Southwest Airlines said early Monday that it had fixed technology problems that delayed hundreds of flights on Sunday, and it expects a normal day of operations.
The Dallas-based airline had been warning passengers to arrive at the airport two hours early Monday and print boarding passes beforehand. When asked early whether fliers should continue with those precautions, an airline spokesman said customers should expect a normal day Monday.
The airline said they still have some bags to deliver to travelers Monday and they hope to be able to passengers displaced or delayed Sunday onto flights Monday.
"It’s never too early to say thank you and to extend our apologies and we want to share those sentiments both with our hard-working employees and our loyal and understanding customers, whom we hope to welcome back for a better experience soon. We’ll continue to work individually with our affected customers to make this right," Southwest said in a statement on their website Monday.
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While things appeared to be back to normal at Dallas Love Field Monday morning, passengers at other airports reported long lines earlier in the morning.
In a statement Sunday, Southwest reported "intermittent" technical issues on its website, mobile app and in its phone centers and airports check-in systems. It said that while it is working on the issues, workers at airports are helping customers with their itineraries. By late afternoon Sunday, Southwest said about 500 of the 3,600 flights scheduled for the day had been delayed.
Representatives for Southwest did not say what caused the problem Sunday, but airline spokesman Brad Hawkins said there was "absolutely no indication now" that the problems were the result of hack.
“Usually these things have to do with some sort of networking switch, or some sort of networking error where two places can’t communicate,” Rick Seaney, a representative from farecompare.com told NBC DFW. "You have four airlines that control 80 percent of all traffic in the United States. We've seen all of their systems suffer glitches this year."
E.J. Schultz, a reporter for Ad Age who was taking a Southwest flight from Chicago's Midway International Airport, said the airline was telling people at the gate that travelers with paper boarding passes were fine. But those who had downloaded their tickets onto their mobile phones were told they had to stand in line, he said.
Schultz said he didn't understand why Southwest didn't announce that people should print out their boarding passes at home before getting to the airport.
"If everyone had done that, it would've saved so much time," he said.
Schultz said there was a line of about 50 people at the Southwest gate. His flight took off roughly 15 minutes after its scheduled departure time of 4:30.
The long lines at check-in may mean some passengers didn't make their flights.
Emily Mitnick, who was flying to Detroit from Denver International Airport, said she missed her 10 a.m. flight even though she parked her car around 8 a.m. She estimated that about 1,000 people were on line at the check-in for a boarding pass. When she went downstairs to the curb-side check-in, she said there were about a couple hundred people in line there as well.
By the time she got in line to go through security, it was around 10:15 a.m.
"The clock was ticking and the flight took off," said Mitnick, who was trying to get to Detroit through a different flight to Chicago.
Last month, American Airlines experienced computer problems that prevented passengers from checking in and briefly halted flights on select routes. Airline officials said at the time that they fixed the problem after less than two hours, and that there was no indication that its system had been hacked.
In July, hundreds of United Airlines flights were delayed after the airline experienced computer problems for the second time in just over a month. A United representative said at the time that the glitch was caused by an internal technology issue, and not an outside threat or hacker.
NBC DFW's Kevin Cokely contributed to this report.