Boarding areas began to fill up at airports across the country.

On Friday afternoon, the FAA said in a post on X that there has been a temporary telecommunications outage.

“Out of an abundance of caution, all flights have been halted,” said the FAA. “Every flight has been accounted for and international flights will be handled on a case by case basis.”

Flight boards are flashing red and orange across all major airports. Transportation officials have not yet said why they issued the ground stop.

In some airports, stranded passengers are congregating in terminals as security check lines grow longer.

The outage occurred the same day the FAA rolled out SMART, a new AI-powered tool designed to help manage air traffic.

Air Space Intelligence, the company behind SMART, said Friday’s disruption was not “based on or a result of the SMART system, any product of ASI or our integration with FAA and ATC.”

Jon Lett, a passenger who was traveling from the Salt Lake City Airport to Kansas City, told Business Insider that everyone on his flight has been told to disembark and wait.

Lett said that, though the mood among passengers remains “chill,” there is no telling whether his flight will be able to depart anytime soon.

Photos show planes parked back-to-back at Chicago O’Hare International Airport.

National ground stops are historically rare for the FAA.

In January 2023, the FAA halted flights because of an outage involving its pilot alert system. Before that, nationwide air traffic was halted following the September 11, 2001, terrorist attacks.

Lines to collect luggage are also growing in some airports. It is unclear whether they are arriving passengers or travelers giving up on their flight for the day.

Not everyone has been ordered to disembark. Photos showed some passengers sitting in unmoving planes.