A security guard found a crude pipe bomb lying near an air charter service at O'Hare International Airport on Sunday night, officials said. The device was detonated safely.
The airport was already on heightened security after an anonymous 911 caller at 9:30 a.m. said there was a bomb on a Mexicana Airlines flight to Mexico.
A flight that had just taken off from the airport for Puerto Vallarta, Mexico, was returned to O'Hare, Hughes said. The passengers were evacuated, but no explosives were found, officials said.
A second Mexicana Airlines airplane also was searched.
Chicago Fire Department Battalion Chief Leslie Noy said a Delta flight also was searched after a threatening call was received by the airline.
The plane was evacuated and searched by Chicago police and fire officials, who found nothing suspicious, she said.