FAA looking into what caused system outage that resulted in mass delays

The Federal Aviation Administration announced shortly before 9 a.m. Eastern that air traffic operations were resuming at airports across the United States, following an overnight outage of the agency’s Notice to Air Missions system, which provides safety information to flight crews. The FAA had previously ordered U.S. carriers to temporarily halt all domestic flight departures as it worked to fix the technical outage, which caused nationwide travel disruptions.

https://www.washingtonpost.com/nation/2023/01/11/faa-notam-outage-flights-us/