LONDON — Delta Air Lines delayed or canceled hundreds of flights Monday after its computer systems crashed, stranding thousands of passengers on a busy travel day.
About six hours into the outage, the airline said that limited flights were resuming but that were delays and cancelations were continuing.
The Atlanta-based airline said that a power outage at a facility in Atlanta at around 2:30 a.m. Eastern started the cascading meltdown.
Flights that were already in the air when the outage struck operated normally, but others were grounded. Over the next several hours, only a handful of flights took off instead of the usual hundreds, according to flight-tracking services.
Airlines depend on huge, overlapping and complicated technology 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.
In Richmond, Virginia, Delta gate agents wrote out boarding passes by hand. In Tokyo, a dot-matrix printer was resurrected to keep track of passengers on a flight to Shanghai.
Technology that appeared to be working was sometimes giving inaccurate information. Flight-status systems, including airport screens, incorrectly showed flights on time, something the company said it was trying to fix.
"Passengers become increasingly reliant on their ability to check in online (and) check their flight status," said Daniel Baker, CEO of tracking service FlightAware.com. "Not only are their flights delayed, but in the case of Delta the website and other places are all saying that the flights are on time because the airline has been so crippled from a technical standpoint."
Delta issued a statement saying it apologized to customers and said teams were working to fix the problem as quickly as possible.
Many passengers, like Bryan Kopsick, 20, from Richmond, were shocked that computer glitches could cause such turmoil.
"It does feel like the old days," Kopsick said. "Maybe they will let us smoke on the plane, and give us five-star meals in-flight too! "
In Las Vegas, stranded passengers were sleeping on the floor, covered in red blankets. When boarding finally began for a Minneapolis flight — the first to take off — a Delta worker told people to go round up their friends who had wandered away from the gate area.
Early confirmation of the troubles first came in an official account that responds to customers via Twitter. The company had said its IT systems were down "everywhere" and "hopefully it won't be much longer." Several applications were affected, including the company's website.
Among those affected was Tanzie Bodeen, 22, a software company intern from Beaverton, Oregon. She left home at 4 a.m. to catch a flight from Minneapolis and learned about the delays only when she reached the airport and saw news crews gathered at the door.
Bodeen said that passengers were taking the matter in stride. "It doesn't seem really hostile yet," she said.
The company said travelers will be entitled to a refund if the flight is cancelled or significantly delayed. Travelers on some routes can also make a one-time change to the ticket free of charge.
Delta shares were down 2 percent in pre-market trading.
Computer outages are a periodic plague for airlines. Last month, Southwest Airlines canceled more than 2,000 flights over several days after an outage that it blamed on a faulty network router. Unions called for the airline to replace the CEO, but the board gave him a vote of confidence.
Investors shrugged off Delta's IT mishap. In morning trading, shares of Delta Air Lines Inc. were up 43 cents, to $38.10.
Koenig reported from Dallas. Matt Small in Washington and Bree Fowler in Las Vegas contributed to this report.