Did Air France Flight 447 break up midair?

Some of the biggest pieces of debris found so far appear to be the plane's tail fin and vertical stabilizer. These parts are made partially of composite materials, and their failure has contributed to several crashes in the past. In the 2001 crash of American Airlines Flight 587, an Airbus 300 with a similar design to the A330, the vertical stabilizer snapped off in severe turbulence. One of the first questions investigators addressed was whether the composite materials used in the component contributed to the crash, according to Mr. Healing.

“The tail that broke off was a composite structure and was attached to the aircraft in six places. The lugs [some made of composite materials] holding it into place failed,” he says.

Healing was on hand in Germany when investigators tested the strength of one of those composite lugs, and he said it appeared to behave as it was designed to, which is called its “rated value.”

“That means that the lug was designed to be strong enough to withstand the forces it might see once in the lifetime of the aircraft,” says Healing. “That particular part failed at 192 percent of its rated value.”

That means it withstood twice as much pressure as it was designed to before it failed, and so such lugs are still being used in newer aircraft, like the A330, according to Healing. [Editor’s note: The original version used the wrong terminology for lugs in the preceding section.]

Composites less tested than metals

But some aviation analysts are less confident in the reliability of composite materials, in part because safety experts have not yet designed as many tests to determine whether this material has been compromised as they have for traditional metals like aluminum and titanium. Over the past 70 years, safety experts have designed a series of nondestructive methods of testing metals, using X-rays, dyes, and other techniques to find imperfections in the metal or cracks that could lead to a crash.

"We have a far less robust understanding of how composites may deteriorate," says Robert Mann, president of R.W. Mann & Co., an aviation consulting company in Port Washington, N.Y.

"The extent of our ability to find faults in composites is something called a tap test, believe it or not. We tap the part and if it rings true, then you say, 'Oh, it must be a good part.' But if you hear a kind of a thud, you say, 'Oh, maybe it has delaminated internally, maybe it's got a void or other problems internally."

Mr. Mann says when he saw the picture of the retrieved tail of Air France Flight 447, one of the first things he wanted to know was whether there was a parallel with AA Flight 586 and whether failure of the composite structures in any way contributed to the breakup of the plane.

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