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5 Answers

Is it ok to take off with a hot magneto

Asked by: 3673 views ,
Aircraft Systems, FAA Regulations, General Aviation, Private Pilot

While doing my run-up this morning on my C172, I found out that the magneto #2 was hot. I decided to postpone my flight but my ex-instructor told me that I didn't have to. I don't like to fly when I know something, anything is wrong with my plane. What do you think? Did I make the right decision or I was too cautious?

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5 Answers



  1. KDS on Aug 05, 2018

    Anyone would be hard pressed to come up with a concrete regulatory yes or no answer to that question. The way things work in the real world is if you had made the flight and nothing happened, there would almost certainly have been no issue raised. If you made the flight and something happened and the broken p-lead got involved in the story, then it would be more likely that something negative would happen. It’s even possible that you might share the information that something was wrong with the airplane and you took off anyway and then something bad happened that was completely unrelated to what you noted as defective and that information would come back to bite you.

    IF the only thing wrong with the airplane was a broken p-lead, then there would be no mechanical reason why you couldn’t make a safe uneventful flight. On the other hand, you KNOW that SOMETHING is wrong with the airplane. It might be that when that problem is examined and corrected that another problem that you didn’t know about is noted and corrected.

    I assume that checking for a broken p-lead is an item on some checklist that occurs before takeoff. Something your school teaches perhaps. If they didn’t think it was important, why would they put it there on the checklist? It would be interesting to go back to your ex-instructor and suggest that he or she should take that view to the flight school and propose that they remove that check from that point and see how things play out from there.

    At this point, I should add that I have seen mag grounding checks on checklists at the end of flights, but I cannot ever recall seeing one before flight. When you think about it, you see the logic.

    However, having said all of that, let me just add this. Whenever faced with such a decision, I have to make myself stop and ask “why am I making this flight” and “what are the consequences if I don’t make this flight?” Am I on an EMS flight carrying a heart to someone who needs a transplant? Am I in combat and the enemy is going to overrun our position and this is the only way out? Am I going to be fired from my lousy Part 135 job by my horrible money-grubbing boss if I don’t go?” (Many a Part 135 pilot has had to deal with that exact question.) If the answer is you want to have fun, then the next question is how much fun are you going to have if you have to worry about whatever it is that made you ask the question in the first place. The cross-wind is 25 Knots and the max demonstrated cross-wind for the airplane is 25 Knots. Am I legal? Yes. Will I have fun? Maybe, maybe not. The p-lead is broken. Will I have fun flying around for a while with a nagging feeling there may be something else wrong with the airplane that I don’t know about?

    Like many things in life, the answer is neither black nor white.

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  2. EAD on Aug 05, 2018

    KDS, I think you may be forgetting that you do a mag check during run-up. This would reveal a hot mag since there would be no RPM drop.

    Bidochon, regarding taking off with a hot mag, realize that doing so is basically taking off without a proper run-up. You would likely not be able to tell if one of the spark plugs was fouled to the point it wasn’t firing. Because of that you also wouldn’t get full rated power from the engine.

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  3. AviatorTrevor88 on Aug 06, 2018

    If mag timing gets off on the mag you can’t shut off, you’ll encounter pre-ignition and/or detonation, and you won’t be able to shut off the bad mag. It’s a risk. Probably not a high chance of happening, but still an additional risk that wouldn’t otherwise be there.

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  4. KDS on Aug 06, 2018

    AviatorTrevor88 is 100% right.You would most definitely be incorrect taking off with such a condition.

    EAD, you can rest assured that although much of my flight time is in aircraft without magnetos, the fact that a mag check is done before takeoff did not slip my mind.

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  5. Brian on Sep 01, 2018

    Doh…and here is been teaching people to spin the prop to check for a hot mag! -_-

    Ps don’t ever do this, sorry for the bad joke!

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