Trump blames Biden for airline ground stop

Donald Trump has made his first public comments on the weekend's air travel issues, blaming the Biden administration for leaving "a broken system".

He has also called on Congress for more funding to upgrade America's outdated air traffic control systems.

Thousands more US flights have been cancelled, with Transportation Secretary Sean Duffy warning travel disruptions would continue for another day.

The Trump administration says the air travel havoc triggered by a no-take-off order on Friday could drag on for another day, pushing back its timetable for a return to normal.

Nearly 2,000 more flights were cancelled on Sunday and questions remained over how such chaos could unfold in the world's largest economy, a country that prides itself on its technological prowess.

Stranded passengers wandered through chaotic US airports for a third day.

Officials have blamed Friday's flight chaos on faulty work to upgrade air traffic control communication cables.

On Sunday, President Donald Trump ended uncharacteristic days of silence on the ground stop, but only to blame his predecessor, Joe Biden, for the debacle.

Mr Trump insisted he inherited a mess from the Biden administration and said Congress, which his party controlled for two years, must approve funds to upgrade America's outdated air traffic control system.

"The Biden administration was an FAA disaster," Mr Trump said, referring to the Federal Aviation Administration.

"Everything they touched turned bad. Big money spent unwisely, making an old and broken system worse than when they began."

FAA chief Bryan Bedford said on Saturday that air travel for millions of Americans stranded at airports would return to normal by the close of business on Sunday.

But Transportation Secretary Sean Duffy said on Sunday morning that it would take longer to get planes, crews and travellers to where they needed to be.

"So, in the airspace, we're going to see things come back to normal today, but probably fully normal tomorrow," Mr Duffy told America's ABC News.

"We had airplanes and crews out of position because of Friday, so it takes a little bit of time to do that."

Mr Duffy also flatly rejected calls for his resignation over the travel chaos, insisting he inherited woefully outdated air traffic control infrastructure such as, he said, radar equipment dating back to the 1960s.

"So when we do work and things go wrong, of course I'm the secretary. But I also have to acknowledge what was delivered to me," Mr Duffy said in an interview on CNN.

As of Sunday afternoon, more than 1,880 flights within, into or out of the United States had been cancelled, according to the travel monitor site FlightAware.

The Trump administration has blamed Friday's nationwide ground stoppage — meaning no planes could take off — on a botched replacement of old copper wire communication lines.

Friday's disruption was only the second time such a ground stop had been issued in US airspace, among the busiest in the world, since the 9/11 attacks.

Mr Duffy has appealed for $US50 billion ($74 billion) in funds to upgrade and modernise the air traffic control system, and called for Congress, which controls the purse strings of the US government, to "meet this moment".

But Democrats quickly pounced to say Congress under Trump's Republicans could already have done this.