Updated from 9:02 a.m. with Delta statement on cancellations and commentary.
The outage began at 2:30 a.m. Monday following a power outage in Atlanta. A ground stop on all Delta flights was lifted about six hours later.
At 10:40 a.m., Delta said it had canceled about 300 flights and operated about 800 flights. The carrier operates nearly 6,000 daily flights.
"Customers should continue to expect delays and cancellations," the carrier said.
Monday morning is normally among the worst possible times for airlines to experience operational problems, due to a profusion of business travelers, but summer vacations may have impacted that pattern.
"Fewer business travelers are on the road this week," travel writer Joe Brancatelli wrote Monday morning in his blog. "But a lot of leisure travelers are flying and they are less experienced and more easily frazzled.
"Obviously, this will take hours -- in fact, days -- to clean up because hundreds of Delta flights and flight crews are already out of position," he said.
A failed piece of Delta equipment led to the outage, Reuters reported Monday.
"It was a failure of Delta equipment," Georgia Power spokesman John Kraft told Reuters, adding, "there wasn't an area power outage," and the Delta problem did not affect other power customers.
Delta has waived change fees for passengers traveling Aug. 8 through Aug. 12. Also, on its website, Delta said that if a flight is canceled or significantly delayed, customers are entitled to a refund.
At 9:52 a.m., Flight Aware, a Houston-based flight data company, said "Delta flights are now departing worldwide at a rate of multiple flights per minute and over 160 flights in the air currently.
"There is still a backlog of hundreds of flights and passengers will continue to experience mass delays and cancellations, but operations are now on track for a recovery," Flight Aware wrote.
Earlier, Flight Aware said that between 8 a.m. and 8:30, only 10 of 181 scheduled Delta departures had taken off. "The flights departing are generally 3-4 hours delayed," the company said.
Despite active selling before the market opened, Delta shares were up 18 cents to $37.85 in mid-morning trading.
This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.