Airbus crash: Experts still puzzled

Neither turbulence from another jet nor pressure placed on the rudder by a desperate pilot should have been enough to snap off the tail of Flight 587, aviation experts have said.

Their conclusion raised the prospect that something was wrong with the plane before it left the ground.

‘‘I think there was a pre-existing structural problem with the tail,’’ said Greg Feith, a former National Transportation Safety Board investigator.

‘‘It was going to fail regardless. It just so happened the conditions were right.’’

The American Airlines Airbus A300 plunged into a New York neighbourhood on Monday, shortly after taking off from Kennedy Airport for the Dominican Republic.

The crash killed all 260 people aboard and five more on the ground.

The cause of the crash has not been determined, but investigators have focused on the jetliner’s tail assembly, which came off sometime before the crash.

The Federal Aviation Administration on Friday ordered airlines to immediately inspect the tail assemblies of their Airbus A300-600 and A310 planes.

American and two cargo carriers, FedEx and United Parcel Service, have about 135 of the French-made jets in their fleets.

The FAA said no conclusions have been reached about whether the tail was related to the accident, but called the inspections a ‘‘prudent’’ move.

NTSB chairman Marion Blakey said the frantic efforts of the pilots aboard Flight 587 to save their plane also should provide clues to what went wrong.

‘‘We do know, just from what we can see on the flight data recorder, that the pilots were trying to actively fly that plane out of the problem,’’ Blakey said, cautioning that this does not imply pilot error.

Investigators have already suggested the pilots wouldn’t have known the tail fin was missing.

‘‘It seems to me this was a very extraordinary crash. In fact, we don’t have a parallel,’’ Blakey said before she and other investigators left New York for Washington, where the inquiry will continue for months.

Investigators say Flight 587 shook violently from side to side after encountering two wakes generated by a Japan Air Lines 747 that took off about two minutes earlier from the same runway at Kennedy.

Because of its size and weight, the four-engine 747 generates heavy turbulence.

While Flight 587 was more than four miles behind the JAL jumbo jet, as required by FAA regulations, NTSB spokesman Keith Holloway said the agency was looking at whether to suggest keeping planes farther apart, since wakes dissipate over distance.

Experts suggested more distance wasn’t needed in this case.

‘‘The wake vortex of a 747 should not bring down an aircraft,’’ said Tom Ellis, a spokesman for the Nolan Law Group, a Chicago firm that represents victims of airline accidents.

‘‘The A300 is designed to withstand forces of that nature. It should be well within its design tolerance. There’s got to be something that interferes with the ability to recover.’’

Based on information from the flight data recorder, investigators found that the plane’s rudder moved sharply during the jet’s three-minute flight.

Experts said the movement could have resulted from the pilot hitting the rudder pedal hard or from a jerk on the other end of the cable as the tail snapped off.

But pilots of large planes don’t usually use the rudder, except when they lose an engine or for help during landings.

Examination of the two black boxes the data recorder and the cockpit voice recorder indicates the pilots were ‘‘working hard’’ in the cockpit before the plane plummeted into the Rockaway Beach section of Queens, Blakey said.

In the only known similar case, a JAL flight in 1985 lost its vertical tail section on a flight from Tokyo to Osaka.

The Boeing 747 flew in circles for half an hour before crashing into a mountain, its pilots still trying to understand why they had lost control. The crash killed 520 people.

Several aviation experts have suggested that there was some unseen weakness in the tail assembly.

The tail fin was held to the fuselage by six fittings. Maintenance records indicate that one of the fittings had to be repaired by the manufacturer before the plane was delivered to American Airlines in 1988.

The problems could have dated from 1994, when the jet was severely shaken by air turbulence, injuring 47 people. The plane was inspected following the incident.

‘‘That’s where the investigation really has to start,’’ Feith said. ‘‘It may be the inspection was just a visible inspection. They’re not going to be looking inside that fin area, they’re going to be looking for obvious damage.

"Something could have happened that, although it didn’t immediately fail the tail at that point, did set up a fail scenario."