Aircraft at Los Angeles International Airport came too close four times in the last month, a spate of incidents that officials attributed to human error and a record number of international flights.
The events, three of which occurred in the last week, are the first runway safety violations recorded at LAX since November.
"Given what we know so far, no one on any of these planes was really in any danger," said Donn Walker, a spokesman for the Federal Aviation Administration. "But we have pretty stringent safety parameters, and they were violated and that does concern us."
Federal aviation officials will investigate the incidents, and then the FAA will classify them as to severity.
In the most serious recent event, which occurred Sunday at 9:45 p.m., the pilot of a United Express jet bound for Santa Barbara had to abort his takeoff and slam on his brakes after a Continental Express jet moved too close to the runway.
Controllers told the Continental Express pilot, who had just landed on the outer runway on the airport's south side, to stop behind several sets of "hold bars" painted on a taxiway at midfield. He correctly repeated the instruction to controllers.
Then controllers cleared the United Express plane for takeoff on the inner runway. Moments later, they saw the Continental Express jet pass over the hold bars and stop about 39 feet from the edge of the runway. They ordered the United Express pilot to abort his takeoff. The United Express plane skidded to a halt by the Continental jet, with just 100 feet between them.
The other three incidents, which occurred since May 23, also involved aircraft crossing or moving too close to a runway where an airplane was readying for takeoff.
Two of those occurred on the south side and one on the north side.
"A combination of the increased flights and the outdated airfield layout -- that's what's driving the spike in runway incursions," said Paul Haney, a spokesman for the city's airport agency.
The events are a reminder that LAX has a reputation among pilots as a dangerous place to be on the ground. From 2000 to 2003, LAX led the nation in near misses between aircraft. From 1997 to 2000, the airport recorded 13 serious near crashes on the ground -- the most among the nation's busiest airports.
Near misses between aircraft have declined since airport officials launched an intensive campaign to educate pilots about the challenges posed by the airport's unique layout. The airport also added lighting and other warning signals on the airfield.
In 2003, LAX posted 11 incidents. Five were recorded in 2004, three of them in the same month last summer.
The airport has two sets of parallel runways, one pair on the north side and a second on the south. Airplanes that land on the outer runways must cross the inner runways, where jets take off, to reach the terminals.
The airfield's runway configuration can lead to confusion among pilots, who repeat controller instructions to stop well before the inner runway but sometimes fail to stop.
"Oftentimes that's the toughest one for us to catch," said Mike Foote, a controller in the LAX tower and local president of the National Air Traffic Controllers Assn. "When they actually read it back correctly, you start to move on and you leave that situation behind and you turn around and you realize the guy has actually crossed the runway."
The other recent incidents at LAX include:
* On May 23 at 8:13 p.m. a controller told the pilot of an American Eagle turboprop bound for San Diego to taxi into position on the inner runway on the south side and hold. The pilot correctly read back the instructions.
The controller then cleared an American Airlines 757 from Newark to taxi across the inner runway. The turboprop took off without clearance but was at least 4,500 feet from the 757.
* On Tuesday at 2:45 p.m., the pilot of a United 737 was told to wait behind the hold bars on a taxiway between the two sets of parallel runways on the south side. The pilot read back the instructions.
American Airlines flight 1606 was taking off on the inner runway when the United pilot told controllers that he had crossed the bars. The controller decided it was too late to abort takeoff. The American MD-80 came within 350 to 400 feet of the United jet.
* On Wednesday at 1:13 p.m., Southwest Airlines flight 2197 landed on the outer runway on the airport's north side. Controllers, distracted by an America West plane that was landing, cleared another Southwest jet to take off on the inner runway. During a mix-up, Flight 2197 came too close to the inner runway and at one point was 200 feet from the departing jet.
The number of international flights at LAX was up about 14% in May and June, according to the city's airport agency. Officials agree that additional flights can lead to more mistakes.
Officials hope to correct the problems on the airport's south side by moving the southernmost runway 55 feet closer to El Segundo and building a taxiway down the middle. That project is part of the first phase of an $11-billion plan to modernize LAX.
The city's airport agency plans to release an environmental study for the project in late July. Mayor-elect Antonio Villaraigosa has said he favors the first phase of the modernization plan, which includes this project.
Airport officials said they are concerned that the incidents mean that some pilots are still unaware of the dangers at LAX.
"After what's happened in the last couple weeks, we will have to get out there and start refocusing people on the problems," said Michael DiGirolamo, a deputy airport executive director.