If Not Terror, What Was It?

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The release on Thursday of information gleaned from the flight-data recorder added support for the theory that the pilots might unintentionally have magnified a relatively minor problem. The jolts that swung the aircraft side to side appear to have been caused by the pilots. "Pilot-induced loads," says NTSB investigator Tom Haueter, "were higher than the wake loads." The rudder was "deflected" 10[degrees], according to the NTSB. Most pilots interviewed last week said a rudder should only be deflected, or moved, a few degrees. Sources told TIME that the rudder may have been jammed even farther over than the NTSB is publicly acknowledging.

In 10 of 15 fatal Airbus accidents prior to AA 587, crew confusion regarding the Airbus computer systems was considered to be a factor. After some of those accidents, Airbus made changes in software or its suggested procedures so that in extreme conditions the crew can override some of the planes' automated systems.

The Airbus A300 that crashed was a middle-age jet delivered to American in 1988, meaning it was not completely fly-by-wire (i.e., computer controlled), and clearly the pilots were the ones doing the flying, not the autopilot. But there have been incidents in which the onboard computer programs have frozen just as the ones in your personal computer do. In May 1999, an American Airlines plane experienced what is called "uncommanded" rudder movements, jamming the rudder pedals. The pilot used other controls to land the plane.

Airbus has also been at the forefront in replacing metal with carbon-fiber composite materials--the materials that constituted the failed tail fin. The tail section of the A300 is made with a composite of plastic reinforced with carbon fiber. Composites have properties of strength and flexibility that are in some cases better than those of metal. The sophisticated U.S. B-2 Stealth bomber is made with composites and can withstand G forces in excess of those that commercial jets are designed to handle.

Composite parts, however, can be weakened by manufacturing flaws, by water seeping in between layers or by direct impact. And the NTSB won't yet exclude sabotage as a possible cause of the crash. Although most security experts say it would be extremely difficult for someone to loosen screws on the tail assembly or damage it in some way, investigators haven't ruled out those possibilities. "People are acting almost as if this airplane was randomly designed," says Paul Czysz, a professor at Parks College of Engineering and Aviation at St. Louis University. "It was fatigue tested, and I'm sorry, but it just doesn't come apart like that."

So as the NTSB continues its investigation, the flying public is left with several possible causes of the crash of Flight 587, none of them particularly reassuring. Flyers will do well to keep in mind more comforting data: 610 million passengers boarded 9 million domestic commercial flights last year, and all but 87 made it home. That's a far lower accident rate than the one for Americans who drive to their holiday destinations.