Mark Sletten
Joined: 10 Jan 2006
Posts: 43
Location: St. Jacob, IL (Near St. Louis, MO)
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 Posted: Wed May 30, 2007 10:07 am Post subject: Interesting story... comments? |
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Aeroelectric listers,
I gleaned this story off another email list. Any comments?
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On straight-in for my home airport, about two miles out, smoke started
swirling around in the cockpit. It wasn't real bad but it was definitely
noticeable by both sight and smell. In hindsight it was clearly an
electrical fire (smell and where the smoke was coming from around the panel)
but I quickly declared an emergency saying I had a fire in the engine
compartment. Don't know why I said that other than that it was what I was
the most afraid of. There was no place to land short of the runway so I
went into high-speed prayer mode, held gear and flaps until the last moment
and landed more or less normally. Shut down on the runway and coasted to a
turnoff. Couldn't do the fuel shutoff quickly so just turned it to in
between left and right. Switches off, canopy up and told my wife to leave
by the nearest exit. By the time she was gone, I was noticing that there
was no new smoke so I decided to hunt around for the fire extinguisher
(where is was supposed to be but under my flight bag.) With still no
indication of a continuing fire, I started turning off switches and, having
by this time convinced myself that the problem was electrical, took the
glare shield off to look around. Saw nothing at first but one of the fire
guys who showed up right after that found a small blackened spot in the
firewall near the top right. Sure enough, the alternator wire pass through
had burned through. The stud and nuts were fused and a small part of the
surrounding e-glass seemed to have burned.
I had two opportunities to catch this early. The first was that amps seemed
to be running on the high side. We put this down to having to charge up the
battery because we had had systems on with the engine off but, in hindsight,
it was a clue. Then about a week ago, I had the same smell on approach to
Boeing. There was no smoke, it went away after a couple minutes and I saw
nothing when I removed the glareshield and inspected. Also no repeat on the
return trip.
Turns out that high amperage connections (like all other connections) can
loosen over time. If they do so, resistance goes up, amperage goes up to
compensate (at least in the case of the alternator wire) arcing takes place
and eventually the whole system burns up. There is no short and therefore
no cb's pop but, as I discovered, the process can start a fire.
The firewall connections are hard to see (at least on the cabin side) but I
am definitely adding that to my annual checklist. If the rest of you are
not sure your connections are as tight as they were when you put them
together, suggest you check. I'm also finding a new place for my fire
extinguisher.
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Mark Sletten
Legacy FG N828LM
http://www.legacyfgbuilder.com
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_________________
Mark Sletten
Legacy FG N828LM
http://www.legacyfgbuilder.com |
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