(ABC 6 News) — The U.S. Department of Transportation says it is prepared to take airlines to court over flight delays. The agency has filed a lawsuit against Southwest, accusing the airline of illegally operating chronically delayed flights and disrupting passengers’ travel plans.

Southwest is disappointed that DOT chose to file a lawsuit over two flights that occurred more than two years ago," a spokesperson for the airline said.

The Department of Transportation defines a flight to be chronically delayed if it is “flown at least 10 times a month and arrives more than 30 minutes late more than 50 percent of the time. Cancellations are included as delays within this calculation.”

Southwest Airlines stock fell Thursday after the Department of Transportation sued the airline over a pair of "chronically delayed flights."

American Eagle flight 5342 collided with a Black Hawk helicopter over the Potomac River, home to some of the country's most restricted airspace.

The Transportation Department is stepping up enforcement of persistent flight delays with a lawsuit against Southwest Airlines and a fine against Frontier Airlines. The agency said the U.S ...

A Southwest ... to the U.S. Department of Treasury, but the other half can be waived if the airline doesn't operate any chronically delayed flights for the next three years. “Airlines have ...

Wednesday night’s crash of an American Airlines commuter plane in Washington is one of the worst disasters for the Fort Worth-based airline in more than two decades.

Search efforts continue after an American Airlines plane from Wichita, with 64 people on board, collided with an Army helicopter near Washington, D.C., and crashed into the Potomac River.

The number of people onboard and any fatalities is unknown at this time. The plane can carry up to 65 passengers and four crew members.

Secretary of Transportation Sean Duffy promised to improve the nation's transportation infrastructure and systems after Vice President JD Vance swore in Duffy on Wednesday afternoon.

A massive search operation is underway after a passenger aircraft carrying 64 people collided midair with a US Army Black Hawk helicopter near Reagan National Airport outside of Washington, DC, according to aviation and defense officials.