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PA28 smoke source mystery

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PA28 smoke source mystery

Old 21st Sep 2023, 19:37
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PA28 smoke source mystery

Hi All,
I have a perplexing question that I am hoping you can help me out with.
I completed an uneventful flight on a PA28 the other day and just as I was parking, noticed what looked like smoke/steam coming out of the ignition.
I immediately switched everything off and it didnt' return when I restarted it, did my run-up checks or flew home without issues.
Unfortunately (other than a suspected oil leak, as the a/c has been losing oil over time) there was no evidence that it ever occured and the the CFI called me into his office earier to ask if I was "sensitive" or "fearful of flying" as there is nothing wrong with the aircraft on inspection. (in short he thinks it may have been in my head, but I know what I saw).
My question is what caused the smoke/steam from the ignition? (which didin't leave a black soot in case you were going to ask/I cant' recall is here was a smell, it all happened very quickly).
I am worried about it re-occuring during flight and scaring another pilot.
Thank you for your help in advance,
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Old 21st Sep 2023, 21:45
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Unless the CFI took the aircraft up with an engineer, s/he does not know what caused the smoke/steam anymore than you do. And shame on them for suggesting you might be a nervous flyer.

When you say 'ignition', can you be more specific - the ignition/start switch or a magneto?

Did the smoke/steam drift out or 'jet' out?

Was it a lot or a tiny amount, and how long did it last ?

My initial thought is an electrical fault in the switch, but electrical faults usually have a 'loud brown smell', as we say.

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Old 21st Sep 2023, 22:20
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The PA-28 ignition switch does only 3 things. It grounds the P lead of the left mag. It grounds the P lead of the right mag. It closes the circuit to the starter solenoid when turned and pressed in. Failure of the start solenoid quench diode could cause start switch arcing which could perhaps establish a conductive path. My PA-28 ignition switch has, to the best of my knowledge, been in service since 1975 and I have never seen it smoke.

I was once sitting in my MG Midget at a traffic light and saw smoke rising from the steering column. Found out that the turn signal switch had burned between the contacts and was smoldering nicely on the carbonized path when the turn signal was turned off. Easily fixed by cleaning out all the burned material. One of my few "Lucas electric" events.

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Old 21st Sep 2023, 22:54
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Thanks guys,
Here is where the smoke came from:
Smoke drifted really slowly like someone slowly blowing out some cigarette smoke loop in slow motion (nothing fast/"jetting" or shooting)
Small ammount and didn't last long as the second I noticed it I shut the aircraft down fully (as the ignitions right in front of me, it didn't have time to build).
If it was a fault at the switch, why would it not also produce smoke on my 2nd start-up?
Is the potential oil leak of any significance? or a red herring?
Someone is flying the aircraft tomorrow and 3 people on Saturday, I'd be interested to see how those guys get on.
Also after it occured, an expereinced instructor looked underneath and couldn't see anything at all/there was nothing off when I looked at the engine briefly when checking the oil)

Everything I'm saying is 100% the Truth but I could tell he didnt' believe a word I was saying today, (may be because once before I had a 0 reading Ammeter (also on an away flight) and had to speak to our Radio room people prior to flying home, this was in case I lost Radio power and needed to join the circuit without communicating so they could anticipate it), but he asked me if I "fly to places and then get nervous about flying home..." I told him that the zero reading Ammeter (which may have simply been the instrument at error I appreciate) was visible to everyone else eg: engineers, insructors also and not connected to some "nervousness"

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Old 22nd Sep 2023, 01:51
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Had two electrical smoke incidents in aircraft..first was in the PTT switch in a condor stick which shorted the second was in a DC9 after landing..first time hardly anything, next sector really noticeable ..took more than an hour to trace it as we thought it was a system connected to landing gear down lock followed by flight ground switch..turned out to be a loose contact in the landing light switch .turned on after gear selection..turned off on turning off the runway.
Had another incident with a loose contact which gave us an irregular slat indication; returned to the ramp twice and eventually a loose contact was found behind the circuit breaker panel.
Had several in cars .. one caused a fire which was in a VW camper and caused by the tow bar wiring wearing out on the road with the earth touching the indicator wire..burnt out flasher unit which then set fire to the wiring under the dashboard.
Had a few others in cars, normally due to heavy load through ignition switch; have installed relays in my Bristol to relieve loads to the electronic ignition system and the dragster fuel pump which happened to blow last week..electrical fault.
As a guess but no idea of the wiring but am guessing either a loose contact causing an intermittent arcing.
As to the CFI whinging ..had a few dim fools tell me similar 50 plus years ago and I’m still flying today - normally lack of intelligence or plain incompetence. Nowt worse than a smell of burning in an aircraft or boat.
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Old 22nd Sep 2023, 05:15
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The most likely (but not definitive) cause of smoke in the cockpit would be an electrical issue.

