U.S. knew of wiring flaws years before the TWA crash

1993 jet fire raised issues, but only after 2 crashes killed 459 did FAA act

By Gary Stoller
USA TODAY

Smoke and a burning electrical smell seeped into the passenger cabin of an arriving SAS jet as it taxied to a terminal in Copenhagen, Denmark. All 110 passengers scrambled out of the plane safely before a raging fire consumed much of the fuselage.

For 8 years, that 1993 incident hasn't been reported in U.S. newspapers, although the U.S. government was involved in the accident investigation.

Now USA TODAY has obtained the Danish government's 72-page accident report, and it reveals that:

The fire on the SAS McDonnell Douglas MD-87 jet may have been a precursor of two deadly North American crashes -- TWA Flight 800 in 1996 and Swissair Flight 111 in 1998 -- in which investigators believe wiring problems and flammable cabin insulation may have played a role.

Two U.S. agencies involved in aviation safety -- the National Transportation Safety Board (NTSB) and the Federal Aviation Administration (FAA) -- assisted the SAS investigation and were aware of wiring and cabin insulation problems years before the North American accidents. Since those accidents, the FAA has issued a series of safety orders regarding inspections and modifications to wiring and the same type of cabin insulation.

A type of wire on more than half of the airline jets flying today can be very dangerous when it fails.

A fierce fire

The SAS accident, which occurred on a flight from Barcelona, was caused by electrical wire that short-circuited, igniting flammable cabin insulation. ''Continued arcing and sparking resulted in ignition of the cabin sidewall insulation material, which eventually developed into a fierce, uncontrollable fire,'' Denmark's Aircraft Accident Investigation Board (AAIB) wrote in its 1996 report.

The AAIB investigation found ''clearly that the primary ignition source was that two wires, carrying an electrical load of 28-volt AC and 115-volt AC, respectively, became pinched between the aircraft structure and the recirculation fan duct.''

The pinching caused the wires' outer insulation to chafe, exposing their metal conductors, the AAIB says. The bare wires touched one another and an adjacent piece of metal, leading to a short-circuit.

Three years after the SAS fire, NTSB investigators headed to the Atlantic Ocean off Long Island to determine what caused the center wing fuel tank of a TWA Boeing 747 jet to explode, killing all 230 aboard. The NTSB didn't determine a probable cause but said last year that the most likely source of ignition was electrical wiring that short-circuited.

In September 1998, more than 2 years after the Danish report was written -- a high-temperature fire ignited before Swissair Flight 111 crashed near Nova Scotia, killing all 229 people aboard. Canadian investigators, who are still investigating the accident and haven't yet determined a cause, say they found short-circuited wires and burned Mylar cabin insulation on the McDonnell Douglas MD-11 jet.

The Danish accident report reveals that the two wires that short-circuited on the SAS MD-87 had been installed between, and ignited, layers of Mylar insulation.

FAA conducted tests

As part of the investigation, the FAA performed fire tests on materials removed from the jet, according to a 1994 FAA letter in the Danish report.

The tests, conducted at FAA facilities in Atlantic City, N.J., showed that Mylar insulation failed the FAA's flammability requirements and could ignite from short-circuited wiring.

Despite those tests, the FAA proposed no regulations to remove Mylar from planes or ban it from new aircraft until after the Swissair crash. In August 1999, the agency ordered airlines to remove Mylar from MD-11 and MD-80 series jets within 5 years.

When asked about the Danish accident report showing the FAA tested Mylar years earlier, FAA spokeswoman Alison Duquette said the agency accelerated Mylar-related research after the Swissair accident.

''Based on our new test that we developed, we found that Mylar does not meet an acceptable level of safety,'' she says.

Ed Block, a private expert who inspected aircraft wiring for an FAA subcommittee formed after the TWA accident, says that the FAA should have taken immediate action when it learned about the dangers of Mylar during the Danish accident investigation.

NTSB's participation

The NTSB, which assisted the Danish government in the SAS investigation, also was aware of the dangers of Mylar but made no call to have it removed.

''There are occasions when information developed in foreign investigations leads to Safety Board recommendations,'' says NTSB spokesman Ted Lopatkiewicz in a written statement. ''No NTSB recommendations were issued as a result of the Danish investigation.'' The board refused further comment on the SAS accident report.

The Canadian Transportation Safety Board (TSB), which is now investigating the Swissair crash, and other countries' aviation agencies also received the Danish government accident report but made no recommendations related to Mylar.

TSB spokesman Jim Harris says the agency can't make recommendations based on another country's investigation. He says the TSB investigates accidents and is not a regulatory body like the FAA in the USA and its Canadian counterpart, Transport Canada.

''Sadly, these agencies are all missing in action,'' Block says. ''They're saying they don't care about the people in their country flying on these planes.''

Peter Thulesen, the head of the Danish accident investigation board, declined to be interviewed or to answer written questions about the type of wiring that short-circuited on the SAS jet.

The FAA's letter in the Danish accident report, however, reveals that the wire type was polyimide, which is often called Kapton. Boeing, which acquired McDonnell Douglas after the SAS plane was built, says Kapton is the general-purpose, or most commonly used, wire on MD-87 aircraft.

It is also the type that runs through most Boeing and Airbus jets, including the Swissair MD-11 that crashed. Short-circuited Kapton wires were found by Canadian investigators in their probe of that accident.

Cracked wire's dangers

U.S. Navy and other electrical engineering studies have shown that a crack exposing a Kapton wire's metal conductor can lead to a powerful short-circuit. Such a reaction could result in a 10,000-degree Fahrenheit electric arc jumping out a wire, a flashover and a high-temperature fire.

In October, British government investigators concluded that Kapton wire malfunctioned, triggering an electrical arc that caused a bundle of wires to catch fire on a United Airlines Boeing 767 in 1998.

The lead investigator in that crash told USA TODAY that Kapton should not be installed on new jets and that older planes found to have cracked Kapton wiring should be grounded. Both Boeing and Airbus use Kapton wire on their new planes.

Last March, the Australian airline Qantas issued a memo prohibiting its mechanics from using Kapton as a replacement wire, citing ''ongoing incidents across the world involving Kapton wire.'' The memo, which was obtained by USA TODAY, calls for purging of all Kapton in inventory.

Officials at FAA headquarters in Washington say there is no evidence of a Kapton problem. Data on planes still being flown don't present serious concerns about Kapton wiring, provided it is carefully installed and maintained, the agency says.

The Danish government accident report, as well as other incidents in commercial and military aviation, provide more than enough evidence of a problem with Kapton, Block says.

''After the SAS fire, FAA officials should have realized they had a problem with Kapton wiring and made some prioritization to deal with Kapton arcing,'' he says. ''They ignored the problem, and it still festers.''

http://www.usatoday.com/usatonline/20010614/3400396s.htm