(Bloomberg) -- Delta Air Lines Inc.struggled to restart its worldwide operations after a computerfailure halted flights for hours and grounded thousands ofpassengers.

About 365 flights were scrapped and delays and cancellationswill continue even as systems come back online, the second-biggestU.S. carrier said Monday on Twitter. A power outage at Delta’sAtlanta base beginning at 2:38 a.m. local time interrupted computeroperations, according to the airline.

The disarray at Delta marked the second time in less than amonth that a system failure forced mass flight cancellations at alarge U.S. carrier. Southwest Airlines Co., the biggest U.S.discount airline, said a disruption July 20 would cost it “tens ofmillions” of dollars after more than 2,300 flights werecanceled.

Whether Delta had an adequate backup system “is certainly alegitimate question,” said Bob Mann, president of aviationconsultant R.W. Mann & Co. and a former airline executive. “Whydidn’t the backup systems perform, or what was it about the systemsthat if they performed, it still didn’t allow the systems tocommunicate?”

Delta fell 0.2 percent to $37.58 at 12:13 p.m. in New York.

Passengers stranded

As of 12:00 p.m. Monday, Delta said it had operated 1,260 of itsalmost 6,000 scheduled flights. The airline carried about 500,000passengers daily during July, its busiest month, Delta said on itswebsite.

Harold Jimenez, 29, had to re-book his ticket for Tuesday to flyto Nashville, Tennessee, from New York’s LaGuardia Airport. He wastraveling to install cameras for a customer of the security firmwhere he works.

“I’ve been here since 6 a.m. I was supposed to takeoff at 8:40a.m., and they told us it would be delayed until 11:30 a.m.,”Jimenez said. “But now they just canceled it.”

While the airline said it was giving snacks and beveragesto passengers facing extended delays, passenger DavidBrennan at London’s Heathrow Airport said food vouchers ranout. He was scheduled to travel to San Francisco through Seattle ona 10-day vacation.

“I have two children. We have been here since 7:30 thismorning,” he said. “It took two hours for them to tell us what hadhappened after the system went down. Then the pilot came and theysaid the flight was canceled because the crew can’t work more than10 hours.”

Waiving fees

Delta is waiving change fees and fare differentials on ticketprices for passengers whose flights were canceled or delayedMonday, according to a statement on its website. Passengers mustbegin their trip by Thursday.

Delta is booking inconvenienced travelers on other airlines inselect cases but is largely accommodating them on its own flights,spokesman Michael Thomas said. No other airlines were affected,according to Hartsfield-Jackson Atlanta International Airport.

The likely cause was an “equipment failure at Delta,” aspokesman for electricity provider Georgia Power said.

Flight-status displays, the website and some mobile and airporttechnology were disrupted, Delta said. The carrier didn’t estimatehow long repairs would take.

‘Financial burden’

“This will obviously mean a financial burden on Delta as it willhave to arrange for alternate travel and hotel costs for passengerswho are booked,” said Mark Martin, founder of Dubai-based MartinConsulting. The airline would probably use agreements with othercarriers to arrange alternative travel for some customers, hesaid.

Last month at Southwest, computers were restored after about 12hours but flights continued to be canceled or delayed for severaldays as the carrier worked to get crews and planes in the rightlocations.

U.S. carriers experienced a series of technical disruptions toflights late last year and early in 2016, including a connectivityflaw at American Airlines that halted flights at its Chicago,Dallas and Miami hubs in September and a reservations-system glitchat Southwest in October.

A United Continental Holdings Inc. computer fault last summerlasted two hours and disrupted travel for thousands of fliers. Itbegan with a router malfunctioning and prevented the carrier fromticketing passengers and dispatching crews.

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