American Airlines is facing the largest-ever fine for keeping passengers waiting on board airplanes during hours-long delays.

The Department of Transportation is levying the $4.1 million fine, "the largest civil penalty that the Department has ever assessed" it said in a statement, for lengthy tarmac delays of 43 flights that impacted more than 5,800 passengers. The flights occurred between 2018 and 2021.

In the longest of the delays, passengers sat aboard a plane in Texas in August 2020 for six hours and three minutes. The 105-passenger flight had landed after being diverted from the Dallas-Fort Worth International Airport due to severe weather, with the DOT alleging that "American lacked sufficient resources to appropriately handle several of these flights once they landed."

Federal rules set the maximum time that passengers can be held without the opportunity to get off prior to takeoff or after landing, at three hours for domestic flights and four hours for international flights. Current rules also require airlines provide passengers water and a snack.

American told CNN the delays all resulted from "exceptional weather events" and "represent a very small number of the 7.7 million flights during this time period."

The company also said it has invested in technology to better handle flights in severe weather and reduce the congestion at airports.

"These efforts are already providing significant benefits to our customers and team members, and we continue to look for innovative ways to further improve," the airline said.

American would pay $2.05 million of the fine to the government and has been credited for paying the other half in passenger compensation.