The Federal Aviation Administration ordered a nationwide ground stop Friday for all airports due a communication issue affecting air traffic control.

The agency's alert said the stop was "due to extraordinary circumstances and for reasons of safety." Transportation Secretary Sean Duffy said in an X statement a short while later that the stop was "due a communication issue impacting all Air Route Traffic Control Centers." "FAA technicians are investigating the issue," he said in an X post.

This is the second time since Sept. 11, 2001. that the FAA has ordered a nationwide ground stop.