Delta Air Lines (DAL  ) CEO Ed Bastian said the airline will need two more days to fully recover from a global cyber outage that has significantly disrupted its operations.

The outage, which began on Friday, has canceled over 4,000 flights and left thousands of passengers stranded, Reuters reports.

The outage severely affected Delta Airlines, with over 800 flights canceled on Monday alone, representing about 21% of its scheduled flights for the day.

Reuters reported that other major U.S. airlines have seen their disruptions largely subside.

A software update by cybersecurity firm CrowdStrike Holdings Inc (CRWD  ) caused system issues for Microsoft Corp (MSFT  ) customers, including many airlines.

This outage rendered about 60% of Delta's critical applications, which are based on Microsoft Windows, inoperable.

Delta's IT teams have been working to manually repair and reboot the affected systems, with the crew tracker application requiring the most time to synchronize.

Bastian and Chief Information Officer Rahul Samant provided updates on the recovery efforts in a video message to employees. Bastian expressed optimism, stating, "Today will be a better day than yesterday and hopefully Tuesday and Wednesday will be that much better again."

The outage occurred during the busiest travel weekend of the summer, leading to widespread frustration among passengers. Many customers reported long wait times for assistance, with some having to rent cars to travel long distances or wait days for new flights.

According to Reuters, Transportation Secretary Pete Buttigieg noted that his office received hundreds of complaints about Delta's customer service and urged the airline to provide prompt refunds and rebooking options.

Price Action: DAL shares traded higher by 0.16% at $43.90 at the last check on Tuesday.