Delta Air Lines has canceled hundreds of flights for the third day in a row, as the airline is struggling to recover from Friday’s global software outage — even as other U.S. airlines are bouncing back and returning to normal operations.

In a public letter released Sunday, Delta’s CEO, Ed Bastian, said the airline paused flying following the Friday outage, resulting in roughly 3,500 flights being canceled from Friday to Saturday and continuing into Sunday. Bastian said the outage occurred on what was considered the airline’s “busiest travel weekend of the summer.”

"Canceling a flight is always a last resort, and something we don't take lightly," he added. "Delta is in the business of connecting the world, and we understand how difficult it can be when your travels are disrupted."

On Monday, however, as most U.S. airlines recovered from the global outage, Delta continued to experience issues, as more flights were delayed or canceled.

As of Monday afternoon, the Atlanta-based airline has canceled more than 800 flights and delayed roughly 1,500 flights, according to flight tracking website FlightAware.

In the public letter, Bastian wrote that several Delta applications run on Microsoft Windows, resulting in many tools being impacted in the outage. More specifically, one of the airline’s crew tracking tools was deemed inoperable and “unable to effectively process the unprecedented number of changes triggered by the system shutdown,” Bastian wrote.

Millions of Microsoft users across the globe were knocked offline following a flawed software update from a cybersecurity group called CrowdStrike.

Delta offered travel waivers to customers on flights impacted by the outage, allowing them to change itineraries and rebook their flights without any added fees.

In a post on X, Transportation Secretary Pete Buttigieg called out the airline on Sunday for its continuous disruptions and “unacceptable customer service.”

"We have received reports of continued disruptions and unacceptable customer service conditions at Delta Air Lines, including hundreds of complaints filed with @USDOT. I have made clear to Delta that we will hold them to all applicable passenger protections," Buttigieg wrote.

Buttigieg added that under new federal regulations, customers are not obligated to accept the travel credit offered to rebook flights but, instead, are entitled to a prompt cash refund.

"Delta must provide prompt refunds to consumers who choose not to take rebooking, free rebooking for those who do, and timely reimbursements for food and hotel stays to consumers affected by these delays and cancellations, as well as adequate customer service assistance," he added.

Delta’s technical issues are similar to those that occurred with Southwest Airlines during the winter holiday season in 2022, as the Dallas-based airline canceled thousands of flights and left millions of travelers stranded.

The U.S. Transportation Department ordered that Southwest pay $140 million in a civil penalty, which was by far the largest the DOT has ever levied for consumers, the department said in a statement announcing the penalty.

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