(CNN) — All flights into and out of Chicago’s O’Hare International Airport and Chicago Midway International Airport were stopped Tuesday.
The ground stop was in effect because of smoke in a radar facility, according to a statement from the Federal Aviation Administration.
“All FAA personnel were evacuated from the Chicago Terminal Radar Approach Control (TRACON) facility in Elgin because of smoke in the building. All TRACON operations were immediately transferred to the Chicago En Route Center in Aurora,” it read.
TRACON air traffic controllers take control of long distance flights as they approach. They then guide traffic to just a few miles from the airport, before handing off to a controller who handles landings on a runway.
The cause of the smoke was not immediately clear.
(editor’s note: Several departures and arrivals between Quad City International Airport and Chicago were cancelled Tuesday, May 13, 2014 as a result of this incident. Some flights to Chicago from other cities were also diverted to Quad City International Airport and later allowed to continue to Chicago.)