Transportation Secretary Sean Duffy says a communication issue affecting all of the FAA's air route traffic control centres caused the nationwide ground stop. His statement is the first official explanation for the halt.
Writing on X on Friday, Duffy said:
"The [FAA] issued a nationwide ground stop for all U.S. airports following a communication issue impacting all Air Route Traffic Control Centers"
He added: "FAA technicians are investigating the issue."
The FAA's own advisory gives no cause and does not mention communications. It cites only "reasons of safety", and the agency has not officially identified what went wrong.
The Washington Examiner, citing two FAA employees and documents it had seen, reports a "rolling frequency outage" at facilities that monitor aircraft. Its reporter Anna Giaritelli posted notices describing a "nationwide ground stop for all centers, all destinations until further notice due to widespread frequency outages". That report rests on anonymous sources and has not been independently checked.
Neither Duffy nor the FAA has said whether a cyber attack or any other security threat is involved.