Some questions that may possibly be worth asking to get a fuller picture:

1. Was there any smell at the time? (And did you try sniffing under panel afterwards?) If there was smoke where you saw it, it may not necessarily be the magneto/starter switch, it may have come from somewhere else behind the panel and just appeared there.

2. Were you stationary at the time or did it happen during taxi?

3. Was the door unlatched during taxi? Storm window?

4. When you said it stopped on shutdown, was that shutdown of the engine or master? Did smoke stop with engine stop or master off? Did it stop immediately when doing this?

5. Were there any systems not working normally during the flight? (radio, cockpit lights, popped circuit breakers etc)

6. Did you notice the behaviour of the ammeter during the flight and prior to shutdown? If so anything unusual?

7. Were the air vents open? Was the cockpit fan on? Has arcraft been used for scattering someones ashes recently? (serious question - people do this by opening the storm window and trying to empty it out through that, will result in a blizzard of dust inside the cockpit that will go everywhere and not easily cleaned out. The loved one will need to be hoovered.).

8. weather conditions? (was it humid?)
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Old 22nd Sep 2023, 06:48
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Jonkster point 1 is very likely. The smoke source which we initially thought was from the instrument panel was from the overhead panel.
I spent a couple of days occasionally sniffing the back of a fridge standing under the stairs..it was only after the smell got worse that I opened the fuse box cupboard a good 6 ft away that I discovered a melted circuit breaker caused by a loose mains wire arcing.
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Old 22nd Sep 2023, 13:27
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Originally Posted by sconnors
Unfortunately (other than a suspected oil leak, as the a/c has been losing oil over time) there was no evidence that it ever occured and the the CFI called me into his office earier to ask if I was "sensitive" or "fearful of flying" as there is nothing wrong with the aircraft on inspection. (in short he thinks it may have been in my head, but I know what I saw).
,
Consider a different flying school...?
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Old 22nd Sep 2023, 16:15
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Had an oil filled capacitor go pop once, the oil mist that it emitted was just like smoke and gone in a few seconds. It was an open cockpit.
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Old 22nd Sep 2023, 18:41
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Question

May I ask the location of the hand held fire extinguisher in your PA28?
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Old 22nd Sep 2023, 21:11
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Originally Posted by jonkster
The most likely (but not definitive) cause of smoke in the cockpit would be an electrical issue.

Some questions that may possibly be worth asking to get a fuller picture:

1. Was there any smell at the time? (And did you try sniffing under panel afterwards?) If there was smoke where you saw it, it may not necessarily be the magneto/starter switch, it may have come from somewhere else behind the panel and just appeared there.
Yes, but I ventilated it and no ther was no smell coming from underneath afterwards

2. Were you stationary at the time or did it happen during taxi?
I just parked (after taxiing) and in that instant noticed it, so yes, stationary

3. Was the door unlatched during taxi? Storm window?
Accidentally helft storm window open through out the flight, only noticed on landing

4. When you said it stopped on shutdown, was that shutdown of the engine or master? Did smoke stop with engine stop or master off? Did it stop immediately when doing this?
Unabel to answer this one specifying whether it was master of engine shutdown, but I can say it did stop, and didn't return on re-starting

5. Were there any systems not working normally during the flight? (radio, cockpit lights, popped circuit breakers etc)
No everything was perfectly fine (pre and post this issue)

6. Did you notice the behaviour of the ammeter during the flight and prior to shutdown? If so anything unusual?
Can't say with certainty

7. Were the air vents open? Was the cockpit fan on? Has arcraft been used for scattering someones ashes recently? (serious question - people do this by opening the storm window and trying to empty it out through that, will result in a blizzard of dust inside the cockpit that will go everywhere and not easily cleaned out. The loved one will need to be hoovered.).
The loved one being hoovered is is indeed a scary image, but no, defintely nothing like that

8. weather conditions? (was it humid?)
Possibly, but completed multips carb heat checks en-route without issues, if thats what you were thinking
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Old 22nd Sep 2023, 21:14
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Originally Posted by sandringham1
Had an oil filled capacitor go pop once, the oil mist that it emitted was just like smoke and gone in a few seconds. It was an open cockpit.
My old flght instrctr thought it may have been some oil from the so-called "leak" dropping on some hot and evaporating.
I reacall taking the key out of the ignition expecting it to be both blackkend and hot, but was surprised to see it was neither
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Old 22nd Sep 2023, 21:17
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Originally Posted by hedgehopper
May I ask the location of the hand held fire extinguisher in your PA28?
I didn't observe a fire or any flames
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Old 22nd Sep 2023, 22:11
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Originally Posted by sconnors
I didn't observe a fire or any flames
With respect, you have not answered my question!

