An electronic warning system designed to prevent planes from colliding on the ground was switched off Sunday night at Chicago's O'Hare International Airport when a passenger jet lifted off above a cargo plane that had just landed on an intersecting runway.
United Airlines Flight 1015, a Boeing 737 carrying 120 passengers to Denver, came within 200 to 300 feet of an Atlas Air Boeing 747 about 10 p.m., according to federal aviation agencies.
The incident was the fifth such near-collision on O'Hare's runways this year. O'Hare has had about 540,000 flights this year, the most of any airport in the world.
A preliminary review indicated that a controller who was overseeing flights on both runways improperly cleared the United jet for takeoff without waiting for the cargo jet to move out of its path, said Laura Brown, Federal Aviation Administration spokeswoman.
The safety system that tracks planes on the airport's runways was not set to sound an alarm at the time of the incident, said Lauren Peduzzi, a spokeswoman for the National Transportation Safety Board. The NTSB sent an investigator to Chicago Tuesday, the second time this year the accident investigation agency has dispatched a team to the airport to study near-collisions.
The alarm was shut off because the FAA is attempting to enhance the system and was training controllers how to use the upgrades, Brown said. It is not clear whether the system could have prevented the incident Sunday night or made it less risky, she said.
The number of serious near-collisions on the nation's runways has fallen in recent years as the FAA has encouraged airports to improve runway lighting and urged pilots and controllers to be more cautious.
The potential for planes to collide on runways nonetheless remains one of commercial aviation's biggest safety problems, according to government and industry experts.
The problems with the warning system also highlight the slow progress in finding a solution.
"This incident is another example of the status quo not being good enough," said John Cox, a former airline pilot who works as a safety consultant.
Current technology can give pilots and controllers warnings before runway collisions, but the government needs to mandate it as soon as possible, Cox said.
The system at O'Hare, known as AMASS, has been riddled with problems. It relies on radar to track planes on or near the ground and sounds an alarm if two planes come too close.
Controllers complain that it often sounds false alarms and does not work in bad weather, when they need it most. AMASS is used at 33 other airports.
"It doesn't work very well," said Joseph Bellino, president of the National Air Traffic Controllers Association at O'Hare. "I think it's an absolute waste of money."
Bellino said the warning system is almost never switched on at O'Hare because it is so prone to errors.
A newer warning system that issues fewer false alarms and is not affected by bad weather has been installed at seven airports. The installation schedule, however, has been slowed by budget cuts. O'Hare is among the airports scheduled to receive the newer system.
The worst accident in aviation history involved a collision on a runway. On March 27, 1977, two Boeing 747s slammed into each other on a Canary Islands runway, killing 574.
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