Burning smell on takeoff. Any suggestions?

Discussion in 'Avionics and Upgrades' started by kicktireslightfires, Jun 10, 2021.

  1. kicktireslightfires

    kicktireslightfires Pre-takeoff checklist

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    Hi ya'll, I recently had a couple of Garmin GSB 15s installed in my Cessna 162 by a reputable avionics shop. On the takeoff roll or a few seconds after takeoff, I start smelling an electrical burning smell. The first time it happened I pulled the Cab Pwr circuit breaker just to kill power to the accessories and the smell started to dissipate. I took a look at the wiring and couldn't find any issues or any sign of burning. Each time I go flying, same smell during the takeoff roll, pull the circuit breaker and the smell starts to go away. What's curious is that there is no smell prior to the takeoff roll, nor during run-up, so there is some correlation between applying full power and the burning smell.

    The only thing I can think of is to take a test flight with a smoke mask and fire extinguisher at the ready and circle near my airport for 30 minutes without pulling the circuit breaker to see what happens and see if pulling the circuit breaker was merely a coincidence to the smell dissipating. If the burning smell worsens or becomes smoke, I'll put on a mask and land and then have the whole thing pulled apart to find out what's going on. You might suggest I do that now at this stage and not do the test flight, but put yourself in my shoes ... right now I've only experienced some minor burning smell and perhaps it's merely something that needs to harmlessly burn away and then the smell/issue will be gone forever. Ideally, I wish I could ground run this issue but I'm not sure how to do that given the issue seems to only present itself under full power. Which I'm assuming is when the alternator is sending the maximum amount of power through the wires.

    Is there some way to simulate max electrical power from the alternator while on the ground?

    The avionics shop opted for installing two in-line fuses rather than adding a whole separate circuit breaker due to the way the Cessna 162's circuit panel is constructed. Is there any possibility that the burning smell is coming from the fuses?

    Any thoughts/ideas? If you've read this and have no constructive suggestions and just want to tell me I'm a dumb*** for even considering a test flight, please move on and don't post. I would appreciate any thoughtful suggestions of how this could be tested most safely but without having to pull apart all the wiring or anything too expensive.

    Thanks in advance.
     
  2. sarangan

    sarangan Cleared for Takeoff

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    Do you see anything unusual on your ammeter? I can't imagine an electrical smoke without a high current draw.

    You could also leave the alternator off and see if the problem still persists. That will help you isolate it to the charging system.

    It is also possible that some piece of wire is touching the exhaust manifold, and as you apply power, it starts to smoke. But that doesn't explain why it goes away.
     
  3. DaleB

    DaleB En-Route

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    My idea would be to let the “reputable avionics shop” take a look at it and see what’s burning. Otherwise the NTSB report will make you look really bad.

    Put another way…. It seems safe to assume that you’re not an A&P, an electrical guy, an avionics technician, or a test pilot. Why would you then be tempted to do the jobs of all of them…. at the same time?
     
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  4. FancyG

    FancyG Pre-takeoff checklist

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    Any change in alternator output reading?
    If rpm specific, is this an exciter issue?

    Also, could you do an extended high rpm runup or short-field and reject takeoff and get more time on the ground to suss this out?
     
  5. Groundpounder

    Groundpounder Pattern Altitude

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    Is there a section on ADM in the private pilot training manual?
     
  6. sarangan

    sarangan Cleared for Takeoff

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    The OP did say not to bother posting sarcastic messages. Besides, I don't see anything particularly reckless with a precautionary flight in day VFR in the traffic pattern. Assuming this electrical smell is true and not imagined, one can always turn off the master switch and land.
     
  7. Groundpounder

    Groundpounder Pattern Altitude

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    I've never been one to follow rules. Or think that it's a good idea to fly an airplane with an electrical burning smell.
     
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  8. PaulS

    PaulS Touchdown! Greaser!

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    Why? What could go wrong? :confused:
     
  9. Salty

    Salty Final Approach

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    Turning off the master switch doesn’t extinguish a fire that has already started.
     
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  10. jsstevens

    jsstevens Final Approach PoA Supporter

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    I’d start by asking the installing shop what they think. If it is indeed pulling the circuit breaker that stops the smell, it should be somewhere on that one circuit. What all does that cover?

    Personally, I wouldn’t fly it. Fires in the air don’t seem like a good plan.
     
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  11. Groundpounder

    Groundpounder Pattern Altitude

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    Lets just hope he doesn't run out of coffee

     
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  12. PeterNSteinmetz

    PeterNSteinmetz Pattern Altitude PoA Supporter

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    I would NOT take off in a plane that has a burning smell. Violates my rule of never making a problem on the ground a problem in the air. Strikes me as a very poor and dangerous idea.

    Lots of ways to work on and isolate this electrical issue on the ground. Including adding large electrical loads. I would tell the shop they are not done yet.
     
