As air travel continues its bumpy return after plunging in the early days of the pandemic, there have been plenty of downs. First came the rounds of cancellations on Southwest and American in June. Then Spirit Airlines had a multiday spiral in August that resulted in hundreds of canceled flights.

Southwest had a repeat this weekend with more than 2,000 canceled flights, citing bad weather and air-traffic control issues that snowballed into a major disruption.

With this track record, what should travelers expect for Thanksgiving, Hanukkah, Christmas and New Year’s trips?

“I’m concerned that it’s going to be a very stressful holiday season when it come to air travel,” said travel industry analyst Henry Harteveldt, president of Atmosphere Research Group. “It’s already stressed with the potential for bad weather and of course, especially at Thanksgiving, very crowded flights.”

Denver Airport saw massive lines and congestion over the weekend of Oct. 10, after Southwest Airlines canceled at least 1,800 flights and delayed 1,500 more. (@rylacy via Spectee)

He said the reduced schedule of flights compared to pre-coronavirus times gives airlines less room to recover from shocks to the system, and full planes mean there are fewer empty seats to put people in if their original flights are canceled.

Harteveldt said Southwest, one of the country’s largest airlines, has a “point-to-point” route network that makes it more difficult to recover than those that have crews and planes based in hubs.

But Richard Aboulafia, an aviation analyst at Teal Group, said the entire air travel system is frayed after downsizing earlier in the pandemic and dealing with a choppy recovery.

“The industry’s never done this before,” he said. “It’s never contracted and expanded like this.”

Disruptions are inevitable, he said, when a business has to balance supply and demand with precision — especially when it’s difficult to predict what customer travel patterns will be in advance.

Aboulafia’s advice to travelers in the upcoming months: “Don’t expect precision. Be flexible. Allow slack.”

He said it would be smart to stick with the airlines that are most dominant in a certain area because there could be a better chance of getting a seat on another flight on that carrier in case of a cancellation.

One other wrinkle ahead: Several airlines including JetBlue, Southwest and American have told employees that they must meet the conditions of a vaccine mandate for federal contractors that requires workers to be inoculated no later than Dec. 8. American told U.S.-based workers last week that they have to show proof of full vaccination by Nov. 24, the day before Thanksgiving, Reuters reported.

JetBlue also told its employees to have their final shot by Nov. 24.

“With the possible federal deadline for vaccination just before the December peak season, it’s important that you schedule your shots now so that you will be able to continue working,” executives told staff in a note. “Our customers count on us to get them where they’re going during the holidays, and we need to be ready to fully comply with the mandate before the holiday peak starts and to help bring this pandemic to a close.”

Pilots have to wait 48 hours after each dose before they can operate a flight, according to the Federal Aviation Administration.

The deadline, Harteveldt said, “could not be worse for airlines.”

Dennis Tajer, spokesman for the Allied Pilots Association, which represents American Airlines pilots, said the union is asking the airline to consider proof of natural immunity for those who have recovered from covid-19 or frequent testing as an alternative to the vaccine mandate.

“Rather than putting a crush on this holiday season, which is already going to be under a crush with a lot of flying, at a minimum we’re looking for an extension so we can address this,” he said. He said about 30 percent of the airline’s pilots have not been vaccinated, some of whom are awaiting word to find out if their requests for medical exemptions will be approved.

Some who oppose vaccine mandates trumpeted the theory that Southwest’s problems over the last few days were caused by pilots protesting the requirement. The airline and its union both said that was not the case.

Mike Boyd, president of Boyd Group International, said Southwest’s issues were so specific to its own operations that they didn’t give him cause for concern in the coming months. But that doesn’t mean all will be smooth sailing.

“Consumers can look forward to the usual appalling chaos they’re used to over the holidays,” he said.