Hundreds of flights were cancelled in the United States on Sunday, leaving passengers to scramble on a three-day holiday weekend. As of 2 pm EDT, Southwest Airlines cancelled over 1,000 flights, or 28% of its schedule, which was the highest rate by far of the major US airlines. Allegiant and Spirit airlines cancelled 5% and 4% of its flights respectively while American Airlines canceled 2% of its flights.

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Southwest Airlines blamed air traffic control issues and weather for the cancellation of flights. 

“TC issues and disruptive weather have resulted in a high volume of cancellations throughout the weekend while we work to recover our operation. We appreciate your patience as we accommodate affected customers, and customer service wait times are longer than usual,” the airline tweeted.

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Casey Murray, the president of the Southwest Airlines Pilots Association (SWAPA), blamed the cancellation on staffing and a “poorly run operation.”

“SWAPA is aware of operational difficulties affecting Southwest Airlines today due to a number of issues, but we can say with confidence that our pilots are not participating in any official or unofficial job actions,” he said in a statement. 

“Our pilots will continue to overcome SWA management’s poor planning, as well as any external operational challenges, and remain the most productive pilots in the world. They will continue to be focused on their highest priority — safety.”

Meanwhile, the Federal Aviation Administration tweeted that there were no air traffic staffing shortages reported since Friday.

“Flight delays and cancellations occurred for a few hours Friday due to widespread severe weather, military training and limiting staffing in one area of the Jacksonville en route center. Some airlines continue to experience scheduling challenges due to aircraft and crews being out of place,” FAA tweeted.