At a news conference in Houston, Southwest spokesman Jay McVay said cancellations increased as storm systems moved across the country, leaving crews and aircraft stranded.

«So we’ve been chasing our tails, trying to catch up and safely get back on track, which is our number one priority, as fast as we could,» he said. «And that’s exactly how we ended up where we are today.»

Unlike many other US airlines, Southwest operates on what is known as a point-to-point flight route system, which means that one plane will fly consecutive routes, picking up different crews along the way.

In normal times, this may allow Southwest to operate more flights during a given 24-hour period than other airlines, said Scott Mayerowitz, executive editor of travel site The Points Guy.

But if an airport goes offline due to weather and a flight can’t make it to its destination, the point-to-point system has a cascading cancellation effect, he said.

“When bad weather hits and you have staffing issues like they do, it creates a situation that’s almost impossible to recover from, and it couldn’t have happened during a worse week,” Mayerowitz said of the Southwest cancellations.

Southwest’s problems appear to have been complicated by earlier staffing problems at its fuel supplier in Denver, CNBC reported. Furthermore, a report from The Denver Post confirmed the authenticity of a leaked internal memo that said Southwest had entered a «state of operational emergency» in Denver last Wednesday due to an unusually high number of no-shows among ramp agents.

It was not immediately clear if that issue was still affecting flights on Tuesday.

Randy Barnes, president of the union that represents ramp agents, said there was no strike. He said the weather was so severe, and the temperatures so low, that normal procedures to ensure staff members could carry out their duties effectively broke down.

«People need recovery time to warm up and go in,» Barnes said. He continued: «That part of the operation can’t move at the same pace, at the same speed that it normally does. So something is going to give.»

Casey Murray, president of the Southwest Airlines Pilots Association, said Southwest had not adequately prepared flights for the storm, hampering ground transportation and maintenance vehicles. The planes had fuel that would freeze and drinking water that would freeze in winter conditions, Murray said.

«The fact is, we weren’t ready,» Murray said.

Adding to the difficulty: Large sections of Southwest crews remain in contract negotiations with the carrier.

«The Southwest of yesteryear is gone,» Murray said. «Now it’s all about threats and intimidation to motivate, instead of the old Southwest with heart.»

Southwest Airlines did not immediately respond to questions about ongoing contract negotiations with its crews.

CNBC also reported that internal technology glitches had hampered crew reassignments.

The Department of Transportation said in a statement that it plans to examine whether the cancellations were «controllable» and whether Southwest is following through on its customer service plan.

The ordeal has caught the attention of some lawmakers, including Democratic Senators Edward Markey of Massachusetts and Richard Blumenthal of Connecticut, who urged Southwest Airlines to «get this right» by «fairly compensating passengers whose flights were cancelled, including not only rebooked tickets, ticket refunds, and hotel, food and transportation refunds, but significant monetary compensation for the disruption of their vacation plans.»

In a message posted on Twitter, President Joe Biden said: «Our Administration is working to ensure airlines are held accountable.»

Mayerowitz said the Department of Transportation, under the leadership of Secretary Pete Buttigieg, has been aggressive about airlines that cause problems for consumers, and he wouldn’t be surprised if harsh penalties were applied.

“We are still waiting to see the actual regulations come out and be implemented, but there has been the most conversation that I have seen in over a decade,” Mayerowitz said.

CORRECTION (Dec 27, 2022, 4:28 p.m. ET): An earlier version of this article got it wrong when Southwest confirmed it would be operating at one-third capacity «for the next few days.» He issued the statement on Monday, not Tuesday.

He also misspelled the last name of the executive editor of The Points Guy travel site. This is Scott Mayerowitz, not Meyerowitz.