DALLAS - (AP) -- We don't cancel flights.

That's been the message for the past two years from Delta Air Lines. Double decker buses roamed the streets of New York, wrapped in ads proclaiming "canceling cancellations." Delta executives boasted about the number of days without a single flight scrapped.

That all literally ground to a halt Monday when a system-wide computer outage led to the cancellation of more than 1,500 flights. Passengers were stranded around the globe with many spending the night in the airport.

Until this outage, Delta had an impressive record, envied by other airlines. By June 9 of this year, Delta had already notched up 100 days where none of its own jets canceled flights -- more than all of its major competitors' no-cancel days combined. And the cancellations during the other 61 days were mostly related to weather, not maintenance issues.

"Our people are hitting it out of the park, delivering on our promise to be a safe and reliable airline and making canceling cancellations a reality," Gil West, Delta's chief operating officer, said in a news release at the time trumpeting its record.

Sometimes, Delta took extreme measures to preserve that record such as letting delays roll on throughout the day instead of canceling. But the lack of cancellations and the airline's mantra of "keep climbing" won over business travelers willing to pay extra for flights that arrive on time.

A decade ago, Delta was getting 90 cents for every dollar charged by its competitors. Today, it gets 110 cents, Delta's new CEO, Ed Bastian proudly noted in a May interview with The Associated Press.

But Monday's outage threatens to wipe away all that trust that Delta has worked to build. It took Delta more than 24 hours to explain what happened: a power control malfunction that led to a power surge and loss of electricity. When the power came back some systems switched to backups, others didn't and that, Delta said, caused "instability in these systems."

"Obviously this is a public relations disaster. But they're not unique. This has happened to pretty much every major airline," said Jim Corridore, of S&P Global Market Intelligence. Since this is the airline's first major outage -- and as long as there isn't another one -- Corridore said "Delta may get a pass here."

Repeated problems can scare passengers away. When United Airlines had a series of computer meltdowns in 2012, loyal business travelers abandoned the carrier. There are only so many meetings -- or chances to tuck your kids into bed -- that road warriors will tolerate missing. Four years later, United's revenue still lags behind its competitors.

Fitch Ratings analysts Joseph Rohlena and Craig D. Fraser noted Monday that Delta can withstand one meltdown but -- citing United's troubles -- said Delta could be harmed if the issue spreads or is indicative of bigger problems.

Delta did some things right, like posting a video of Bastain apologizing to customers at 1:30 p.m. Monday -- a fairly quick response for an airline.

The airline also offered anybody delayed three hours or more a $200 voucher toward a future trip.

But there were also stumbles.

It didn't help that Delta wasn't upfront, telling passengers what happened. Instead the airline initially blamed it on a power outage. But the local utility company, Georgia Power, was quick to fire back saying it was actually Delta's equipment that had failed.

While rare, airlines do have computer outages from time to time. Last month, Southwest Airlines canceled more than 2,000 flights over four days after an outage that it blamed on a faulty network router.

But nobody has attached as much importance to never canceling flights as Delta.

Sometimes, though, that can lead to measures that passengers might not prefer. Instead of canceling a flight, Delta will just delay and delay and delay.

That happened Monday night to Megan Milan who was on an 8:45 p.m. flight from Atlanta back home to Denver.

"I had about four different notifications that my flight was pushed out, pushed out, pushed out and then at midnight I got the notification that it was cancelled," Milan said. "I would have rather received a cancellation yesterday instead of waiting around all night."

That philosophy of delaying, but not canceling, isn't unique to this computer outage.

Back on July 1, a massive thunderstorm caused giant delays in New York. Other airlines proactively canceled flights to give the few remaining ones a better chance of getting out of the airport.

Delta didn't.

One flight after another was delayed and delayed but not canceled.

Albert Choi was heading to Iceland with some friends for his birthday celebration.

Their 9:15 p.m. flight kept getting pushed back an hour or two at a time. At 4 a.m., the gate agent offered an apology but no further update.

"We couldn't sleep because we thought we were going to board at any time," Choi recalled on Tuesday.

Finally, the flight departed around 1 p.m. It might have been 16 hours late, but it was never canceled.

Choi says he would have preferred a cancellation so he could have gone home, slept in his own bed and then returned to the airport to catch a rescheduled flight.

"It was just a bad experience and left a bad taste in my mouth," he said.

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Follow Scott Mayerowitz at twitter.com/GlobeTrotScott. His work can be found at http://bigstory.ap.org/content/scott-mayerowitz