Here's what's behind the Southwest Airlines cancellations

Southwest canceled more than 1,800 flights over the weekend, causing a cascading effect of chaos throughout its network and leaving thousands of passengers stranded around the U.S. and Central America. Many more flights were delayed, and problems continued into Monday.

Southwest initially said on Saturday that the delays were caused by a combination of bad weather in Florida and air traffic control delays. The Federal Aviation Administration, which manages air traffic control, said that it did not have any active delays, causing confusion — Southwest later clarified that it was referring to after-effects from the Friday night delays.

The confusion in initial messaging, coupled with Southwest's looming compliance with the federal vaccination mandate, led to a rash of rumors that pilots and others — including air traffic controllers — were staging a walkout in protest of vaccine requirements, with politicians quickly jumping onto the narrative.

Southwest did not return multiple requests for additional comment on Monday.

Sources at both Southwest and air traffic control denied to TPG that there was a walk-out or other labor action, despite some employees vocally opposing the ban and threatening job actions (airline worker strikes are prohibited under the Railway Labor Act).

Still, rumors of a walk-out continued to spread. According to Brooke Binkowski, managing editor of TruthOrFiction.com, a website that debunks deliberate disinformation, the way the rumors continued to spread had the hallmarks of a standard disinformation campaign.

"You can always tell the mechanism of these campaigns because you start seeing swarms of these previously anonymous accounts clustering around journalists, and other high-profile Twitter users, trying to distract and stoke anger around hot button topics," Binkowski said, noting that she has seen that type of activity surrounding the flight delays.

"There are different types of distraction campaigns, like 'firehosing,' or just changing the subject, or 'I know you are but what am I,' and the goal is always to move things to make it exclusively about another topic," she added.

In the latest statement from Southwest, received by TPG Sunday night, the airline described several causes for the disruption but did not directly address the rumors of the walkout.

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"We experienced weather challenges in our Florida airports at the beginning of the weekend, challenges that were compounded by unexpected air traffic control issues in the same region, triggering delays and prompting significant cancellations for us beginning Friday evening," Southwest said in the statement. "We've continued diligent work throughout the weekend to reset our operation with a focus on getting aircraft and Crews repositioned to take care of our Customers."

The airline added: "With fewer frequencies between cities in our current schedule, recovering during operational challenges is more difficult and prolonged."

The problem appeared to be multifaceted with several converging causes.

Southwest has operated with little margin for error all summer as it filled its schedule to capacity to try and take advantage of returning travel demand, despite having lost about 630 pilots to buyouts and early retirements during the early days of the pandemic — about 6% to 7% of its total pilot workforce, as pointed out by Jon Ostrower of The Air Current.

That's caused Southwest to face delays all summer, leaving it particularly vulnerable to disruptions, such as the scattered storms Friday.

The airline was particularly short-staffed for its schedule this weekend. On Sunday, Southwest scheduled 3,600 flights, its highest number since March, 2020, straining its already limited resources.

Additionally, a U.S. Navy training off the east coast of Florida complicated air traffic control routings and procedures.

Simultaneously, the Jacksonville air traffic control center — which controls airspace in much of the Southeast — experienced a staffing shortage Friday, something that is relatively common at air traffic control centers around the country. A memo from the Jacksonville Aviation Authority chief operating officer, first reported by Jacksonville reporter Ben Becker, attributed the short-staffing to normal approved leave and mandatory 48-hour waiting periods after controllers receive a dose of the vaccine before they're allowed to work again, a policy meant to prevent minor side effects from distracting on-duty controllers.

That short-staffing increased the delays, making it more difficult for Southwest to recover given its packed schedule a reduced margin for error. Southwest was left with planes and crews in the wrong places, forcing it to cancel flights to try and correct its network.

"Although we were staffed for the weekend, we could not anticipate the significant disruption that was created from unexpected ATC issues and bad weather across our Florida stations," Alan Kasher, Southwest's executive vice president of daily flight operations, told staff in a memo Sunday.

The Southwest Airline Pilots Association (SWAPA), the airline's pilots' union, adamantly denied that there was any kind of walkout or job action taking place.

"I can say with certainty that there are no work slowdowns or sickouts either related to the recent mandatory vaccine mandate or otherwise," members of SWAPA leadership wrote in a statement on Sunday, echoing a Saturday statement in which the union said "we can say with confidence that our Pilots are not participating in any official or unofficial job actions."

Notably, according to SWAPA president Casey Murray, there was no increase in pilots calling out sick over the weekend.

"The sick call rate over the weekend was no different than it has been since June and the pilots actually picked up open flying as well," Amy Robinson, a spokesperson for SWAPA, told TPG on Monday.

Still, SWAPA asked a federal court last week to temporarily block the vaccine mandate, arguing that the airline decided to implement it without required talks with the union.

Southwest's latest schedule meltdown was remarkably similar to the one experienced by Spirit Airlines in August, when the airline was forced to cancel more than 2,000 flights as it tried to reset its network following a similar disruption.

In that case, as in the current Southwest incident, it was the tight staffing with no slack, coupled with a chain-reaction of events, and a point-to-point network making it difficult to get operations back on track, that caused the airline to suffer the catastrophic disruption while other airlines were hardly affected.