NTSB wants older 747s checked and rewired

In this story:

• 'Unsafe conditions...may exist'
• Sharp edges on terminal blocks
• Problems were discussed in December
• 'Inappropriate repairs' found

April 7, 1998
Web posted at: 10:51 p.m. EDT (0251 GMT)

WASHINGTON (CNN) -- The National Transportation Safety Board on Tuesday recommended mandatory inspections and rewiring of the fuel tanks in hundreds of older Boeing 747 jets in response to faults found in the wreckage of TWA Flight 800 and on other aircraft.

In a 10-page letter to Federal Aviation Administration chief Jane Garvey, NTSB chairman Jim Hall asked the FAA to require wiring and fuel probe inspections on three early series of the jumbo jet -- the 747-100, 747-200 and 747-300.

Hall also recommends that other types of airplanes with fuel gauge systems similar to those on older 747s be checked, including those on Boeing 707s and C-130 military transport planes.

Hall said the NTSB found damaged wiring in the fuel gauge systems of TWA 800 and a few other older 747s, including three that have been retired.

Wreckage from TWA Flight 800

While stopping short of blaming the TWA crash on any specific source, Hall wrote that "unsafe conditions ... may exist in other older B-747s and should be addressed by the Federal Aviation Administration."

TWA 800 plunged into the sea off New York in July 1996, killing all 230 people on board, after an explosion ripped the plane apart. Safety investigators have been trying for months to pinpoint an electrical source that ignited fumes in the jet's center fuel tank.

Sharp edges on terminal blocks

The NTSB said it:

• Found that the terminal blocks on the fuel gauge systems of older 747s had sharp edges that could cut through wire insulation, and recommended that they be replaced.
  
  
• Wants the FAA to require separation or rerouting of fuel-monitoring wires away from other wires that carry higher electrical charges. The agency fears that those wires, which carry up to 350 volts, could send a jolt to one of the fuel wires.
  
  
• Asked the FAA to require electrical surge protection in all transport aircraft -- not just Boeing 747s -- to prevent electrical jolts from reaching fuel tanks.
  
  
• Recommends that the FAA conduct studies into copper sulfide deposits that are found in airplane fuel tanks "to determine the levels of deposits that may be hazardous."

Taken together, the recommendations mean that all 750 older Boeing 747s still in service would have to undergo inspections and, possibly, extensive rewiring.

The rest of the recommendations could affect 500 to 600 newer 747s -- as well as other types of planes -- since the NTSB wants them applied to "all applicable transport airplane fuel tanks."

"The safety board recognizes the difficulty and expense associated with physically separating (fuel-monitoring) wires from other wires and adding shielding to wires on in-service air carrier airplanes," Hall wrote.

"However, the separation of the ... (fuel-monitoring wires) from other power sources by shielding and separation can protect fuel tank wires from power sources that can potentially ignite an explosive vapor in a fuel tank."

Sources in the industry say the rewiring would be a massive and expensive undertaking.

Problems were discussed in December

Most of the problems addressed in the letter were discussed at a December hearing in Baltimore and are already being addressed by the FAA and Boeing. But Hall's letter seemed designed to get more action from Boeing and the FAA.

Hall acknowledged, for example, that a more complete inspection of fuel gauge wiring was to be addressed in upcoming Boeing service bulletins, but he noted that such bulletins are not mandatory.

Only the FAA has the power to mandate the changes, and it released a statement Tuesday saying it agreed with the intent of the NTSB's recommendations. But it pointedly reminded the board that it had kept it informed of action already under way.

"The FAA is working actively with the NTSB and Boeing to develop both short- and long-term solutions for addressing fuel-tank ignition sources and reducing or eliminating explosive fuel-air mixtures," the statement said.

FAA officials say among the actions taken already is ordering a replacement for the terminal block that may have caused the fraying of the fuel gauge wiring.

In a short statement, Boeing said it was working on a series of fuel system service bulletins that it believed would address the NTSB's recommendations.

'Inappropriate repairs' found

The chief suspect in the TWA disaster is a combination of events involving damaged wires and corrosion on a fuel-measuring rod that may have introduced a spark or flame into the center fuel tank.

The tank was virtually empty and the vapors in it heated up as the plane sat on the runway on a hot day waiting to take off.

At NTSB hearings last year, experts from Boeing testified that the company has been testing different ways to protect the center fuel tank from exploding -- including using different types of fuels.

Hall's letter said the NTSB also found two "inappropriate repairs" in the fuel-monitoring wires for TWA 800's wing-tip fuel tanks, although investigators do not believe they contributed to the crash.

TWA issued a statement saying the repairs had been performed in accordance with Boeing and FAA procedures.

Correspondent Christine Negroni and Reuters contributed to this report.

Related stories:

• CNN Transcript: Aviation analyst Susan Coughlin explains the NTSB recommendations
• Critics: Too much emphasis on terrorism in air safety push - February 14, 1998
• Airlines move to improve crash avoidance systems - December 16, 1997

Related sites:

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• NTSB - Home Page
• Welcome to The Boeing Company
  • 747 Family Background
• Air Transport Association
• U.S. Department of Transportation

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