CHICAGO — When a computer system that distributes flight plans nationwide came rolling to a halt this week because of a software glitch, so did airplanes on tarmacs from Orlando, Fla., to Chicago. The ensuing delays drove home just how easily an apparently isolated problem can trigger network-wide disarray in the country's aging air traffic control system.

"It's aggravating to us ... over 600 flights were affected — which is about 60,000 people — because of one computer glitch," Hank Krakowski, chief operations officer of the U.S. air traffic system, told The Associated Press yesterday.

Most flights around the country were back to normal yesterday, a day after problems with the National Airspace Data Interchange Network computer south of Atlanta.

Those problems occurred during routine software work on the computer, one of just two in the country that play the vital role of distributing flight plans to controllers who monitor planes as they fly to their destinations, Krakowski said.

The Georgia center processes flight plans for the eastern half of the U.S, and a Salt Lake City computer normally handles the western half.

"We were doing a normal, daily software load that we do a couple times a day," Krakowski explained. "As we were doing the software load something got corrupted in the file, and it brought the system down."

The data usually handled by the Atlanta-area computer automatically switched over to the one in Salt Lake City. The Utah system was overwhelmed by the sudden surge of information — and could no longer process all the flight plans being filed and refiled.

No flight plans equals huge problems.

Unless they receive plans for all the more than 6,000 planes in the air at any one time, controllers don't know what route planes are taking or where and when they intend to land — posing safety hazards.

In a 24-hour period the FAA processes more than 300,000 flight plans in the U.S., according to that agency.

If computers stop distributing flight plans, airport controllers stop giving takeoff clearance to planes whose plans haven't been given out. That's what happened Tuesday afternoon.

The Atlanta computer system, which is about 20 years old, was already scheduled to be replaced later this year with a system with far greater memory, Krakowski said.

Even so, he said, Tuesday's problems illustrate that piecemeal upgrades of the air traffic network — which the FAA says has at least 40,000 pieces of equipment — are not good enough.

The FAA has been pushing for a long-term modernization that would include replacing the current method of tracking planes, using World War II-era radar technology, by switching to a satellite-guided system that equips planes with GPS.

"This is one of the largest project management challenges the U.S. government has had since we put somebody on the moon," he said. He called Tuesday's glitch "the poster child" for the FAA's modernization proposals.

The air traffic controller union said yesterday it supports modernization. But National Air Traffic Controllers spokesman Doug Church said the FAA appears too fixated on future technology and "has taken its eye off the ball when it comes to maintaining current equipment."

"We continue to lose confidence in the reliability of the equipment we are tasked to use to keep the system safe and efficient," Church said.

With one computer down and the other one overwhelmed on Tuesday, some controllers turned to serving as glorified secretaries, calling pilots on radios and then punching flight plans into computers and sending them out themselves, said Doug Pincock, an air traffic controller in the Salt Lake City area.

Those duties, he explained, meant controllers couldn't focus solely on getting planes in the air.

According to the FAA, 646 flights were delayed as a direct result of the problem.

The Georgia center began processing flight plans again as of 1:15 a.m. yesterday, FAA officials said.

Tuesday was not the first time problems there affected flights. A hardware problem Aug. 21 that officials said was unrelated to Tuesday's also resulted in problems in processing flight plans. The glitch that day delayed the departure of at least 134 flights, the FAA said.