(Chicago)  Federal officials Thursday fined Southwest Airlines $1.6 million for trapping passengers on the tarmac on 16 flights at Midway Airport for more than three hours last January.

The fine is the largest civil penalty ever imposed by the U.S. Department of Transportation for violation of tarmac-delay rules, the Sun-Times is reporting.

Those rules ban airlines from holding domestic flights on a tarmac for more than three hours without giving passengers an opportunity to leave the plane. Exceptions are allowed only for safety, security and air traffic control issues.

Federal officials contend Southwest experienced tarmac delays of more than three hours on Jan. 2 and 3, 2014. A malfunction of the crew scheduling system and an unexpected staff shortage hurt the airline’s ability to clear aircraft from its Midway gates, according to a statement from the U.S. Department of Transportation.

In addition, a “severe weather event at Midway” contributed to delays, the agency said.

Chicago was hit with a snow storm on Jan. 2, 2014, followed by temperatures so low on Jan. 6 and 7 the period was dubbed “Chiberia.”

— Chicago Sun-Times

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