Growing evidence yesterday suggested that the tail fin of American Airlines Flight 587 broke from the plane, initiating the aircraft's rapid downward spiral two minutes after it took off from John F. Kennedy Airport on Monday.
Based on radar records, investigators have carefully mapped the flight path of the aircraft, as well as that of a Japan Airlines 747 that took off from Kennedy just ahead of it.
The proximity of the two planes is consistent with a condition called "wake turbulence," in which swirling masses of air from the first plane trail downstream and can create problems for planes nearby. Investigators said they were exploring whether turbulence could have been sufficient to tear off the plane's tailpiece.
A review of the cockpit voice recorder showed that seven seconds after hearing a loud rattling, one of the pilots made a comment about a "wake encounter," investigators said. The pilots struggled for control of the plane, but it made a steep nose dive and crashed 30 seconds later, killing more than 260 people.
Investigators said they expect information retrieved from the plane's flight data recorder will reveal whether such turbulence was a factor.
"We don't know if it contributed in any way, but we are looking at it closely," said Marion Blakey, head of the National Transportation Safety Board.
Earlier yesterday, investigators feared the plane's "black box" had been too badly damaged to yield its detailed records of the aircraft's flight. But after sending the recorder to its manufacturer in Florida for repair, investigators began receiving readouts from it yesterday afternoon.
The development meant more progress for an investigation that is collecting evidence rapidly.
The two engines, which detached from the Airbus A300 as it descended, were taken yesterday on flatbed trucks to a hangar at Kennedy for shipment to an FAA investigation site in Tulsa, Okla.
A closer review of the cockpit voice recording yesterday showed that the engines were still running after pilots expressed difficulty controlling the plane.
And while there is still no evidence that terrorism played a part, investigators continue to look for such clues.
Attorney General John Ashcroft said that about 130 FBI agents assigned to the crash investigation have interviewed more than 200 witnesses and more than 70 airline and airport workers connected with the flight.
FBI explosives experts are combing the crash site and wreckage for any traces of residue from any explosive device. Agents also are reviewing the list of passengers and crew members.
Those steps are standard for a large-scale crash investigation, and the NTSB remains the lead agency, said Ashcroft.
"We're actively investigating all possibilities, including terrorism," he said. "To date, we have not found any evidence that this was anything other than a tragic accident."
NTSB investigators continued yesterday to follow a checklist of possible causes that include human error, weather and engine malfunction. But their focus clearly is on the aircraft's tail.
Additional clues bolster the theory that the plane's demise began when the tail somehow detached. Evidence shows it was sheared cleanly from the plane.
Parts of the aircraft were found along a direct line - beginning in Jamaica Bay, where an upright section of the plane's tail was recovered, to the neighborhood of Queens hit by the fuselage.
The sites where the tailpieces, including the vertical stabilizer and rudder, were found corresponded approximately with the point where Flight 587 lost radar contact, investigators said.
There was no evidence on the exterior of the stabilizer that it had been struck by another part of the plane or by some foreign object that might have knocked it off, investigators said.
"I want to stress that we do not know the specific facts beyond this," Blakey said. "All we can do is observe the phenomena here. Beyond that we'll have to wait and see."
The stabilizer is made of a carbon-based composite, and Blakey said the FAA's chief scientist on composite structures was en route to New York to assist in analyzing the evidence.
Airbus officials said the results of that analysis would dictate whether widespread inspections will be made or corrective measures taken. Officials said the company is poised to inspect its entire fleet for flaws, if necessary.
Despite the possibility that air flows from one plane might have disrupted the flight of another, Blakey said evidence indicated that air traffic controllers had kept the planes the required distances apart.
Investigators also said they are looking at the plane's maintenance history, particularly work done after an encounter with severe turbulence seven years ago during a flight from Barbados to Puerto Rico.
In the Nov. 28, 1994, incident, the plane had just reached a cruising altitude of 35,000 feet when it hit turbulence so strong it sent the nose of the plane up and down, injuring 47 of the plane's passengers and crew members.
Though the plane has undergone major maintenance since then - the latest in December 1999 - aviation experts say the earlier turbulence could have created some unnoticed cracks.
"Certainly the investigators need to take a look at that to see if there is any damage that went undetected," said Tom Ellis, a spokesman for the Nolan Law Group, a Chicago firm that represents victims of airline accidents. "With any maintenance, there is always the possibility of human error."
The loss of a tail fin in flight is extremely rare. Most forces exerted on an aircraft are from front to rear. The tail fin is designed to flex from side to side. But whether it could be snapped off by a lateral force is unclear.
Sun staff writer Gail Gibson and wire services contributed to this article.