Environmental effects are usually due to weather and geography. Wire ages at different rates in warm and humid conditions vs. cold and dry or any other combination. Temperature, humidity, and sun UV (ultraviolet) exposure can premature aging. The impact of environment can be different for different locations in the aircraft.
Physical abuse can immediately break the copper conductor or insulation. Stepping on a wire bundle can ruin your day and the wires. Unsupported wires can flex or rub on the structure. Wires with missing or broken wire clamps held in place with very tight wrap ties can crush the wires. Cutting the wrong wire in a bundle or removing/breaking the wrong connector pin is worth one "Awe ----!"
Improving the various processes for wiring system analysis requires establishing processes based on available technology, acquiring proper tools, and performing preventive repairs. These activities may be addressed through good maintenance and diagnostic practices; appropriate training; technically sound repair and modification techniques; and adequate documentation. These issues could be a study in themselves for another time. Let me end by saying, we don't make money if they don't fly so "Keep 'em Flying."
Fred Workley is the president of Workley Aircraft and Maintenance Inc. in Alexandria, VA, Indianapolis, IN, and San Jose, CA. He holds an A&P certificate with an Inspection Authorization, general radio telephone license, a technician plus license, ATP, FE, CFI-I, and advance and instrument ground instructor licenses.
Economic Values for Evaluation of FAA Investment and Regulatory Decisions, FAA-APO-98-8, June 1998, US DOT, FAA
Review of Federal Programs for Wire System Safety, November 2000, National Science and Technology Council
Transport Aircraft Intrusive Inspection Project, December 2000, Aging Transport Systems ARAC.
"Wire Integrity Programs," Brown, March 2001, GRC International Inc.
Typical wire failure modes
The typical wire failure modes for aircraft are:
- Chafed wire insulation leading to short circuit and /or arching
- Short circuit, unspecified cause (includes arcing incidents)
- Broken wires
- Connector failure
- Unspecified failure
- Failure due to corrosion
- Loose connection
- Insulation failure
- Circuit breaker failure
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