Turbulence bounced jet before crash, data show

Information consistent with an encounter with air trails of nearby plane

November 16, 2001|By Marcia Myers | Marcia Myers,SUN STAFF

In the final seconds before it spiraled downward Monday morning, American Airlines Flight 587 was bounced severely back and forth by turbulence, according to preliminary data released yesterday by investigators.

The data, they said, are consistent with a "wake turbulence" encounter - a condition created by swirling masses of air trailing from a nearby plane, in this case a Japan Airlines 747 that had taken off just ahead of it.

The data show that Flight 587 had been forced sideways - though under less severe pressure - a few seconds earlier in a similar incident.

The information bolstered the theory that wake turbulence played a role in the crash. But investigators said yesterday that they are still a long way from knowing why the Airbus A300 went down, killing 260 people on board and five in the Queens neighborhood where it crashed.

"This is really the tip of the iceberg in New York," said Marion Blakey, head of the National Transportation Safety Board.

After a day spent removing large pieces of scorched plane parts from the crash site, the investigative team said it is nearing the end of its work there and expects to close the site by tomorrow.

"It will be many months of pulling a lot of this information together before we have a complete and clear picture," said Blakey.

Investigators said yesterday that even with the new information, they don't know what caused the tail of the jetliner to break off, the event they suspect initiated the plane's free fall.

Questions about the plane's tail parts - the stabilizer and rudder - remained at the center of the inquiry yesterday.

At the Federal Aviation Administration, officials plan to require inspections of the vertical tail stabilizer on all Airbus A300 aircraft in the United States. American is the only commercial airline that uses the plane, which also is part of FedEx and United Parcel Service fleets. American had already announced it would make inspections of its 34 remaining A300s.

The details emerging yesterday were the first significant evidence retrieved from the plane's "black box" - the flight data recorder that holds valuable information on more than 200 aircraft functions.

Investigators are looking closely at an 8-second period after the aircraft's second encounter with turbulence.

During the first encounter, a few seconds earlier, the plane's position changed little, said Tom Haueter, assistant director of the NTSB. There was no change in attitude of the flight, no pitching up or down.

But the second encounter severely buffeted the plane sideways - twice from one side, then once from the other. The strength of the forces hitting the plane was "very significant," he said, amounting to one-third or more of the plane's weight.

Even so, that alone is unlikely to have caused the crash, said Vahid Motevalli, director of the aviation safety and security program for George Washington University's Aviation Institute. Investigators say the plane's tail fin was torn cleanly from the aircraft and appeared to be the first piece to fall from the plane.

"It shows that it is getting pushed around sideways, which is more odd than anything," Montevalli said. "For an airplane, it is a good bit of jolt, but it's not something that would break anything structurally. I don't think it explains ripping off a stabilizer."

Afterward, the black box stopped tracking the movement of the plane's rudder. Experts said that could mean the tail piece had broken off. Among the factors investigators are considering is the performance of the stabilizer's carbon-based composite material under such conditions.

Shortly after it was buffeted the second time, the plane began a severe roll, banking sharply to the left as it began its nose dive. Investigators said the control wheel during this time was turned to the right, evidence that the plane was not responding to the efforts of pilots to bring it under control.

Investigators said they have not yet correlated the data recorder information with the cockpit voice recorder - a step that will provide a clearer picture of how the events unfolded.

After reviewing maintenance and inspection records of the plane kept after an encounter with turbulence that injured 47 people in 1994, investigators said no repairs to the plane had been warranted as a result.

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