Avionics News December 2022 - 51

A review of occurrences reported to the UK Civil Aviation
Authority between 1997 and 2002 indicated that damaged
or deteriorating electrical wiring was a causal factor in 221
events.
In New Zealand
In the last 10 years, according to reports to the Civil
Aviation Authority, there've been about 220 incidents
attributed to faulty wiring, and some of those due to aging.
A good number of those have been discovered by a
" haze " in the cockpit, the smell of electrical burning, a
failure of a system, or a warning light.
Many have been the result of poorly secured wiring
looms or broken terminations. Others have been due to
chafed insulation due to the loom resting on mechanical
control cables.
There have also been failures of relays and contactors
and circuit breakers.
Time to reconsider?
Most of the aging aircraft electrical programs have
been directed at larger aircraft but not so much at general
aviation aircraft.
In GA, there've been mechanical aging inspections,
which have focused primarily on corrosion and airframe
fatigue in aging aircraft.
So is it time to consider the following?
*
Is it widely understood that aircraft wiring is an
important consideration in the maintenance, repair
and modification of aging aircraft?
* What are the causes of aging wiring?
* What are the consequences of aging in wiring
systems?
*
*
Is the continuing airworthiness of wiring being
considered adequately by those doing inspections
and new installations in aircraft?
What are potential solutions to manage aging
wiring?
* How best can operators and maintainers be informed
about the importance of maintaining airworthy
wiring?
*
Is the maintenance/repair of wiring perceived as
being too costly?
Circuit breakers
Circuit breakers also deteriorate over time.
The main purpose of a circuit breaker is to protect the
aircraft wiring should a short circuit occur.
The airworthiness standard for circuit breakers is that, if
an overload or circuit fault exists, the device will open the
circuit regardless of the position of the operating control.
A degraded circuit breaker that fails to trip clearly
doesn't meet this standard.
Faulty circuit breakers are considered one of the key
sources of electrical arcing. As aircraft age, the likelihood
of an arcing event increases.
Older circuit breakers are, at times, very difficult to trip
manually, due to corrosion on the contacts or buildup of
grime inside the mechanism.
Exercising (cycling) of circuit breakers under no load
will help remove any possible internal surface corrosion.
Several circuit breakers, such as those in some Cessna
aircraft, cannot be manually cycled, due to their design.
It's difficult to test these circuit breakers in-situ, so after a
period of time in service, it's appropriate to replace them.
This also applies to switches and other electromechanical
devices.
I would, therefore, strongly recommend inspection and
possible replacement as part of the aircraft's scheduled
maintenance. q
›› REFERENCES
* Aging Aircraft Wiring: A proactive
management methodology by
Vasileios Tambouratzis, June 2001.
* Best Practices Guide for
Maintaining Aging General Aviation
Airplanes endorsed by AOPA (USA),
AAA (USA), EAA (USA) and FAA,
September 2003.
* Aging Aircraft Electrical Wiring
Inspections by Ric Peri, Aircraft
Electronics Association, January
2004 and March 2021.
* CASA AWB 24-011 Issue 1, Aircraft
Circuit Breaker Maintenance and
Operation, April 2016.
avionics news * december 2022 51
Avionics News December 2022

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