UNDER SUSPICION Failure at the attachment points that held the Airbus' vertical stabilizer, also known as the tail fin, to the fuselage is evident in this NTSB photo of AA 587's tail fin recovered from Jamaica Bay.

Investigators wonder if a defect in the carbon fiber/epoxy composite tail--possibly related to earlier repairs or forces exceeding design limits--contributed to the accident.

Questions are also arising about composite materials, which entered flight-critical applications some 15 to 20 years ago and have been used increasingly ever since: Are composites subject to fatigue like metals are? Can delamination, where layers of carbon fiber fabric lose the resin matrix bond, lead to such failures?

Scott W. Beckwith, president of Beckwith Technology Group of Murray, Utah, and technical director of the Society for the Advancement of Material & Process Engineering, doubts fatigue led to the accident. He is not involved in the investigation. "Certainly with composites, fatigue is less of an issue than with metals," he says.

Michael Hoke, president of Abaris Training, a Reno, Nev.-based school for advanced composites fabrication, says delamination is a common problem in composites--like cracking is in metal--and isn't necessarily serious. But, he notes, "it is possible there was a defect in the structure that led to a failure."

The Federal Aviation Administration (FAA) has ordered the visual inspection of all Airbus A-300-600 and A-310 aircraft--both among the first planes to incorporate composite tails. FAA says possible warning signs include edge delamination, cracked paint, surface distortions, and other surface damage.

Hoke points out that more sophisticated techniques including ultrasonic, X-ray, and thermal-imaging methods do a better job of detecting delamination than visual inspection does.

But even these techniques can't detect what he calls "kissing delamination," where layers become unbonded but without a detectable air pocket. "If there was a problem like that, it would have been impossible to detect in the normal maintenance cycles on the airplane," he notes.

Flight 587 isn't an isolated incident. Hoke says composites have failed in military and homebuilt aircraft, but not in parts that are critical for flight. "To my knowledge, this would be the first failure of a primary structure that led to an accident," he says.

Beckwith adds that the crash of AA 587 may bring closer scrutiny to composites, just like the incident involving Aloha flight 243 in 1988, which made the airline industry more aware of metal fatigue and corrosion. "More attention will have to be paid to composites."

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