“Continuing challenges are impacting our customers and employees in a significant way that is unacceptable,” the airline said. “We’re working with safety at the forefront to urgently address wide-scale disruption by rebalancing the airline and repositioning crews and our fleet ultimately to best serve all who plan to travel with us.”

As for most airlines, the unprecedented cold that blanketed much of the nation spoiled many flights, beginning at Denver International Airport on Dec. 22. Virtually every airline was affected during the worst of the winter storm, but other airlines have begun to recover, where Southwest has not.

The trouble seems to center around Southwest’s airline crew scheduling system. At Denver, Southwest had a number of staff absences, according to The Denver Post. The situation deteriorated from there as the system could not keep up with matching pilots and flight attendants to new flights, stranding them at their last location.

“Our pilots can’t get hotels, they’re sleeping in airports,” Casey Murray, president of the Southwest Airlines Pilot Association union, said on the “Today Show” Tuesday. In the same segment, Lynn Montgomery, president of Transport Workers Union Local 556 at Southwest Airlines, said flight attendants have been unable to reach Southwest’s scheduling line, with some waiting for a new assignment for over 17 hours.

It’s not the first time Southwest has struggled to recover more than other airlines. Last year over Indigenous People’s Day weekend, Southwest had a similar meltdown but only tallied 2,000 flights canceled through the single weekend, citing bad weather and air traffic controller problems. The situation was once again unique to Southwest, with aviation experts at the time suggesting that crew availability was more likely to blame.

DOT has touted a new consumer dashboard that allows passengers to quickly see what benefits each airline offers when things go wrong, and are working on several regulations intended to shore up protections for airline passengers — but those will take some months to complete.

Meanwhile, Southwest’s customers are having a particularly difficult travel season.

Videos surfacing on social media at hubs such as Phoenix Sky Harbor, Baltimore-Washington International, and Chicago Midway airports showed hundreds of people waiting in line with bags piling up, with intercom announcements telling Southwest customers to go home and return another day.

Passengers took to Twitter to complain that they have not received emails or text about canceled flights, and remain unable to reach the airline’s customer service line to reschedule. Other passengers said they couldn’t modify their itinerary on either the app or website.