Aging Aircraft (Part II)

Ramon (Ray) Raoux, P. Eng.

Background

Feedback Issue 1/2003 described the structural concerns and the subsequent maintenance activities that were developed for maintaining the airworthiness of aging aircraft. While the structural matters were being addressed in the 1990s, concerns were raised that the electrical systems in older aircraft might also need similar action. There had been a number of onboard fires, such as the Air Canada DC-9 near Cincinnati in 1983 and the fuel tank explosion in a B737 in Manila in 1990; however, these events did not lead to any high profile committees to study electrical systems. It was the 1996 explosion and crash of TWA B747 Flight 800 off Long Island, New York and the subsequent extended newsworthy investigation that put electrical systems and wiring under the microscope. In the USA, the White House Commission on Aviation Safety and Security recommended to the FAA "In cooperation with airlines and manufacturers, the FAA's Aging Aircraft program should be expanded to cover non-structural systems". This recommendation spurred the establishment in late 1998 of the Aging Transport Systems Rulemaking Advisory Committee (ATSRAC) to address, initially, electrical systems including wiring, connectors, and other components such as circuit breaker devices. The onboard cabin fire and crash of Swissair MD 11 Flight 111 near Peggy's Cove, Nova Scotia in September 1998 hastened the announcement of the creation of ATSRAC and added to the urgency for addressing electrical system concerns.

ATSRAC Membership

ATSRAC has representation from airworthiness authorities, manufacturers, airlines and other interested groups. The FAA, the European Joint Aviation Authority and Transport Canada represent the airworthiness authorities; Airbus, Boeing and Dassault represent aircraft manufacturers; AirTran Airways and Northwest Airlines represent the airlines. Some of the other ATSRAC members are NASA, the US Department of Defense, Air Line Pilots Association, International Association of Machinists, Air Transport Association of America and General Aviation Manufacturers Association. In general terms, ATSRAC has been tasked to advise on regulations and supporting advisory material which may be necessary to assure that transport airplane non-structural systems are designed, manufactured, and maintained in a manner that will assure their safety throughout their service life.

The approach taken by ATSRAC to address aircraft wiring concerns was similar to the approach that was used to address aging aircraft structures. In the first phase, five working groups were formed and given specific tasks. One working group (WG) coordinated the inspection of wiring [in accordance with a specific inspection protocol] in over 100 large transport-category aircraft while they were undergoing heavy maintenance checks, in order to determine the general condition of the wiring and associated hardware. Wirerelated service bulletins (SBs) and airworthiness directives (ADs) were reviewed to determine if SBs should be mandated or ADs amended to incorporate terminating actions. Intrusive inspections [where sections of wire bundles are removed] were performed on six aircraft recently retired from service and the removed wire bundles were sent to laboratories for further testing, primarily to categorize the effects of age-related service on the insulation characteristics of the wires. Another WG evaluated the effectiveness of maintenance programs with respect to wiring systems. A review of training programs and Electrical Standard Wire Practice Manuals (ESWPMs) were scrutinized by two other WGs.

ATSRAC WG Findings

Not surprisingly, these WGs submitted a multitude of recommendations based on their investigations. With respect to the condition of wiring on these older aircraft, typical findings, to mention just a few, included clamps being too small or too large, wires chaffing against structure, wires not adequately secured, wires tied to fuel lines, oxygen lines and hot air pipes. However, the most commonly found condition [and the one likely of most concern] was the accumulation of dirt and debris consisting of lint, fluid spills and metal shavings; cleanliness would need to become paramount. The need for better wire marking and wire separation was noted. The difficulty of inspecting wires, particular due to inaccessibility and when in thick wire bundles, was also recognized.

In general, the need for a cultural change in the industry's and the regulator's approach to wiring was noted. During visual inspections, wires should no longer be considered as obstacles to be navigated around in order to perform other maintenance actions. A coffee spill does not just wet carpeting. As expected, there were training-related recommendations for more emphasis on wiring, recommendations for a standard format and standard minimum content in ESWPMs, and recommendations supporting the need for an Enhanced Zonal Analysis Procedure (EZAP).

ATSRAC WG Recommendations

It took these five ATSRAC WGs two years [Phase 1] to complete their taskings and submit their recommendations. In Phase 2, the ATSRAC, in light of the recommendations that were made, was tasked to recommend appropriate rulemaking action to effect implementation of the Phase 1 recommendations. Working Group 6 was formed to incorporate new wire system certification standards into Federal Aviation Regulation (FAR), Part 25 [Airworthiness Standards; Transport Category Airplanes]; revising this FAR would ensure that the ATSRAC recommendations addressing such matters as wire separation and markings would become a requirement for new aircraft designs. Guidance material for the development of Wire System Training Programs was produced that would be applicable to Air Carriers, Repair Stations and Training Institutions. Training would be tailored to each group's requirement; and there would be detailed procedures and precautions for hands-on mechanics and inspectors and general awareness information on the importance and criticality such as for flight and cabin crews and airline managers. The requirement to implement EZAP into an operator's approved maintenance program would be mandated by the FAA issuing a Special FAR. In addition, there would be regulatory action to mandate a one-time inspection of wiring systems within a five year time period. Although the FAA regulatory actions would only be applicable to US-registered aircraft, Transport Canada (TC) and European Joint Aviation Authority (EJAA) shared the FAA's concern and participated in ATSRAC activities; this was intended to allow TC and EJAA to mandate similar requirements simultaneously with the FAA.

Although the aging aircraft activities have been focused on large transport-category aircraft, it is recognized that small [less than 30 passengers and/or 7500 pound payload] transport-category aircraft are not immune to age-related deterioration of wiring. Accordingly, as part of the ATSRAC Phase 2 activities, WG 10 performed evaluations of 39 business-jet aircraft representing eight models by five manufacturers. The findings of WG 10 indicated that the wiring observations for both large and
small transport-category aircraft were similar.

Mandating the initiatives mentioned above is a start to addressing wiring system concerns, but more activities need to be, and are being, done. A future issue of Feedback will describe the importance of EZAP and the other activities underway to address wiring concerns.

For those readers who wish more details about ATSRAC, a comprehensive description of the ATSRAC activities is posted on its web site www.mitrecaasd.org/atsrac/index.html.

Ray Raoux
Manager, Corrective Action
Continuing Airworthiness
Aircraft Certification
Transport Canada

Photos: Courtesy of J.R. (Rod) Digney