Page 25 - Nov 2015 Volume 9, Number 11

four little wires, and one of them went from the line contactor to the GCU. Eureka!
Success at Last
We repaired that wire, as well as the Q6 and Q7 transistors in the GCU again, and put everything back together – the R/H generator has stayed faithfully online ever since. Hot diggity dog! It’s a great feeling when everything finally works. My only lingering problem is understanding how the replacement of Q6 and Q7 translated into $1,000 core bill backs each time I returned a GCU. When John did the job, it was $50 in parts and an hour of labor – clearly I’m in the wrong business!
This GCU saga was one for the books for a number of reasons. The location in the leading edge isn’t subject to much expansion/ contraction, so why did it short out consistently when going through 12,000 feet? And why didn’t the megger testing indicate a short in the leading edge wire bundle? The wire bundle was properly tied up and even had spiral wrap added in places. Everything appeared totally normal each time the leading edge was removed.
This was quite the wild goose chase and completely unexpected in a King Air. At one point in my career, I maintained a couple of Citations for about 10 years. Chafed wires were an everyday problem. Those Citations became the bane of my existence.
Keeping the Craft in Beechcraft
King Airs do not typically get chafed wires. What happened with this F90 is rare for any King Air. In production, when the wire bundles go in, care is taken to allow for the expansion and contraction brought on by fluctuations of altitude, temperature and pressure. At least that’s how it used to be.
It’s been awhile since I’ve visited the factory, and now the Beechcraft
DECEMBER 2015
line is under the same umbrella as Cessna. I do not wish to cast aspersions; I just hope that the standards of excellence achieved under the watchful eye of Olive Ann Beech will be continually upheld and implemented.
I wish everyone a fabulous holiday season, a productive and prosperous New Year, and a King Air free of chafed wires. KA
If there is a particular main- tenance issue you would like Dean to address in a future issue, please email Editor Kim Blonigen at kblonigen@cox.net.
About the Author: Dean Benedict is a certified A&P, AI, and has 40 years of experience in King Air maintenance. He is president of Honest Air, Inc., which specializes in Beechcraft King Air maintenance and repair.
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