Maintenance and Certification - Industry Culture Shift Regarding Aircraft Wiring Badly Needed

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by Wilfrid Côté, Civil Aviation Safety Inspector, Aircraft Evaluation, Operations, Aircraft Maintenance and Manufacturing, Civil Aviation, Transport Canada

Based on events (smoke and fires in aircraft) that happened in the last few years, it would be fair to say that wiring installed in aircraft, small and large, has not received the care it should. A sustained aviation personnel culture shift towards aircraft wiring must occur to reduce incidents and accidents caused by faulty wiring systems.

During cargo and baggage loading, and servicing and maintenance activities, wiring is subjected to a lot of abuse. It is stepped on, pulled on, stretched, contaminated with metal shavings, has various liquids spilled on it, and is sometimes used as a handhold. It may not be apparent at that particular time that the wiring suffered some degree of damage. The damage may appear as an intermittent fault or other mysterious performance of some systems. Cleanliness of wiring systems must also be addressed during the lifetime of the aircraft.

Awareness campaigns and continuous training directed at all personnel who are involved in aircraft manufacturing and maintenance would greatly improve the state of wiring systems in aircraft. Awareness campaigns and continuous training should be focused on cleanliness around wiring, the importance of following the standards related to installation practices, the appropriate size of wires for a particular application, adequate wire separation, clearance to structure, and routing. Replacement wires and wires used when installed under a supplemental type certificate (STC) must be compatible with those of the aircraft manufacturer and in compliance with the related installation standards.

The ageing aircraft wiring inspection mandated by the Ageing Transport System Rulemaking Advisory Committee (ATSRAC) found many discrepancies, such as, questionable wires (wires not qualified for airborne use) often utilized to perform a repair or a modification (STC installations), damage to wires, improper separation, inadequate clamping, damaged clamps, chafed wires, and inadequate support. The ATSRAC Web site is a very good source of information related to wiring issues; the Internet address is:

Most of these discrepancies would have been found and corrected by maintenance personnel if the guidelines detailed in the aircraft manufacturers' wiring standards manuals had been followed.

The onus is on the original equipment manufacturer (OEM) to provide complete instructions for continued airworthiness (ICA) including wiring inspection and maintenance instructions. The Federal Aviation Administration (FAA) Advisory Circular (AC) 43-13-1B and -2A are appropriate standards that the OEM may use to help create their ICA. Maintenance personnel should also consult those FAA ACs for appropriate guidelines where shortcomings exist in the manufacturers' wiring standards manuals. Even though the subject AC is primarily for unpressurized aircraft, it is quite appropriate to follow its guidelines to supplement the gaps that exist in the aircraft manufacturers' wiring standards manual.

Wires were also found that were not marked in compliance with the requirements of the regulations. This condition leads to difficulty in performing required system maintenance, faultfinding and may also lead to maintenance errors.

To attain a true culture shift toward safe wiring practices, top management of the aviation industry, as well as everyone involved in the manufacturing of aircraft, air operators and maintenance organizations, must adopt a new attitude related to the handling of wiring systems on board aircraft, to ensure those systems receive the attention and care they deserve. This culture shift will ensure improved safety for the travelling public.

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