DALLAS (AP) — Southwest Airlines scrubbed thousands of flights again Tuesday in the aftermath of the massive winter storm that wrecked Christmas travel plans across the U.S., and the federal government said it would investigate why the company lagged so far behind other carriers.

A day after most U.S. airlines had recovered from the storm, Southwest called off about 2,600 more flights on the East Coast by midafternoon. Those flights accounted for more than 80 percent of the 3,000 trips that got canceled nationwide Tuesday, according to tracking service FlightAware.

And the chaos seemed certain to continue. The airline also scrubbed 2,500 flights for Wednesday and nearly 1,200 for Thursday as it tried to restore order to its mangled schedule.

At airports with major Southwest operations, customers stood in long lines hoping to find a seat on another flight. Some tried to rent cars to get to their destinations sooner. Others found spots to sleep on the floor. Luggage piled up in huge heaps.

Conrad Stoll, a 66-year-old retired construction worker in Missouri, planned to fly from Kansas City to Los Angeles for his father's 90th birthday party until his Southwest flight was canceled early Tuesday. He said he won't get to see his 88-year-old mother either.

"I went there in 2019, and she looked at me and said, 'I'm not going to see you again.'" Stoll said. "My sister has been taking care of them, and she's just like, 'They're really losing it really quick.'"

Stoll hopes to get another chance to see his parents in the spring, when the weather is warmer.

The Dallas-based airline had little new to say about its woes. The company did not offer any updates on Tuesday morning, and information on the cancellations was last updated on the company's website Monday.

The problems began over the weekend and snowballed Monday, when Southwest called off more than 70% of its flights.

That was after the worst of the storm had passed. The airline said many pilots and flight attendants were out of position to work their flights. Leaders of unions representing Southwest pilots and flight attendants blamed antiquated crew-scheduling software and criticized company management.

Casey Murray, president of the Southwest Airlines Pilots Association, said the airline failed to fix problems that caused a similar meltdown in October 2021.

"There is a lot of frustration because this is so preventable," Murray said. "The airline cannot connect crews to airplanes. The airline didn't even know where pilots were at."

Murray said managers resorted this week to asking pilots at some airports to report to a central location, where they wrote down the names of pilots who were present and forwarded the lists to headquarters.

Lyn Montgomery, president of the Transport Workers Union representing Southwest flight attendants, was scheduled to talk later Tuesday with Transportation Secretary Pete Buttigieg, who has criticized airlines for previous disruptions and is now taking an interest in Southwest's woes.

"I'm taking it to the highest level — that is how done we are," said the frustrated Montgomery. "This is a very catastrophic event."

Buttigieg's office confirmed that he planned to speak with Montgomery, but declined further comment on the mess at Southwest.

Late Monday, the Transportation Department tweeted that it would examine "Southwest's unacceptable rate of cancellations" and whether the airline was meeting its legal obligation to help stranded customers.

Southwest spokesman Jay McVay said the cancellations snowballed as storm systems moved across the country, leaving flight crews and planes out of place.

"So we've been chasing our tails, trying to catch up and get back to normal safely, which is our number one priority, as quickly as we could," he told a news conference late Monday in Houston. "And that's exactly how we ended up where we are today."

Bryce Burger and his family were supposed to be on a cruise to Mexico departing from San Diego on Dec. 24, but their flight from Denver was canceled without warning. The flight was rebooked through Burbank, California, but that flight was canceled while they sat at the gate.

"Just like my kids' Christmas sucks. It's horrible," Burger said Tuesday by phone from Salt Lake City, where the family decided to drive after giving up the cruise.

The family's luggage is still at the Denver airport, and Burger doesn't know if he can get a refund for the cruise because the flight to California was booked separately.

Burger's call logs show dozens of unsuccessful attempts to reach Southwest over two days. The company did respond to a tweet he sent. He said they offered him and his family each a $250 voucher.

The size and severity of the storm created havoc for many airlines, although the largest number of canceled flights Tuesday were at airports where Southwest is a major carrier, including Denver, Chicago Midway, Las Vegas, Baltimore and Dallas.

Spirit Airlines and Alaska Airlines both canceled about 10% of their flights, with much smaller cancellation percentages at American, Delta, United and JetBlue.

In upstate New York, Buffalo Niagara International Airport — close to the epicenter of the storm — remained closed Tuesday.

Kristie Smiley planned to return home to Los Angeles until Southwest canceled her Tuesday flight, so she waited at the Kansas City airport for her mother to pick her up. Southwest can't put her on another plane until Sunday, New Year's Day. She called other airlines, but the cheapest flight she could find was $4,000.

"Now they are, like, on it, you know — capitalizing on it," Smiley said. She still doesn't know what to think of Southwest.

"They like acted like (Tuesday's flight) was going to go until they started saying, 'Oh, five more minutes. Oh, 10 more minutes.' I'm not sure what's up with them. It seems a little off."

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Associated Press writers Heather Hollingsworth in Kansas City, Missouri, and Thalia Beaty in New York contributed to this story.