Delta has to manually reset each computer system affected by the mass IT outage

• Delta Air Lines has continued to cancel hundreds of flights on Tuesday after Friday's mass IT outage.
• The technology issues have left Delta needing to manually repair affected systems.

Delta Air Lines is canceling hundreds of flights four days on from a mass IT outage connected to a defective update issued by the Texas-based cybersecurity firm CrowdStrike.

As most airlines began to recover following the technology issues, Delta has struggled to restore operations to full capacity, now resorting to manually resetting each system affected by the meltdown.

In a statement on Monday, Delta said over half of its IT systems globally are Windows-based.

"The CrowdStrike error required Delta's IT teams to manually repair and reboot each of the affected systems, with additional time then needed for applications to synchronize and start communicating with each other," the statement said.

It explained that the airline's crew-tracking-related tool, which ensures flights are fully staffed, has needed manual support to repair.

On Sunday, Delta CEO Ed Bastian said the critical tool could not effectively process the number of changes prompted by the Microsoft Windows operating system's shutdown.

On Friday, air travel was hit particularly hard by the outage, with passengers facing chaos at airports as over 5,000 flights worldwide were canceled and over 40,000 were delayed, according to FlightAware, a flight tracking data platform.

Delta grounded 1,207 flights on Friday, almost a third of its total scheduled departures. The airline with the next highest number of cancellations was United Airlines, with 694 cancellations.

Since Friday, Delta has canceled over 5,000 flights, per FlightAware data.

Delta canceled 394 flights on Tuesday as of 6.50 a.m. ET, representing 11% of its scheduled departures, and almost 40% of total flights canceled across airlines around the world, FlightAware data showed

Cancellations for other airlines have reduced to the tens and single digits, including for United, which canceled about 1% of its flights.

Passengers at Delta's largest hub, Hartsfield-Jackson Atlanta International Airport, have grappled with travel chaos, with cancellations and delays continuing into the week.

Delta announced that it extended a travel waiver, offering customers with flights booked from July 19 to 23 the option to change their itinerary free of charge.

Bastian also said on Sunday that passengers who experienced flight disruptions were being offered travel and meal vouchers, hotel accommodations, transportation where available, and Delta SkyMiles, the airline's loyalty program that gives points to flyers for upgrades and flights.

Pete Buttigieg, the Secretary for Transportation, said in a post on X Tuesday that the Department of Transportation has "opened an investigation into Delta Air Lines to ensure the airline is following the law and taking care of its passengers during continued widespread disruptions."