ATLANTA (RNN) – Travel is slowly returning to normal, as Atlanta’s Hartsfield-Jackson International Airport recovers from an 11-hour power outage Sunday that resulted in hundreds of canceled flights and thousands of stranded travelers.

Georgia Power CEO Paul Bowers appeared in a video on Twitter on Monday afternoon to apologize for the outage, and to explain what took place.

“The outage was the result of a fire that occurred in the service tunnel that serves the concourses at the airport,” he said in the 66-second video. Bowers added that the backup power service also was damaged by the fire.  

Delays and cancellations bled into Monday with Delta canceling 300 flights scheduled for Monday morning, mostly arrivals into Atlanta to allow the world’s busiest airport to recover faster. Delta, which uses Atlanta as its primary hub, said its flight schedule is expected to return to normal by Monday afternoon.

Authorities are encouraging passengers to check their flight statuses through their airline’s website or app.

But it’s not all smooth sailing. About 90 percent of the power is back at the airport. CNN reported early Sunday that electronic readers at the security checkpoint were still not working, meaning passengers were not able to use their online boarding passes and airline apps at the checkpoint and needed paper boarding passes printed out by the airline.

Additionally, the underground rail transit system at the airport was not working Monday morning. Travelers were still able to walk between concourses. 

Delta also suspended travel by unaccompanied minors until the delays are resolved.

Several airlines are waiving change fees for passengers booked for Monday to, from, or through Atlanta, according to the Atlanta Journal-Constitution.

Georgia Power restored power to the airport shortly before midnight.

Though power was restored shortly before midnight, more than 1,000 flights in and out of the airport were canceled Sunday, leaving passengers stranded on planes for as long as eight hours. Some passengers were removed from planes with portable staircases, and others were brought food and water while they waited for power to be restored and gates to become operational.

Thousands more were stuck inside the airport with little to no information about what has caused the outage or when it would be over.

According to Atlanta Mayor Kasim Reed, all passengers at ATL were de-planed by 10 p.m Eastern. They were offered room to stay at the Georgia International Convention Center and free parking until 8 a.m. Monday.

Papa John’s is delivering pizza to stranded passengers, following Chick-fil-A’s lead. The chicken restaurant, which is not typically open on Sunday, provided passengers with meals and water.

Reed apologized during an evening news conference and said the power outage, which started shortly before 1 p.m., was caused by an electrical fire.

The fire damaged two substations serving the airport, including the system that provides backup power, according to CNN.

Security checks were done, and Reed says there’s no sign the fire was set deliberately.

After the outage, the Federal Aviation Administration called for a ground stop for flights headed to ATL.

“A ground stop means that flights headed to Atlanta are held on the ground at their departure airport,” the FAA wrote on Twitter.

Hartsfield-Jackson, which serves 104 million passengers a year, is the world’s busiest airport, according to the Associated Press.

The airport serves an average of 275,000 passengers daily, and nearly 2,500 planes arrive and depart each day.

Among the stranded passengers was former Secretary of Transportation Anthony Foxx, who served under President Barack Obama. He tweeted about his experience throughout the day Sunday while trapped on a plane for more than five hours. He later posted he was trying to rent a car and drive to Charlotte for a flight.

Country music star Travis Tritt also tweeted he was among the affected travelers. Tritt said he was stuck in Fort Lauderdale, FL, after his flight to Atlanta was canceled. He indicated he planned to charter a private jet to different airport near Atlanta and offered condolence to other passengers not as fortunate.

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