Fuses and Breakers
Fiddle with them in Flight? (Part 1)

"It was a dark and stormy night . . . ." Those of you who have read my work in the past probably already understand where I'm headed here. For new visitors to these archieves, please understand that what follows is a comment on the hazards of imprecise speech and an attempt to glean useful information from a story long on emotion and short on physical facts. We all like to hangar-fly and "wing and a prayer" stories are entertaining. However, it's not unusual for stories to be offered as information upon which non-professional airplane builders should make design and operational decisions. If the facts and moral of the story are clear, great. The following story and my interspersed comments are an attempt to understand the physics of what happend in order that we might keep the event from repeating itself! If anyone is offended or feels picked on, please accept my appologies and know that I do not wish to attack or abuse anyone personally. The Internet is and should be the great equalizer. If someone finds my logic lacking and would care to point it out, I'll be most pleased to discuss it right here . . . in front of anyone who cares to listen in. Alternate viewpoints are welcome. It's very important that participants in the discussion share a common goal: let us provide the very best information we can to those who follow in our footsteps and look to us for guidance.

  • Wandering through the archives of several list servers, I found some old discussions on breakers, grounding, etc. to which I can now respond and perhaps suggest some alternative views. . . . . .

    Last week a pilot friend of mine who flies for a commuter air line and has military time in many craft ( I have a good deal of time in the seat beside him and would not hesitate to have my family fly with him ) was bringing a piper lance home from NY to Maine. 45 minutes into the trip the panel lights went dark as the main bus breaker popped (over the mountain of new Hampshire at night ). A remote breaker would have made this impossible to solve, a fuse is hard to change in the dark a local breaker is easy to reset.

    Okay, here's the problem . . . could it be our guy wasn't flying in a thoughtfully designed amateur built airplane with built in alternatives? No, he was stuck with a certified machine designed to produce the problem he now faced. First, what's this main bus breaker that kills the whole panel? None of the airplanes I fly have such critters. Second, why did it pop? What were the physics of the matter that produced the breaker's behavior. Was it a nuisance trip? If so, it had happened before and nobody did anything about it the first time it happened. If something was really BROKE, why would you WANT to reset the breaker in flight?

    He turned off all the radios and lights and all electrical systems not critical to flight and reset the breaker, it held ! He then turned on the systems one by one watching the amp meter for load . Each item by it self was ok except for the pitot heat which was greater than normal well as he said dam*** high. But by itself would not trip the breaker it was on, or the main. But with every thing else on it was enough to take the main out.

    The "main" breaker should not exist . . . I don't know why this airplane has one . . . it's an unnecessary, single point of failure for everything on the panel. Worse yet, our pilot has removed his captain's cap and put on a mechanic's hat while he trouble shoots his airplane. If pitot heat was ON earlier, may we assume this guy is IFR in the clouds? None-the-less, his attention is now diverted from piloting while he takes on what should be a totally unnecessary mechanic's task. By the way, the "main breaker" concept has found it's way into may amateur builder's initial plans for electrical system architecture. There's a fertile notion that if our houses have a "main breaker" our airplanes should have one too. This is absolutely not so. Why the Lance had one is totally beyond my comprehension.

    The trip was completed with the pitot heat and one radio bank off to keep system load in limits . . .

    I presume here that the pilot is observing an alternator or generator load meter. I'm wondering what the "radio bank" is . . . most airplanes of this era power the whole compliment of radios through an avionics master switch (yet another single point of failure for LOTS of useful stuff). "One radio bank off" doesn't give us a very clear picture . . .

    Landing lights were not used. The battery was found to be the cause of the problem. The pitot breaker was replaced because it did not trip and made him nervous so as he said for peace of mind it went. ( as voltage drops amperage rises ).

