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Jet Likely Ran Into Wake Turbulence

Crash: NTSB analyzes the paths and altitudes of Flight 587 and the jetliner ahead of it. Airline to inspect its A300 planes for possible tail fin flaws.


NEW YORK — American Airlines said Wednesday it will begin inspecting its Airbus A300 jets for possible weaknesses in their tail fins as evidence mounted that Flight 587 ran into turbulence from a larger plane shortly before it crashed.

The American Airlines jet is now believed to have been closer than previously thought to a Japan Air Lines Boeing 747 that had taken off one minute and 45 seconds earlier, National Transportation Safety Board investigators said. Nonetheless, at four to five miles apart, the two planes were still within prescribed separation standards.

NTSB Chairwoman Marion C. Blakey said the flight paths and altitudes of the two planes, coupled with wind speed and direction, "would be consistent with a wake vortex encounter."

Wake turbulence is invisible, caused by horizontal tornadoes that spin from the wings of a larger aircraft. It is a long-recognized cause of control problems for pilots--but usually in smaller aircraft. The phenomenon was blamed for the 1994 crash of a private jet that was following a much larger Boeing 757 landing at John Wayne Airport in Orange County. All five people aboard the business jet died.

Meanwhile, the Federal Aviation Administration said it had sent its chief scientist to the accident scene and stood ready to mandate inspections or other corrective actions at any sign of a tail fin problem that might affect other aircraft. There are about 430 of the twin-engine, wide-body A300s in service around the world.

NTSB investigators also began reading information from Flight 587's data recorder, after resolving an initial problem caused by crash damage. The recorder provides a detailed history of the flight, logging information on more than 100 technical aspects, including power and flight control settings, engine performance, altitude and gravitational forces. The device on the A300 uses the latest digital technology.

Although investigators have not yet established that turbulence caused Flight 587 to crash, the plane lost its tail fin after apparently encountering such a disturbance. It plunged into a residential neighborhood in Queens in a fiery crash Monday that killed 265 people.

The loss of the tail fin as the plane was climbing would have made it virtually impossible for pilots to keep control. The combination of events involving a jet taking off, potential wake turbulence and the loss of the tail fin is virtually unheard of. "There's certainly nothing in our database like this accident," said NTSB member George Black.

The only previous commercial plane crash involving a tail fin failure occurred in 1985. However, the circumstances were much different. The tail fin of a Japan Air Lines Boeing 747 was heavily damaged after the plane suffered a sudden loss of cabin pressure en route from Tokyo to Osaka.

A portion of the fin is believed to have fallen away, but the pilots were unaware of the extent of the destruction. All they knew was that many of their controls were suddenly inoperative. The plane flew in circles before crashing into the side of a mountain, killing 520 people. Five people survived.

NTSB investigators said Flight 587 and the Boeing 747 that took off ahead of it on Monday morning flew nearly parallel paths. The Japan Air Lines jumbo jet became airborne about one-third of a mile farther down the runway, and turned left over Jamaica Bay. Flight 587 followed, also taking off into the wind and making a left turn. Its flight path put it about 800 feet below and several hundred yards downwind from Japan Air Lines Flight 47, which is significant because wake turbulence tends to sink and move with the wind.

Air traffic controllers do not appear to have made an error in the spacing of the two flights. "We're not seeing a pattern that would indicate an air traffic control problem," Blakey said. Nonetheless, the position of the two planes and comments captured by the cockpit voice recorder indicate that Flight 587 probably ran into wake turbulence.

Under any normal circumstance, such turbulence should not have caused an aircraft to lose a tail fin.

"If the vertical fin failed, that is a very serious structural problem, and that is a gross understatement," said a former government air crash investigator who asked not to be identified by name.

The tail fin--known as a vertical stabilizer--is made of a composite material that is lighter and stronger than most metals. It is secured to the fuselage by six sets of fittings. Fittings on the fuselage and on the tail fin are bolted together.

Two sources close to the investigation said that the tail fin broke off above the area where bolts connect the two sets of fittings. The fittings on the fuselage are steel, while the fittings on the tail fin are made of the composite material. The tail fin appears to have torn away near the composite fittings.

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