Responding to increasing evidence of cracked electrical wire insulation in the fuel tanks of commercial airliners, the Federal Aviation Administration said Tuesday that it will expand the hunt for bad wiring to additional types of planes so that potential short-circuits do not become life-threatening
situations.
Airlines applauded the FAA’s call for a voluntary widening of inspections, which now include the DC-10 and L-1011 TriStar jumbo jets. The National Transportation Safety Board, however, complained that the action falls far short of its recommendation for immediate, mandatory checks on all 4,500 passenger planes in the U.S.-registered fleet.
The safety board, an independent federal agency that investigates accidents, is aiming its spotlight on cracked or deteriorated wire insulation, already found in 69 percent of the 341 passenger planes the FAA ordered checked over the last three weeks and repaired with a protective Teflon coating.
The FAA’s measured march to inspect more planes–but not all of them–ignores decades of findings that a thin layer of protective insulation is vulnerable to vibrations, age and other factors, said safety board spokeswoman Shelly Hazle.
Safety board investigations have concluded that cracked insulation allows electrical sparks to escape and reach other cracked wires that run to aircraft fuel tanks.
The scenario is considered the probable cause of fatal blasts that ripped apart two jetliners: A Boeing 747 on TWA Flight 800 two years ago near New York City and a Philippine Airlines Boeing 737 that exploded on a Manila runway in 1990.
A primary safety concern, Hazle said, involves airplane manufacturers’ space-saving standard of combining up to 40 wires into a single bundle.
Such a design, accepted only a decade ago as a way to maximize space for fuel storage, is no longer utilized on many new aircraft because an insulation crack in one wire potentially could reach nearby wires, setting off a spark that could mix with fuel vapors and oxygen and trigger an explosion.
Safety board officials believe segregating fuel tank wires from other bundled wires is a necessary and immediate goal for all passenger planes, Hazle said, dismissing the potential expense to the airlines.
The FAA, which is not bound by the safety board’s recommendations, disagrees, citing statistics showing that passenger planes remain the safest form of transportation.
“We saw problems with 737s earlier this year and took immediate action. We will do that again if we see more serious problems,” said FAA spokesman Bob Hawk.
On Tuesday, the FAA called for voluntary inspections by U.S. airlines of Lockheed Martin Corp.’s L-1011 and McDonnell Douglas’ DC-8, DC-9 and DC-10, as well as the MD-11, MD-80, MD-90 and KC-10. The aircraft were selected because they share some design similarities and in most cases have electrical conduit that runs through fuel tanks, officials said.
The FAA asked that results of the voluntary spot inspections, which officials said will likely be conducted on 10 percent of each type of aircraft, be reported to the agency by Aug. 21.
“We expect to widen the scope of these inspections in the next few weeks as we talk to (other) manufacturers,” Ronald Wojnar, manager of the FAA’s Transport Airplane Directorate, said in a letter to the Air Transport Association, which represents the major airlines.
No inspections are anticipated for Boeing’s newest planes or those made by the European consortium Airbus Industrie.
The bid for voluntary compliance follows an FAA mandate that led to the unprecedented grounding May 10 of 179 older-model Boeing 737s after mechanics found exposed wiring, signs of chafing and pin-size holes on the fuel pump wiring apparatus of some planes.
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Insulation problems discovered during voluntary inspections April 25 by Continental Airlines and May 9 by United Airlines led to the order, the FAA said.
Previously, the FAA has undertaken mandatory or voluntary inspections involving primarily Boeing models, including the 707, 727, 737, 747 and 767.
“The FAA has moved rather fast so far, but I still see a need to go after younger airplanes– even those only 6 or 7 years old–in light of the severe wear and tear on the wiring that has been uncovered so far,” said Stuart Matthews, president of the Flight Safety Foundation, an international clearinghouse on aviation safety.
But Matthews stopped short of the NTSB’s call to inspect all aircraft, saying, “it’s not a reasonable thing to do.”
FAA officials acknowledge that despite expertise in structural problems associated with older aircraft, they are just now learning about the role of wiring as a weak link in safety.
Safety board officials said the FAA should have been concerned about the effects of vibration and chafing on wiring 20 years ago.
The trail of evidence is highlighted by a 1978 ban by the Department of Defense that deemed two insulation types, Poly-X and Kapton, unreliable for military use. Both brands of insulated wire are found in up to 25 percent of the nation’s passenger fleet.
The FAA and the manufacturers say there is no evidence that any brand of wire is prone to failure or poses a safety risk.
Wiring issues gained notice primarily in 1990 with the explosion of the Kapton-wired Philippine Airlines 737.
And safety board investigators said they are 99 percent sure that a spark between two wires with cracked insulation caused the 1996 explosion of Flight 800, a Boeing 747 that was wired with Poly-X throughout the fuel tank area.
Critics charge that the FAA did little to understand the complexities of age and design involving fuel tanks until the fatal blast on TWA 800, which killed 230 people, and say the agency moved sluggishly until this month as evidence mounted that wiring plays an integral role in safety.
On the heels of the FAA’s call for more inspections, the major airlines are taking steps to show they are in front of the problem before mandatory action is ordered.
“Delta is moving forward immediately to perform the voluntary inspections, although we are not aware of any problems with the aircraft mentioned today,” said Delta Air Lines spokeswoman Tracy Bowen.