Associated Retired Aviation Professionals


August 20, 2000 

Tragedy's Lesson 

Flight 800 crash makes old wiring an aircraft issue 

by Sylvia Adcock Staff Writer

It was June 18, 1996. Ed Block was firing off yet another letter to the Federal Aviation Administration. The letter -- like dozens he'd written before -- was full of details about Block's concern about the potential danger of wiring in aircraft. He told of problems he'd seen in his years as a wiring specialist with the Defense Department. He told of F-14s grounded by the Navy because of cracked wires. He pointed out that miles of wiring in older planes are never replaced and rarely, if ever, inspected. "There needs to be a complete assessment/analysis of all wiring currently in use,” Block wrote. 

The responses -- often ending with the phrase, "Thank you for your interest in aviation safety” -- filled boxes in his suburban Philadelphia home.  But something was about to happen that would bring Block's concerns to the forefront. One month after his June 18 letter, a Boeing 747 from Kennedy Airport exploded nine miles off the coast of Long Island. The crash of TWA Flight 800 killed 230 people and eventually focused attention on the dangers of wiring in older aircraft in a way that Block's letters alone could never do.  Today, the FAA has launched an ambitious program on aging aircraft that targets wiring problems in older planes. In Albuquerque, N.M., government engineers are taking apart an old DC-9 and testing its wiring to find out how it ages. And last spring, Block met with top presidential advisors. "He certainly helped raise the awareness of this issue at the White House,” said Charles Huettner, President Bill Clinton's chief policy advisor on aviation, who heads a new White House commission on aging wiring which is expected to issue a report in October. 

The change didn't happen overnight. But the scrutiny that Flight 800 has put on wiring and aging aircraft could be the greatest legacy of the crash, aviation experts say. When wiring insulation is cracked or damaged by chafing, the damaged wire can start an in-flight fire, short out an electronic flight system, burn through hydraulics that control flight, and even eat a hole through the aircraft's aluminum skin. "Nobody had considered the aging of the wiring harnesses,” said John Hansman, a professor of aeronautics at the Massachusetts Institute of Technology. 

This week, the National Transportation Safety Board will wrap up its four-year investigation into Flight 800 with a two-day meeting. While the NTSB's final report does not pinpoint what ignited the fuel tank explosion that brought down the plane, it is expected to name the wiring to the fuel-measuring system as a likely culprit. And the report is expected to contain new details about the performance of wiring inside the 25-year-old Boeing 747 that was Flight 800. 

It wasn't long after the July 17, 1996, crash that NTSB investigators determined that the nearly empty center fuel tank on the plane had exploded, and they began to consider ways a spark could get into the tank. Although no evidence had been found, a bomb or missile were still possibilities. And investigators considered a number of mechanical failures in the plane's systems that could have ignited the flammable vapors -- among them the fuel-measuring system inside the center fuel tank. 

The system uses a series of six-foot-high probes and a very low electric current -- 10 times less than the energy required to ignite a fuel-air mixture -- to determine the depth of the fuel in the tank. The wires from the system run from the tank to the cockpit, where they connect to gauges that tell the flight crew how much fuel is left. 

In August, 1996, just weeks after the crash, Boeing performed a test that appeared to discount the fuel-measuring system as the source of the spark. The engineers found that applying a high voltage to the system would cause a color change on the fuel quantity indicator in the cockpit -- and the recovered indicator from the wreckage of Flight 800 didn't show such a color change. 

While NTSB investigators continued to consider the system a potential ignition source, they began to turn their attention to other possible sources. Meanwhile, as summer turned to fall, more pieces of the fuel measuring system were being recovered from the wreckage site as trawlers sifted the sand as if hunting for gold. But it wasn't until the spring of 1997, months after the recovery operation ended, that an NTSB investigator noticed a darkened spot on a fragment from the fuel-measuring system inside the tank. The spot was near a wire connector and it caught his attention because it looked like soot -- and that might be evidence of an arcing wire. 

A scanning electron microscope showed the spot wasn't soot; it was a buildup of copper and sulfur deposits. It wasn't evidence of arcing -- but it did raise the possibility of something that could create a conductive path inside the tank. "That was when we started seriously looking at probes,” an NTSB source said. 

