Live by the POH; die by the POH.

If there is information/instructions in the POH, or omitted from the POH, that you feel is life threatening, why not file a formal ASR/MOR or something like that, instead of making an anonymous post on a public forum which is neither read by the authorities (at least not officially) nor by the engine or airframe manufacturer?

I've said it earlier, and I'll say it again: Based on the limited information given, I feel that the cause of the fire was overpriming. And that's something that the POH warns against indeed.

When the runup failed due to rough running during the magneto check, the occupants did exactly what they were supposed to do, according to the POH: Abort the flight. But the plug fouling, not leaning the mixture during taxi, and not knowing the procedure for clearing fouled plugs - most of which is not described in the POH - did not cause the fire.

The fact that a few things happened at the same time does not mean that there is a direct causal relationship between them.

[Big Pistons Forever]

But the plug fouling, not leaning the mixture during taxi, and not knowing the procedure for clearing fouled plugs - most of which is not described in the POH - did not cause the fire.
.

Assuming the details of the incident as presented are correct, then two facts stand out.

1) The instructor allowed the engine to be grossly overprimed

2) The POH procedure for an engine fire at start up was not followed

Fact 1 speaks to a poor appreciation of good practices in the operation of a pretty simple piston engine which is pretty sad, but fact 2 speaks to a wholly unacceptable lack of skill and knowledge by the instructor.

[Desert185]

You're misconstruing what I said. Read it again. I think I made the chain of events and the causal factors pretty clear.

There much more to leaning and mixture control than what the POH outlines. I would guess that you aren't an advocate of flying lean of peak.

[BackPacker]

I think I made the chain of events and the causal factors pretty clear.

Nope. That's exactly what I dispute. Suppose they did not overprime when starting the engine for the second time. Would a fire have broken out then? I don't think so. So the plug fouling and everything else that did or did not happen before the second start did NOT contribute to the fire.

The only thing that the plug fouling did was cause the flight to be aborted, and that eventually caused a necessity for a second start. But it was the overpriming that caused the fire. And the fire would have happened too if the plugs were not fouled up, but there would have been another reason for the restart where the same sloppy priming technique would have been used.

I would guess that you aren't an advocate of flying lean of peak.

You show me an O-320 installation in a PA28 that can reliably and consistently be leaned to LOP, and you've made me a convert. But until then I'll just lean until rough running sets in, and then enrich a tad more to restore smooth running. Heck, most O-320 installations I've seen don't even have an EGT gauge.

Can't understand what this has to do with the present discussion though. Unless it's intended as a low blow with which to end the discussion. In that case I'd say: Bring in the Nazis. Godwin's law - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Godwin's_law)

[Victorian]

So the plug fouling and everything else that did or did not happen before the second start did NOT contribute to the fire.



With respect to Backpacker, I don't really agree with that. I think that there are lots of aircraft that are difficult to start, or re-start, or some other finnicky behaviour because of lazy maintenance.

These behaviours lead to equally innovative starting proceedures, especially (in the Warrior) throttle pumping, the results of which I've described on here before. Essentially, if you pump the throttle more than about 3 times with the engine stopped, you will have neat fuel runniing down the inside of the cowling. No amount of 'continue cranking' etc will put that out if it ignites, at least until the engine starts.

So there's the point - why does it ignite? Unfortunately, the badly maintained engine that won't start in the first place is the same one that's likely to backfire or have fuel burning in the exhaust. So if your engine is reluctant to start, get it fixed before someone - quite possibly an instructor - devises a 'sure fire' personal technique with catastrophic results.

[A and C]

Just to put a little more accuracy to this, if you move the throttle from idle to full power once with the engine not turning you will get fuel running down into the air box below the carb, how much of that fuel gets into the bottom of the cowling depends on the temperature in the carb and cowl at the time.

[Desert185]

The only thing that the plug fouling did was cause the flight to be aborted, and that eventually caused a necessity for a second start. But it was the overpriming that caused the fire. And the fire would have happened too if the plugs were not fouled up, but there would have been another reason for the restart where the same sloppy priming technique would have been used.

