Avionics News July 2019 - 33

troubleshooter working in any aviation arena. Here are some
examples from Part 23, Part 25 and an OEM.
OEM
Trek Lawler and Tim Larberg lead Garmin's field service
engineering team, 15 technicians in Olathe, Kansas, and
another five in Salem, Oregon. Stumped troubleshooters
email or telephone their challenges, and if the answering
tech can't immediately provide an answer, it goes to
a member of the team who has the necessary skill set,
according to Lawler. Integrated systems is one segment, but
"retrofit is the largest, going all the way back to the GPS
155," he said. Yes, a number of them are still flying.
Larberg has been filling his pool of troubleshooting
memories since the 1980s. Bubbling to the surface is a
problem from the era of "the straight GNS 430." Integrating
it with components from different manufacturers was an
expected source of challenges, so Garmin built the GAD
43 adapter box that integrates the GNS (and today's GTNs)
with older HSIs with autodriven course pointers.
"A dealer was connecting a GNS 430 to a Collins EFIS
85 system, and the course pointer would only appear on the
CRT (display) for certain radials," Larberg said. "Depending
on the radial generated, the course pointer would only show
up for about a 10-degree gap. We went round and round
for two weeks trying to figure out what was going on and
talking to our engineers."
Larberg found the solution by surprise while going through
a troubleshooting folder left by a technician who'd moved on.
"It turned out we were overdriving the GAD's output signal,"
he said. Adding some external resistors reduced the output
from 7.9 volts to 5 volts, "and low and behold, it works."
This gremlin has appeared in several other situations, and
this knowledge applied to their solutions. "Since then, this
remedy has been incorporated in install manuals," Larberg
said. His tone implied that reading the manual thoroughly
before starting work is an excellent way to avoid selfinflicted troubleshooting challenges.
Some self-inflicted challenges are not so easily solved.
"Heading problems are some of the biggest problems we
get," said Lawler, because the GMU "magnetometers we use
in our systems are extremely, extremely sensitive."
About three years ago, he said, an MU-2 retrofitted with
a dual G600 system, flew for 18 months without a problem.
Then, after maintenance that didn't involve the avionics,

it "started getting random heading failures when flying
certain headings."
Unable to resolve the problem long distance, Lawler flew
to Oklahoma to work (unsuccessfully) on the airplane, and
he conducted tests on its flight to Olathe because they could
not reproduce the problem on the ground. "We found that at

Photo by Scott M. Spangler

Jim Karpowitz at his bench at Skycom Avionics in Waukesha, Wisconsin.

certain headings, they were losing some of the magnetic field
values from the magnetometers," he said.
After six weeks of troubleshooting, they couldn't figure
out why. As relocating the GMUs was working its way to
the head of the solution line, "we asked the owner what was
done during the maintenance." One item was a new metalflake paint job. "That metallic paint with the static wicks
were not dissipating enough of the P-static, which is why the
problem only manifested in-flight," Lawler said.
"The airplane would not generate P-static when sitting
on the ground, so the owner hired a third party to jack the
airplane up and conduct a P-static test so we could verify the
exact same results the airplane was seeing in-flight." The test
confirmed the expensive new paint was the culprit, and the
solution was stripping it from the horizontal stabilizer.
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Avionics News July 2019

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