05/27/2008 05:12 am ET | Updated May 25, 2011

The Legacy of TWA Flight 800

Something neither the airlines nor Boeing nor Airbus will have been keenly anticipating is a new rule, due this month, that is perhaps the final flicker of regulatory response to the TWA Flight 800 crash, which happened 12 years ago this July. The Federal Aviation Administration's recent new toughness, subjecting airlines to increased scrutiny, grounding many planes for inspections, is hard to read when it comes to TWA 800. That tragedy, which killed 230 passengers and crew and destroyed an aging but airworthy and reliable Boeing 747, was the subject of much speculation at the time.

But the National Transportation Safety Board and the FBI, which did not so much share the investigation as each run its own investigation into the crash, found no evidence to support the theory that a bomb or missile had caused the gigantic explosion seen by hundreds and heard on the South Shore of Long Island, nine miles north of the crash site, as a loud bang.

No, according to the NTSB the airplane was destroyed by an explosion inside its huge center fuel tank, located inside the fuselage, between the wings, beneath the passenger cabin. The fact that the tank had been emptied of fuel did not mean it could not have exploded because, the NTSB speculated, as much as 50 gallons of Jet A aviation fuel could have remained inside the empty tank without registering on the cockpit fuel gauges. Flight engineers point out that the residual fuel sloshing around in the bottom of a 13,000 gallon tank can get dirty and also a bit watery too, with moisture dribbling down the sides of the tank --- factors which would tend to make the fuel less likely to produce an explosive vapor. One only has to remember that drivers who filled up at one New Jersey gas station recently found that their engines died on account of water that had got into the fuel.

Nevertheless, and without evidence of how the vapor had ignited, within months of the crash the NTSB became certain that the center tank had exploded, and before the end of 1996 had issued a safety recommendation urging the FAA to find a way to eliminate flammable vapors from fuel tanks, so that a similar airliner catastrophe would never happen again.

The regulation took some time to formulate, and along the way the FAA experimented with ways to "inert" fuel tanks with nitrogen to replace the oxygen without which combustion is not possible. The FAA came up with its own design for equipment to install in aircraft to accomplish the inerting.

Early this year, after several postponements, the FAA finalized its new rule to reduce the exposure of tanks to flammable vapors and sent it over to the Office of Management and Budget for a final, 90-day review. That was on Feb. 15, and those three months are now over, but the rule has not been issued. According to FAA spokeswoman Alison Duquette on May 14, "It is still at OMB, the final step."

Whether the FAA has the nerve to impose a new expense of several hundred thousand dollars per aircraft on the cash-strapped airlines remains to be seen.

Whether the rule is necessary is another question. No passenger aircraft before TWA 800 had ever suffered an in-flight explosion of such violence -- except those known to have been downed by bombs or missiles, like PanAm 103, bombed in 1988, or the Iran Air Airbus hit by U.S. Navy missile fire, also in 1988; in fact, Jet A kerosene fuel had enjoyed a remarkable safety record since its introduction during the 1940s and '50s, proving far safer than the more volatile JP-4 fuel it replaced. Thus the TWA Flight 800 explosion was truly an aberration.

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