  13. Dan Thomas

    Dan Thomas Final Approach

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    Even if it does stop the fire, there will be expense involved. Seems to me that spending the money on some knowledgeable troubleshooting would be a lot safer and probably cheaper. Replacing wiring isn't cheap, especially when the fried wire is in a bundle of wires, and the surrounding wiring has now had its insulation compromised.

    When the alternator speeds up as the throttle is opened, the field current drops. That's just alternator principle. When it's turning slowly, the field must be stronger to maintain circuit voltage against whatever loads are on it. The regulator feeds more current to the rotor. At higher speed, less current is needed, since a faster-moving magnetic field generates more current.

    The alternator's output does not rise, since there are no components in the airplane that need more power once the airplane is moving or flying. No battery-powered ignition. Does the 162 have electric flaps, and are they used for takeoff? Is that smell happening on flap retraction?

    My bet is on some wire shorting a bit against the airframe, flexing due to acceleration. Or the engine's prop-torque reaction moves it against some wiring. If it doesn't happen on the ground with the brakes locked and the throttle wide open, the acceleration factor is more likely.
     
  14. Dan Thomas

    Dan Thomas Final Approach

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    Yup. The old saying: It's better to be on the ground wishing you were in the air, than being in the air and wishing you were on the ground.

    But some folks are determined to save money no matter how much it costs.
     
    Last edited: Jun 11, 2021
  15. Doc Holliday

    Doc Holliday Pattern Altitude

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    You say this was a new install, and this is happening after the shop gave you back the airplane.

    Why not give the airplane back to them, and ask them to correct the problem?

    If you continue to “test it”, and something does end up burning, it’s on you, not the shop.
     
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  16. Bell206

    Bell206 En-Route

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    There is by turning on all the power consumers but it won't be "max" as the electrical load should only be at 80% or less of the rated system capacity.
    FYI: Just to add to the above comments on letting the shop handle it. Most installs and new equipment come with a warranty period and conditions. In some cases if you note a problem with the install or equipment and do not follow the warranty conditions they may void the warranty due to your current troubleshooting process.
     
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  17. Salty

    Salty Final Approach

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    No, they are Johnson bar.
     
  18. pigpenracing

    pigpenracing En-Route

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    This is why I love my Cub so much! nothing electrical to smell :) cub 1.png
     
  19. Steve Costello

    Steve Costello Pre-takeoff checklist

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    Read that last sentence again and really think about risk management and what you'd think if you read a post from someone else.

    If you try this, your screenname may just become a self-fulfilling prophecy.

    Take it back to the shop. They aren't done with their work.
     
  20. DaleB

    DaleB En-Route

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    So, OP, what did you end up doing?
     
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  21. Lindberg

    Lindberg En-Route

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    All things considered, day VFR in the traffic pattern is probably the best-case scenario for an in-flight fire. Nevertheless, taking off into a foreseeable in-flight fire still seems pretty reckless to me.
     
  22. DaleB

    DaleB En-Route

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    Sure, you can die just as easily in the traffic pattern as anywhere else.
     
  23. kicktireslightfires

    kicktireslightfires Pre-takeoff checklist

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    Thank you, all, for the insights above! It turns out it's not an electrical issue after all and the smell just coincidentally goes away two minutes after take-off, hence why I thought pulling the circuit breaker was responsible for the smell disappearing. (Went up with the circuit breaker pulled from the start and the smell still occurred, which confirmed it had nothing to do with pulling that circuit breaker.)

    I went up with 20,000 hour pilot and he said it smells more like burning rubber and his best guess is that it could be a hose or something in the engine compartment that is rubbing up against an exhaust manifold or something hot. I'm going to take off the cowling and have both myself and my A&P take a good hard look to find the source of the problem.

    Oddly, the smell goes away, consistently, 2 minutes after takeoff. It doesn't reemerge during full power climbs either. The smell ONLY presents itself during takeoff. Which is strange because you'd think it would be associated with applying full power, so I'm not sure what to make of it that the smell activates during and for 2 minutes following takeoff, but is not present during full power climbs. We took off, got the smell, it went away, did full power climb, still no smell, landed, took off again, smell came back on takeoff.

    My A&P did just correct the timing of the magnetos recently. Is it possible this has any connection to the magnetos that anyone can think of? They pass the mag checks just fine on runup and I'm not sure what's involved in retiming a magneto, but that's the most recent thing that was done in the engine compartment.

    At this point, it seems likely that my A&P may have incorrectly reinstalled something. The question is what.

    The mystery continues.
     
  24. FastEddieB

    FastEddieB Touchdown! Greaser!

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    Only on takeoff? Tire/brake related maybe?
     
