Safety of Aging Aircraft Electrical Systems Under Unprecedented Examination

Air Safety Week, July 19, 1999

Operators of airliners more than 20 years old are facing potentially three waves of inspection and repair requirements to assure that the aging electrical systems in these aircraft are kept safe to fly.

If we may hazard a prediction, these unfolding actions may well add to the cost of operating older jets, not only in terms of direct maintenance actions but lost revenue from out-of-service time.

The first wave features the publication in upgraded alert status of 29 service bulletins (SBs) previously issued affecting Douglas aircraft. All of them are likely to be translated into mandatory actions in the form of air-worthiness directives (ADs) issued by the Federal Aviation Administration (FAA).

This wave of SBs is the initial impact of a three-pronged effort to assess the safety of wiring and electrical components in so-called "geriatric jets." The effort is spearheaded by a joint governmentindustry task force, the Aging Transport Systems Rulemaking Advisory Committee (ATSRAC). The committee met last week to discuss progress to date and future activities. The ATSRAC began work last January as an outgrowth of the FAA's non-structural systems program. In the seven months since its inception it has brought an unprecedented degree of attention to aging aircraft electrical systems.

The committee is looking at electrical systems from three different perspectives, each of which will impact operators to some degree: the service history of older jets (here defined as those certificated 20 or more years ago), visual inspections of the internal wiring and components on older jets while they are undergoing heavy maintenance, and a series of "intrusive" inspections to come, in which connectors, wire bundles, etc., on a representative sample of recently-retired jets will be undertaken to identify problems that may have gone undetected in the ongoing visual inspections.

Herewith, highlights of these activities:

* Service history review. Roughly 2,900 service bulletins on Boeing [BA] Long Beach model aircraft (Douglas DC-8/9/10, MD-80 series) were searched by hand, a necessary action because the Douglas data was not digitized. They were searched for service history trends by 21 keywords that would point to problems emanating from wear in service. As a result of this effort, 29 SBs were upgraded to alert status.

The service history review of Boeing, Lockheed [LMT] and Airbus Industrie aircraft continues:

-- Boeing: Nearly 1,000 documents are undergoing the same keyword search for items related to aging systems affecting 727, 737 and 747 aircraft. "They're going through them one by one," said David Marcontell, who chairs the Air Transport Association's (ATA) aging systems task force. Marcontell also is the director of engineering at Airborne Express [ABF].

- Lockheed: A keyword search of the service history of the L-1011 fleet is due to be completed by September.

- Airbus: Similarly, a keyword search on the A300 aircraft, the only Airbus product certificated more than 20 years ago, also is in progress.

It seems likely that some number of previously-issued SBs on these aircraft will be upgraded and re-issued as alert service bulletins. And some of these could well be translated into mandatory ADs. Marcontell said the current plan is to complete the service history reviews by December. "We have to complete this work to make sure the fleet is safe," he declared.

* Visual inspections: At the same time aircraft service histories are being been scrutinized, other teams have been conducting visual inspections of geriatric jets while they have been undergoing heavy maintenance. These zone-by-zone inspections (wheel wells, wing trailing edges, wing roots, etc.) paid particular attention to:

- High vibration areas

- Areas with harsh environments

- Corrosion-prone areas (e.g., under lavatories)

- High maintenance traffic areas (A Boeing official observed, "We're seeing a correlation between accidental damage and the number of times people enter the area in an airplane.").

Depending upon the model of aircraft, the inspection teams identified anywhere from 5-15 zones to be inspected. "There were detailed inspections, six inches away in strong light" consuming some 30-40 hours of inspection time per aircraft, Marcontell explained. To date, 71 aircraft have been inspected. L-1011's were not inspected because none was scheduled for heavy maintenance these past few months; however, three L-1011's will undergo intense visual inspection later this summer and in the fall. Indeed, by that time some 90 aircraft will have gone through this visual inspection regimen.

To be sure, it is not a statistically-significant sample size, Marcontell concedes, but all the inspections incorporate a common report form. Marcontell pointed out that the number of aircraft inspected represents virtually all of the ATA member carrier airplanes that will have gone through heavy maintenance since last February. "We had to push pretty hard at high levels" to obtain clearance for these inspections, he said, "But we think we have pretty good insights based on what we're doing over and above what would normally be done," he said.