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Posted for "Ted Stanley" <ted@vineyard.net>:
Little Things Can Bite You
Here's the short story of a 2¢ U-Type Speed Clip Fastener. It's one of those
little metal clips that typically fits over the edge of a piece of sheet metal
to create a hardened threaded hole. There are many variations on this type of
fastener. See:
http://www.boltproducts.com/tinnerman/clips-u-type.html
A fairly new A36 Bonanza with only a few hundred hours of total time was
released to the owner after an annual inspection. The owner departed from his
shop's airport and headed home. Upon arrival at his home airport he entered the
traffic pattern and moved the landing gear switch to the "down" position. The
gear began to extend but stopped in mid-motion, the 30 amp landing gear motor
circuit breaker popped, and an electrical smell permeated the cabin.
I was washing my car at the airport when the crash alarm sounded. I moved into
my office, turned on my office radio, and called the tower on the phone. I
recognized the pilot and his plane. The owner had been kind enough to let me
borrow it only a few weeks prior. We discussed the problem on the radio and he
manually extended the landing gear. His landing was uneventful and two airport
crash-fire-rescue vehicles followed him down the runway to his hangar.
The pilot was relieved as were the airport firefighters, but it was the shop
owner who was most anxious to learn of the cause of the incident. I was asked to
investigate.
I jacked up the plane, removed the copilot seat, and the two plastic spar box
cover access covers. I looked around and at first saw nothing unusual. I decided
to attempt to duplicate the problem. I engaged the 30 amp landing gear breaker,
pulled the 5 amp relay breaker, turned on the master switch, advanced the
throttle lever to close the safety switch, and selected "gear up". I then
"bumped" the gear using the 5 amp relay breaker as a switch. The gear partially
retracted without a problem. I then selected "gear down", only this time when I
bumped the gear I saw a faint spark down inside the spar cover.
I looked closer. Now you can too if you look at the attached pictures which tell
the rest of the story.
Where did that speed clip come from? The oval opening to the spar box cover is
normally closed with a plastic cover attached by six screws. Four screws go into
nut plates riveted to the spar box cover, but the two nearest the front of the
aircraft go into speed clips. It was one of these speed clips that managed to
fall on top of the landing gear motor relay. It was probably pushed out of place
during installation of the spar box cover.
So, was it bad design? A faulty fastener? Poor installation technique? Improper
inspection after the work performed? Bad luck? Or some bizarre combination of
all of these? It doesn't matter much NOW, but next time you drop a tiny fastener
think about this story and how the ending might have been very different.
So what do we do now? Just learn from our mistakes and move on? Start
certificate action against the mechanic? NO, that would be a waste of time. He's
learned HIS lesson, but this is a case where an old adage applies, "Learn from
the mistakes of others, you won't live long enough to make them all yourself".
Pass this on to someone you know who will benefit.
Ted Stanley - A&P-IA/ATP
Direct Flight, Inc.
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