Discrepancies Discovered in Visual Inspections of Aging Aircraft Electrical Systems

Air Safety Week, Jan 24, 2000

Partial inspections of the electrical wiring and electrical systems in fewer than 100 high-time U.S. jetliners have uncovered more than 3,000 items worth noting.

The term "item" is used deliberately, as the exact nature of the deficiencies has not been released. However, of these 3,000 items, some 144 were deemed potentially hazardous. Operators should be wary of this low fraction of significant findings (4.5%). Not all the wiring on each aircraft was inspected, the rigor of the inspections may have varied from aircraft model to model, and forthcoming "intrusive" inspections may yield problems not discovered by visual examination. While the results of the visual inspections provide some comfort, there is little reason for complacency about the integrity of old aircraft wiring.

The inspections were conducted as part of the activity of a government-industry task force charged with evaluating the condition of non-structural systems in aging aircraft, which have been defined as those with 20 years or more service. A report of these nonintrusive inspections of the electrical systems in so-called "geriatric jets" is perhaps the first work product to result from the efforts of the Aging Transport Systems Rulemaking Advisory Committee (ATSRAC). This body is undertaking a two-year effort to assess the condition of non-structural systems in jets with 20 or more years service.

The program is an outgrowth of the 1997 report of the White House Commission on Aviation Safety & Security (the "Gore Commission"). The Commission recommended a comprehensive review of systems to complement the aging structural inspections that were put in place throughout the industry after the explosive decompression of a high-time Aloha Airlines B737 in 1988. The present ATSRAC effort is intended to identify possible design changes or modified maintenance practices to electrical, hydraulic, pneumatic and other systems in old jets as they age in service.

Visual inspections completed

The ATSRAC began its work in earnest last January. Among its top priorities was a non-intrusive (i.e., visual) inspection of the condition of wiring and electrical components on a representative sampling of the fleet. As of last July, some 70 aircraft had undergone inspection. At the ATSRAC meeting last week the final report was presented of inspections that ultimately covered some 81 aircraft out of a candidate fleet of 3,078 jets at or beyond the 20-year point. The inspections were conducted under bright light while the aircraft were undergoing heavy maintenance (i.e., at a time when interior cabin fittings, panels, and thermal/acoustic insulation blankets were removed, exposing wiring and bundles to inspection). The inspection teams used a common report form to record the results of their examinations.

The inspections represent the second of three waves of activities affecting operators of older jets. The first wave was a service history review that resulted in the publication of previously issued service bulletins as alert service bulletins. For example, nearly 20 service bulletins for the DC-9 alone were upgraded to Alert status.

The visual inspections represent the second wave of activity, and intrusive inspections, now getting under way, represent the third wave. Actually, there are two components to this third wave: (1) a detailed visual inspection followed by (2) non-destructive testing (NDT) using the latest test methods.

"All is well," with some exceptions

From the visual inspections, ATSRAC officials said they found nothing that would warrant an airworthiness concern, defined as "requiring immediate fleet action." However, a number of significant areas "warranting improvement" were uncovered. These 144 items of "potential hazard" have been referred to the manufacturers for analysis and possible action. Although the January 11 Final Report of the non-intrusive electrical systems inspections was the first definitive work-product to emerge, coming at the halfway point of the ATSRAC's two-year effort, the 16-page document did not outline the specific nature of either the less or the more severe findings. One of the complicating factors here is that most of the inspections were completed before last September, when the ATSRAC defined its terms, such as "significant item".

As definitions were late in arriving, the final report of the inspections necessarily couched the results in general terms. For example, the report did not outline the nature of the 3,000 items, such as the number or percent involving chafed wire, inadequately supported wire bundles, inadequate grounding, etc. Nor did the report contain a tabulation of the 144 serious items.

As an example of the kind of assertion offered without supporting data, the report declared, "Time in service and the systems that they service seemed to have no appreciable bearing on the condition of the wiring installation.... The working groups did not note any direct correlation between the condition of the wire and the actual time in service."