Another jet's turbulence possible explanation for crash

NEW YORK -- Investigators raised the possibility Wednesday that turbulence from the wake of a 747 led to the crash of American Flight 587, saying the doomed plane took off less than the standard two minutes after the jumbo jet.

"We do not know whether this contributed in any way to the actual accident, but we are looking at this very closely," said Marion Blakey, chairwoman of the National Transportation Safety Board.

Wake turbulence, the swirl of air behind a plane, can endanger planes flying too close behind or below. The phenomenon has been blamed for at least one deadly crash in the past.

Investigators want to know whether it caused Flight 587 to break apart three minutes after takeoff from Kennedy Airport on Monday, killing all 260 people aboard and as many as five on the ground. The plane's tail assembly sheared away and its twin engines fell off as the jet went down.

Question of protocol

Standard protocol says there should be at least two minutes between takeoffs. However, Blakey said it appeared there was less than that between Flight 587, an Airbus A300, and a Japan Air Lines Boeing 747 that left ahead of it from the same runway.

"We believe that in fact it was 1 minute and 45 seconds," Blakey said.

She said it appears air traffic controllers followed proper procedure, and that tower clearances for the two takeoffs came 2 minutes and 20 seconds apart.

But investigators believe there was a delay from the time Japan Air Lines got clearance to take off and the time it actually did so, NTSB spokesman Ted Lopatkiewicz said.

Pointing to a map of the two planes' flight paths, Blakey noted that although the jumbo jet's path was 800 feet above Flight 587's, the winds probably pushed the turbulence lower.

Planes' proximity

The cockpit voice recorder from Flight 587's final minutes revealed two rattling noises and indicated the pilots complained about the wake of another plane before their aircraft went down.

Walter Sheriff, a retired American Airlines captain who studies the phenomenon, said the wake turbulence from the four-engine 747 could have struck the Airbus with "tornado-like lateral force."

The Federal Aviation Administration has set minimum distances for planes flying near each other, based on aircraft size. After a 1992 crash in Billings, Mont., that killed eight people, federal investigators found that the pilot failed to follow the established "vortex avoidance procedure" and flew too close to a jet.

Blakey, at a news conference, also said that Flight 587's other black box -- its flight data recorder -- was repaired by the manufacturer, allowing investigators to extract data on the last minutes of the doomed flight. The recorder had been scorched and banged up in the crash.

Both of the plane's engines have been recovered and taken to a hangar at Kennedy.

Authorities have not ruled out sabotage or other causes but have said all signs point to a mechanical failure.

"That does not mean we have concluded there was no crime. We simply have no evidence to date of a crime of terrorism," Attorney General John Ashcroft said.

The flight data recorder monitors nearly 200 separate functions in the European-made A300, including rudder movements.

"We'll be looking very carefully at how the tail failed," the NTSB's George Black Jr. said.

An FAA expert was headed to the site Wednesday to study the plane's tail assembly, an analysis that could lead to corrective measures or inspections. Blakey said American Airlines has also volunteered to do a sample inspection of its Airbus A300 fleet to ensure there are no problems with tail assemblies.

The tail fin was largely intact when it was fished out of Jamaica Bay, a short distance from the crash site; the rudder, in pieces, was found nearby. The rudder, which is supported by the tail fin, controls turns from side to side.