The U.S. Department of Transportation said Monday that it would fine American Airlines $4.1 million for unlawfully stranding passengers in planes on the tarmac for hours at a time, the largest such civil penalty ever handed down by the government. Authorities said that, in violation of federal rules, more than 5,000 passengers on 43 American flights between 2018 and 2021 were forced to sit on the tarmac for more than three hours without the opportunity to deplane. “Whether the issue is extreme tarmac delays or problems getting refunds, D.O.T. will continue to protect consumers and hold airlines accountable,” Transportation Secretary Pete Buttigieg said in a statement. A spokesperson for American Airlines said the flights in question were the result of “exceptional weather events” and that it had apologized to the affected fliers. The delayed flights, the spokesperson said, were just a small fraction of the 7.7 million flights the carrier operated in the years over which the government’s investigation extended.