The Federal Aviation Administration grounded all flights in the United States on Friday afternoon, citing "extraordinary circumstances and for reasons of safety" and halting departures until further notice. Flights already in the air were allowed to land, but no new aircraft were permitted to take off. The agency reportedly issued the ground stop due to several impacts to air traffic control frequencies and radar capabilities, and its command center told airlines it did not have further information on the timing or cause of the problem.

U.S. Transportation Secretary Sean Duffy said in a post on X that the stop was related to a communication issue affecting Air Traffic Control Centers, and that agency technicians were investigating. The halt followed widespread reports of radio frequency outages at several of the nation's most critical control centers, including those in Boston, Chicago and New York. Controllers rely on designated radio frequencies to communicate with pilots and monitor airspace safety, and the FAA had also recently rolled out a text-based communication system alongside voice links. Reached for comment, an FAA spokesperson did not provide additional details.S2

Nationwide ground stops are rare; the last comparable halt of all air traffic came on September 11, 2001, and in January 2023 a ground stop was issued after an outage to the NOTAM system that distributes real-time warnings to pilots. Susan Hotle, a Virginia Tech transportation engineering professor who once worked at the FAA, said the episode underscored the need to modernize the air traffic control system, noting that a single failure can now affect a wide region at once. Earlier on Friday, Duffy had asked congressional leaders to act swiftly on the Transportation Department's request for $30.1 billion in funding updates to the system.S2

The disruption was compounding existing problems at some airports, including San Francisco International, where high winds had already delayed a number of flights before the nationwide stop. Travelers gathered to speak with airline staff, and a United Airlines employee announced over the intercom at Terminal 3 that the FAA had issued a nationwide ground stop. Michael McCormick, a former air traffic controller at Embry-Riddle Aeronautical University, warned that if the outage lasted more than a couple of hours, airlines and passengers could take days to recover, with aircraft and crews stranded in the wrong places.S2