https://arstechnica.com/cars/2023/01/potential-travel-chaos-as-faas-notam-service-goes-down/

Today might not be the best day to fly. Earlier this morning, the Federal Aviation Administration suffered an outage to its Notice to Air Missions system. Better known as NOTAMs, these provide information to pilots about potential hazards along their routes, including temporary flight restrictions such as a rocket launch or air show, perhaps.

Consequently, flight operations across the US have been affected. At first individual airlines delayed flights, but at 7:19 am Eastern the FAA announced a nationwide pause in all flight departures until 9 am eastern time.