(CNN) -- Flights resumed Friday afternoon on a "reduced rate" at Chicago O'Hare International and nearby Midway Airport after a fire in an air traffic control center shut down operations, authorities said.
The air traffic control center in Aurora, Illinois, was evacuated after a 36-year-old contract employee set the fire in the control center basement before 6 a.m. Friday and tried to kill himself with a knife, said Aurora Police Chief Greg Thomas.
The man is from Naperville, Illinois, and was being treated at a Chicago-area medical facility, Thomas said. He will face federal charges, the chief said.
CNN's Ted Rowlands said officials told him there was no explosion and the incident was not related to terrorism. Controllers at other airports were helping manage traffic to and from Chicago.
O'Hare last year handled 883,000 takeoffs and landings, ranking it as the second-busiest airport on the planet, according to Airports Council International.
The airline tracking website FlightAware reported about 1,700 Chicago flight cancellations by Friday afternoon -- 1,256 at O'Hare and 453 at Midway.
The Chicago Department of Aviation said in a press release that delays were averaging 30 minutes or more for flights that are still scheduled.
An FAA statement said that "flights have begun arriving and departing to and from the Chicago area at a reduced rate."
Social media lit up with complaints by travelers like @JoeMFox who tweeted, "I'm starting to consider whether a five-hour drive would get me there faster than United. #ohare"
Other control centers pitch in to help
In a typical backup plan for a disabled FAA center, the FAA could assign air traffic control authority to FAA centers in other cities, such as Indianapolis, Cleveland, Minneapolis or Kansas City.
Doug Church, a spokesman for the National Air Traffic Controllers Association union, said air traffic controllers were bracing for a tough day. "Indianapolis Center is one of the major facilities bearing the brunt of the extra workload today due to the Chicago Center situation," Church said.
Indianapolis FAA Center has brought in additional controllers on overtime, Church said. Also, controllers are dealing with increased traffic along the nation's east-west corridors because of the stoppage.
The fire closed the control center around 5:42 a.m. The FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives are investigating. Workers were evacuated, FAA spokeswoman Elizabeth Isham Cory said.
The airport is a main hub for United Airlines and other major carriers, with flights headed to international destinations. When controllers stop flights scheduled to fly to O'Hare, it has the potential to trigger a line of falling air traffic dominoes that will ruin travel plans for countless would-be passengers.
Illustrating the point, the flight tracking website FlightRadar24.com showed no aircraft flying in an area stretching from eastern Iowa to central Michigan.
Smoke at FAA facility stopped flights in May
Friday's flight stoppages come four months after smoke at an FAA radar facility in Elgin, Illinois, prompted flight cancellations and delays at O'Hare and Midway.
In that May 13 incident, most flights in and out of O'Hare were delayed by an average of an hour or more, and more than 600 flights were canceled, the Chicago Department of Aviation said. Some 75 flights were canceled at Midway.
The smoke in that May incident was caused by a faulty motor in an air conditioning system, the FAA said at the time.