Travelers wait to check in for for flights at Hartsfield-Jackson Atlanta International Airport in Atlanta, Monday, Dec. 18, 2017.

Image Credit: AP Photo/David Goldman

ATLANTA - The nation's air-travel system struggled to get back on schedule after a weekend power outage at the Atlanta airport, the world's busiest, forced the cancellation of over 1,400 flights just days before the start of the Christmas rush.

A fire in an underground service tunnel brought Hartsfield-Jackson Atlanta International Airport to a standstill Sunday. The fire broke out next to equipment for a backup system, causing that to also fail. Power wasn't fully restored until about midnight.

During those hours in the dark, thousands of travellers waited on planes or in the terminals. Disabled people had to be carried down stairs and escalators in the chaos. Inbound flights were diverted to other cities and outgoing flights were halted.

A spokesman for Delta Air Lines, which has its hub in Atlanta, said the majority of its stranded passengers have been booked on other flights that will leave Monday. Spokesman Michael Thomas said he expected said the airline would be "largely if not completely" back to a normal schedule by Tuesday, well before the peak travel weekend ahead of Christmas Day.

Delta is by far the largest carrier in Atlanta.

Anthony Foxx, who served as U.S. transportation secretary under former President Barack Obama, blasted airport officials, saying the problem was "compounded by confusion and poor communication."

Foxx said he was among the many travellers stuck for hours on a plane on the tarmac.

"Total and abject failure here at ATL Airport today," he tweeted, adding that there was "no excuse for lack of workable redundant power source. NONE!"

Georgia Power's top executive issued an apology, saying he realized the outage inconvenienced thousands of people.

CEO Paul Bowers said in a phone interview Monday a switch gear failed, causing a fire that then spread to cables coming in from two substations. But he said it wasn't clear what caused the switch gear to fail.

Delta customers flying to or from Atlanta were able to make a one-time change to travel plans without incurring a $200 change fee. The airline encouraged travellers not to pick up their bags Monday because of congestion at the airport.

Juan Rivera, 46, arrived in Atlanta on Sunday for a layover on his journey from Huntsville, Alabama, to Newark, New Jersey. He waited on the plane on the tarmac for more than two hours until passengers disembarked into a dark airport.

After staying in a hotel Sunday night, he returned to the airport Monday morning. Unable to get on a flight to Newark, he was now scheduled to fly to Philadelphia on Monday evening. Despite the 10 hours ahead of him at the airport, he had a smile on his face.

"I come from Puerto Rico," he said, noting that many there have been without power since Hurricane Maria pounded the island in late September. "This is nothing compared to what's happening over there."

When Delta flights were grounded last spring, it took the airline five days — and about 4,000 cancelled flights — before it fully recovered.

The April storm hit at a busy travel time when there weren't many empty seats for customers from cancelled flights. At the time, CEO Ed Bastian vowed that Delta would make "significant improvements" to its system for scheduling and tracking aircraft crews to recover more quickly from disruptions.

Delta cancelled about 1,000 flights Sunday and another 400 Monday. American Airlines cancelled 24 departures and an equal number of arrivals, spokesman Ross Feinstein said.

Some passengers complained about a lack of information from airport officials and little help from first responders to get the disabled and the elderly through the airport without the use of escalators and elevators.

"They had these elderly people, handicapped people lined up in wheelchairs," stranded passenger Rutia Curry said. "The people were helpless. They can't get down the stairs. It was just a nightmare."

Sara Melillo and her husband, Greg Presto, were travelling from Kenya, where they live, to Pittsburgh to spend Christmas with his family when they were stuck on the tarmac for six hours. The couple had landed shortly after the lights went out in Atlanta.

Melillo said the pilot had little information for travellers but the plane had air conditioning and flight attendants offered water and juice a few times. She described the Delta terminal as "big chaos" with not enough customer service for the hundreds of people trying to find a flight to their next destination and a place to sleep for the night.

In an email, Melillo told The Associated Press that the couple was scheduled to leave for Pittsburgh around midday Monday. The Delta check-in process was organized and lines were moving, she wrote. Airport workers were handing out doughnuts and other breakfast foods.

College student Joe Ryan had planned to fly home to Chicago with his fiancee on Sunday after a four-day seminar in Atlanta. They spent Sunday night on a carpeted floor outside a third-floor elevator, and hoped to get standby status on a Monday-afternoon flight. But he said he's been told it could be Tuesday before he gets a flight home.

"American Airlines doesn't have much information," he said.

American Airlines spokesman Feinstein said the airline was back on a normal schedule by late Monday morning

At Southwest Airlines, about 70 Atlanta departures out of 120 scheduled for Sunday were cancelled, an airline spokesman said in an email. United Airlines and JetBlue Airways were among carriers reporting delays or cancellations.

Hartsfield-Jackson, which serves 104 million passengers a year, is the world's busiest airport, a distinction it has held since 1998.

The airport serves an average of 275,000 passengers daily, according to its website. Nearly 2,500 planes arrive and depart each day.

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Associated Press writers David Koenig in Dallas, Tom Krisher in Detroit, and Kate Brumback, Johnny Clark and Robert Ray in Atlanta contributed to this report.

News from © The Associated Press, 2017