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3 Answers

Electric fires, failures, circuit breakers, and bus bars

Asked by: 2807 views , , ,
Aircraft Systems

I am currently flying a TB20, amazing airplane performance.

the question I have is about what to do in the event of an electrical fire or alternator failure. The POH says, just like most, to disengage all electricity, and then slowly bring things back on to either find out what is causing the fire, or, if an electirc failure, to reduce electric load and only bring on the minimum Items needed to preserve power. The TB20 has 3 bus bars, each with their own pull-type breaker. It says, in case of fire, to methodically bring each bus back on, and identify which bus is the problem, and then to identify which item on that bus is the problem, engaging each individual item one at a time. 

My two questions are...

how do you test individual items if they dont have a pull type breaker, but only a push to reset? Is there a way of disengaging the non-pull breakers?

Is this a safe practice, is it worth trying to find the faulty item, or should I just accept that it is the entire bus that is bad? The important  things (gear, etc) have their own pull breaker.

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3 Answers

  1. Sam Dawson on Jan 22, 2013

    I would recommend against resetting electrical systems that are not critical to the safety of the flight in the event of an electrical fire. The TB20 POH was probably written before the NTSB and FAA came out with some recent recommendations on circuit breaker resetting and electrical system failures.
    Here is a copy of the NTSB accident report that led to these recommendations. Important stuff reference electrical systems and failures begins on page 15.

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  2. Bob Watson on Jan 23, 2013

    Thanks for the link to the report.

    That’s enough to keep me from doing any in-flight troubleshooting of the electrical system. Page 22 of the report mentions how resetting a tripped breaker without knowing what tripped it can cause a problem to get out of hand if the wiring is damaged each time the breaker is reset.

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  3. Sam Dawson on Jan 23, 2013

    Here is a link to the FAA safety bulletin that wash published in response to this accident.


    Interesting to note that the FAA recommends that this information be reviewed during initial training, recurrent training and flight reviews.

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