The Federal Aviation Administration stopped departing flights at every airport in the United States Friday afternoon, after a communication problem hit the centers that guide aircraft between airports.

The order, issued by the FAA's Air Traffic Control System Command Center at 1:53 p.m. Mountain time, said all airports were ground stopped "due to extraordinary circumstances and for reasons of safety." It told operators that "all departing traffic should remain ground stopped until further notice" and said inbound international flights would be handled case by case, according to the FAA advisory.

Transportation Secretary Sean Duffy said in a post on X that the stop followed "a communication issue impacting all Air Route Traffic Control Centers."

"FAA technicians are investigating the issue," Duffy wrote. "We will provide immediate updates as we have them."

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The FAA, in a statement quoted by CNBC, described communication issues affecting "multiple" centers. The centers manage high-altitude traffic between airports across the country, including the Denver center in Longmont that covers Colorado.

As of 2:45 p.m., neither the FAA nor the Department of Transportation had said what caused the problem or when flights would resume.

Flights already in the air were not ordered down. A second FAA advisory, issued at 2 p.m., told pilots to expect "airborne holding" at airports throughout the system because of equipment outages, which means planes may circle before they are cleared to land.

The trouble showed up first in Chicago. About 35 minutes before the nationwide order, the FAA halted flights bound for Chicago Midway International Airport from across the country, citing an equipment outage. The Chicago center later stretched its flight-plan processing time to three hours because of an equipment outage, according to FAA advisories.

The order covers every commercial airport in Colorado, including Denver International Airport. Travelers should check with their airline before leaving for the airport. The FAA posts current airport conditions at nasstatus.faa.gov.

Nationwide ground stops are rare. The last one came in January 2023, when the failure of the FAA's Notice to Air Missions system held departures across the country for about 90 minutes. Before that, the FAA cleared the skies after the September 11, 2001, terrorist attacks.

This is a developing story and will be updated.