ATLANTA: Delta Air Lines Inc expects to cancel more flights this week as the carrier tries to recover from a crippling technology outage.

The airline grounded nearly 900 flights as of Monday afternoon, bringing its total since Friday’s meltdown to almost 4,700.

Delta said it was working “around the clock” to restore operations, with more than half of its worldwide information technology (IT) relying on Microsoft Corp’s Windows operating system affected by the software error.

Chief executive officer Ed Bastian said it could be days before Delta moves past the incident, according to a video message sent to employees on Monday.

Delta has fared the worst among US carriers, with most other airlines getting back on track over the weekend.

The problems began last Friday with an outage caused by CrowdStrike Holdings Inc, rendering the airline unable to process changes to many flights and their crews.

That created a cascading effect - not unlike that which paralysed Southwest Airlines Co in December 2022 - leaving Delta unable to get its crews and planes fully aligned.

“By the time they got their crew management system back online, they had a more complex problem to solve than the other airlines,” said Bob Edwards, a former chief information officer for United.

“It’s taken them days longer to recover” from the initial blow.

The situation comes after Delta earlier this month reported worse-than-expected financial results, sending its shares tumbling.

Delta’s stock fell 3.5% on Monday, cutting its gain for the year to about 9%.

US Transportation Secretary Pete Buttigieg, who was a vocal critic of Southwest for its IT issues, admonished Delta over the disruptions and said that the department had received reports of “unacceptable customer service conditions” in a post to social media platform X.

Delta said CEO Bastian, who has apologised for the disruption, discussed the flight cancellation issues with Buttigieg on Sunday.

The cancellations lingered into a fourth day as rival carriers American Airlines Group Inc, United Airlines Holdings Inc and Southwest parked a combined 79 planes as of mid-afternoon New York time, according to flight-tracking website FlightAware.

United’s operations were back to normal on Monday, CEO Scott Kirby said in a letter to customers and employees.

More than 26,000 computers and devices had to be manually fixed after “almost all” of the carrier’s systems were hit by the outage, he said.

American Airlines didn’t immediately respond to a request about its IT systems.

Delta said that one of its most critical systems, which ensures all flights have crews assigned to its planes, “is deeply complex and requires the most time and manual support to synchronise”.

The problems brought back memories of Southwest’s meltdown during a winter storm that overwhelmed its crew-scheduling system and forced the airline to scrap more than 16,700 flights over 10 days.

Delta’s response raises questions about what lessons the airline industry learned from Southwest’s mishap, especially since it appears both crises were exacerbated by snowballing snafus involving difficulties in getting crews to cockpits.

In both cases, the two airlines were forced to resort to analog-type workarounds to relieve the stress on their overburdened IT systems.

Bastian, Delta’s CEO, conceded it hasn’t been Delta’s finest hour in the video to employees.

“It’s been a horrible weekend for us all,” he said. “This issue came out of nowhere.”

That comes as cold comfort to passengers who’ve grown accustomed to velvet glove treatment and being charged a premium for that.

The company’s business model relies on the carrier’s reputation for on-time, no-drama flight service. But that’s being challenged.

Irate passengers took to social media to vent their frustrations, with some comparing Delta unfavourably with lower-cost rivals.

Some travellers have vowed never to fly the airline again, but it’s unclear how much of a long-term impact this will have.

 - Bloomberg