Crash investigators are paying special attention to a single section of the tail fin that snapped off American Airlines Flight 587 because it may show evidence of previous damage.
The carbon-fiber piece has a series of cracks that do not appear on the other five points that snapped between the tail and the fuselage, sources familiar with the investigation told USA TODAY.
Investigators and experts familiar with composite materials like the one that broke on the jet caution that it is too early to say whether the cracks were on the tail before the crash or resulted from the tail being wrenched from the jet. But if the cracks were present before the accident, it could help explain why the vertical tail fin flew off the Airbus A300, sending it spinning out of control.
Flight 587 crashed Nov. 12 less than 2 minutes after taking off from John F. Kennedy International Airport on a flight to the Dominican Republic. All 260 people aboard and five local residents on the ground died.
The jet was buffeted by relatively minor turbulence, and later swung sideways sharply three times. But National Transportation Safety Board (NTSB) officials have said that these forces should not have been severe enough to structurally damage the jet's tail fin.

Some kind of pre-existing damage had weakened the tail, which allowed it to break loose. The jet did encounter a major turbulence incident in 1994, but American Airlines inspected it afterward and found no damage. The tail design was not strong enough. However, Airbus extensively tested the tail and subjected it to severe stresses that exceeded what the company believed it would receive in flight. Some force that investigators have not yet identified caused the tail to snap. In theory, an unusually strong gust of wind could break the tail, though investigators have no evidence this occurred and consider it unlikely. 
Similarly, the jet's rudder, which moves the nose right and left, swung sharply several times shortly before the tail section came loose. It is possible that the pilots moved the rudder too much in response to earlier turbulence and those rudder movements created forces that damaged the tail. Jets are built to withstand the most extreme rudder movements to one side. But some experts worry that swinging of the rudder from side to side could cause stresses that designers had not anticipated.
The vertical fin, which helps a jet fly straight and stable, had been attached at six points at the top of the fuselage. At most of those points, the fin's carbon-fiber plastic material tore off just above where it was bolted to metal attachments on the fuselage.
But on the front left attachment, the carbon-fiber material broke at the area where the bolt is located. And, unlike the other five attachments, the material contains a series of cracks near the breaking point. Such cracks could indicate "delamination," which occurs when the multiple layers that make up the material begin to separate. Delamination can significantly weaken the material.
As work on the investigation transfers from New York to Washington, experts both in and outside the NTSB will begin inspecting the material to determine whether delamination could have played a role in weakening the structure.
Paul Lagace, a Massachusetts Institute of Technology professor who is a specialist in the composite materials that severed, cautioned that it takes long and careful examination before scientists can determine whether delamination caused a break or occurred as a result of the structure coming apart.