What ATC Zero Means as the FAA Grounds Flights Across the U.S.

ATC Zero describes a situation in which an air traffic control unit cannot provide services safely. The Federal Aviation Administration (FAA) uses the operational classification when a facility’s ability to organize and monitor flights falls below the level needed to ensure safe operations. The term drew attention during an aviation emergency in the United States on Friday, November 13.

ATC stands for air traffic control. A facility classified as ATC Zero may lack the resources or communications needed for controllers to maintain safe separation between aircraft. Depending on the circumstances, the designation can result in departures being suspended, aircraft movements being restricted, or flights being redirected to other control areas.

The classification can apply to individual facilities, including airport control towers and regional centers responsible for managing aircraft in specific areas. It does not automatically mean that a country’s entire airspace is closed. However, flights that depend on the affected unit may face restrictions or be unable to depart while the unit cannot operate safely.

On Friday, the FAA ordered departures suspended across the United States after identifying communications problems affecting all 22 of the country’s regional air traffic control centers. Those centers coordinate aircraft traveling between airports. Without adequate communications, controllers may be unable to manage traffic flows or ensure safe distances between planes.

The FAA described the nationwide suspension as a precaution. Aircraft that had not yet taken off were ordered to remain on the ground, while international flights bound for the United States were assessed individually. The disruption caused delays, cancellations and diversions. Aviation analytics firm Cirium said about 11,000 flights were scheduled to depart U.S. airports after 4 p.m. Eastern time that day, affecting passengers in multiple parts of the country.

Homeland Security Secretary Markwayne Mullin said a telecommunications failure caused the incident. He said there was, at that point, no evidence of a cyberattack, while authorities continued investigating the source of the problem. The nationwide grounding of departures is unusual: Friday’s action was the second such nationwide stoppage since the September 11, 2001, attacks. The previous one occurred in January 2023, when a failure in the FAA’s safety-notification system halted departures for about 90 minutes.