The Federal Aviation Administration halted all departing flights across the United States and Canada on Friday, citing "extraordinary circumstances and for reasons of safety . . . until further notice," according to NBC News. The order, a rarity in U.S. aviation, followed what regulators described as a widespread air traffic control communication failure. As of 5:20 p.m. ET, FlightAware.com, a live flight tracking service, recorded more than 9,000 delayed flights within, into, or out of the United States, alongside 440 cancellations.

What caused the ground stop?

The FAA issued the stop "due to several impacts to ATC [air traffic control] Frequencies and/or Radar capabilities," The Air Current, an aviation industry news service, reported. The FAA command center told airlines it does not have further information on the "timing or cause of this outage," the outlet added.

United States Secretary of Transportation Sean Duffy attributed the disruption to a systemic breakdown. In a post on X, he said the ground stop "follows a communication issue impacting all Air Route Traffic Control Centers" — the facilities that manage aircraft flying at high altitude between airports. "FAA technicians are investigating the issue. We will provide immediate updates as we have them," Duffy said.

Was it a security threat?

Officials moved quickly to rule out hostile action. Homeland Security Secretary Markwayne Mullin told reporters at the White House "there is no indication that we've had, no reason to believe, that as of right now this was a threat to the United States," according to CNN. He later added: "this was a telecommunication outage."

Inbound international flights will be managed on a case-by-case basis, Axios reported. Fast Company has reached out to the FAA for comment.

How rare is a nationwide ground stop?

The decision marks only the third such order in modern U.S. aviation history, according to available records. The last nationwide ground stop occurred on January 11, 2023, when an FAA contractor "unintentionally deleted files related to a key pilot safety system," CNN reported at the time. That incident disabled the NOTAM system — Notice to Air Missions, the mechanism that alerts pilots to hazards on flight routes.

Prior to 2023, the only comparable order followed the terrorist attacks of September 11, 2001. The 23-year gap between the 9/11 order and the 2023 NOTAM failure underscores how extraordinary Friday's decision was.

What is the operational scale?

The numbers frame the disruption. FlightAware's count of more than 9,000 delayed flights covers all traffic within, into, or out of the United States as of 5:20 p.m. ET on the day of the stop. The 440 cancellations logged by the tracker add to the operational toll on carriers and airports.

Ground stops (orders that hold aircraft at their departure airports) are normally issued for localized weather or equipment problems. A nationwide order affecting all Air Route Traffic Control Centers indicates a failure at the infrastructure level of the National Airspace System rather than a localized event.

How long will it last?

No restoration timeline has been confirmed. The FAA's own command center told airlines it had no information on the timing or cause of the outage, according to The Air Current. Secretary Duffy committed to "immediate updates" but offered no estimate.

On Bluesky, musician Flavor Flav reported from Atlanta's airport that the ground stop would last "multiple hours," though the figure appeared to be informal rather than official. "This has been Flavor Flav from the Atlanta Airport," he posted. "And now to Chuck D from JFK."

This is a developing story. For airline passengers, the immediate consequences are concrete: departures held indefinitely, inbound international flights subject to case-by-case handling, and a delay count that climbed past 9,000 before the evening ended.