Last update: 4:10 p.m. ET.

Flights are taking off again at Atlanta’s busy airport, but another day of significant disruptions awaited fliers Monday after a power outage snarled flights there Sunday.

The power was back on Monday, but more than 400 flights were canceled at the Hartsfield-Jackson Atlanta International Airport as of 4 p.m. ET, according to flight-tracking service FlightAware. Fortunately for fliers, that number had not increased since the early morning hours.

Even before Monday morning, Delta preemptively grounded 300 of flights the night before in a move the carrier hoped would give it some slack as it tried to reboot its flight schedule at its busiest hub.

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“Most of the 300 cancellations Monday are early morning, inbound flights to Atlanta to give the operation there an opportunity to more quickly return to normal,” Delta said in a statement. “Delta’s flight schedule in Atlanta is expected to return to normal by Monday afternoon."

The Federal Aviation Administration echoed that sentiment, saying via Twitter that "operations at @ATLairport are expected to be back to normal by midday."

Whether "normal" would return by afternoon remained to be seen. And that still left thousands of passengers grounded by Sunday's outage looking for new flight options. Many other passengers were seeking there own ways to get to their destinations after their Atlanta-bound flights diverted to other airports Sunday.

For now, all big airlines flying to the airport were waiving change fees for customers scheduled to fly through the airport Monday.

For those who do fly through Atlanta Monday, a normal day seemed unlikely. Long lines were expected everywhere from airport roadways to check-in and security queues. That comes as all of those affected by Sunday’s problem returned to the airport, joining the throng of fliers that were already scheduled to fly Monday from the airport, the world’s busiest.

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On average, more than 270,000 fliers pass through the airport each day. The counts for the peak holiday travel period will be much higher.

Adding to Monday's complications, NBC News reports that Delta’s electronic boarding pass system was offline in Atlanta early Monday, forcing those bumped from Sunday’s flights to wait in line for paper tickets.

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The disruption is unwelcome news for air travelers just as the busy holiday season ramps up.

Flights run full this time of year, especially on the peak travel dates of Thursday (Dec. 21), Friday (Dec. 22) and Tuesday, Dec. 26. That means there are few empty seats to accommodate fliers during mass disruptions like the one that's currently affecting Atlanta.

For Delta and the other airlines flying from Atlanta, the hope will be that this problem came early enough in the holiday travel window that enough slack can be found to get stranded fliers to their destinations in a reasonable time frame. Had the problem occurred just two days later, things would have been much worse for holiday travelers.

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