Whether the cause was terrorism or a massive mechanical failure, the fire and explosion that brought down American Airlines Flight 587 over a quiet neighborhood in New York's borough of Queens dealt a huge setback to the aviation industry.
Reeling from the unprecedented events of Sept. 11, the nation's airlines had been slowly winning back confidence - and customers - with pledges of tighter security. President Bush on Friday called up more National Guard troops, a move designed to bolster confidence at airport checkpoints for Thanksgiving. Most flights were taking off almost full, even though the airlines were still operating with a reduced schedule.
So when the Airbus 300-600, a plane with an excellent safety record, went down Monday morning with 255 people aboard, the shock rattled the whole industry.
"It couldn't have come at a worse time. The carriers are already in weak condition," says Richard Gritta, an aviation economist at the University of Portland in Oregon. "It's like watching a prizefighter get hit over and over again. You wonder how much more they can take."
How the flying public reacts to Monday's crash will depend in large part on the cause. If terrorism does turn out to have played a role, confidence in the security of commercial aviation will have been vastly undermined - demonstrating that terrorists can, if fact, still bring down a plane. If the cause turns out to be mechanical, the public response may be more muted and the cutback in flying less severe.
"Whether it's just the normal temporary setback in traffic, or whether it's going to be substantial, depends on things we can't know yet, because we've never been through anything like this before," says Aaron Gellman, a transportation expert at Northwestern University in Evanston, Ill.
As of this writing, aviation and government officials said there was no indication that terrorism was involved. But they were also not ruling it out.
Witnesses say the plane, which was headed to the Dominican Republic from Kennedy Airport, appeared to have a normal takeoff. Then fire burst from the area around the right wing, there was an explosion, and the plane nose-dived. The engine and possibly part of the wing landed separately from the rest of the plane, which was engulfed in fire and heavy black smoke.
"It could have been an engine problem, trouble with the wing, or a bomb in the hold," says one aviation expert, who asked not to be identified. "Whichever way, it has serious implications."
American Airlines has 35 Airbus 300-600s, which fly predominantly to Europe and the Caribbean. While the model has been involved in five crashes since 1988, all have been overseas. Witnesses to the Monday morning crash say the engine appeared to separate and fall from the rest of the plane.
In 1979, an engine did fall off an American Airlines DC-10. At the time, there was concern over the integrity of the plane itself. But investigators for the National Transportation Safety Board and Federal Aviation Administration later determined the cause to be a maintenance practice that inadvertently weakened the metal around the engine. That practice has long since changed.
"If it turns out that this was a mechanical failure of some sort, people may be reluctant to fly that kind of aircraft for a while - like they were with the DC-10s," says Clint Oster, an aviation economist at Indiana University.