Below is a meld (didn't want to use the word 'composite') of articles in the Nov. 15 NYTimes and Washington Post. Investigators are zeroing in on a vertical stabilizer composite failure as setting in motion the accident sequence. A question to be answered is whether the composite section had a pre-existing condition that caused it to fail below, or even much below, design limits. I was intrigued by Belgique's post in the A-300 engines thread. American tended to use the A300 in the tropical environment of its Caribbean and Central American services.
"The vertical tail section of American Airlines Flight 587 cracked off when its modern reinforced plastic "composite" fittings failed, investigators said today, and the National Transportation Safety Board
announced that American will inspect the tail section of all its similar Airbus A300-600 widebody planes. The Federal Aviation Administration said it was dispatching its chief scientist to examine the composite materials as well.
"Safety Board Chairman Marion Blakey said there was no evidence of physical damage to the vertical tail fin, which was recovered from Jamaica Bay soon after the Airbus crashed into a Queens neighborhood Monday.
"But she presented radar data indicating that wake turbulence from a Japan Airlines 747 that took off just before Flight 587 could have hit the American widebody. The 747's path was to the west and about 800 feet higher than the A300's, she said, with the wind blowing from the northwest at about 12 mph.
"Because the swirling winds that flow from an aircraft's wingtips tend to move down slightly and drift with the wind, the aircrafts' paths "would be consistent with a wake vortex encounter," Blakey said.
"But board member George Black said he was unaware that any civilian aircraft had ever lost a vertical tail fin to wake turbulence.
"Investigators could not explain what outside force, combination of forces, human error or aerodynamic forces could have produced enough force to rip the vertical tail fin and rudder off the plane and rip both engines from the wing.
"The board last night released some preliminary data from the recovered flight
data recorder indicating that the vertical tail fin came off first. Both engines continued to operate normally for a short period after the crew said on the cockpit voice recorder that they had lost control.
Investigators at first believed the plane landed nose-down -- because of the lack of wider destruction that would have resulted had it hit the ground at a shallower angle. That did not explain, however, why they found so many intact or nearly intact bodies so quickly.
"Several sources now believe the explanation may be the speed of descent. The plane, they believe, having lost its heavy engines and vertical tail, made a relatively slow belly flop, nose tilted down and turning sideways. Its engines were found about 800 feet away --with the left and right engines exactly
opposite to where they would have been attached to the plane, indicating the plane might have been upside down or flopping around.
"Blakey announced American's planned inspection of all 24 of the tail fins on its Airbus A300-600 fleet.
"Officials with Airbus, the European manufacturer of large airplanes, were
discussing whether to advise other airlines to do the same.
"She [Blakey] also said the FAA was sending its chief scientist to the Flight 587 scene to study the possible relevance of composite materials. FAA spokeswoman Laura Brown said that if the scientist and other FAA officials find that more inspections or corrective actions are needed in other parts of the aircraft industry, "the FAA will mandate that immediately."
"Hans Weber, an airline engineering expert in San Diego, said most airliners still have metal tails. He also said that although the composite tails on Airbus planes are made with carbon fiber, the composition of that fiber has been constantly evolving as the plane maker tries to keep costs down.
Composite tail structures are five times more expensive than aluminum -- $1,500 a pound compared with $240 a pound.
"The tail was torn off, leaving the attachment points, which are made of the same composite, still bolted to the plane's
metal frame, investigators said. They have not found any evidence that an explosion or contact with another object in flight caused the damage.
"Among the questions for investigators are
whether the fin separated because of stresses that its design should have been able to handle or if the plane, in the air less than two minutes on a day with light winds and clear air, somehow encountered extreme air conditions.
"Airbus, far more than Boeing, its main rival, relies heavily on composite materials, to save weight and to avoid
corrosion. Experts say that composite materials are stronger per pound than aluminum, and are less prone to fatigue, in which repeated flexing weakens the material.
"But composite materials also can weaken. Sometimes the reinforcing carbon comes lose from the matrix that forms the bulk of the composite, or layers come apart, a process
called delamination.
"According to the maintenance log recovered from the crash site, there had been no major repairs recently, and no items awaited repair.
"The fittings that hold the fin to the fuselage are visually inspected every five years; the most recent inspection for the plane that crashed was in December 1999.
"Before the plane was delivered in 1988, the composite material in one of the six fittings holding the tail in place was found to be delaminating, meaning its layers were
coming apart. It was fixed by adding layers and inserting rivets, and the manufacturer decided that no extra inspections were required afterward.
"One new area for investigators is the composites, which are harder to read for clues than metal parts. They have been
used for years, but usually in doors or panels, not in the plane's skeleton. American Airlines will use a variety of
inspection techniques, including a tap test, in which technicians hit the part and listen for sounds that would indicate a void, said Thomas Haueter, the board's deputy chief of aviation safety.
"The carbon and plastic composites used by aircraft manufacturers tend to be extremely strong and resistant to cracking, and were strenuously tested, Robert T. Bocchieri
said. Dr. Bocchieri is an expert in assessing failures of composite materials and a senior engineer at Applied Research Associates, an engineering firm in Sunnyvale,
Calif.
"Cracks develop in metals or plastics as they age, but cracks tend to be stopped in these materials by the embedded fibers, he said. Still, "aircraft makers have tended to be extremely conservative in their use of
composites," he said.
"Because the materials, when proposed for airliners, were intended for a new domain in which hundreds of lives were at stake, they "were put through massive numbers of cycles of full-scale testing," Dr. Bocchieri said. "They had to simulate the entire life history of the aircraft."
"Airbus has made progressively greater use of composites. It plans to expand their use even further in its A380 superjumbo jet. According to Airbus, each A300 uses 14,600
pounds of composites, and by doing so, saves 3,300 pounds of weight.
"The fin of the A300 is almost all composite. Mr. Black said yesterday that when it was pulled from Jamaica Bay, the fin looked good.
""With the exception of the area where it separated, it is almost in new condition," he said.
"Both the fin and the rudder, the movable panel at the back of the fin, can float, he said. Aviation experts said that both could have traveled a significant distance from the
spot at which they separated from the plane. Thus, although they were found closer to the airport than the main wreckage, investigators are not certain that they were the first to come loose."