Delta Air Lines continues to cancel flights for the fifth day in a row and faces a federal investigation after the CrowdStrike global blackout hit the airline industry. While many other companies appear to have regained stable footing after a faulty update crashed 8.5 million Windows PCs, Delta continues to struggle.

CBS reports that as of 7:30 p.m. ET on July 23, the airline has canceled 478 flights and delayed another 1,440 flights. This prompted the U.S. Department of Transportation's Office of Aviation Consumer Protection to issue a Notice of Official Investigation. According to a statement provided to CBS by the Department of Transportation, the agency is investigating Delta “due to continued widespread flight disruptions and reports of poor customer service.”

Delta's flight cancellations are far more frequent than those of other U.S. carriers, and some travelers have chosen to purchase expensive tickets on other airlines just to get to their destinations faster.

In a statement from Delta CEO Ed Bastian on Monday, July 22, he explained that it would take “a few more days” for the airline to truly recover from the effects of this disruption. Delta has extended travel waivers for customers that were in place after the incident and may seek refunds for unboarded flights.

“This issue affected Microsoft's Windows operating system. Delta has a number of applications that use this system, and one crew tracking-related tool in particular was affected and was unable to effectively handle the unprecedented number of changes caused by the system shutdown,” Bastian wrote.

Fixes for the machines affected by the flawed update were made a few days after the outage, but many companies are still counting the cost of the disruption. This is because in many scenarios, the fixes need to be implemented directly by human IT technicians. Companies like Delta Air Lines, where several different parts of the business are affected, face an uphill battle and countless man-hours to get everything working again.

Delta is not alone in facing official scrutiny. Yesterday, it was revealed that Crowdstrike CEO and co-founder George Kurtz has also been asked to testify before the House Homeland Security Committee.