By Stephen Thorne / The Canadian Press

Ottawa - Potentially lethal cracking and chafing of electrical wiring aboard some Boeing 747 jets persisted seven years after regulators ordered the problem addressed, a company document shows.

Damage to Kapton-insulated wires in the advanced cabin entertainment and service systems (ACESS) of the 747-400 series of jumbo jets was the subject of a 1991 directive from the U.S. Federal Aviation Administration.

But the order only demanded a one-time check for what appears to be age-related wear, and now the problem - first cited by Boeing in 1990 - has turned up again, shows a March 1998 report obtained by The Canadian Press.

"Passenger seat ACESS Kapton wiring can chafe, short and arc," warns the fleet issues summary report, distributed internally to Boeing technical staff. "No interim solution has been identified."

Electrical arcing in wires insulated with aromatic polyimide tape, known by the Dupont trade name Kapton, could have been a factor in the crash of Swissair Flight 111 off Nova Scotia last fall. All 229 aboard were killed.

Canadian authorities, who are studying the Boeing 747 problem, have found signs of the lightning-like jumps between wires from the downed jet that could be the result of damage such as cracks or chafing. They have also found cracked and chafed wires on other MD-11s.

Boeing didn't notify the FAA of the continuing problem with its 747s or issue an alert service bulletin warning airlines of the dangers involved as it did five times between May 31, 1990 and Nov. 19, 1992.

Such bulletins, which recommend corrective action, are the strongest measures a manufacturer can take. They are usually followed by airworthiness directives from the regulator, which can ground aircraft and require airlines to follow the manufacturer's advice.

Instead, Boeing issued a routine service advisory in June 1998 reminding operators of the wires' handling characteristics and referring them to previous measures, said Gary Lesser, a spokesman for Boeing's 747 program.

The document was generated by a single incident involving one passenger, he added.

"There have been no further alert service bulletins or airworthiness directives on that subject," Lesser said from Everett, Wa. "So as far as Boeing is concerned, the issue is closed."

Faulty wiring on aging transport jets is a rising concern in commercial aviation but garnered scant attention from regulators before the FAA implemented an inspection program after the Swissair crash.

Wiring is believed to have been a factor in several previous crashes, including TWA 800 off Long Island, N.Y., and Valujet 592 in Florida, both in 1996.

It is an expensive problem to fix. Most bulletins and FAA directives call on operators to incorporate corrective measures during routine maintenance.

"Otherwise it becomes a significant economic issue for them," said Lesser adding, however, that Boeing "will do whatever we need to do to ensure the structural integrity of the fleet."

Last year's Boeing document recommends inspecting ACESS wiring on active aircraft and repairing or replacing it where problems are found. It also suggests a fifth revision to Boeing's alert service bulletin issued in 1990.

But airlines never saw the suggestions.

"It's a Boeing internal document," said Lesser. "These don't go to customers."

The problem affects between 151 and 164 aircraft built between 1988 and 1991. Models of the 747-400 built after 1991 used Tefzel insulation in the entertainment systems instead of Kapton.

The 1990 bulletin was followed by a 1991 airworthiness directive from the FAA ordering airlines to inspect the ACESS wire bundle for chafing and wear.

"The amendment is prompted by reports of chafed wiring resulting in short circuits which led to burned wire bundles," the FAA said. "This condition, if not corrected, could result in smoke and fire in the passenger cabin."

The problem with such directives, says FAA member and wiring expert Ed Block, is that they only require a one-time inspection.

"If the issue is repeated rubbing or chafing or shorting, it should be a periodic inspection," Block said from Pennsylvania.

"These latent defects just simmer and fester unbeknownst to the flight crew or anyone else until they result in a fatality or catastrophic failure, and then it's too late."

Post-crash analyses are the only means left to determine whether a crash was caused by catastrophic wire failure, Block pointed out, and by then the evidence is burned up.

In spite of Boeing's decision to change to Tefzel from Kapton, company spokesman Doug Webb said the issue with the 400 series - as with the MD-11 - is installation, not insulation.

"Really, the problem is not normal wear on wire or aging as much as it is an installation problem," said Webb. "We've found that most of the damage done to wire is done during installation.

"That's why we take such precautions to install it properly."

Removing and installing seats is what causes the 400 series problem, not inflight vibration or the like, he said. Once airlines are notified and corrective measures are recommended, follow-up checks during routine maintenance are a given, he said.

"Each time you reconfigure (the seats), you have the opportunity to check those cables to see if there's any wear."

Boeing is monitoring the situation through daily service reports from airlines, Webb said.