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Took me 6 hours to chase down a 3 inch wire chafe in a King Air 200
Had a flap disagree light coming on maybe once every 3 or 4 flights and of course it never did it on the ground. I pulled half the tail apart looking at the flap motor and the position sensors before I finally found it. Turned out a wire bundle behind the aft pressure bulkhead had been rubbing on a rib for who knows how long and the insulation was worn through in one tiny spot. I only caught it because I wiggled the harness by hand with the meter hooked up and watched the reading jump. Any of you guys got a trick for finding chafes like that without pulling every panel on the plane?
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henry_schmidt693d ago
For years I swore by the wiggle test and thought that was as good as it got, just sit there shaking every harness until something moves. Then an old A&P showed me to hook up a meter with a beeper and lightly pull and flex each bundle while watching for the tone to cut out, way faster than staring at a needle. He also said to load the circuit if you can, throw a small bulb or resistor across it, because a chafe that only shows up hot or under load will hide from a plain ohm check all day. The other thing that changed my mind on this whole deal is using a tone generator and probe, you clip it on one end and trace the wire, and when you get near a rub spot the signal gets flaky. Takes maybe twenty minutes to set up the first time but it saved me a full afternoon on a 1900 last month. Your bulkhead chafe is exactly the kind of thing that trick catches, since you can hear it crackle right at the rib.
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