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Sun Country Airlines passengers stranded in Mexico this weekend discovered too late that an airline ticket is no guarantee of a ride home.

Flight delays, cancellations and general discomfort are expected in air travel. Still, passengers assume airlines will rebook them or provide other help in worst-case situations like a cancellation.

But when Sun Country canceled a flight each from Los Cabos and Mazatlan to Minneapolis-St. Paul on Saturday, the airline couldn't rebook passengers on its next available flight from either place because it had no more flights scheduled until June.

The Eagan-based carrier, known chiefly for low-cost flights to vacation spots, finished winter seasonal service to and from the two Mexican resort cities on Saturday. With the record-setting snowstorm shutting down Minneapolis-St. Paul International Airport for eight hours, Sun Country couldn't get the planes down to Mexico and back in time for them to begin the new routes they were assigned to on Sunday.

The circumstance, infrequent but not unprecedented, stranded approximately 250 people and became a costly lesson in the trade-offs involved in choosing airlines. For the airline, it has become a PR problem, prompting grievances on social media and a rebuke from U.S. Sen. Tina Smith, D-Minn.

"As many travelers are already financially squeezed by the airline industry, it is troublesome to see a domestic carrier abandoning its passengers in a foreign country, forcing them to find their own way home and to incur further expense of time and money," Smith wrote in a letter asking the U.S. Department of Transportation to investigate Sun Country's move.

Sun Country notified the passengers through an e-mail and refunded the cost of the return leg of the canceled flights. The airline said its call-center personnel worked overtime to help the stranded passengers in Mexico and throughout its system after Minneapolis-St. Paul airport closed Saturday.

Asked Monday what the airline could have done differently, Brian Davis, a Sun Country senior vice president, said, "If any of us could have anticipated the snowstorm was going to be as bad as it was going to be, maybe giving customers a heads-up that this was the last flight of the season so they could make their own travel decisions."

Sun Country's situation also showed how airlines, especially low-cost carriers, schedule their aircraft tightly with little room for error. "They typically schedule to the maximum availability of aircraft and crew resources, with no spares or slack for irregular operations," said Robert Mann, an aviation consultant and former airline executive.

Larger carriers such as Delta, American and United have bigger fleets and more wiggle room when something goes wrong. "They do have those extra assets and they will deploy them when necessary," Mann said.

Davis said Sun Country couldn't send another plane to retrieve the stranded passengers because it didn't have any to spare. Sending an aircraft would have meant canceling another flight, causing more problems through its network.

"At some point we have to make that call," Davis said. "So the decision was made early on, because if we can't physically reaccommodate, the fairest thing to do is to make the decision early so they can find another way home."

If the cancellation was due to a maintenance issue, the airline would take on more responsibility, Davis said. Airlines outline their legal obligations to customers in what's called a "contract of carriage" — a requirement made of the carriers by the Department of Transportation.

"But does anyone stop to read the contract of carriage? Not unless you are a lawyer," Mann said. "Sometimes the consumer protections aren't really worth much."

Sun Country offered affected passengers a refund on their return ticket. But for most passengers, that refund likely covered just a small portion of a replacement flight, typically expensive when booked at the last minute.

Airlines should always try and make a good-faith effort to charter a replacement flight or rebook the passengers on other airlines' flights, Mann said. "So you do the right thing to begin with and then you show them you tried, even if you can't do it," he said.

Davis said he wasn't sure if Sun Country called other airlines or charter companies to see if they could make arrangements for passengers left in Mexico.

Stranded passengers complained of difficulty reaching Sun Country's customer-service agents on the phone. Davis said blizzard conditions prevented many call-center workers from reaching work in a timely manner, exacerbating the backlog. Still, he said, once they got to work, many of them worked past their shift and slept in the call center to help.

"I'm reluctant to say we are proud of anything right now, but the team has really stepped up," Davis said.

The disruption came just as the airline's local owners, Mitch and Marty Davis, are completing its sale to Apollo Global Management, a private equity firm. The Davis brothers hired a new chief executive, Jude Bricker, formerly an executive at Allegiant, last summer.

Bricker started changes to make the airline more efficient, adding new fees and changing the cabin and seat configuration of aircraft. The airline also recently announced it would transition some ground services to a contractor.

Davis said this weekend's cancellations had nothing to do with those broader moves. "At no point in time did we have an option presented to us that we declined because of cost-cutting," he said.

Kristen Leigh Painter • 612-673-4767