The outage came on the eve of a busy travel day, with Monday a peak time for business travelers to start trips and the holiday travel season already starting.
The winter holiday travel period started last Friday and runs through Thursday Jan. 4, with 51 million passengers expected to fly over the full period, according to industry group Airlines for America.
That means tens of thousands of travelers are affected and many flights will be full, making it more difficult for those whose flights were cancelled to get rebooked the following day.
While a storm in the forecast allows airlines to cancel flights in advance and gives travelers a chance to adjust their travel plans and in some cases stay home, the sudden outage left thousands of travelers stranded at a dark and powerless airport in the middle of their trips. Some may have to wait days to get to their destinations.
A sudden outage also catches airlines flat-footed, and can mean planes and flight crews end up in the wrong cities, making it more difficult to restart operations on schedule.
“You can’t have the nation’s largest airport down for hours without impacts rippling across the nation,” according to travel expert Joe Brancatelli.
Multiple airlines said they would waive certain change fees for passengers with flights booked Monday to, from or through Atlanta who want to change their travel plans.