TWA blast report urges repairs to jets' fuel tanks

Thousands of airliners worldwide may have to be modified following an urgent recommendation by official investigators into the crash of TWA Flight 800 that steps be taken to eliminate the possibility of fuel tank explosions in mid-air.

The warning is the first public statement by America's National Transportation Safety Board (NTSB) on safety measures that should be taken after five months investigating the causes of the TWA crash. The evidence points overwhelmingly to the conclusion that the deaths of all 230 passengers aboard the Boeing 747, which left New York for Paris on the evening of 17 July, were the result of a mechanical flaw and not - as was first thought - a terrorist bomb.

British airlines reacted cautiously yesterday, but a Boeing spokesman quoted in the Washington Post admitted that the NTSB recommendations could have "far-reaching consequences for the entire industry".

The wreckage of the TWA aircraft has been almost entirely recovered from the Atlantic Ocean and assembled like a giant jigsaw puzzle in a hangar on Long Island. The FBI, having submitted the twisted remains to minute forensic examination and after deploying its agents around the world in search of possible suspects, has failed to come up with any evidence suggesting the explosion was a criminal act.

The most convincing theory to have emerged so far is that a build-up of static electricity in the plane's centre fuel tank resulted in a spark that caused fumes to ignite. The NTSB's recommendation, addressed to the Federal Aviation Administration in Washington, concentrated on measures that should be taken in the event of such a spark occurring in other aircraft in the future.

The FAA has a record of agreeing with 90 per cent of the NTSB's urgent recommendations, and any order issued by the US aviation authorities is generally complied with worldwide. This latest recommendation covers not only the approximately 1,000 Boeing 747s in operation around the world but probably the vast majority of commercial airliners. All Boeing aircraft have centre fuel tanks, located in the fuselage under the passenger seats, with the exception of the new 777.

Both British Airways and Virgin Atlantic plan to wait until they receive specific recommendations from the Civil Aviation Authority before they carry out any additional safety checks. BA has been checking aircraft fuel tanks "as a precaution" since September. "The process will be that the NTSB will make recommendations to the FAA, who will then pass them on to the CAA in Britain," said a spokesman.

The NTSB listed a number of precautionary measures that might be taken in the short term to reduce the temperature in the fuel tank. The TWA plane had sat in the sun at New York's Kennedy Airport for several hours with its air-conditioning running; both factors would have generated heat in the fuel tank. One proposal is that fresh, necessarily cooler, fuel be added to the mix shortly before take-off.

Another is that TWA change its flight manual so that pilots will be more alert to the temperature build-up produced by the air-conditioning system.

A spokesman for TWA, which like Boeing would have preferred the verdict to be that the plane had been blown up by terrorists, was at pains to stress that the NTSB had not yet reached a formal "probable cause determination". "We would simply ask that everyone keep an open mind," the spokesman said.

James Kallstrom, the FBI official heading the investigation, also strived to suggest that it was too early to conclude that the millions of dollars and hours devoted by his agency to the task of finding a criminal cause had conclusively come to naught. But privately senior NTSB officials were reported to be jubilant, confident in the belief that they had solved the mystery.

A senior law enforcement official quoted anonymously by the Washington Post said: "It is time to let go of bombs and missiles and admit to ourselves that a mechanical problem probably destroyed this plane."