CHICAGO &

Air traffic control errors like the one that almost caused two airliners to collide near Chicago this week remain extremely rare and staffing levels are adequate despite controllers' complaints of fatigue and overwork, a federal aviation official said Friday.




The reassurance comes just ahead of the start of the holiday travel season and at a time when even the White House has publicly acknowledged the worsening problem of air congestion.




"These incidents are very, very rare," said Federal Aviation Administration spokeswoman Elizabeth Isham Cory, responding to questions about the near-collision between a United Express plane and a Midwest Airlines plane over northern Indiana on Tuesday night.




FAA air traffic controllers handled nearly 50 million flights in 2005, the last full year for which the agency provided statistics, and committed about 1,500 errors &

one for every 33,000 flights &

she said.




Evidence points to most of such errors occurring when a controller is handling fewer numbers of flights, Cory said, indicating there is no reason to expect an increased likelihood of errors during a hectic air travel period such as Thanksgiving week.




She also cited a 2003 FAA study that found 78 percent of errors happen when air traffic is light or average, with only 22 percent occurring when a controller is handling a higher workload of 11 to 15 flights.




"We're anticipating a very safe holiday travel season," she said. "We are currently in the safest period of aviation history, and we have every intention of keeping it that way."




However, Jeff Richards of the Chicago Center controllers association, said staffing levels have changed since the years of those statistics. And air traffic controllers in the Chicago region and elsewhere have said they were weary and more error-prone after having to work repeated six-day weeks.




Joseph Bellino, president of the National Air Traffic Controllers Association local for O'Hare International Airport, said chances are "pretty good" that the frequency of errors will increase at busy times &

especially now.




"Any time you have people on six-day work weeks, it always increases," he said. "It's like a major-league pitcher &

they can only throw so many pitches. You reach a point of diminishing returns. It's cumulative."




The Tuesday incident occurred at a time when the airplanes were being directed by the Chicago Center, a regional traffic control facility located in Aurora, Ill., that handles flights in an eight-state area when they are 14,000 feet and up. A collision between the flights at about 25,000 feet was avoided when a cockpit safety device in one of the planes alerted pilots, according to the FAA.




Officials said the controller directed the Midwest Airlines plane flying east from Milwaukee into the path of the United Express jet heading west out of Greensboro, N.C. The planes came as close as 1.3 miles apart horizontally and 600 feet apart vertically, according to the FAA. The mishap remains under investigation.




Cory said it happened amid a shift change during a busy time at the radar facility, which she said is adequately staffed. "Staffing is at the approved range for Chicago facilities," she said.




Richards disputed that and reiterated union assertions that the FAA was ill-prepared for the high number of retirements of seasoned controllers, resulting in a shortage. Three controllers a day are retiring nationally and three per month locally, he said. As a result of the stretched staffing, he said, the Chicago facility has had three errors since Oct. — after having only one all last year.




"These controllers are fatigued from working such long stints and very few breaks compared to just three years ago," Richard said in an e-mail.