HAMPTON, Virginia (CNN) -- Reporters got their first look Friday at a tail fin believed to have played a significant role in last year's crash of a jet minutes after takeoff from New York. But researchers said they have not yet found the cause of the deadly accident.

American Airlines Flight 587 -- an Airbus 300-600 -- left John F. Kennedy International Airport about 9:15 a.m. EST on November 12 en route to the Dominican Republic. Less than three minutes later, the aircraft was a blazing inferno in the heart of a Queens neighborhood. All 265 people aboard were dead.

The tail fin and rudder of the plane sheared off as it accelerated, investigators said.

"Not only was it the second deadliest crash in U.S. history, but it also was the first example where we had an in-flight failure of a major structural component of an aircraft that in fact was made of composite materials," said National Transportation Safety Board (NTSB) Chairwoman Marion Blakey.

"This is really a new day, if you will, in terms of accident investigation."

Because of the difficulties inherent in the investigation, the NTSB has called on NASA to assist.

Blakey said that the investigators have ruled out engine failure, some kind of explosion or a bird strike as causes of the crash, and are following two main scenarios toward what they hope will be an explanation.

"Although there are a number of reasons ... that the vertical stabilizer could have separated from the aircraft, we can boil them down to really two major alternatives," Blakey said. "The tail fin separated either because it was subjected to aerodynamic loads that exceeded the design limitation, or because it didn't perform up to the design strength that should have been inherent in the structure."

After the initial phase of the NASA engineers' investigation -- what Blakey said was a "non-destructive examination," or NDE -- was completed, investigators cut pieces of the tail fin from undamaged sections for more in-depth examination.

But, Blakey said, investigators had not closed off any path that could lead to the cause of the tail fin's failure.

Investigation a 'meticulous' one

Jim Starnes, a NASA expert on the use of composite materials -- items made of a series of layers laid in a particular order and orientation -- said the use of such materials is likely not itself a cause of the crash.

"From a scientific basis, we've had 30 years of experience where we built aircraft," Starnes said. "I can see nothing that would suggest that using composite materials in a primary situation is not a good idea."

Blakey said the investigation is a "meticulous" one likely to take several months before a more concrete conclusion is reached. In addition to examining the structure of the tail fin, she said investigators will evaluate load stresses on both the aircraft and the crew using NASA-built models. A particular focus will be the wake vortices caused by a larger Boeing 747 that took off from JFK just before the Airbus.

Blakey cautioned reporters not to jump to conclusions when they saw the parts of the aircraft under examination at NASA's Langley Research Center.

"The damage is something that will give rise to a lot of theories," she said. "From our standpoint, there are a lot of questions. Was the damage the result of the separation from the aircraft? Was the damage pre-existing? Could the damage have occurred during the recovery?

"If it were that simple," she said, "believe me, we would have sorted it out by now."