I was hoping that an indication of its location would help refine my thoughts as the extinguishers are in various positions dependent on model and mod status.
Without the info, hypothesis:
1. the “Powder” extinguisher is located under the pilots seat,
2. it’s trigger is facing forward
3. when changing tanks in flight or turning off on the ground, you move your left leg to a position under the seat thereby allowing easier access the fuel valve, and “Momentarily Kick” the trigger allowing a short burst of medium to escape.
4. After a few seconds this appears into view and appears as a “ Waft of fine Smoke”
No signs of fire, flames or residue.
HH



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Old 22nd Sep 2023, 22:18
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apologies, no 100% not the fire extinguisher, it was in the back of the aircraft, I made no contact with it
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Old 22nd Sep 2023, 23:01
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You need a close look at all parts of the wiring. The most likely source of smoke without fire is electrical insulation being vaporized.This leaves the copper wire uninsulated and far more easily susceptible to a short circuit that can do unexpected damage or disable critical circuitry. It is most likely from a high resistance short from wearing through against a part of the structure or a place where the conductors have fatigued and multiple strands have broken, leaving the few remaining strands overloaded. There is also a possible overload elsewhere, perhaps in the engine, that is intermittent, and that overloaded a wire behind the panel.

I agree that checking capacitors for failure is a good idea.


What does the instructor expect to be normally so hot as to vaporize oil? Find a good mechanic who does electrical work.
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Old 22nd Sep 2023, 23:30
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not the fire extinguisher, it was in the back of the aircraft
Readily accessible during a fire then!
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Old 23rd Sep 2023, 07:36
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I fly a PA28, tbh, I’m surprised there’s not a fire extinguisher under the seat.

Out of interest, when you say you shut it down immediately,

You did pull the mixture to shut down, not just turn the mags off?

You seem to say you turned the mags off.

“I shut it down, the ignition (sic), was right in front of me”.


Could you clarify that?

Has anyone done a dead check on the aircraft?
(Totally unadvisable usually, turning the mags to off and back again on a running engine, to make sure they still short.)

I’d be looking for a share, with shares, the aircraft can be grounded, as it doesn’t have to earn it’s keep. In my experience, schools do not like to ground aircraft. Flew one with “intermittent flaps” once, “yeah, sometimes they work, sometimes they don’t”.

anyway, sounds electrical, but could you answer the 2 questions above?


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Old 23rd Sep 2023, 08:56
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Originally Posted by sconnors
Hi All,
I completed an uneventful flight on a PA28 the other day and just as I was parking, noticed what looked like smoke/steam coming out of the ignition.
I immediately switched everything off and it didnt' return when I restarted it, did my run-up checks or flew home without issues.
............
I am worried about it re-occuring during flight and scaring another pilot.
You were worried about other pilots being scared, but this incident didn't alarm you enough to stop you flying home, without investigating and finding the problem? Did you ever consider you might have faced an electrical fire on the way home?

If you wish to continue otherwise "uneventful" flying could I politely suggest the benefit of a philosophical think about your own self-preservation? Seriously.
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Old 23rd Sep 2023, 09:35
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But regardng the fire extingusiher, both of my feet were on the pedals for the entire flight, for the entire landing, taxiing and for braking, so I dont' think it was that, it was a solo flight. I'm not convinced it was the fire extinguisher tbh.

I did have someone at the landaway airfield look at it and he found nothing, and I spoke to the club (and I have the guy who looked at it speak to my club) and I spoke to someone else at my club and if they said it was safe I would believe them (more on the grounds of my own inexperience rather than any self-preservation), But I take on board what I thik you are saying, ie: I should have not flown it back that day unless it was formally investigated.

Regarding shut down, as far as I can reacall I shut the aircraft down in the normal way. But can't link the smoking stopping to a specific action.
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