Tail fin failed as jet hit turbulence

Relatives of the victims of American Airlines Flight 587 will gather today for a memorial service in a park a few blocks from the crash site as investigators struggle to discover what caused the airliner's tail fin to snap off.

Officials may be months from understanding fully the sequence of events that sent the Airbus 300, bound for the Dominican Republic from John F Kennedy in New York, spiralling last Monday into Queens. The accident killed all 260 people on board and five people on the ground.

The field phase of the investigation, at the crash site and along the path of the aircraft as it broke up, was set to be completed last night. All body parts have been recovered. Most of the investigative work by the National Transportation and Safety Board, NTSB, will now shift to different laboratories around the US.

The focus has settled on the tail fin, the materials it was made of and the actions of the pilots. After studying cockpit voice tapes and the flight data recorder, investigators said the fin separated from the fuselage first. The engines apparently fell off seconds later, as the plane plummeted. The final crash sequence started shortly after the plane encountered turbulence left by a jumbo jet which had taken off just before it.

While sabotage or terrorist intent has still not been ruled out, few officials were taking any such scenarios seriously, pointing instead to catastrophic mechanical failure. This seemed to invoke relief at first, but the implications for the flying public – that planes can break up when they hit rough air – seemed hardly reassuring. The tail fin, which was recovered from the sea some distance from the main area of impact, was made of a modern composite material called carbon fibre-reinforced plastic.

"I think there was a pre-existing structural problem with the tail," said Greg Feith, a former investigator with the NTSB. "It was going to fail regardless. It just so happened the conditions were right." If some generic flaw is found to have existed in the material, the impact for the aviation industry could be massive, because such composites are increasingly used both by Airbus and by Boeing.

The Federal Aviation Administration on Friday ordered airlines in the US to inspect the tail assemblies of their Airbus A300-600 and A310 planes without delay. "The FAA is absolutely right to check all the tails on the 300s," commented Peter Golz, a former director of the NTSB. "The truth is, when we started using composite materials to construct planes, there was no actual history of how long these composites would maintain their rigid characteristics."

Aviation insiders have long worried about the long-term trustworthiness of some of the composites. They are harder to inspect, partly because any damage does not show very easily to the eye. "It's our belief, at least that at this point, that we need to be examining the broad issue of composite materials," Marion Blakey, the chairwoman of the NTSB confirmed on Friday. This may be worrying to Airbus, which pioneered the use of composites which were both less heavy than standard aluminium and held the promise of being stronger and more durable.

Investigators plan to travel to Airbus headquarters in Toulouse, France, where the plane's manufacturers have a flight simulator that can accept data from the flight recorder. That way, they can explore what forces may have been applied to the tail. They were also studying two video tapes last night of the plane's final minutes. A traffic camera on a nearby bridge captured the plane's ascent and the start of its break-up, but the images are extremely poor, officials said. A construction worker at JFK filmed the first minute of the plane's ascent, but stopped before trouble hit.

The aircraft suffered two sets of sideways buffeting, according to the data recorder. They were caused by the wake left by a Japan Airlines 747 that took of just one minute and 45 seconds before. The time between take-offs was less than the recommended minimum, but the distance between the planes was allowable. Shortly after the plane was shoved more violently from side to side. That movement was apparently caused by unusual rudder movements initiated by the pilot. Investigators want to know if the pilot caused huge forces to be applied to the tail fin by overcompensating with the rudder pedal.

Safety records showed that the same aircraft had been severely shaken when it hit air turbulence seven years ago. Experts are also looking at whether that incident, which was violent enough to send a trolley crashing through panels in the ceiling, could have weakened the plane.

George Bush called the Dominican Republic's President Hipolito Mejia on Friday to express his condolences for the 175 Dominicans killed. Today's memorial service will bring together residents of Washington Heights, home to the city's Dominican community, with residents of Breezy Point, where the plane came down.