The DOT on Wednesday fined American Airlines $1.6 million for violating a federal regulation that prohibits long tarmac delays.

The figure equals the largest fine the DOT has levied for a violation of the 2010 rule that prohibits carriers from keeping aircraft on the tarmac for more than three hours without offering passengers the chance to deplane. Southwest was also fined $1.6 million in a 2015 DOT decision.

American, the DOT found, allowed 27 planes to remain on the tarmac for more than three hours between 2013 and 2015. Most of those incidents happened on just two days, with 20 of the violations committed by U.S. Airways during a snowstorm in Charlotte on Feb. 16, 2013, prior to the companies' 2015 merger, and six committed by American at Dallas-Fort Worth during heavy rain and snow on Feb. 27, 2015.

The carriers, the DOT found, did not adequately prepare for those weather events.

In a statement Wednesday, American said that it is pleased the matter is resolved.

"It's worth noting that a large portion of the settlement is related to a winter weather event that occurred nearly four years ago in Charlotte," the carrier said. "Regardless, every situation is a learning opportunity and we remain committed to taking care of our customers."

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