  25. TrueCourse

    TrueCourse Pre-takeoff checklist

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    Applying hot temperatures during slow speeds, such as a takeoff, will allow the smell to be picked up temporarily. After takeoff with the higher speeds and higher airflow in the cowling and cabin this may be dissipating the smell, possibly disguising what is still occurring. Just my theory. Do some slow flight and see if the smell comes back.
     
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  26. PaulS

    PaulS Touchdown! Greaser!

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    Pulling stuff apart and putting it back together again inevitably results in oil getting where it should not be. Hopefully you are just smelling that burning off.
     
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  27. Ed Haywood

    Ed Haywood Pre-takeoff checklist

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    Maybe give the engine a good washdown and see if the smell persists.
     
  28. Dan Thomas

    Dan Thomas Final Approach

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    Better to look at it the way it is and see if there are soot stains or rubber crumbs somewhere that can point to the source. What if it's a fuel or oil hose rubbing on an exhaust stack? Life expectancy will be very low if that's the case and it isn't found. Test-flying it is tempting fate. If it stinks in the takeoff roll, then the takeoff roll should be all that is done; no flying. Even then a big fuel leak could be lethal before one got the airplane stopped.
     
    Last edited: Jun 22, 2021 at 11:17 AM
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  29. Daleandee

    Daleandee Cleared for Takeoff

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    What is the odor of the smell? No I'm not being obtuse. Different items create different odors as they burn. Shorting wires will have a noted difference than burning oil and overheated brakes will have an even different odor. But it may take someone with a good sense of smell and some familiarity with different odors to point you in the right direction.

    Sometimes an odor can be created by the strangest things. During a building inspection a couple of years ago one of the rooms had an odor that was much like dead fish. A search of all areas around the room including the drop ceiling, mezzanine, and wall cavity areas found nothing. It wasn't until someone noticed how hot the light switch cover plate was that we realized that it was the smell of the material in a wall switch that was overheating even though the switch was still functioning correctly.

    As others have said ... don't be a statistic by flying a plane with a known problem. It just ain't worth the risk.
     
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  30. kicktireslightfires

    kicktireslightfires Pre-takeoff checklist

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    To be more precise, it’s not the takeoff roll, it’s the departure leg where the smell is apparent. It’s not noticeable while on the runway. It’s only after liftoff and in the initial climb that the smell presents itself. After liftoff and certainly before reaching 600 feet. So I would say somewhere between 50 feet and 600 feet on departure is where it’s most noticed.

    It’s not brake smell. #1 My plane has a 100hp engine and it wouldn’t accelerate down the runway very well if the brakes were causing friction. #2 I know brake smell from cars very well and unless airplane brakes smell different, it’s definitely not brake smell. Can’t imagine how it could be the tires. They aren’t rubbing on anything and no marks of problems; the tires are also only a few months old — as are the brake pads.

    I’m thinking perhaps I should do a full throttle run-up and keep it full throttle on the ground for 60 seconds and see if the smell presents. What do you guys think?
     
  31. TrueCourse

    TrueCourse Pre-takeoff checklist

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    That would safer than flying around with a mask at the ready.
     
  32. Rushie

    Rushie Pattern Altitude

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    I agree. Do full throttle run up on the ground. If Truecourse is right about it being full throttle but not when you are at altitude and climbing as opposed to slower speed just after takeoff, just because higher airflow is carrying the smell away, you might smell it on the ground, then shut down right away, get out and go sniffing around to see if you can narrow the location.
     
  33. Groundpounder

    Groundpounder Pattern Altitude

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    Make sure there isn't any loose pavement, gravel, rocks, bullet casings, etc where you are planning on doing the runup. They may get sucked up by the prop.
     
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  34. Rushie

    Rushie Pattern Altitude

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    Lol, bullet casings.:)
     
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  35. DaleB

    DaleB En-Route

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    Hey, for all we know he could be flying out of Oakland.
     
  36. Matthew Rogers

    Matthew Rogers Cleared for Takeoff

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    Or basically anywhere with you guys around. Plenty of talk about pilots carrying their loaded guns and ammo around everywhere 24/7.
     
  37. DaleB

    DaleB En-Route

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    I would never leave brass laying around. That stuff is reusable, you know. Plus... FOD.
     
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  38. PeterNSteinmetz

    PeterNSteinmetz Pattern Altitude PoA Supporter

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    But for there to be empty bullet casings, one has to be discharging them on the airport, not just carrying a loaded firearm.

    Also has resale value, why let it go to waste?

    I wonder if @Groundpounder has encountered some runways in New Hampshire where people, likely not pilots, use infrequently used runways as shooting ranges?
     
    Last edited: Jun 22, 2021 at 6:52 PM
  39. PaulS

    PaulS Touchdown! Greaser!

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    Not necessarily, they could be falling out when opening a door after a fly by shooting.
     
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  40. PeterNSteinmetz

    PeterNSteinmetz Pattern Altitude PoA Supporter

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    Good one. LOL. :)
     
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