The US Federal Aviation Administration lifted a nationwide ground stop on Friday evening after a telecommunications outage disrupted air traffic control systems and halted departing flights for more than four hours.
The order, imposed at 3.54pm Eastern Time, was lifted at 8.15pm, although Transportation Secretary Sean Duffy warned that flights would return gradually as airlines worked to restore their schedules.
“We’ve opened up the airspace,” Mr Duffy said. “It’s going to be slow.” He urged passengers to check directly with their airlines, saying departures would depend on the availability of pilots and cabin crew.
The disruption affected thousands of flights across the US. FlightRadar24 reported that more than 4,700 flights had been cancelled and 10,000 delayed on Friday, while a further 700 had already been cancelled for Saturday.
Cirium said about 11,000 flights carrying more than 1.5 million passengers had still been scheduled to depart from US airports after 4pm. By 7.05pm, at least 827 flights had been diverted, including 670 which returned to their departure airports and 157 sent elsewhere.
What caused the US nationwide ground stop?
The FAA said the stoppage was triggered by a telecommunications failure affecting air route traffic control centres, which manage aircraft travelling between different parts of the country.
Mr Duffy said switches and routers had become overloaded with data and gone down. He said the incident did not result in a total loss of communications or radar capabilities.
Aircraft already in the air were allowed to continue to their destinations and land. International flights were dealt with individually, with some permitted to depart during the restrictions.
Homeland Security Secretary Markwayne Mullin said there had been no cyberattack and that the public had never been in danger. “Everybody’s safe,” he said, adding that it was not “another 9/11”.
The stoppage was only the third nationwide halt to all departures since the attacks of September 11, 2001.
Passengers face further delays
A nationwide ground stop requires departing aircraft to remain on the ground until they are cleared for take-off. The measure is intended to prevent more aircraft entering the airspace while safety or operational problems are dealt with.
Tens of thousands of travellers were left stranded. At Los Angeles International Airport, passenger Nicholas Erdodi said he had travelled from New Zealand and spent 16 to 18 hours in transit before being held at the airport for another six hours after passengers were ordered off their plane.
“The challenge is you cannot ask anyone here what to do,” he said, describing the lack of information and the cost of finding accommodation. Although he had been rebooked, he remained unsure whether his next flight would leave.
“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,” Mr Erdodi said.
Aviation analysts warned that it could take days for airlines to restore their schedules. Mr Duffy said it would “take us some time to get back to capacity”, but expected operations to be “back up and operational as we come into the heat of travel during Thanksgiving”.
Thanksgiving travel begins in less than two weeks and is normally one of the busiest periods of the year for US air travel.
Todd Curtis, an aviation safety expert, said that even if the technical problem had been fully resolved, it would take more than a day to reschedule aircraft and passengers across the interconnected airline network.
Mr Duffy called for $50 billion in upgrades to the US air traffic control system. Passengers have been advised to check their flight status with their airline, as cancellations and delays are expected to continue.
