A nationwide ground stop was issued Friday afternoon.
It’s the first time since 2023, and before that was September 11, 2001 after the terrorist attacks in New York.
READ MORE: What is a ground stop?
The FAA has described the problem as a temporary telecommunications outage affecting regional air traffic control centers.
A ground stop does not necessarily mean the FAA has lost communication with aircraft already in the air.
Planes can still be directed through whatever operational communication systems remain available.
According to the FAA, depending on the aircraft and where it is flying, those options can include voice radio, digital text-based communication systems, or switching over to emergency radio frequencies.
The FAA has not identified the specific technical error that caused the nationwide communications outage or said which of these alternatives aircraft already in the air are using.
About 3,100 aircraft bound for U.S. airports were already in the air when the ground stop began, according to Flightradar24.
Homeland Security Secretary Markwayne Mullin said all airborne flights had been accounted for and could land safely.
The FAA said international flights would be handled individually while departures remained halted.