Agreed. I never said plug fouling caused the fire. Error one was the taxi out with mixture rich, and subsequent fouling causing the excessive mag drop. If they hadn't done a restart after receiving some counseling on the mag drop, they would not have made a bad hot start with the resulting fire. I hope this is clear enough.



Quote:
I would guess that you aren't an advocate of flying lean of peak.
You show me an O-320 installation in a PA28 that can reliably and consistently be leaned to LOP, and you've made me a convert. But until then I'll just lean until rough running sets in, and then enrich a tad more to restore smooth running. Heck, most O-320 installations I've seen don't even have an EGT gauge.

Can't understand what this has to do with the present discussion though. Unless it's intended as a low blow with which to end the discussion. In that case I'd say: Bring in the Nazis. Godwin's law - Wikipedia, the free encyclopedia

The reference to lean of peak was because you apparently strictly adhere to the recommendations of the POH. POH's generally don't discuss running LOP, even though the practice is entirely accepted these days on fuel injected and the occasional carbureted engines. That was the reference intended.

I generated this thread in the spirit of educating those who might not understand the concept of mixture control, and the consequences thereof. If arguments are your preference, fine. They aren't mine, especially when referencing Nazis, which has nothing to do with the present discussion.

[BackPacker]

I never said plug fouling caused the fire.

You said poor mixture control caused the fire. In the title of the thread even.

If they hadn't done a restart after receiving some counseling on the mag drop, they would not have made a bad hot start with the resulting fire.

If they hadn't gotten out of their beds that morning, the fire also would not have happened. That's not the same as saying that their getting out of their beds that morning caused the fire.

I'm here on this forum to learn from the mistakes of others, because I don't have time (or enough lives) to make them all myself. That's why I'm interested in what really caused the fire. Which is still, in my opinion, the sloppy starting technique - overpriming - on the second (hot) start.

What caused the hot start to be needed is largely irrelevant to the cause of the fire. It could also have been a passenger forgetting to turn his cellphone off and putting it in a wing locker, or a forgotten pitot cover.

Having said that, I do agree to Victorians argument that people may start to develop "innovative" starting techniques on engines that are hard to start. And engines with fouled plugs may be harder to start than normal. Still, that's no excuse for overpriming - something that the POH warns against. If anything, a hot engine requires less priming than normal.

The reference to lean of peak was because you apparently strictly adhere to the recommendations of the POH.

I don't, but I do expect instructors to teach their students to fly the aircraft according to the POH in the first place. Only once they've fully mastered that, should I expect them to teach stuff beyond what's in the POH. So I don't automatically condemn an instructor for not leaning during taxi, if that's not something that's written in the POH.

[Desert185]

Quote:
I never said plug fouling caused the fire. You said poor mixture control caused the fire. In the title of the thread even.


Fuel makes fire...and fuel at an aircraft carburetor is controlled by...? :ugh:

[mad_jock]

Live by the POH; die by the POH.

That must be one of the most stupidest statements on here in a long time.

If there was anything in the POH that is a risk to life the authorities would never allow it to be in there.

If there was such a procedure which could risk life. The POH would have been changed or a design MOD done to remove the risk.

Do you think they make these documents up for fun?

[Desert185]

Some of you folks are taking this too literally. The POH doesn't cover every eventuality, so if you strictly adhere to the recommendations as if they were limitations, you're doing yourself and your aircraft a disservice. There is more to operating an airplane safely and efficiently than adherance to the POH.

[tmmorris]

I agree the POH isn't the be all and end all. In the PA28 (owned by A and C) that I fly most often, I tried recently the POH engine start procedures instead of the ones I was taught as a student pilot.

Lo and behold... the engine doesn't start...

Back to what I was taught... fires every time.

[cockney steve]

PURELY CONJECTURE.....
The POH was formulated on the basis of a new aeroplane
It would NOT have taken account of today's pilots, who are not mechanically inclined or empathetic.
It would not have considered a carburettor ~40 years old, with worn float-needle and seat, worn throttle-butterfly spindle and Carb body, worn linkages..Maybe a bit of backlash in the Mag-drives, Plug-leads in less than A! condition....
Then there's the afore-mentioned Pilot Empathy.........Back in the day, they would have been enthusiasts , generally,- It was a rich man's hobby and the cost of a mechanic to keep everything spot-on was , overall, fairly insignificant.

