PHOENIX, Arizona: Some 1,800 Southwest Airlines flights were canceled nationwide from Saturday to Sunday.
Airlines officials blame the cancellations on weather, as well as air traffic controller weather procedures.
Southwest is the nation's largest domestic airline.
As of 11 a.m. ET on Sunday, Southwest had canceled 27 percent of the the airline's scheduled flights, the highest of any U.S. airline.
American Airlines reported canceling 63 flights, or 2 percent of its operation, while Spirit Airlines canceled 32 flights, or 4 percent of its flights, according to FlightAware.
This was a busy travel weekend due to the Monday federal Columbus Day holiday.
"We experienced significant impact in the Florida airports yesterday (Friday) evening after an FAA-imposed air traffic management program was implemented due to weather and resulted in a large number of cancellations. We are working hard behind the scenes to minimize challenges and fully recover the operation, as we take care of displaced crews and customers as quickly as possible. We will continue to reset our network today and hope to return to close to normal operations as we move into Sunday,'' Southwest said in a statement.
Meanwhile, industry observers have questioned whether disruptions are being caused by opposition to a vaccine mandate the airline announced a week ago.
"Southwest Airlines must join our industry peers in complying with the federal government's COVID-19 vaccination directive," Southwest CEO Gary Kelly said on Oct. 4.
Meanwhile, Casey Murray, president of the Southwest Airlines Pilots Association (SWAPA) blamed the flight cancelations on staffing and a "poorly run operation."
Murray said the rate of pilots calling in sick has not jumped this weekend, noting that three out of four pilots working Saturday had trips rerouted due to the flight cancelations.
In a statement posted to its website Saturday, the union said, "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.