About 1,120 flights were canceled Tuesday at Chicago's two major airports after an electrical problem sent smoke into a regional radar facility's control room, forcing officials to temporarily halt all air traffic at one of the busiest U.S. aviation hubs.
The Federal Aviation Administration said all personnel were evacuated from the radar facility in suburban Elgin at about 11:30 a.m. They were allowed to return about three hours later.
Read More All incoming and outgoing flights at Chicago airports halted
The Chicago Department of Aviation said a limited number of landings and departures had resumed by late afternoon.
Elgin Fire Capt. Anthony Bialek said a bathroom exhaust fan in a ceiling overheated and melted insulation on some wires, and smoke was pushed through the facility's ventilation system and into the control room.
Bialek said it took about an hour to find the source of the smoke at Chicago Terminal Radar Approach Control, or TRACON. There were no injuries.
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Controllers at the TRACON facility are responsible for managing the region's air traffic as it leaves and approaches all of the area's airports. Once an aircraft is within about 5 miles (8 kilometers) of an airport, TRACON workers hand over control to that airport's tower.
Inbound flights already in the area at the start of the shutdown were handled by a backup air traffic facility in the city of Aurora, just west of Chicago. Some flights were diverted to other airports.
Aerial TV footage Tuesday afternoon showed a large backup of aircraft along taxiways at O'Hare International Airport. Inside the terminals, people trying to rebook on later flights formed long lines.
As of about 3:30 p.m., arrivals at O'Hare were about 75 percent of normal—72 an hour compared with the normal of about 106 per hour, said Doug Church, a spokesman for the National Air Traffic Controllers Association, the union that represents controllers. Departures were operating normally, he said.
O'Hare is the second-busiest airport in the country by numbers of passengers and is a major hub. Around half of passengers there are connecting to other flights.
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Any disruption to its operations has an enormous ripple effect on the nation's aviation system.
The Chicago Aviation Department said departures were delayed about 90 minutes late Tuesday at O'Hare and 2½ hours at Midway International Airport.
A computer glitch at a similar facility last month forced a 45-minute shutdown at Los Angeles International Airport.
—By The Associated Press