A Delta Air Lines plane is seen on the tarmac of the Fort Lauderdale-Hollywood International Airport on July 14, 2016 in Fort Lauderdale. (Photo by Joe Raedle/Getty Images)

Delta Air Lines canceled another 250 flights on Tuesday as it works to recover from a computer network crash that halted or delayed all flights for hours.

The Atlanta-based airline canceled about 1,000 flights Monday and is still advising passengers to check their flight status before they leave for the airport.

“We were able to bring our systems back on line and resume flights within a few hours yesterday but we are still operating in recovery mode,” said Dave Holtz, senior vice president in charge of operations, in a statement. “We are sorry for what many of our customers have experienced over the past 24 hours, including those who remain at airports and continue waiting for their flights. We are doing everything we can to return our operation to normal reliability, but we do expect additional delays and cancellations.”

Delta is offering compensation and refunds to passengers whose flights were cancelled or significantly delayed.

It’s still unclear what caused the malfunction. Delta attributed it to a power outage, though Georgia Power said it is was mostly likely an internal computer glitch.

Delta CEO Ed Bastian posted a video apology to customers Monday.