Tuesday, November 6, 2012

Blind Spots

Some lessons just need to be learned over and over and over, or so it would seem. I thought I had a pretty good handle on my propensity to develop blind spots. As evidence I point to the fact that despite taking the sixteen hour course that will permit me to sign off the annual condition inspections on N284DG, I intend to continue the practice of paying a local AP/IA to take a look at it once a year just as I've done every year that I've owned the RV-6. I think this is a prudent thing to do, especially after he found a crack in the elevator trim tab that I had to have looked at hundreds of times, but never saw.

It happened again with the CHT problem. After getting some hints from Van's on what to look for in my quest to isolate the problem, I asked Pete to come down to the hangar and help out. It's much easier to trouble shoot wiring when there are a couple of people working on it - someone has to hold a multi-meter probe at each end of the questionable wire and with a long wire, that can be difficult to do alone.

As we were looking around at various wires to test, Pete asked about a PURPLE/YELLOW wire that was hanging loose from the wire bundle. I had seen that wire before, but because I was looking for a PURPLE/BLUE wire, and because it is not uncommon to have cut/stubbed wires on a Dynon D-180 to Skyview conversion, I ignored it. I ignored it even after learning from the wiring diagram that I was, in fact, very interested in the condition of PURPLE/YELLOW wires. In other words, I was looking right at the problem, but a blind spot that I had developed it was precluding me from actually seeing the problem.

Sure enough, fixing that broken wire fixed the CHT problem.

Man, did I ever feel like an idiot!

It's fixed now, though, and we can press on with the next items on the to-do list.

I'm not sure why the wire broke in the first place, and that's going to nag at me for awhile. I do have a theory: that particular bundle is the only one that doesn't seem to have enough slack. In fact, it seems that there is quite a bit of stress on it. I think it's possible that starting the engine introduced enough vibration to simply rend the wire in half.  I'm going to have to find a way to relieve the stress on the bundle so this doesn't happen again.

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