Here’s what we know about the Atlanta airport outage

The cause of the fire that knocked out power to the world's busiest airport still isn't known, but Atlanta Mayor Kasim Reed offered the city's apologies to stranded passengers at a Sunday night press conference.

Reed and Hartsfield-Jackson International Airport General Manager Roosevelt Council said crews are working to re-establish commercial flight operations by midnight.

Here’s what we learned about the fire and what happened happen:

• At 12:38 p.m., Georgia Power officials noted multiple faults in its system that were discovered to be the result of a fire at an underground power station.

• Many criticized the airport, asking how power could fail throughout the sprawling complex, and how it could be that an airport couldn't switch to redundant systems. Reed said the fire was so intense it knocked out a switching system that would move service to redundant power networks.

• The cause of the fire is still unknown, but there is no evidence of foul play. Reed said Georgia Power and airport crews are focused on getting systems back online. Authorities are sweeping the airport grounds, but an act of terrorism at this point has not been ruled out, Reed said. "Because we don't know source of the fire, we don't know" if system might have been tampered with, he said.

• Tens of thousands of airport passengers were stranded when the power went out.