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Mech Summer 2002
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By Lt. Jim Schmitt |
Perhaps the desert sand of the Middle East has
awakened the stray electrons that occasionally cause electrical
glitches and failures on our four, permanent-detachment, MH-53E
helicopters. But electrical gripes have become more regular, and
they're the types that puzzle even the most experienced AE. I read
the stories in Mech about the E-2's problems [April-June 2001, "The
Resurgence of an Old Enemy" and Fall 2001, "Almost Bitten on a BITS
Flight"-Ed.], and I want to share a few problems I've noticed with
the H-53.
Every few days, the caution lights for the fuel-filter bypass
intermittently would flash on one of our helos. After
troubleshooting the engine, the AEs finally found the light came on
only at night. Even more bizarre, they would go out when the switch
for the caution-panel lighting was moved from the dim position
(normal) to bright. The culprit finally was found; it was bad
Kapton
wiring behind the caution panel.
Another aircraft had a flickering master-caution light with no other
associated caution lights. It would flicker only a couple times
during each flight and nearly
was impossible to troubleshoot.
When tracing the wires, electricians
finally found cracked
Kapton wiring.
In the past year, our Bahrain detachment has completed
120
maintenance actions and spent more than 400 hours on problems with
faulty Kapton wiring. These MAFs were not specific to a single
system, but many of the gripes involved mission-critical systems.
Our det has been fortunate to fly hundreds of mishap-free
operational missions since it formed more than two years ago. Most
of the broken wires were discovered during daily, turnaround,
preflight, and phase inspections. The timely recording of gripes led
to the repair of faulty wiring before it could cause a major
failure. But every flight is the roll of two dice: One to determine
which aircraft will have the next failure, and the other to decide
which wire will fail. Despite our maintainers' successes in dealing
with Kapton wiring, in time, the failures will increase and,
unfortunately, could lead to a catastrophic failure or a mishap.
The most difficult part about flying an aircraft prone to faulty
Kapton wiring is the unpredictability of the electrical system. No
one knows how a faulty wire will affect any aircraft's electrical
system. Because wires crack one at a time, a helo typically will not
lose an entire system or component, just parts of it. The wires
still carrying current will cause the component to act erratically.
Even worse, the failures are intermittent because the crack in the
wire opens and closes when an aircraft vibrates and maneuvers.
This
makes it nearly impossible to troubleshoot and leads to many gripes
being signed off as "could not duplicate."
Cracked wires (as opposed to a clean break) are susceptible to
arcing and can cause a fire. An in-flight fire especially is bad
when flying blue-water ops, which is what the det does most of the
time.
Aviation safety and mishap prevention relies on the removal of
uncertainty. That is why pilots use checklists and maintainers
follow MIMs. Trying to stay safe when dealing with uncertainty
requires a lot of skill and a bit of luck.
Based on the problems
I've seen with Kapton wiring, we have been more lucky than good, and
I'm worried our luck eventually will run out.
Lt. Schmitt flies with HM-14. |
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Mech Fall 2001
Almost Bitten on a BITS Flight
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By AD2 Jason Dubose |
The scheduled flight was a back-in-the-saddle
(BITS) flight for a co-pilot on a sunny April morning. The two
pilots and I had a standard NATOPS brief and preflight, but the
flight was not close to normal.
After a routine start and takeoff, we climbed above 1,000 feet,
and the aircraft commander cleared me to do a post-takeoff
walk-around inspection. This meant monitoring the internal
aircraft systems for oil and fuel leaks, checking avionic
systems and circuit-breaker panels, and doing integrity checks
of the cabin and cockpit areas.
I started my walk-around in the ramp area (aft end of the
fuselage). As I
began my inspection, the cargo-ramp lights went out, so I
checked the light-switch panel at the aft crew station, and
everything appeared normal. Next, I went to check the
circuit-breaker panel behind the cockpit, known as the
main-electrical-distribution box (MEDB).
I found two interior-light circuit breakers had popped. I was
about to push them back in, but, before I could, more circuit
breakers popped. This time, the interior- and exterior-lighting
circuit breakers had tripped, and I noticed a big puff of smoke
coming from the top of the MEDB. I immediately reported to the
pilots what I did. They had smelled something burning, so we
pulled out our checklists and began to review NATOPS procedures
for an electrical fire of unknown origin. These emergency steps
helped isolate the affected electrical systems.
The pilots declared an emergency with ATC and turned the
aircraft toward Norfolk. After checking around the cabin area, I
could not find any evidence of fire or smoldering wires.
When we landed and shut down at Chambers Field, the AEs were
waiting to troubleshoot the gripe. They found the interior- and
exterior-light wire bundles chafed and shorted.
It was a scary experience,
and I didn't like being held captive by
Kapton
wire, but I had learned how to handle another emergency.
Petty Officer Dubose flies with VRC-40.
This incident happened shortly after we ran a story about a
Kapton wiring problem in a Hawkeye flown by VAW-112. For more
information, read "The Resurgence of an Old Enemy" in the
April-June issue or visit www.safetycenter.navy.mil/publications/mech
to read the electronic version.--Ed. |
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