The US Federal Aviation Administration (FAA) has lifted a nationwide ground stop imposed on Friday that halted departing flights, an order it issued citing “extraordinary circumstances and reasons for safety”.
The halt, which grounded thousands of flights across the country, was lifted on Friday evening.
This was the third nationwide ground stop of all departures since the September 11, 2001, attacks.
“Everybody’s safe,” Homeland Security Secretary Markwayne Mullin said, adding that this was not “another 9/11”.
Here is what we know:
What happened?
The FAA issued a nationwide ground stop at 3:54pm Eastern Time (20:54 GMT) on Friday due to a telecommunications outage affecting air route traffic control centres, which handle flights travelling across the country.
The FAA confirmed that the nationwide ground stop had been lifted.
US Transportation Secretary Sean Duffy said airspace reopened at 8:15pm ET (01:15 GMT on Saturday), after more than four hours of disruption.
“We’ve opened up the airspace,” Duffy said, warning that flights would not resume immediately.
“It’s going to be slow,” he added, urging passengers to check with their airlines.
Duffy said flights would resume depending on the availability of pilots and flight attendants, with authorities trying to get as many flights moving as possible on Friday night.
Aviation analytics firm Cirium said that after 4pm ET (21:00 GMT) on Friday, about 11,000 flights carrying more than 1.5 million passengers were still scheduled to depart from US airports.
By 7:05pm ET (00:05 GMT on Saturday), at least 827 flights had been diverted, according to Cirium. Of those, 670 returned to their departure airports, while 157 were diverted elsewhere.
Aircraft already in the air were allowed to continue to their destinations and land during the ground stop.
During the ground stop, international flights were handled on a case-by-case basis, with some allowed to depart despite the restrictions.
How many flights were affected?
More than 4,700 flights were cancelled and 10,000 delayed on Friday, while another 700 had already been cancelled for Saturday, according to FlightRadar24.
Aviation analysts said it could take days for airlines to restore their schedules.
Reporting from Los Angeles international airport, Al Jazeera’s John Hendren spoke to passenger Nicholas Erdodi, who travelled from New Zealand and was trying to reach Chicago for a conference.
Erdodi said he had been travelling for 16 to 18 hours before spending another six hours at the airport, where passengers had been forced to leave their plane.
“The challenge is you cannot ask anyone here what to do,” he told Al Jazeera.
“Lack of information is what bothers me, I mean, and not to mention find the hotel for the night, not to mention all the cost.”
Erdodi said he had been rebooked but remained uncertain whether his next flight would depart.
“I work in tech, I understand what could be going on, but someone needs to tell us,” he said.
“It doesn’t matter if someone tells us that we don’t know what’s happening, but please just let us know what’s going on,” he added.
What does a nationwide ground stop mean?
A nationwide ground stop temporarily requires departing aircraft to remain on the ground until cleared to take off.
Flights in the air are generally allowed to continue to their destination, but new departures are on strict orders to stay grounded.
The measure is intended to stop any further aircraft from entering the airspace as the authorities deal with the safety issues.
What caused the FAA nationwide ground stop?
The FAA said the ground stop was caused by a telecommunications outage affecting air traffic control systems.
Duffy said the outage was caused by switches and routers that became overloaded with data and went down, adding that the incident did not involve a total loss of communications or radar capabilities.
Todd Curtis, an aviation safety expert and chief executive of AirSafe.com, told Al Jazeera that the failures appeared to be concentrated in the country’s air route traffic control centres.
“There are 21 across the United States, one in Alaska and the other 20 in the lower 48,” he said.
“These are the folks who handle the aircraft that are transiting from one part of the country to the other, and they rely on multiple handoffs between controllers.”
Speaking before Duffy provided further details, Ron Bartsch, a professor of international aviation law at the University of the South Pacific, raised questions about the apparent failure of backup systems.
“The whole aviation community is based on redundancy,” he told Al Jazeera.
“So the fact that a redundant system hasn’t kicked in immediately just raises more questions than what we’ve seen answers to at this stage.”
Mullin said that there was no cyberattack linked to the nationwide ground stop and that the public was never in danger.
Duffy acknowledged that tens of thousands of travellers had been stranded and called for $50bn in upgrades to the nation’s air traffic control system.
When will US flights return to normal?
Duffy said it will “take us some time to get back to capacity”, but he expected operations to be “back up and operational as we come into the heat of travel during Thanksgiving”.
The Thanksgiving travel period, which begins in less than two weeks, is usually one of the busiest times of the year for air travel in the US.
Aviation safety expert Curtis also warned that the disruption could continue affecting passengers even after the technical problems were resolved.
“If it’s fully resolved, it would take more than a day to get back to normal, to reschedule aircraft,” he told Al Jazeera.
He explained that many airlines operate interconnected networks, meaning passengers often have to change planes at major hubs.
“So there could be a bit of a hassle on the part of the airlines trying to figure out how to get everyone to where they have to go,” he said.
Passengers have been advised to check their flight status directly with their airlines, as delays and cancellations might continue.
