A Federal Aviation Administration-ordered halt to all domestic flight departures across the United States was lifted Wednesday after the system providing pilots with pre-flight safety notices was restored following an overnight outage that caused extensive disruption.
The stop order in place after the failure of its NOTAMS -- or Notice to Air Missions -- system was lifted by the FAA shortly before 9 a.m. Eastern Time as the agency said normal air traffic operations were resuming across the country.
It was anticipated that some airlines could continue to delay or cancel flights because of ongoing congestion caused by the incident. An airline source familiar with the situation said airlines may implement ground delay programs, which could potentially lead to further timetable issues.
Airlines for America, an association representing US airlines, earlier said the outage was "causing significant operational delays." Major US carriers including United Airlines, Delta and American Airlines all said had grounded flights in response to the situation.
US President Joe Biden said there was no immediate information on what had caused the outage -- the second US aviation crisis in a matter of weeks. He said he had been briefed on the situation and was in touch with Transportation Secretary Pete Buttigieg.
"I just spoke with Buttigieg," he told reporters as he departed the White House. "They don't know what the cause is. But I was on the phone with him the last 10 minutes. I told them to report directly to me when they find out. Aircraft can still land safely, just not take off right now."
He continued, "They don't know what the cause of it is. They expect in a couple of hours they'll have a good sense of what caused it and will respond at that time."
Asked whether it was a cyberattack, Biden said: "They don't know. They will find out."
Earlier, White House Press Secretary Karine Jean-Pierre said in a statement that there was "no evidence of a cyberattack at this point," but that Biden had ordered a Department of Transportation investigation.
FlightAware, which tracks delays and cancellations, showed more than 4,000 flights to, from and within the United States as being delayed as of 8:50 a.m. ET, and 696 flights canceled so far.
International flights bound for the United States were continuing to take off from Amsterdam and Paris despite the situation. A Schiphol Airport spokesperson told CNN that "a workaround had been issued" and flights were still departing from Amsterdam.
No flights have been canceled from Paris' Charles de Gaulle airport, but delays were expected, according to the airport's press office. Frankfurt Airport also told CNN it had not been impacted.
A London Heathrow Airport spokesperson told CNN that they were "not aware of canceled flights and that flights to the US had left recently," however there were passenger reports of significant delays.
Shabnam Amini told CNN that she and other travelers had been sitting on board Americans Airlines flight 51 to Dallas for almost three hours at Heathrow because of the FAA outage.
She said they had been informed that there were delays but were still boarded onto the aircraft.
Commercial airline pilots use NOTAMS for real-time information on flight hazards and restrictions. The FAA stipulates NOTAMS are not to be relied on as a sole source of information, and so some flights may be able to satisfy safety requirements by using other data.
Wednesday's incident comes on the heels of another aviation crisis. A huge winter storm over the end-of-year holidays caused extensive disruption and helped trigger a Southwest Airlines meltdown that affected thousands of passengers.
-- This is a developing story. It will be updated.
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