Police searched three airplanes at O'Hare International Airport on Sunday after two separate telephone bomb threats. No explosives were found.
A Mexicana Airlines flight that was already in the air was called back and the passengers evacuated for the search, said Megan Hughes, a city aviation spokeswoman.
A second Mexicana Airlines plane was also searched before people were asked to board.
It was not immediately clear whether the planes were allowed to depart.
The second call, made to Delta Air Lines officials in Boston, said that a flight en route to O'Hare from Atlanta had a bomb on board, Hughes said. The flight landed in Chicago shortly afterward.
Police and fire officials evacuated and searched the plane, but found nothing suspicious, Hughes said. Its final destination was New York's John F. Kennedy International Airport.