Delta's meltdown worsens with 800 cancellations Monday; now 4,000 since Friday

Find updated coverage here: Delta under DOT investigation as meltdown hits Day 5, and 5,000 cancellations

Cancellations at Delta Air Lines continue to pile up more than 72 hours after an IT outage affecting industries around the world first disrupted travel Friday.

By 3:30 p.m. EDT Monday, the Atlanta-based carrier had canceled more than 815 flights — and counting — according to data from flight-tracking site FlightAware. That's more than a fifth of its operation.

The disruptions came after a nightmarish weekend at U.S. airports, as airlines — primarily Delta and United Airlines — continued to recover from Friday's tech outage that affected Microsoft Windows clients around the world.

Delta has, by far, suffered the worst lingering effects of any U.S. airline. After canceling 1,200 flights both Friday and Saturday, the airline scrubbed more than 1,300 departures Sunday, per FlightAware.

And it's not entirely clear when the disruptions might end.

"We've got everyone around the company working around the clock to get this operation where it needs to be," Delta CEO Ed Bastian said in a video message to employees on Monday. "Keep taking great care of our customers and each other in the coming days."

Delta's woes continue

A big reason Delta continues to reel from Friday's third-party I.T. glitch is the vast number of Microsoft applications the airline relies on — around half of its entire digital infrastructure, the carrier said in a statement Monday afternoon.

The malfunction, Delta explained, required the company's I.T. teams to manually repair and reboot each affected system, and then it takes time for each application to synchronize with one another.

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Heavily affected, the airline said, is a critical crew scheduling system that "is deeply complex," and is "requiring the most time and manual support."

In recent days, the problems have played out at airports across the country — Delta hubs in particular — with long lines for customer service and passengers sleeping on terminal floors, in some cases.

Numerous U.S. and international carriers were affected by Friday's IT outage, which stemmed from a program update at Austin-based cybersecurity firm CrowdStrike.

Several airlines paused flying Friday morning, and that triggered cascading flight disruptions over the course of the day.

Though some carriers quickly recovered, operations took longer to get back on track at United, which canceled hundreds of flights over the weekend.

But Delta passengers have continued to deal with widespread disruptions, with Sunday its worst day for cancellations since the IT outage.

What should you do if your flight is canceled?

Though the issues stemmed from a problem at a third-party vendor, the U.S. Department of Transportation is treating these flight cancellations and delays as disruptions within the airlines' control, a spokesperson told TPG Friday.

That means airlines would be on the hook for guarantees listed on the agency's Airline Customer Service Dashboard, from meals to hotel accommodations and ground transportation, depending on the traveler's circumstances.

For days, Delta has affirmed it's providing those benefits to affected travelers, along with flight vouchers and SkyMiles.

Overnight, though, Transportation Secretary Pete Buttigieg criticized the airline's response.

"We have received reports of continued disruptions and unacceptable customer service conditions at Delta Air Lines," Buttigieg wrote on social media, citing hundreds of complaints filed with the DOT. "I have made clear to Delta that we will hold them to all applicable passenger protections."

Among them: federal refund policies. DOT rules specify that passengers whose flight is canceled or significantly delayed are entitled to a cash refund back to their original form of payment — if they don't accept rebooking and choose not to travel.

The airline clarified its refund policy in a statement Monday afternoon:

" Customers whose travel has been disrupted due to a canceled or significantly delayed flight may choose to cancel their travel and receive an eCredit for the unflown portion of the trip," Delta explained. "...or may instead request a refund at delta.com/refund."

Related: What to do if your flight is canceled or significantly delayed

A tumultuous few days for Delta

Delta sees the disruptions of recent days as a major departure from its usual operational reputation. Between Jan. 1 and July 18, the carrier canceled 0.3% of flights, per FlightAware.

Its cancellation rates easily eclipsed 30% on Friday, Saturday and Sunday.

The airline touted its operational reliability on the company's earnings call earlier this month.

"It's the longer-term lasting damage and lingering operational recovery which can really impact an airline," John Grant, industry analyst at data firm OAG, wrote in a post Monday.

In all, Delta has already canceled more than 4,000 flights since Friday.

Related: Best credit cards for trip cancellation and interruption coverage

It's perhaps the biggest multiday operational snafu any U.S. airline has seen since Southwest Airlines' holiday 2022 meltdown, during which the latter carrier canceled nearly 17,000 flights.

Unsurprisingly, Delta's home base, Hartsfield-Jackson Atlanta International Airport (ATL), remains by far the hardest-hit U.S. airport, with hundreds of cancellations Monday alone.

Though it's not clear when Delta's disruptions might resolve, the carrier has already said unaccompanied minor flying for children is paused through at least Tuesday.

Related reading:

• Your complete guide to the Delta SkyMiles program
• Best Delta credit cards
• What is Delta Air Lines elite status worth?
• Maximize your airfare: The best credit cards for booking flights
• The best credit cards to reach elite status in 2023
• How to survive basic economy on Delta Air Lines