The emergency alert, issued at 3:54 p.m., provided little explanation, instructing that “all departing traffic should remain ground stopped until further notice.”
The sudden disruption triggered widespread flight cancellations and delays across the United States. By 6:20 p.m., more than 2,000 flights had been cancelled and over 10,000 delayed, according to FlightAware, as lawmakers demanded an explanation for the incident.
The FAA said inbound international flights would be handled on a case-by-case basis.
At the time the directive was issued, 4,042 flights bound for destinations in the United States were already airborne, according to Flightradar24, a Swedish flight-tracking service.
Homeland Security Secretary Markwayne Mullin said there was “no indication as of yet” that the incident was caused by anything “nefarious,” adding that an initial assessment pointed to a telecommunications outage.
Mullin said President Donald Trump had been briefed on the situation but stressed that officials were “not ruling out anything at this point” as investigations into the communications failure continued.
He also sought to reassure passengers already in the air, saying there was no reason for concern.
“We are assured that everybody is safe,” Mullin said.