    If the battery had a shorted cell the nominal 14 volt setting for a 6-cell battery would be way too high for the recently acquired 5-cell battery; alternator output would have been excessive whether or not pitot heat was on. In the shorted cell scenario, with everything but panel lights OFF, the pilot should have noted an excessive load before bringing anything else back on line. Further, adding pitot heat to the system loads would NOT have been incrementally higher than normal. The statement about "as voltage drops amperage rises" is bogus; if the pitot heater produced a load that was incrementally too high, then the bus voltage was too high also . . . which argues with the shorted cell scenario. Obviously, there's a lot of data missing from this story for accurate diagnosis of the failure. The story continues . . .

    Several years ago I was flying a twin Seabee when I went to lower the gear the breaker would pop, after three attempts I lowered it with the hand pump. The motor had to be changed. But in this case the breaker was a good visual indicator of the problem. Hidden away I would have only known that the gear would not go down but not why. Knowing the problem appeared to be electrical in nature I used the hand pump and left the geared down until we landed and it could be checked and fixed.

    Open breakers are not especially useful tools for inflight diagnosis. The pilot's first indication of a problem was that he flipped the gear handle and things did not progress as he expected. Where is a value in knowing that a breaker was open? Suppose for a moment that the problem preventing gear extension was an broken circuit instead of a high current and the breaker didn't open? The situation is the same either way . . . the gear is retracted and nothing happens when the handle is moved. What difference does it make that the pilot could see and then in some way deal with an open breaker? Systems die and open breakers; sytems die and don't open breakers. It didn't change the pilot's need to revert to Plan B and pump the gear down by hand. Observing a open breaker was non-information.

    Ricki Nelson's airplane caught fire and most aboard died because someone kept resetting a breaker that powered a cabin heater. A the first sign of system malfunction, wouldn't it be better to play it safe and use the hand pump? I can't believe this pilot (and any passengers) were better off by attempting to tease the wheels down in spite of a clearly annunciated system failure! Hand pumps (and other backups to important systems) are there for a good reason. They are the "Plan B" to get you on the ground when "Plan A" isn't working. Resetting a breaker multiple times is courting more trouble than I care to deal with in the air. The writer continues . . .

    Breakers should be used, not fuses and should not be hidden or tucked away out of reach, or out of site. You your family and passengers depend on your choices now and in the future. Please give them every chance you can. I hope you don't over work your guardian angle! What is that old saying? A WORD TO THE WISE! IF ANYTHING CAN BE DONE TO MAKE OUR DREAMS SAFE LETS DO IT SO WE CAN DREAM ON FOR MANY YEARS TO COME!

    In spite of multiple attempts to reset a breaker the problem in this story didn't go away. I'll suggest that having that breaker in-sight and in-reach was not an operational and safety asset. I choose not to fly with guardian angels . . . the ones I know are not qualified for piston-powered flight. I'd rather understand the systems upon which I depend and assume that everything I install is subject to in-flight failure. Rather than depend upon any single device for comfortable termination of flight, I'll have backups. As amateur builders we're able to eliminate all nuisance trips of circuit protection devices. What's left are the really good reasons fuses or breakers to open . . . something is broke. Leaving them alone until on the ground is the best course of action. The guy flying the Lance in this story was stuck with his dutifully certified design. I presume that one of the reasons you choose to build your own airplane is because you want to be better educated than the average pilot and build better airframe systems than one may expect from the certified world. Stay plugged into your list-servers . . . this is where critical design review has to take place . . . in front of the whole world. Ideas brought forward here will either stand the test of qualified review or shot down in flames, either way we all benefit.

    Goto Part II

    ©1998 Bob Nuckolls, Wichita, Kansas

    This document may be reproduced and circulated by any electronic or print media if printed in it's entirety and free of intervening comments. Editorial comments accompanying any reproduction may excerpt sentences/phrases from the original for clarity of the editorial objective.

    As always, everyone's contributions in the form of critical review or additional input to the subject are welcome. I'll maintain and publish a thread elsewhere on this website . . . .