Last Updated Aug 9, 2016 5:31 PM EDT
DALLAS - Travelers on Delta Air Lines (DAL) endured hundreds more canceled and delayed flights on Tuesday as the carrier slogged through day two of its recovery from a global computer outage.
Delta said it had canceled about 620 flights as it moved planes and crews to "reset" its operation. Nearly 1,200 Delta flights had been delayed, according to tracking service FlightStats Inc.
"We are still operating in recovery mode," said Dave Holtz, the airline's senior vice president of operations.
The disruptions followed about 1,000 cancelled flights and 2,800 delayed flights on Monday after a power outage at Delta's Atlanta headquarters tripped a meltdown of its booking, communications and other systems.
The airline was back online after a few hours Monday, but the outages were so widespread that it was still dealing with the ripple effects a day later.
"We'll still have some cancellations and delays today and probably into tomorrow morning, but we expect by tomorrow we'll be pretty much up and running full scale," said CEO Ed Bastian.
More than 1,000 people spent the night at Narita Airport outside Tokyo because of the shutdown. While flights resumed in the morning, Delta spokeswoman Hiroko Okada said more delays were expected.
Delta also extended a travel-waiver policy to help stranded passengers rearrange their travel plans.
The airline posted a video apology by Bastian. And it offered refunds and $200 in travel vouchers to people whose flights were canceled or delayed at least three hours.
Delta's challenge Tuesday will be to find enough seats on planes during the busy summer vacation season to accommodate the tens of thousands of passengers whose flights were scrubbed.
Airlines have been putting more people in each plane, so when a system of a major carrier crashes, as has happened with others before Delta, finding a new seat for the waylaid becomes more difficult.
Last month, the average Delta flight was 87 percent full.
Confusion among passengers Monday was compounded as Delta's flight-status updates crashed as well. Instead of staying home or poolside at a hotel until the airline could fix the mess, many passengers learned about the gridlock only after they reached the airport.
They were stuck.
"By the time I showed up at the gate the employees were already disgruntled, and it was really difficult to get anybody to speak to me or get any information," said Ashley Roache, whose flight from Lexington, Kentucky, to New York's LaGuardia Airport was delayed. "The company could have done a better job of explaining ... what was happening."
Delta spokesman Trebor Banstetter said that after the power outage, key systems and network equipment did not switch over to backups. The investigation of the outage is ongoing, but Banstetter said that there is no indication that the problems were caused by a hack or intentional breach of the system.
Georgia Power, which controls the system where the outage began, said it appears that a failure of Delta equipment caused the airline's power disruption. No other customers lost power, a spokesman said.
Airlines depend on huge, overlapping and complicated systems to operate flights, ticketing, boarding, airport kiosks, websites and mobile phone apps. Even brief outages can now snarl traffic and, as the Delta incident shows, those problems can go global in seconds.
Last month, Southwest Airlines canceled more than 2,000 flights over four days after an outage that it blamed on a faulty network router. United Airlines and American Airlines both suffered outages last year -- United has struggled with several meltdowns since combining technology systems with merger partner Continental Airlines.
Some passengers said they were shocked that computer glitches could cause such turmoil. Others took it in stride.
Ryan Shannon, another passenger on the Lexington-to-New York flight, said passengers boarded, were asked to exit, waited about 90 minutes and then got back on the plane.
Once Delta cleared flights to take off, "we boarded and didn't have any problems. There is always a delay, or weather, or something. I travel weekly, so I'm used to it," Shannon said.
The Department of Transportation told CBS News that is discussing the problem with Delta and continues to monitor the situation.
Flights that were already in the air when the outage occurred continued to their destinations, but flights on the ground remained there.
Delta ranks as the third-largest in the world by number of passengers carried, with 138.8 million travelers last year, according to industry group IATA. It was narrowly beaten only by American Airlines and Southwest Airlines (LUV), with all of them flying mostly within the United States.
Airlines depend on huge, overlapping and complicated systems to operate flights, schedule crews and run ticketing, boarding, airport kiosks, websites and mobile phone apps. Even brief outages can snarl traffic and cause long delays.
That has afflicted airlines in the U.S. and abroad.