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WASHINGTON (NEXSTAR) — The union representing Southwest Airlines flight attendants says the “perfect storm” of factors led to this week’s mass cancellations that have stranded tens of thousands of passengers.

A massive winter storm plus hundreds of thousands of holiday travelers plus decades-old computer technology was a disaster waiting to happen, the union says.

“We had a lot of things happen at one time. And what that did was exposed the real underlying issue, which is our challenges in our technology and our inability to quickly recover,” TWU Local 556 2nd Vice President Corliss King said.

King, who has worked for Southwest for 12 years, said employees have long warned executives about the flaws in the employee scheduling system, but no one listened.

“We’re the first people to know when the operation on paper is failing,” she said, “…but we do not necessarily have a seat at the table or the input that we should have.”

A third of Southwest’s flights were back on schedule Thursday — though 2,300 were still canceled. It said it will fly a “nearly normal” schedule Friday, with only a few dozen flights canceled. The airline has apologized for the breakdown and blamed it on the weather.

“For now, we’re focused on restoring the reliability and level of customer experience we expect of ourselves and that you expect from us,” Chief Commercial Officer Ryan Green said. “We’re continuing to work to make this up to you and you’ll hear more about that soon.”

The U.S. Department of Transportation has promised to hold the airline accountable, with Secretary Pete Buttigieg saying the problems were not all weather-related. He said the department is working with Southwest to guarantee all affected customers get refunds.

Lawmakers have also promised to take action when they return to Washington next week.