Update 1/11/23 9:03am ET: According to the FAA, the ground stop has been lifted, and air traffic is resuming "gradually" across the country. The agency continues look into the cause of the problem with the NOTAM system.
The Federal Aviation Administration has ordered airlines to pause all domestic departures in the US until at least 9:30AM Eastern time while it's restoring its Notice to Air Missions (NOTAM) system. On early Wednesday morning, the agency issued a notice through an Air Traffic Control System Command Center Advisory that the US NOTAM system had failed. "Operations across the National Airspace System are affected," the FAA said in a tweet, along with the information that it was working to fix the outage.
In follow-up tweets, the agency said that while some of the system's functions are coming back online, it was still working to fully restore it. Pausing all domestic departures will give it time "to validate the integrity of flight and safety information." The FAA originally announced that it was pausing all domestic flights until 9AM, but a newer notice from the agency said ground stops will continue until at least 14:30 Zulu/UTC (9:30AM ET).
According to Simple Flying, this is the first time the US NOTAM system has failed, affecting flights across the country. People have been reporting delayed flights since at least the evening of January 10th — based on the the FAA's advisory, the system failed at 2028Z or 20:28 Zulu/UTC (3:28PM ET). Reuters said over 400 flights flying within, from and into the US had been delayed by 5:31AM ET today, January 11th.
The FAA has also issued a newer advisory announcing the nationwide ground stop and promising further communication once system restoration is complete. It's unclear whether the FAA will be able to fully remedy the issue by the suggested time. As the news organization noted, a NOTAM contains information that's essential to flight personnel. Some NOTAMs for long-haul international flights could have as many as 200 pages and include important details, such as runway closures and low-altitude construction obstacles.
White House press secretary Karine Jean-Pierre has tweeted that the President has been briefed about the outage and that he has directed the Department of Transportation to conduct a full investigation to find out what caused it. At this point, Jean-Pierre said, there's no evidence of a cyberattack.