The regulation is an outgrowth of the efforts of the Aging Transport Systems Rulemaking Advisory Committee (ATSRAC), which determined that the state of wiring on old aircraft (those with 20 or more years of service) was deficient. Based on those findings, ATSRAC recommended wiring inspections for the entire fleet of transport category aircraft. The ATSRAC recommendation was based in three factors. The first was the National Transportation Safety Board’s (NTSB) investigation of the fuel tank explosion that destroyed TWA flight 800. Inspection of other aged aircraft – done as part of the investigation – found numerous wiring problems. Second, laboratory tests of wire and wire bundles removed from old aircraft revealed numerous deficiencies that stemmed, in part, from poor or nonexistent maintenance. Three, intensive detailed visual inspections of six recently retired aircraft found about 1,000 visual findings per aircraft, mostly mis-installation or traumatic damage.

The ATSRAC concluded that “visual inspection is effective in identifying certain conditions” such as “heat damaged/burnt wire and vibration damage or chafing.”

Non-destructive evaluation (NDE) serves as a superior method to visual inspection for reliably finding cracked insulation or degraded repairs. One form of NDE involves sending pulses of electricity down wire and measuring where leaks in the current occur. Such leaks can be the telltale sign of breaches to the insulation. However, this type of NDE on installed wiring can be time consuming and costly. Visual inspections, on the other hand, can reveal the most egregious wiring faults, and the FAA has opted for this course as a first order of business.

To implement the required wiring inspections, operators may first wish to train their inspection personnel. To this end, the FAA has produced an excellent series of slides and illustrations known as Job Aid 1.0. This 165-page document summarizes the wiring problem (poor installation, strengths and weaknesses of various types of wire insulation, the problem of modifying a manufacturer’s initial wire installation through the supplemental type certification process, and so forth). The heavily illustrated document demonstrates practices to be emulated and installations to be avoided. It is important to note that the examples it provides of chafing, misrouting, heat damage and arcing were seen on recently retired aircraft – and probably had been on these aircraft for years.

Job Aid 1.0 covers the basics. It includes advice that appears basic and reflective of common sense:

“4 Protect wires in wheel wells and other exposed areas.”

“4 Route wires above fluid lines.” (That is, not below them.)

“4 Keep slack to allow maintenance and to prevent mechanical strain.”

“4 Support wire with suitable clamps, grommets, or other devices at intervals of not more than 24 inches.”

Yet these recommended practices were not found in the fleet. In fact, horrible examples of what might be called wiring malpractice were found, and often enough to likely indicate an endemic problem. The most blatant examples, and their cure, are contained in Job Aid 1.0. To be sure, the wiring inspections mandated by the FAA on 8 November will be buttressed by as many as a dozen advisory circulars (ACs) laying out good wiring practices.

But for training personnel, Job Aid 1.0 is perhaps the best briefing and teaching tool currently available. What follows are some examples culled from Job Aid 1.0; they provide mute evidence of the hazards, and the need to treat wire as a standalone system like hydraulic and pneumatic components. It should be obvious that the redundancy built into an aircraft’s electrical system  (and other systems) can be compromised by bad wiring. As shown in the photographs, more than a single wire is often affected, which can lead to multiple and confusing system failures. (To download Job Aid 1.0, go to www.lectromec.org/faa_job_aid-aircraft_wiring_practices.ppt)

Figure A

An example of wire chafing, caused by the eroding effect of wires riding on other wires.

Figure B

This example shows a number of problems: Wires in a bundle not tied properly. The wire bundle is riding hard on the hydraulic lines. The bundles appear to be contaminated with hydraulic fluid residue.

Figure C

This picture shows a wire bundle that is in close contact with a control cable. Adequate distance between wire bundles and control cables should be maintained to account for movement due to slack and maintenance.

Figure D

Too much wiring in a clamp or improperly installed clamps can lead to pinching of the wires.

Figure E

This photograph shows an example of heat discoloration on protective sleeving which is part of the wire bundle. In this case, the wiring not covered in sleeving shows no signs of heat distress. An adjacent light bulb was radiating enough heat to cause discoloration over time to the protective sleeving. Although this condition is not ideal, it is acceptable.

Figure F

The top two wires in this photograph are experiencing stress due to a preload condition. Also note that the wire bundle is not properly clamped. Splices should be staggered, which is clearly not the case here.

Figure G

Foreign object damage (FOD) is a big problem with damaged conduit covering.

Figure H

The damaging affects of multiple circuit breaker resets. In this case, the original arcing event was not able to be determined due to the severe secondary damage following the circuit breaker resets.

Figure I

Protective sleeving should overlap at least 30% to ensure 100% coverage of the wire bundle.