Southwest is under investigation for flight cancellations. Here's why and what's next

Major U.S. airlines were broadsided by the massive weekend winter storm that swept across large swaths of the country but largely recovered heading into Monday, except for one.

Southwest Airlines canceled more than 70% of its flights Monday, more than 60% on Tuesday, and warned that it would operate just over a third of its usual schedule in the days ahead to allow crews to get back to where they needed to be.

American, United, Delta and JetBlue, suffered cancellations rates of between none and 2% by Tuesday.

Why Southwest's flight cancellations are being investigated

The disparity has triggered a closer look at Southwest operations by the U.S. Department of Transportation, which called the rate of cancellations "disproportionate and unacceptable," and sought to ensure that the Dallas carrier was sticking by its obligations to stranded customers.

The size and severity of the storm created havoc for airlines. Airports were overwhelmed by intense snowfall and drifts. Airlines canceled as many as 20% of their flights Saturday and Sunday and Buffalo Niagara International Airport, close to the epicenter of the storm, remains closed Tuesday.

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Yet it has become clear that Southwest is suffering a disproportionate disruption. Of the 2,890 flight cancellations in the U.S. early Tuesday, 2,522 were called off by Southwest.

The Department of Transportation said on Twitter that it was "concerned by Southwest's unacceptable rate of cancellations and delays & reports of lack of prompt customer service." The tweet said the department would look into whether Southwest could have done anything about the cancellations and whether the airline was complying with its customer service plan.

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Why did Southwest cancel so many flights?

Southwest spokesman Jay McVay said at a press conference in Houston that 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 said. "And that's exactly how we ended up where we are today."

Passengers stood in long lines trying to rebook their flights.

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'It's horrible'

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 or notice, he said Tuesday. 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 by phone from Salt Lake, 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.

What is Southwest's cancellation policy?

As of Tuesday morning, Southwest had implemented a system-wide waiver for customers who had a flight disruption between December 25 and January 2. According to a statement on Southwest's website, customers may rebook a new flight to their destination in their original class or travel on standby within 14 days of their original trip for no additional charge. There is a form to request a refund on Southwest's website.

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.

According to a statement released by Southwest on its website, hold times on its customer service phone line averaged two hours and got as high as four hours.

Southwest also said it will "honor reasonable requests for reimbursement for meals, hotel, and alternate transportation." Affected travelers can submit receipts for hotels and food by e-mailing Southwest, the company said.

How many Southwest Airlines flight cancellations are there today?

As of Tuesday morning, over 2,500 Southwest flights were canceled, which is 63% of all scheduled Southwest flights. 413 flights, or 10%, were delayed, according to FlightAware.

At Phoenix Sky Harbor International Airport, 104 Southwest departures on Tuesday were canceled as of Tuesday morning, or about 48% of all Southwest flights departing from Phoenix Tuesday, according to Sky Harbor's website.

Southwest also canceled 125 arrivals into Phoenix, or 52% of all Southwest arrivals scheduled Tuesday.

When will Southwest be back to normal?

Southwest CEO Bob Jordan told The Wall Street Journal in an interview that the airline would operate just over a third of its usual schedule to allow crews to get back to where they needed to be.

"We had a tough day today. In all likelihood we'll have another tough day tomorrow as we work our way out of this," he said Monday evening. "This is the largest scale event that I've ever seen."

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The Associated Press contributed to this report.

This article originally appeared on Arizona Republic: Why Southwest canceled so many flights and what's next for the airline