Thousands of people are still stranded, a day after Delta flights were grounded by a power cut.
Another 300 flights had to be cancelled on Tuesday, as the airline tried to catch up with a ripple effect spread through its network by 1000 cancellations and 2800 delays in the preceding 24 hours.
FlightStats, a flight tracking services, tallied almost another 600 delayed flights as Delta tried to help out tens of thousands of passengers whose travel plans were disrupted.
The airline has apologised to passengers and offered refunds and $200 in travel vouchers to people affected.
Airport check-in systems, the airline's website and smartphone apps were all affected by the systems failure, blamed on a power failure in Atlanta, near its Dallas headquarters, that caused its computer systems to crash.
More than 1,000 people spent the night at Narita airport outside Tokyo because of the shutdown and, while flights were resuming Tuesday, Delta spokeswoman Hiroko Okada said more delays were expected.
Other passengers said the airline should have kept passengers better informed.
“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.”
The disruption was so widespread that at one point on Monday, the airline warned travellers that information on its website, its app, and even given by its own employees in airports, may be outdated.
Trebor Banstetter, Delta spokesman, told the Associated Press that after the power cut, key systems and network equipment did not switch to backups. The investigation continues, but he added that there was no evidence the problem was caused by hackers or an intentional breach.
Delta Air is the third-largest airline in the world by number of passengers carried, with 138.8 million travelers last year, according to industry group IATA, behind American Airlines and Southwest. Airlines.
