ATLANTA -- Delta was hit by a crippling computer outage on Sunday night that caused big delays and the cancellation of at least 250 flights.
It's the second time in less than six months the airline has suffered a major IT problem resulting in travel chaos and angry passengers.
The Federal Aviation Administration announced a nationwide ground stop late Sunday on all domestic Delta flights. The measure remained in place for at least 2 1/2 hours until it was lifted.
Shortly before 10 p.m. MST, Delta said its IT systems were starting to return to normal and flights were taking off again. But in a 2 a.m. MST statement, the airline said about 170 Sunday night flights had been canceled, and that 80 Monday flights had already been canceled, with more cancellations and delays possible.
"I want to apologize to all of our customers who have been impacted by this frustrating situation," CEO Ed Bastian said. "This type of disruption is not acceptable to the Delta family."
During the peak of the outage, Delta flights at Denver International Airport were delayed an average of 90 minutes but still moving.
The airport said there will continue to be some delays as the airline catches up.
The airline's website and mobile apps also went down, adding to customers' frustrations.
Delta said that flights already in the air weren't affected by the outage but that some passengers were experiencing delays after landing.
The FAA said in its advisories that Delta's international flights weren't affected by the ground stop. But some people said on Twitter that flights to foreign destinations were disrupted.
Delta didn't immediately respond to a request for further information on international flights.
Delta's computer problems came about a week after United Airlines temporarily grounded domestic mainline flights due to an IT issue.
A previous Delta outage caused travel chaos around the globe.
In August, the airline lost power at its operations center in Atlanta setting off a system failure that resulted in around 2,000 flight cancellations over several days.
After that fiasco, Delta agreed to give affected customers refunds and vouchers for future travel. This time Delta said it would waive its normal fee to change flights for customers scheduled to travel Sunday and Monday and for rebooking travel by Friday.
Last week, a computer outage forced United Airlines to ground all domestic flights.