Panel switch/ circuit breaker recommendations

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Dan Thomas

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Breaker resetting information: https://www.faasafety.gov/files/notices/2009/Dec/SAIB_CE-10-11.pdf

In over 20 years of aircraft maintenance I never had a breaker-tripping complaint except for bad breakers. One of the key factors in electrical safety is proper inspections, provided, of course, that the system was put together using standard aircraft practices, with wires properly routed, supported, terminated and everything else that goes along with assembling an airplane. During annuals/100/200-hour inspections I sometimes found wires being chafed by sharp corners of structure, by control system stuff like cables or mechanisms, and so on. Find it and fix it. Sometimes the damage had obviously been happening a long time and never caught because nobody ever looked for it, even though legal inspection requirements include such checks. And sometimes it was happening because someone had changed or installed something and not made sure that the wiring wasn't against sharp corners or anything else. Once I found that the elevator travel was restricted by a cable bundle under the panel that had been tied up by some avionics guy after an avionics upgrade. No one had run the controls through their travels to make sure they were free of everything.

Getting your head under the panel often means taking the seats out. Looking at cables under the floor means taking the carpets and inspection panels out. It's a lot of work and costs time, which is money, so many airplanes have this stuff happening and the owner thinks he's safe. Also under the panel are the vacuum system filters, and I often found those many years past their replacement times, sometimes good and clogged, and the vacuum relief filter crumbling with age. Nobody was looking at anything under there. Nobody. For years. Once found an aluminum vacuum system tube rotted right through; the new owner of this old airplane complained that the gyros didn't work very well. I guess not. I could have stuck a pencil way up into the tube through that hole.

Basic stuff. But people are often oblivious or just lazy. I read of a Cessna 180 or 185 that had an inflight elevator seizure. The batteries in those airplanes are in the tail, right next to the elevator, trim and rudder cables. Someone had replaced the battery positive cable to the contactor with a longer cable that looped over and was against an elevator cable. After some time that control cable ate through the battery cable's insulation, and shorted to ground through the elevator system. No breaker there, of course. It welded the elevator hinges, and the cable finally burned through. The pilot managed to land the thing using the stabilizer trim.

And I later found the same thing ready to happen in a 180.

If you don't learn from the mistakes of others, you might make them yourself.
 
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