'Look at that crazy fuel flow indicator there on No. 4. See that?" exclaimed Capt. Ralph Kevorkian. Sitting in the pilot's seat on TWA Flight 800, a B747, Kevorkian was remarking to fellow crew members about a spike in the fuel flow reading in the No. 4 engine as the airplane passed through 13,000 feet after takeoff on July 17, 1996, from JFK International Airport for an overnight flight to Paris.
It wasn't a surge in fuel use, but a false reading caused by a surge in electricity.
Less than two minutes later the plane blew up, killing all 230 passengers and crew members. The National Transportation Safety Board concluded that flammable vapors in the center fuel tank under the passenger deck exploded, tearing the airplane apart. Electrical arcing in a wire bundle outside the tank, which contained the circuit for the No.4 engine fuel flow, caused a power surge that jumped from wire to wire and ultimately to the wires connecting the fuel-quantity indicators in the center tank.
The electric current traveled down these normally harmless wires into the tank and ignited the vapors. All the vapors needed was an ignition source - a match, as it were - to trigger an explosion. What Kevorkian saw on the fuel gauge was a spurious reading portending imminent doom.
Now, 10 years after the crash, the National Transportation Safety Board is mightily frustrated with the lack of progress in efforts to improve fuel tank safety. "The most prominent issues raised by the TWA 800 accident concern protection against flammable fuel tank vapors and aging electrical systems," the NTSB told the Federal Aviation Administration earlier this year.
What has the FAA done to address those issues in the years since the Flight 800 tragedy?
There have been endless and earnest meetings, and various directives have been issued seeking to prevent ignition sources in fuel tanks. But the FAA has only issued a proposed requirement to prevent fuel-tank explosions through an "inerting" process that fills voids in the tanks with nitrogen-enriched air. It also has left airline manufacturers to their own devices by only proposing - not yet requiring - inspections of aircraft wiring.
On its new B787, Boeing is installing an inerting system for both the center section and the wing fuel tanks. European manufacturer Airbus has designed the A380 double-decker without a center wing tank and claims it has eliminated all potential sources of ignition from its wing tanks so the weight and complexity of an inerting system is not necessary.
Thus, we come to one of the problems the FAA has created for itself. The agency has suggested that inerting systems are needed only for center tanks with nearby heat sources (such as air-conditioning packs, which warmed the fuel vapors on TWA 800). But the NTSB has recommended that flammable vapors be eliminated from all tanks.
The May 4 explosion of a Transmile Airlines B727 at Bangalore, India, in which a wing tank exploded as the airplane was being repositioned for ground maintenance, seemed to bolster the NTSB position. In a July 20 letter to the FAA, the NTSB, which was supporting a probe by Indian aviation authorities, said investigation of the incident "revealed that the ignition occurred where [fuel] pump motor wires had melted though aluminum conduit, exposing the fuel vapors to potential ignition energy." Although the aircraft had been modified in accordance with an FAA directive to prevent the wiring problem, the design change was clearly ineffective. Inerting is necessary, the NTSB said.
The NTSB recommendations appear to be further supported by the April 3 crash of a U.S. Air Force C-5 jet transport at Dover Air Force Base in Delaware. The C-5 has an inerting system. The airplane crashed, but it did not erupt into a fuel-fed fireball. Even though the crew was soaked in jet fuel, all 17 aboard were able to escape the wreckage.
The aviation industry has responded that its recent efforts to eliminate ignition sources are sufficient to ensure safety, although the Transmile incident suggests otherwise. The U.S. industry remains flatly opposed to a costly program to retrofit the existing fleet with inerting systems, and the Europeans are opposed to requiring such systems on new planes such as the A380. The problem with the industry's approach is that if reducing ignition sources is not sufficiently effective, inerting would still guard against catastrophic failure. Consider it the belt and suspenders approach to safety.
The Families of the TWA Flight 800 Association have asked: "Can the airline industry and FAA afford another mass loss of life similar to this accident?"
Unfortunately, it may take another disaster on the scale of TWA 800 to re-energize the effort to make fuel tanks truly safe through inerting.
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