The US Federal Aviation Administration issued a national ground stop of all departing flights on Friday “due to extraordinary circumstance and reasons for safety” after the agency earlier reported serious air traffic control communications issues.

The announcement means flights in the air may land, but flights on the ground cannot take off.

Shortly before the announcement, the FAA halted traffic in Chicago due to air traffic control communications issues. The agency said, “All departing traffic should remain groundstopped until further notice.” The FAA said international flights will be managed on a case-by-case basis.

Transportation Secretary Sean Duffy told the Associated Press that a communications issue is affecting regional air traffic control centers that direct planes between airports nationwide.

FAA technicians are investigating, AP reports.

Friday was the second nationwide ground stop of all departures since the September 11, 2001, attacks. The other happened in January 2023, when the FAA paused all domestic departures for less than two hours.

Last year, Congress approved $12.5 billion to fix the FAA’s aging communications system, and on Friday the FAA and White House asked Congress for another $30.1 billion to address other issues.

(Reporting by David Shepardson and Jasper Ward in Washington; Editing by Caitlin Webber, Franklin Paul and Rod NIckel)