Why 500 flights out of Chicago were cancelled

An electrical fire at an air traffic control facility near Chicago, halted all flights at O'Hare and Midway airports Tuesday afternoon and shutting down one of the nation's busiest aviation crossroads.

An electrical fire triggered by a faulty bathroom exhaust fan forced the evacuation of an air traffic control facility near Chicago, halting all flights at the city's two airports and shutting down one of the nation's busiest aviation crossroads.

Controllers were allowed to return to the facility in suburban Elgin about two hours later, but it was not immediately clear when flights would resume.

Elgin Fire Capt. Anthony Bialek said a bathroom exhaust fan in a ceiling overheated and melted some wires and smoke was pushed throughout the facility's ventilation system.

The Federal Aviation Administration said all its personnel were evacuated from the Chicago Terminal Radar Approach Control, or TRACON, facility at around 11:30 a.m.

Bialek says it took about an hour to find the source of the smoke. There were no injuries.

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 showed a large backup of aircraft along taxiways at O'Hare. Inside the terminals, people trying to rebook on later flights formed long lines.

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 of an airport, TRACON workers hand over control to that airport's tower.

Chicago Department of Aviation spokeswoman Karen Pride said she has not yet gotten word on whether flights have resumed.

The FAA did not have an update.

O'Hare airport is the second-busiest in the country by numbers of passengers and is a major hub. Around half of passengers there are connecting to other flights.

Any disruption to its operations has an enormous ripple effect on the nation's aviation system.

The aviation tracking website FlightAware.com showed O'Hare cancellations mounting to over 500 by about 2:30 p.m. Disruptions were less severe at Midway.

A computer glitch at a similar facility last month forced a 45-minute shutdown at Los Angeles International Airport.

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