Reuters - Thursday July 13, 3:10 pm 

FAA explores nitrogen to prevent TWA 800 repeat

By Tim Dobbyn

WASHINGTON, July 13 (Reuters) - A shot of nitrogen into the fuel tanks of passenger aircraft in hot weather may be the ultimate defence against a repeat of the explosion of a TWA jumbo jet off New York nearly four years ago.

The Federal Aviation Administration is due to begin testing that idea next month when fuel tanks in a Boeing 737 will be ``inerted'' with nitrogen gas in a new programme conducted jointly with aircraft manufacturer Boeing Co. (NYSE:BA - news), agency officials said Thursday.

Advances in gas-separation technology have brought costs down to where it may be feasible at the airport to fill the vapour space in aircraft fuel tanks with nitrogen-rich air that cannot support combustion.

FAA Associate Administrator Tom McSweeny said the technology, described by some as ``de-icing for summer'', looked promising. ``We are excited enough about it to want to keep pushing it,'' he told reporters.

TWA Flight 800 fell to the sea in flames shortly after take off from New York bound for Paris on July 17, 1996.

All 230 people on board were killed in the tragedy traced by investigators to the explosion of the Boeing 747s centre fuel tank though the precise ignition source remains elusive.

The National Transportation Safety Board, ruling out a bomb or a missile as the cause, has encouraged the FAA and the aviation industry to do more to eliminate ignition sources and find ways to reduce the flammability of fuel tanks.

Fuel tank explosions are rare and only a 1990 blast in the Philippines involving a Boeing 737 on the ground is thought to have a direct resemblance to the TWA 800 accident.

Nevertheless, since the crash, the FAA has issued 37 airworthiness directives that mandate action on items ranging from fuel tank inspections to modifications of pumps and wiring related to the tanks.

A final meeting of the safety board on the crash is due to take place in late August. A review of the post-crash research and lessons learned is expected to conclude without a definitive answer to what touched off the blast.

``It's the most intensely investigated accident in aviation history,'' FAA aircraft certification director Beth Erickson said. ``We all know there was a fuel tank explosion but the ignition source for that explosion remains unknown.''

In other developments, McSweeny and Erickson said work was advancing more quickly than expected on better circuit breakers for planes that would trip sooner, much like a safety power outlets in many bathrooms today.

FAA also plans to issue advice to airlines to use cool air supplied at the terminal rather than on-board air conditioning when waiting at the gate.

TWA 800 sat for hours at New York's John F. Kennedy Airport running its internal air conditioning units that are located underneath the centre fuel tank.  During the probe it emerged that the U.S. Air Force had been concerned for years about such heating and the increased chances of a fire or blast.

Using external air conditioning could lower the time a plane's centre tanks were potentially flammable to 22 percent of the plane's operational time from 30 percent, FAA said.

But it was inerting that Erickson said held so much promise, with calculations it could decrease the period during which the centre tank was potentially flammable to just two percent.

A recent study requested by the FAA said the ground infrastructure required for inerting would cost $1.6 billion over 13 years. It remains to be seen how much modification of planes might be required and at what cost. 

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