The Aviator would know and really understand the operating -principles and demands of the petrol-engine....remember, Pre-war cars commonly had "mixture" "advance-retard" and "hand-throttle" controls for the driver to manipulate and keep his engine running efficiently.

Anyone who has read the Trevor Thoms series should be able to pass the exams....It's learning by rote! UNDERSTANDING is a different animal.
It's the understanding that enables someone to depart from the "one size fits all" POH GUIDELINES and operate their engine in an efficient and safe manner.

the "push a button" brigade will continue to have problems....An IC engine in reasonable condition (A defacto requirement of a C of A, i would think) will always start if it's given the right fuel-air mixture and the right ignition at the right time.......I'll admit that fixed mag-timing is set at optimum for cruise and therefore is not the ideal timing for starting -but that's what an impulse -coupling is for!

Know and understand your machinery apply logic to the symptoms and you will arrive at the correct solution

TMMorris is right!

[riverrock83]

Fuel makes fire...and fuel at an aircraft carburetor is controlled by...? :ugh:
Both mixture control, throttle AND PRIMER .
Engine fire was caused (probably) by TOO MUCH PRIMING. Mixture could have been at ICO and it could still have caught fire.
Nothing to do with the mixture control.

You said in your original post that there was repeated cranking during the attempted hot start. You were over 100m away. Could the repeated cranking not be part of the engine fire during startup procedure? The POH says that if the fire doesn't stop while continuing to crank after a few seconds, the aircraft should be abandoned. By the time you had got your extinguisher and travelled more than 100m it will have taken at least 15 seconds, probably much more. Unless the FI says they didn't continue to crank (and they may have been in shock straight afterwards) then how can you know whether they did or not?

They were following the authorised procedures until probably over cranking.

Clearing mags is not part of most training (I only know about it because it happened during my training). Its not in any text book that I've seen. I think you are doing the FI a disservice.

I can't comment on their hot start procedure as there are lots of engine variants around, but this one http://www.ddac.com.au/documents/aircraft/PA28.pdf suggests not priming at all unless it doesn't start first time, the only difference between hot and cold start is a higher throttle setting for a hot start. If priming was the cause (and their aircraft is similar to this one), then they weren't following the POH...

[Desert185]

Clearing mags is not part of most training (I only know about it because it happened during my training). Its not in any text book that I've seen. I think you are doing the FI a disservice.

I learned that technique in 1967. Mediocre POH...good flight instructor. The FI screws the pooch multiple times...and I am doing him a disservice!? Seriously?

They didn't know about the fire until I was within about 50 feet of the airplane when the smoke started billowing. There was no attempt by them to continue cranking, even after seeing smoke emanating from the cowling. They had no idea there was a fire until that point.

We watched the entire series of events unfold while sitting in front of the hangar adjacent to the grass runway. It was a goat rope from the first start and runup.

[phiggsbroadband]

The problem was that priming was used. Even an engine that has only run for 40 seconds will have its combustion spaces sufficiently hot enough for no
priming to be necessary.

A taxi to the runway and back, maybe of over one mile, would have got the cylinders extremely hot... Maybe the crankcase and crankshaft and oil would not be up to cruising temperature, but the bits that matter would be very hot indeed (i.e. don't touch!)

I once saw an injected c172 spend about 5 minutes after re-fueling, trying to start a hot engine, there was a good cup full of fuel on the ground under his engine, which fortunately did not catch fire when it eventually started.

[JamieE]

When I learnt to fly we had some old knackered PA28's that were allowed to go 100 hours between checks by the authority as a concession.

If they had too much fuel in the system, we used to start them by fully opening the throttle, fully closing the mixture and then swapping the levers round once it fired.

This work every time as long as you managed the swap fast enough, and if not, a normal start worked after this procedure.

I have no idea if that's what we were supposed to be doing, but most of the instructors were ex-military test pilots!!

