Southwest Airlines canceled 63% of its flights on Tuesday and may cancel similar portions of its schedule for the next several days.
Southwest had canceled close to 2,600 flights as of 2:30 p.m. Eastern time Tuesday, according to FlightAware. Those cancellations come on the heels of 8,150 cancellations between Dec. 22 and Dec. 26, amounting to 43.3% of the carrier's entire schedule over the long holiday weekend.
Meanwhile, the Transportation Department is looking into Southwest's most recent operational failures.
On Tuesday, a DOT spokesperson said, "The rate of cancellations and delays on Southwest Airlines is unacceptable and dramatically higher than other U.S. carriers. This afternoon, Secretary Buttigieg spoke with the CEO of Southwest Airlines and conveyed that he expects the airline to live up to the commitments it has made to passengers, including providing meal vouchers, refunds and hotel accommodations for those experiencing significant delays or cancelations that came about as a result of Southwest's decisions and actions. Southwest, as all airlines, is also obligated to provide a cash refund for passengers whose flights were canceled and decided not to travel.
"The Secretary also spoke with union leaders that represent Southwest's flight attendants and pilots. They conveyed to him that many flight attendants and pilots are stranded alongside passengers, sleeping on cots or having to book their own hotel rooms. He also conveyed to Southwest's CEO that he expects Southwest to do right by their pilots and flight attendants -- and all their workers -- in these situations.
The Department will take action to hold Southwest accountable if it fails to fulfill its obligations and we will stay engaged with Southwest Airlines to make sure the airline does not allow a situation like this to happen again."
On Monday, Southwest said that it would continue flying only roughly one-third of its schedule "for the next several days."
The carrier is encouraging flyers to visit Southwest.com/traveldisruption to rebook a flight or request a refund. The site also provides instructions for submitting reimbursement receipts for hotel, rental car and food bills incurred due to cancellations and delays.
However, the many flyers who are now without their checked luggage will find little guidance.
"We recognize that many of our customers are currently separated from their belongings, and we're working to resolve the situation as quickly as possible," is all the site says.
Winter Storm Elliott moved from the Mountain West all the way to the East Coast early during the holiday weekend, causing a mass of flight disruptions on various carriers. Overall, from Dec. 22 through Dec. 26, U.S. carriers canceled 17.5% of flights, FlightAware shows.
However, several carriers had improved their operations by Sunday and Monday. Over those two days, for example, American canceled just 26 mainline flights. Southwest, meanwhile, canceled more than 4,500 flights.
Most airlines continued to fare better on Tuesday, with Spirit having the second highest cancellation percentage among large U.S. airlines at 11%.
In a statement Monday, Southwest said that it had been fully staffed and prepared for the Christmas weekend before Winter Storm Elliott disrupted its network. But the airline said that being the largest U.S. carrier in the majority of the major U.S. travel markets forced changes to its flight schedule "at a volume and magnitude that still has the tools our teams use to recover the airline operating at capacity."
Southwest was hit especially hard by Elliott's impacts on Denver and Chicago, where the carrier's two largest operations are located.
The carrier's point-to-point business model, which involves flying individual aircraft to several cities in a day, also put it at a disadvantage compared to its largest competitors, Delta, American and United. Those airlines often fly planes out and back from hubs -- a model that can keep delays regionalized and makes it easier to adjust crew scheduling.
But inadequate technology appears to be the leading cause of Southwest's continuing operational failure.
In a statement to company employees on Sunday, Southwest CEO Bob Jordan acknowledged as much, stating that the carrier needs to invest more in crew scheduling.
"Part of what we're suffering is a lack of tools. We've talked an awful lot about modernizing the operation and the need to do that," Jordan said, according to the Transport Workers Union of America Local 556, which represents Southwest flight attendants.
The union said that thousands of crew members have been left stranded across the country. Holding times on the carrier's crew scheduling line have been as long as 17 hours.
"The many years of failure by management, despite many unions' demands to modernize, has left flight attendants fatigued, stranded, hungry and cold -- on Christmas! This impacts lives and threatens safety for all," Local 556 president Lyn Montgomery said.
This report was updated on Dec. 27 to add DOT comments about Southwest.