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Attention shifts to breakup of tail fin

Shortly after American Airlines Flight 587 took off Monday morning, the pilots heard a rattling sound.

The captain told the first officer that the plane seemed to have encountered wake turbulence from another big jet. Then came more rattling.

The first officer realized the plane was in trouble. He told the captain he needed maximum power.

But two seconds later, the situation was so dire that the pilots talked about whether they were losing control. Within 14 seconds, the tape ended.

The Airbus A300 crashed into a cluster of homes on the Rockaway peninsula, killing all 260 people on board. Five people on the ground are missing and presumed dead.

The pilots' conversation, captured on the plane's cockpit tape, provided early clues about Monday's crash. But the tape and other new details raised as many questions as they answered.

The National Transportation Safety Board said investigators found no evidence that the engines had exploded, nor any evidence of a collision with birds. Officials said they still are treating the crash as an accident because they have found no indication of terrorism. But they said they have not ruled it out, either.

"We are making real progress with the investigation and with the recovery," said NTSB Chairwoman Marion Blakey. "Things are proceeding rapidly."

The flight data recorder was found in the wreckage Tuesday afternoon and flown to the NTSB's Washington lab. It is a sophisticated model that took about 200 measurements of the flight, so investigators were hopeful it will answer their questions about the crash.

So far, the focal point of the investigation is the large tail fin known as the vertical stabilizer, which was in remarkably good condition when it was pulled from Jamaica Bay.

Its location suggested it was the first piece to fall off the plane. Its pristine condition indicated it might have been sheared off.

Now investigators have to figure out why.

They are studying the radar track of the Dominican Republic-bound plane to see if it might have encountered the wake of a Japan Airlines Boeing 747.

Wakes are invisible tubes of spinning air that are the size of large sewer pipes. Planes encounter them every day. To passengers and pilots, it feels as if the plane is on a bumpy dirt road.

But under the right circumstances, a wake can startle a pilot or even begin a series of events that lead to a crash. In Pittsburgh in 1994, a wake initiated a bizarre chain of events that led to the crash of USAir Flight 427.

However, investigators still must determine if the pilots were truly feeling a wake.

"Just because they mentioned a wake encountered doesn't mean the plane encountered a wake," said Jim McKenna, an aviation safety analyst. "There might have been some other vibration they were encountering."

Greg Feith, a former NTSB investigator, said a wake might have triggered other problems that led to the crash. But he said there would have to be a serious malfunction or even sabotage to break off the tail fin.

"As soon as that vertical stabilizer leaves the airplane, it's uncontrollable," Feith said. "It's over."

Tuesday night, investigators added a wrinkle to the scenario. They said the plane's rudder was adjusted 10 degrees to the left. Pilots adjust or "trim" the rudder to account for winds and make the plane easier to fly. But 10 degrees is an unusually large amount for the A300. NTSB officials did not speculate on the reason.

Investigators said the captain of the plane had more than 8,000 hours of flying experience while the first officer had more than 4,000.

The NTSB has interviewed witnesses who have consistently said that the plane "wobbled" and that pieces fell off. The plane then spiraled down at a steep angle that kept the crash site relatively compact, investigators said.

NTSB sound experts are reviewing the cockpit tape of the two-minute flight.

"Not only are words important on a tape, but sounds are important," said George Black, an NTSB board member.

The safety board's sound expert, Jim Cash, is a former Air Force fighter pilot reknowned for identifying unusual sounds. He uses a computer program that translates a sound into a series of lines and then he matches it against known sounds like a detective matching a fingerprint.

He is likely to compare the Flight 587 sounds with those from the USAir flight and other wake turbulence incidents.

The NTSB also has obtained a videotape of the American Airlines flight shot by a construction worker at the airport, but he stopped recording the flight shortly after the plane lifted off the runway.

"He doesn't have any of the actual event on videotape," Black said.

Investigators have determined the wreckage is roughly in a line heading south from JFK toward the crash site. The tail fin fell into the bay first, followed by the rudder about 200 yards later. They are within a half mile of the main impact site.

Investigators have focused on the engines because at least one of them broke off in flight and landed in the waterfront neighborhood south of JFK. But Black said there was no evidence of an "uncontained failure," in which an internal part causes the engine to explode.

"Initial inspection shows no evidence of any sort of internal failure of either engine," Black said.

TEXT ACCOMPANYING ILLUSTRATION NOT PROVIDED FOR ELECTRONIC LIBRARY, PLEASE SEE MICROFILM.

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