What caused such a drastic delay at America’s busiest airport? An electrical fire in an underground tunnel damaged the main and backup power systems.
“Fire shouldn't paralyze the country's busiest airport for half the day,” said Joseph Schwieterman, public policy professor at DePaul University. “ It may take a couple hours to bring alternative power to the airport, but if the airport infrastructure itself was undamaged, it shouldn't have been nearly as painful."
Schwieterman attributes this to airlines not planning for disasters.
You can read more about the blackout and the airline industry in the link below…
http://money.cnn.com/2017/12/18/news/atlanta-hartsfield-jackson-power-outage-cause/index.html