US lifts nationwide ground stop affecting all air travel, White House says 'no indication of nefarious act'

United States aviation officials have lifted a nationwide ground stop that halted flights across the country for around four hours.

US Transportation Secretary Sean Duffy confirmed that US airspace is open again, but said the fallout from the disruption could continue for days, reported BBC.

The ground stop was ordered at around 5am Singapore time on Nov. 14. US aviation officials cited "extraordinary circumstances and for reasons of safety".

It was lifted around four hours later, US media reported.

At the time of the outage, more than 3,000 flights were bound for US airports, according to Flightradar24.

Ground stop unrelated to ongoing Microsoft outage

US Homeland Security Secretary Markwayne Mullin sought to reassure the public that the ground stop was not caused by a "nefarious act".

He repeatedly stressed that the incident "isn't another 9/11".

Mullin added that there is no reason to connect today's issues to the ongoing Microsoft outage.

Caused by communication issues and "old legacy equipment that failed"

The outage was caused by "old legacy equipment that failed", according to US officials.

Duffy told reporters that the US has "an incredibly old air traffic control system". He explained that the routers became "overloaded with data", which led to inconsistencies in the data received from them.

Criticised Congress over air traffic funding

During a briefing by US cabinet secretaries, Duffy criticised the Republican-controlled Congress for not allocating more funding to air traffic infrastructure.

"I can't build things if I don't have money," he said, while shaking his head.

Duffy is asking Congress for US$50 billion (about S$65 billion) to build new air traffic control systems to replace the current ones, which he described as incredibly old.

Stranded travellers

US airports were filled with stranded travellers and stuck families, NYT reported.

NYT reporter Jack Healy was himself stuck on the runway on a United Airlines flight due to leave Chicago for Rochester, New York, when the ground stop came into effect.

Reporting from his seat, Healy said flight attendants were doing their best to keep passengers comfortable by "passing out cookies and water", but added that frustration was growing because passengers had no information on when the situation might end.

Guy Gratton, an Associate Professor of Aviation and the Environment at Cranfield University, told BBC Verify that this is the longest US air traffic grounding event since 9/11, but is "clearly not on that scale".