What caused the delay in Delta restoring normal service after the outage?

A service disruption caused by a software update released by cybersecurity company CrowdStrike sparked a series of flight cancellations at multiple major U.S. airlines – however, the impact was most severe and prolonged at Delta Airlines.

Overall, the airline axed more than 2,500 flights during a time frame that extended from the start of the outage last Friday until the middle of this week.

The U.S. Department of Transportation launched an inquiry into Delta this week regarding its uniquely intense flight disruptions.

“All airline passengers have the right to fair treatment,” Transportation Secretary Pete Buttigieg stated on Tuesday in a post on X.

In a statement on Tuesday, Delta stated that it is fully cooperating with the investigation. “Throughout our operations, Delta teams are working tirelessly to care for and rectify the situations for customers impacted by delays and cancellations as we strive to reinstate the reliable, punctual service they have grown accustomed to from Delta,” the company stated.

The company also issued an apology on Wednesday for the problems caused by the outage.

“Please accept our sincere apologies for the disruption to your recent travel plans caused by a vendor technology outage affecting airlines and companies worldwide,” the airline said in a statement.

“It’s a surprise that a multi-billion-dollar corporation like Delta would allow this to happen,” Henry Harteveldt, a travel industry analyst at Atmosphere Research Group, informed ABC News.

“I’m hopeful that the worst is behind us now. While we can breathe a sigh of relief, I think a lot of people are understandably nervous about flying Delta,” Harteveldt added.

Delta did not immediately respond to an ABC News request for comment.

Airline and cybersecurity experts spoke to ABC News about what made the CrowdStrike outage so disruptive, and why it took days for Delta to resume normal service.

What caused the CrowdStrike outage to be so disruptive for Delta?

The CrowdStrike outage had a significant impact due to the severity of the IT failure and the extent of its reach within Delta’s internal operating systems, experts informed ABC News.

“For a corporation like Delta, they depend on numerous partner services for various operations such as pilot and plane scheduling, meal provision, and seat selection for customers,” David Bader, a cybersecurity professor at the New Jersey Institute of Technology, stated to ABC News.

“The CrowdStrike issue disrupted many critical services that are essential for the airline’s full operation,” Bader added.

Mark Lanterman, the chief technology officer at Computer Forensic Services, mentioned that the outage was a result of a faulty software update initiated by CrowdStrike. The resulting computer glitch interrupted crucial services due to CrowdStrike’s deep integration within Delta’s operating systems, he added.

“The CrowdStrike update is deeply embedded in the operating system. Once it was installed, there was faulty code present in the update. When Windows encountered the faulty code, it malfunctioned and crashed,” Lanterman explained.