WASHINGTON--The United States Transportation Department (USDOT) on Monday fined American Airlines $4.1 million for unlawfully keeping thousands of passengers on the tarmac for hours, the largest-ever penalty for violating the rule. Of the $4.1 million assessed, $2.05 million will be credited to the airline for compensation provided to passengers of impacted flights. USDOT said an extensive investigation by its Office of Aviation Consumer Protection found that between 2018 and 2021, American allowed 43 domestic flights to remain on the tarmac for lengthy periods without providing passengers an opportunity to deplane in violation of the department's tarmac delay rule. On one of the 43 flights, passengers were not provided with food and water as required. Most delays occurred at Dallas Fort Worth Airport. The tarmac delays affected a total of 5,821 passengers. “This is the latest action in our continued drive to enforce the rights of airline passengers,” U.S. Transportation Secretary Pete Buttigieg said. “Whether the issue is extreme tarmac delays or problems getting refunds, DOT will continue to protect consumers and hold airlines accountable.” American told USDOT these delays were the result of exceptional weather events, and that the flights represented less than 0.001% of the approximately 7.7 million flights operated by American and its regional partners during the period of 2018 to 2021. "We have since apologized to the impacted customers and regret any inconvenience caused," the airline said on Monday. The airline said it has committed "substantial time and resources to improve its performance on tarmac delays." While accepting this compromise settlement "American respectfully disagrees that certain of these tarmac delays warrant enforcement action under the extreme circumstances presented," it added. In 2016, USDOT fined American Airlines a then record-matching $1.6 million after it found the carrier had allowed a number of domestic flights to remain on the tarmac without allowing passengers an opportunity to get off the plane. USDOT in January said it planned to seek higher penalties from airlines and others that broke consumer protection rules, saying they were necessary to deter future violations. The department has fined numerous airlines in recent years, including a $135,000 penalty on British Airways over a 2017 tarmac delay in which it failed to ensure the timely deplaning of passengers.