The safety board investigators began focusing on a scenario that involved several failures. If wires outside the tank became abraded over time, with the insulation wearing off, the current from a high-voltage wire might have leapt into the fuel-measuring system wires. Another failure of wire inside the tank, coupled with the copper and sulfur deposits, could mean an ignition source. The investigators knew that the low-voltage wires to the fuel tank were bundled with high-voltage wires in several places. 

Another force had already been at work to bring wiring issues to the fore. Shortly after Flight 800 exploded, the White House appointed a blue-ribbon panel, called the Gore Commission, to come up with a host of recommendations on aviation safety and security. Along with the terrorism experts on the panel was Mike Loh, a retired Air Force general, who couldn't help drawing a connection between what happened on the 25-year-old TWA plane and wiring problems he had seen firsthand. Years earlier, when the Air Force had begun to retrofit a fleet of old Boeing 707s for use in the Persian Gulf War, the wiring in the retired commercial plans was so badly damaged that the Air Force had to completely rewire the planes. 

In February, 1997, the Gore Commission made its recommendations. Included was one written by Loh, who said the FAA should expand its aging aircraft program. Since 1989, the FAA has required stepped-up inspection schedules on the structure, or aluminum skin, of older planes, but no such requirements applied to wiring. Loh's recommendation couldn't be ignored; he had the force of the Gore Commission behind him. Loh also personally passed his concerns on to NTSB Chairman Jim Hall. 

It wasn't what the industry wanted to hear. Top FAA officials had already told the Gore Commission that they didn't think a new aging aircraft program was needed. 

But by the first anniversary of the crash of Flight 800, the FAA had quietly begun a study of the wiring of old DC-10s that were being modified by a cargo carrier. "People asked the question, is there a problem with aging wiring?” said Tom McSweeny, associate administrator for the FAA. "We had not seen any . . . But you find yourself asking, ‘What do you really know? Do we want to wait until we find a problem?' The answer is no.” 

By October, 1998, the FAA announced it was expanding its aging aircraft program to include wiring and other internal systems. The program is eventually expected to require increased inspections for older planes, something that would be expensive for airlines. And the FAA is also now considering whether regulations need to put a definite lifespan on aircraft wiring, requiring wholesale replacement at a certain age -- something that would be so expensive it would likely put older models out of service. 

An FAA/industry task force has inspected the wiring on 81 in-service aircraft. The group said it found no immediate flight-safety concerns, but it did find 182 instances "significant enough to require additional review for possible corrective action,” according to a draft report. 

Years ago, Ed Block had complained that FAA databases don't accurately reflect wiring problems. A report documenting a malfunction in an avionics system, for instance, wouldn't mention that a wire had shorted out. Today, the FAA agrees its own data don't accurately reflect the state of wiring. The database of documented aircraft problems "just isn't as helpful as it could be,” said Beth Ericson, the FAA's director of aircraft certification. "We are working to come up with more descriptive ways to collect that data.” 

At the NTSB meeting this week, safety investigators are expected to present new studies done on the type of wiring used on the Flight 800 plane. Aircraft wires can frequently be exposed to liquids from spilled beverages, leaking lavatory water and condensation. Using wire from an older Boeing 747, a contractor dripped salt water and lavatory waste water on damaged wires. The contractor found that the wires eventually began to arc, producing flashes of light and popping noises. Such strong arcing could damage adjacent wires, according to a report from Lectromec, a private contractor that performed the tests. 

But Boeing, in its submission to the NTSB, points out that there is no evidence that a specific electrical system or component of the fuel measuring system ignited the fuel vapors in Flight 800. 

"Exhaustive laboratory testing for potential ignition sources were essentially negative,” the company said. 

As for Ed Block, he's still writing letters, but he's no longer such an outsider. Today, he sits on the FAA-industry task force on aging wiring, and recently flew to Italy to inspect the wiring on a junked aircraft. He remains convinced that the FAA and industry are not paying enough attention to specific types of wiring, and recently filed a minority opinion when he disagreed with a draft report from the task force. 

"Do I feel vindicated? It's a sad, bittersweet sort of vindication,” Block said. "Because people had to die.” 

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