A Workhorse of the Skies, Perhaps With a Deadly Defect
By MATTHEW L. WALD and AL BAKER
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The carbon-and-plastic composites used by aircraft manufacturers tend to be extremely strong and resistant to cracking, and were strenuously tested, said Dr. Robert T. Bocchieri, a senior engineer at Applied Research Associates, an engineering firm in Sunnyvale, Calif., and an expert in assessing failures of composite materials.
Cracks that develop in metals or plastics as they age tend to be stopped in these materials by the embedded fibers, he said. Also, "aircraft makers have tended to be extremely conservative in their use of composites," he said.
And the materials, when proposed for airliners, were "put through massive numbers of cycles of full-scale testing," he said. "They had to simulate the entire life history of the aircraft."
Boeing also now makes extensive use of composites, and its proposed Sonic Cruiser would carry the trend even further. Some aviation experts say that Airbus has been more aggressive than Boeing in employing composite materials, but Boeing officials deny that.
Back in 1987, when Airbus was leading the way with composites, American ordered 35 A300's, and sent them out on popular routes between New York and Miami to the Caribbean, Boston and New York to London, and Miami to Central and South America — the short, fat runs, as they are known among industry insiders.
National Transportation Safety Board
Investigators have been looking at whether a composite material used in the tail fin of American Airlines Flight 587 played a role in its crash.
American Airlines purchased N14053 because it was determined to be a good fit for its trips to the Caribbean. Passengers on those flights often check in with lots of luggage, and the A300 has large bays and cargo holds for their belongings.
"I can tell you that one of the reasons we bought it was because it was a very good candidate for flying from J.F.K. into the Caribbean," said John L. Hotard, an American Airlines spokesman.
It turns out, though, that N14053 needed a repair to its composite tail fin even before it was delivered by the factory in Toulouse, France, on July 12, 1988. The layers of the tail fin had begun to come apart from within one spot, where the tail connects to the plane's fuselage. It was repaired by adding extra layers of composite and binding the area with rivets.
When the manufacturer delivered the plane, it said no further inspections of the part were required. The good news was that the defect, called delaminating, was discovered. But the problem showed that composite can suffer from flaws in its fabrication. That part of the tail that was fixed appeared to be intact when the tail was examined after the crash.
Now, investigators are looking at the other points where the tail connected to the fuselage to determine if flaws similar to the first one had developed. The question is whether the composite fin was designed or built with a flaw that developed into a weakness, was damaged over time, or somehow encountered forces greater than it was designed to handle and ripped away from the plane's spine on a routine climb.
For much of its flying life, American reported various problems with N14053 to the F.A.A., but these were typically minor things — like broken aisle floor lights, and a warning of low fluid levels in the hydraulic systems that was apparently the result of a problem with a sensor.
There were also incidents of smoke and odors in the plane, which forced the plane to land, that were traced to problems with the equipment that provided air to the cabin. The problems were repaired, records indicate.
But perhaps its most interesting in-flight experience happened in 1994, when it had a jarring encounter with turbulence. In the air near Puerto Rico, the plane shook so violently that 47 passengers were injured.
Planes are built to handle extraordinary encounters with turbulence; even turbulence strong enough to kill people on board is often not enough to approach damaging the airframe. But it is also possible for turbulence to do damage to a plane, and some safety experts wonder if damage went undetected.
American conducted a visual inspection of the plane immediately after the 1994 incident and found no structural damage. But another question for experts is whether the inspection could have missed any damage that might have showed up under more intense inspection.
When Flight 587 rolled down runway 31L at Kennedy International Airport last Monday shortly after 9 a.m., it weighed 350,000 pounds, including 63,000 pounds of fuel, passengers and cargo. Inside it was roomy enough, with its decks removed, to drive an 18-wheel truck into it.
On the ground, Abraham Farber, 40, a finance manager, was driving west to work along Beach Channel Drive in the Rockaways. Suddenly, in the open sky over the tops of houses, he saw what looked like "a jet engine plop out of the sky."
"I looked up and I saw the first engine come down, followed by another within two seconds after that," said Mr. Farber, who told his story to the police and the F.A.A. "Moments later I saw a fireball erupt from the area of impact several blocks in. It was so surreal."
He and another man got out of their cars. Shards of aluminum and other debris started raining down. N14053 had come apart in midair. |
