The Associated Press
CHICAGO Ÿ Flights across the country were temporarily halted after the main computer at the Federal Aviation Administration's Midwest air traffic control center failed again Tuesday.
Air traffic controllers say two planes flew too close to each other because of the outage.
It was the sixth major computer breakdown in the past year to disrupt air traffic in the six-state region where up to 9,500 flights a day are controlled by the FAA's air traffic center in suburban Aurora.
Until the primary computer was restored, the region was put on a backup computer that lacks an alarm to alert controllers when planes get too close to each other.
Dennis Burke, the center's air-traffic manager, said the close call occurred an estimated 30 to 40 miles east of Moline, Ill., at 8:22 a.m., when an alarm went off on an American Eagle plane bound to O'Hare International Airport from Des Moines, Iowa.
The pilot, realizing another plane must be too close, contacted an Aurora controller, who verified that a private twin-engine plane was only 700 feet above and 31/2 miles apart from the American Eagle, which promptly descended.
Planes are supposed to keep five miles apart laterally and 1,000 feet vertically.
Ron Downen, local vice president for the National Air Traffic Controllers Association, criticized the lack of an alarm on the backup system. ''Your margin of error without that is zero,'' he said.
But FAA regional spokesman Don Zochert said the controller still could have seen the planes' location on his computer screen.
Air-traffic control specialist Dave Cottingham acknowledged the information is available, but said, ''A controller, being human, cannot control and see all situations at one time.''
Asked if he would put his family on a plane under the circumstances, Cottingham said he wouldn't, adding, ''I've got a perfectly good car.''
FAA Administrator David R. Hinson said in Washington that technicians in Aurora believe they have corrected the primary computer's problem, but would continue operating on the backup until Tuesday night. Technicians hope to complete the switch back to the main system before dawn Wednesday.
Chicago-bound flights were grounded at airports across the country for about 40 minutes, beginning around 9:24 a.m. Tuesday, while controllers dealt with the computer problems, said Lisa Howard, spokeswoman for the city Aviation Department.