Two of the nation’s busiest airports, O’Hare and Midway, were brought to a halt Friday after a contract employee was suspected of setting fire at a suburban Chicago air traffic control center

The incident caused delays and cancellations through the air-travel network from coast to coast.

Emergency crews found the man suspected of setting the fire in the basement with knife wounds and burns to his body. It was unclear whether he was intending to commit suicide, said Thomas Ahern, a spokesman for the Bureau of Alcohol, Tobacco, Firearms and Explosives.The authorities ruled out any ties to terrorism.

The 36-year-old FAA contractor, who was authorized to be at the site, was taken to a hospital and was expected to survive.

The ground stoppage at O’Hare and Midway airports raised questions about whether the Federal Aviation Administration has adequate backup plans to keep planes moving when a single facility has to shut down.

By late afternoon, nearly 1,800 flights in and out of Chicago alone had been canceled. A few flights began taking off and landing again around midday, after a nearly 5-hour gap.

The planes were moving at a much-reduced pace, officials said, and no one could be sure when full service would resume.

The early morning fire forced the evacuation of the control center in Aurora, about 40 miles west of downtown Chicago. It was the second unexpected shutdown of a Chicago-area air-traffic facility since May.

The Aurora facility – which had become a crime scene – remained shut down while investigators examined the site.

The shutdown quickly spread travel misery around the country, with airports as close as Milwaukee and as far as Dallas canceling flights.

Southwest Airlines said it was scrapping all of its flights at Midway and Milwaukee for the entire day.

At O’Hare, long lines formed at ticket counters. Some passengers simply gave up and returned home.

The Aurora facility, known as an enroute center, handles aircraft flying at high altitudes, including those approaching or leaving Chicago airports. Air traffic closer to the airports is handled by a different facility and by the control towers located at the airfields.