ATLANTA — Federal scrutiny is growing. The chief executive is apologizing to customers.
And as the meltdown at Southwest Airlines, one of the worst that industry observers have seen in decades, entered yet another day on Wednesday, irate customers remained stranded, separated from their families and some still carrying Christmas gifts they planned to deliver days ago.
There was no relief early Wednesday: Southwest had canceled more than 2,500 flights, or 62 percent of its planned flights for the day, according to FlightAware, a flight-tracking service. The company has said it could be days until the knots are untangled and normal service resumes.
“I’m not mad at them,” said Tearsa Aisani Parham, standing in a winding line at Hartsfield-Jackson Atlanta International Airport’s North Terminal on Tuesday afternoon, hoping to find a Southwest employee willing to listen. “I’m mad at the way they did it.”
Southwest’s operational configuration, which differs from most other major carriers, has come under intense scrutiny after a winter storm last week disrupted travel plans across the United States. Southwest has been uniquely unable to get its planes back in the air after the storm, while thousands of customers have been left stranded and struggling to rebook.
On Friday, around 1,300 Southwest flights — about 34 percent of its scheduled flights that day — were canceled. Other airlines in the United States also struggled on Friday, with about 22.5 percent of all non-Southwest flights canceled, according to FlightAware.
But as other airlines regained their footing — 13.3 percent of non-Southwest flights were canceled on Saturday, 9.7 percent on Sunday and 5.7 percent on Monday — the problems worsened at Southwest.
Southwest canceled 39 percent of its flights on Saturday. The number grew to 46 percent on Sunday, 74 percent on Monday and 64 percent on Tuesday.
In total, nearly 11,000 Southwest flights have been canceled since Thursday, according to FlightAware.
Pete Buttigieg, the transportation secretary, said in an interview on “NBC Nightly News” on Tuesday that it was “an unacceptable situation” that would demand a closer look at Southwest’s scheduling system.
“We all understand that you can’t control the weather,” he said, adding that “this has clearly crossed the line from what is an uncontrollable weather situation to something that is the airline’s direct responsibility.”
Senator Maria Cantwell, chair of the Senate Commerce Committee, said in a statement on Tuesday that the committee would be investigating the causes of the meltdown, and that “the problems at Southwest Airlines over the last several days go beyond weather.”
“Many airlines fail to adequately communicate with consumers during flight cancellations,” she said. “Consumers deserve strong protections, including an updated consumer refund rule.”
Southwest’s chief executive, Bob Jordan, apologized to customers in a video on Tuesday night, saying that the “giant puzzle” of staffing could take days to solve.
“Our plan for the next few days is to fly a reduced schedule and reposition our people and planes,” Mr. Jordan said. “We’re making headway, and we’re optimistic to be back on track before next week.”
The issues stem from the carrier’s unique “point to point” model, in which planes tend to fly from destination to destination without returning to one or two main hubs. Most airlines follow a “hub and spoke” model, in which planes typically return to a hub airport after flying out to other cities.
When bad weather hits, hub-and-spoke airlines can shut down specific routes and have plans in place to restart operations when the skies clear. But bad weather can scramble multiple flights and routes in a point-to-point model, leaving Southwest staff out of position to resume normal operations.
It leaves passengers like Ms. Parham scrambling to make alternate plans, and sometimes unable to do so.
Ms. Parham planned to spend the days after Christmas at Disney World with her family — a birthday gift to one of her sons and his wife, and a Christmas gift to her grandson. She flew from Atlanta to Baltimore to meet up with her eldest son, who does not like to fly alone, then returned to Atlanta in advance of a Christmas Day flight to Tampa.
Her younger son and his family made it to Disney. Even her bags made it to Florida.
But her Sunday flight was canceled, and she spent Christmas Day at the airport. After waiting until 4:30 a.m. the next day, she said she was told she’d be placed on a 6 a.m. flight. That flight was overbooked, and Ms. Parham became a standby passenger. The flight took off with her bags, but without her. The next flight was delayed, then canceled. Then another delay, and another cancellation. And the flight after that? Canceled as well.
“I need my makeup,” Ms. Parham said with a laugh.
Waiting in line at the Atlanta airport on Tuesday, Anthony Malloy, 63, of Queens, N.Y., said that he would not be able to get on a flight before Friday. He said he had no choice but to come to the airport after his Tuesday flight home was canceled, as the Southwest customer service line was disconnected and changes were unavailable online.
He was eager to return home, as his twin brother was flying from California to meet him in New York. Mr. Malloy arrived in Atlanta a week ago to visit a friend.
“To think this is the way it has to end is really debilitating,” he said.
It was not Mr. Malloy’s first disappointing trip with Southwest, as he was among thousands of passengers affected by delays and cancellations in June 2021. At the time, he spent $98 on an Uber from a distant airport to get home to Queens and didn’t receive his luggage for three days. As an apology, the airline provided him with a flight voucher, which he used for his trip to Atlanta.
“Redeeming the voucher might not have been such a good idea,” he said.
Tanya Sichynsky reported from Atlanta, and Daniel Victor from London.