LOS ANGELES -- It could be weeks or even months before aviation officials can say what caused the collision Friday night between a USAir Boeing 737 and a SkyWest commuter plane at Los Angeles International Airport.
But aviation safety experts outline three scenarios as the most likely.
"The jet that was landing could have landed on the wrong runway; you might have had the SkyWest taxiing in front of the 737; or youcould have had both airplanes doing exactly what they were told to do," said John Nance, a former commercial airline pilot and author of books on aviation safety.
"You [could] either have one or both airplanes in the wrong place," said Mr. Nance, who has landed 727s, DC-8s and 747s on runway 24-Left, the runway the USAir jet apparently had just touched down on when the collision occurred.
Two runways -- 24L (left) and 24R (right) -- are side by side, and both were being used for arrivals and departures Friday night.
"I've landed on 24L as many times as 24R, and sometimes the tower will have you sidestep to the next runway as you're coming in," Mr. Nance said, explaining that more often, 24L is used for departures.
Another scenario was offered by a longtime air-traffic controller who asked not to be identified. The 737, he said, might have "blown a tire [as it landed], then the pilot lost control of the plane."
A third scenario focused on the possibility that the commuter plane might have strayed onto the active runway. It was fueled by some broadcast reports that a member of the USAir flight crew claimed that the jetliner had made a successful landing when it struck the smaller aircraft.
Incidents where two planes end up on the same runway at the same time are called runway incursions. Though incursions rarely result in an accident, safety experts worry that the number of such incidents has increased.
"This has been an increasing problem," Mr. Nance said. The increase in airline traffic, outmoded voice control technology and poor, insufficient markings and lights on runways all play a part, he said.
The National Transportation Safety Board several times has made recommendations that it believes may help reduce the number of incursions, but some safety experts have questioned the speed with which the Federal Aviation Administration has acted to adopt those suggestions.
"The FAA has been responsive, but I'm always concerned about the lag time between NTSB making recommendations and the FAA adopting needed changes," Mr. Nance said.
"Over the years there have been quite a few runway incursions at LAX [Los Angeles International], and they do happen all over the country," said John Galipault of the Aviation Safety Institute.
"There's a spot on one runway right near the terminal at LAX where, if a pilot doesn't make a turn immediately but takes the second turn instead, he will be crossing another runway," Mr. Galipault said. The airport has posted stop signs and warning lights there, he said.
Of particular concern is a taxiway the commuter plane apparently had just left. The taxiway is west of the new Bradley terminal building at LAX. The terminal building blocks the airport tower's view of the taxiway, creating a blind spot.
"I'm familiar with the blind spot problem, and while you can't discount that, I would think the major problem is the single voice that we have controlling so many airplanes. It's one voice and 1938 technology," Mr. Nance said.
Eyewitness accounts, such as those broadcast shortly after the crash saying the 737 did not have its landing gear down, are generally unreliable, Mr. Nance said.