The U.S. Department of Transportation said Monday it is fining American Airlines $4.1 million for unlawfully keeping passengers stuck in planes on the tarmac for lengthy periods of time. 

American Airlines violated the DOT's rule prohibiting airlines for keeping passengers on planes for tarmac delays lasting three hours or more, the department said in a statement. During delays of this length, airlines are required to allow passengers to deplane. 

The fine is the largest civil penalty ever issued for tarmac delay violations, according to the agency. Passengers are owed more than $2.5 billion in refunds related to the delays.

Between 2018 and 2021, 43 domestic American flights sat on the tarmac for lengthy periods of time without allowing passengers to deplane, a violation of Transportation Department rules, the agency's Office of Aviation Consumer Protection found. 

"This is the latest action in our continued drive to enforce the rights of airline passengers," U.S. Transportation Secretary Pete Buttigieg said in a statement. "Whether the issue is extreme tarmac delays or problems getting refunds, DOT will continue to protect consumers and hold airlines accountable."

There are exceptions to the federal rules aimed at deterring airlines from keeping travelers confined on departing flights. For example, airlines aren't required to allow people to deplane if there are legitimate safety reasons to keep them on board. But the Transportation Department's investigation found that none of the exceptions to the tarmac delay rule applied to the 43 flights in question. 

The airline also did not provide customers with food or water, which is required, during the delays, according to the agency. Most of the delays, which affected roughly 5,800 passengers, occurred at Dallas Fort Worth International Airport, the regulators said.

"While these delays were the result of exceptional weather events, the flights represent a very small number of the 7.7 million flights during this time period," American Airlines told CBS News. "We have since apologized to the impacted customers and regret any inconvenience caused."

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