[cockney steve]

[QUOTE]If they had too much fuel in the system, we used to start them by fully opening the throttle, fully closing the mixture and then swapping the levers round once it fired.[QUOTE]

Yes, that's exactly the solution.....Now, If you had studied your "Trevor Thoms" assiduously, you'd know why it is correct and it works!


Too much fuel - air-fuel mixture won't ignite ....close mixture, shuts off fuel supply......cranking the engine dilutes the ratio of fuel to air (as you have given it an unrestricted supply of air to "mop up" te excess fuel Until you reach a combustible ratio,at which point the engine starts firing and rapidly consumes the residual fuel.....swap levers quickly and the balance is maintained....common sense and basic physics , really:} -It's got sod-all to do with "difficult...bad starter....temperamental...etc.

[172_driver]

Live by the POH; die by the POH.

That must be one of the most stupidest statements on here in a long time.

Not sure if it's so stupid..

A friend of mine had an engine failure at 8000 ft on a hot & dry day in SoCal. The POH drill said Mixture - Rich! But it wasn't until he leaned the mixture that it finally ignited for him again.

[mad_jock]

Which would have happened anyway when he had lost some height.

And you don`t just have an engine failure that then restarts. Usually you have to do something stupid outside the POH for it to stop

[172_driver]

Or a badly adjusted Fuel Control Unit that delivered too much fuel for the ambient conditions. But that's not the point…

It's not always black & white … someone who had not understood fuel-air ratio and flammable limits would perhaps not have lived to tell the tale. Lower altitude might have solved it.. yes.. maybe..

[The Flying Pram]

This is neither the first, nor last instructor, to not have a clue about the workings of an engineThat strikes me as more than a little worrying. When I learned to fly a microlight in 1990 the syllabus included basic engine (both 2 & 4 stroke) theory. I was, perhaps, fortunate that I already had years of practical experience with motorbikes and cars. But nonetheless I still ended up having a disagreement with my instructor (Hi, Mike) over fuel/oil ratios - it was 2 stroke pre-mix with the Rotax. The question was what is preferable: too little oil or too much? I said too much, as I had practical experience of what the other lead to. However he pointed out what I hadn't appreciated - more oil in the same volume of fuel mixture means less petrol, and consequently a lean running engine. I was initially not convinced, but then realised that it's very rare to have a car or bike operating at full power for more than a few seconds, unlike an aircraft taking off and climbing to cruising altitude, so the situation is rather different.

Back then full engine management systems were not universal, and most drivers had a reasonable idea what went on under the bonnet. Nowadays there is virtually nothing you can do with a new car, so even those who do have an understanding are helpless. But since the majority of light aircraft still rely on stone age technology, a good understanding of ignition and fuel delivery SHOULD to be taught to all students.

As to listening and learning from "old hands" - I've flown quite a bit with a local pilot in his C150 and remember one evening when he did the run up checks and found a significant rev drop on one mag. He spent some time trying to clear it with mixture leaning, to no avail, and we taxied back to the hanger and discovered a plug with a nice globule of lead across the electrodes. I am also aware of the "cut the fuel/mixture and continue cranking" advice if a fire breaks out whilst starting, and the "open throttle and close mixture" method of dealing with over priming is also familiar to anyone of my age. This sort of knowledge should be imparted more widely than seems to be the case in the OP's incident, even if it means upsetting a younger FI.

[Big Pistons Forever]

I would suggest that any engine that fouls the plugs under the stated conditions has the idle mixture set too rich.

An easy way to check is to note the momentary rise in RPM as the mixture is pulled to idle cut off. There should be a rise of 25 to 50 RPM. If the rise is excessive the idle mixture is too rich and if there is no rise the mixture is too lean.

A friend was recently complaining about his plugs fouling on the taxi. I found a rise of over 100 RPM so we had the mixture adjusted and his plug fouling problem went away.

BTW the proper way to do a "burn out", that is clear plug fouling, is to go to runup RPM and lean until the engine is so lean it is running rough. Hold that for about 15 second then return to full rich and check the mags. If that does not clear the plugs you have other problems.

Avoid excessive running with the mixture grossly leaned. If 15 seconds of lean running won't clear the plugs, more time won't help.