ATLANTA -- While power has been restored to the world's busiest airport, the travel woes will linger for days.
Thousands of people were stranded Monday morning at Hartsfield-Jackson Atlanta International Airport, where more than 1,000 flights were grounded just days before the start of the Christmas travel rush.
A sudden power outage that Georgia Power said was caused by a fire in an underground electrical facility brought the airport to a standstill Sunday about 1 p.m.
All outgoing flights were halted, and arriving planes were held on the ground at their point of departure. International flights were being diverted, officials said.
At Denver International Airport, two Atlanta-bound Delta Air Lines flights were canceled on Monday morning and two others were delayed. A Frontier Airlines flight for Monday night was canceled.
Flights from Atlanta to Denver were also affected, with one United Airlines flight canceled and another delayed. A Frontier flight was canceled and a Delta flight was delayed.
More delays and cancellations were expected throughout the day.
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Delta, with its biggest hub in Atlanta, will be hardest hit. By Sunday evening, Delta had already canceled nearly 900 flights and another 300 Monday, nearly all of them in Atlanta, according to tracking service FlightAware.com.
Robert Mann, an aviation consultant and former American Airlines executive, said it likely will be Tuesday before Delta's operations in Atlanta return to normal, and for passengers "it could be most of the week" because there aren't many open seats on other flights in the last week before Christmas.
One bit of good news, according to Mann: Delta has more spare planes and available crews in Atlanta than anywhere else, which should help it to recover.
Delta customers flying to or from Atlanta can make a one-time change to travel plans without incurring a $200 change fee.
The airline also encouraged travelers not to pick up their bags Monday because of anticipated congestion at the airport.
Still, when flights at Atlanta were grounded for most of one day last spring, it took Delta five days -- and about 4,000 canceled flights -- before it fully recovered.
Like Sunday's outage, that April storm hit Delta's largest hub at a busy travel time when there weren't many empty seats to accommodate customers from cancelled flights.
At the time, CEO Ed Bastian vowed Delta would make "significant improvements" to its system for scheduling and tracking aircraft crews to recover more quickly from disruptions.
Other airlines also canceled flights for the rest of Sunday. American Airlines canceled 24 departures and an equal number of arrivals, said spokesman Ross Feinstein.
The airline also diverted three planes that were headed to Atlanta when the outage struck, sending them instead to Dallas; Nashville, Tennessee; and back to Philadelphia.
The city of Atlanta provided shuttle service to the Georgia Convention Center on Sunday for travelers needing a place to stay.
According to a Georgia Power statement, the utility believes a piece of equipment in an underground electrical facility might have failed, causing the fire. The fire was next to equipment for a backup system, causing that to also fail.
"No personnel or passengers were in danger at any time," the statement said.
No areas outside of the airport were affected by the power loss. The utility said there are "many redundant systems in place" to ensure the power supply to the airport and that such outages at the airport "are very rare."
Airport workers were distributing bottled water, and Dunkin' Donuts was giving out doughnuts. Chick-fil-A, which is usually closed on Sundays, opened to provide meals for travelers, according to the airport's Twitter feed.
Officer Lisa Bender of the Atlanta Police Department said officers were at the airport to help with crowd control and managing traffic around the airport.
At Southwest Airlines, about 70 Atlanta departures out of 120 scheduled for Sunday were canceled, an airline spokesman said in an email.
United Airlines and JetBlue Airways were among carriers reporting delays or cancellations.
American Airlines reported only a handful of diversions and cancellations because the carrier does not use Atlanta as a hub, airline spokeswoman Alexis Aran Coello.
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.AlertMe