That's the end of the press conference with US Homeland Security Secretary Markwayne Mullin and Transportation Secretary Sean Duffy.
Here's a quick recap of what we learned:
The national ground stop order has been lifted.
Flights will begin taking off in the coming hours.
Officials say old technology was to blame for "intermittent" communications outages that led the FAA to block most flights from taking off.
Duffy could not confirm whether similar technical difficulties can be prevented in coming weeks.
There has been "zero evidence" uncovered that the outages were the result of a cyberattack.
Both officials accused Congress of dragging its feet on providing enough funding to efficiently upgrade the communications system, though Duffy deflected when it was pointed out Republicans have had control of Congress and the White House for the last two years.
Stay with us here for more updates as they come to hand.
Duffy is asked what was different about today
Duffy is asked if there was any difference today that might have caused the nationwide incident.
The transportation secretary says he doesn't know whether this scenario will occur again but notes smaller-scale incidents have occurred in the past.
"We're still working on the details of what went wrong today," he says.
"Our team is working overtime to try and navigate what happened here, what was the cause, and how do we prevent it in the future."
He reiterates that new equipment, including an AI system, was not at fault for the communications failure.
Duffy says communication issue wasn't a 'complete blackout'
Duffy has clarified that the issues with the communication and radar systems were "intermittent".
"It wasn't a complete blackout, so we were able to keep some of those communications going," he said.
"When you have issues and you can't immediately communicate or immediately see where aircraft are at, that is a risk we are unwilling to tolerate."
Duffy deflects questions about funding not coming from Republican Congress
The ground stop came just weeks before the holiday season in the US, with Thanksgiving less than two weeks away.
Duffy is asked how Americans can be confident a similar issue won't arise in the coming days, given this was caused by old technology becoming overwhelmed with data.
He says it's a "great question" and reiterates his calls for more funding from Congress to upgrade those telecommunications systems.
"We should talk to our senators and our members of Congress," he says.
"This is not the first time. We had this in New York when global leaders were flying in for the UN.
"How many times does this have to happen before Congress gives the money to fix it?"
A journalist then points out that Republicans have had control of the House, Senate and White House for the last two years and have not appropriated more funding to fix the issue.
"Where do you work? NBC? Maybe you haven't covered the hundred-plus press conferences that I've done on the issue, that have been led by the president, but I know Fox has, ... many of you have covered the story about the president's ask, and my ask, to get the money."
He insists that "oftentimes, you need a bipartisan vote", despite "partial funding" being appropriated in Trump's landmark One Big Beautiful Bill Act.
Duffy blames 'old hardware'
Like my colleague mentioned just before, Transportation Secretary Duffy says today's incident was caused by old technology.
"What we have is an incredibly old air traffic control system," he says.
Duffy says President Donald Trump has been asking congress to fund a new air traffic control system.
"We have analogue telecoms, our routers actually got overloaded with data … and they started to give us inconsistencies in the data … because of that we shut the system down," he says.
"It is the old hardware that went down."
Duffy stresses issue was 'not the fault of the airlines'
Duffy is asked what rights affected travellers have with regards to cancelled or delayed flights.
He says the government is in communication with the major airlines and is keeping them updated "with what the major issues are".
"This is one of those situations where it is not the fault of the airlines," he says.
Crucial flights weren't affected by ground stop
Some crucial flights, such as those carrying organs for transplants and those needed for law enforcement, were still able to take off, despite the nationwide ground stop.
Duffy has given some more detail on why that was the case.
"Because it wasn't a complete outage, it was just, we were getting varying degrees of our inputs from radar and from telecoms, we were still able to fly those flights safely."
Duffy: Will try to move flights tonight, but it will be slow
US Transportation Secretary Sean Duffy has warned that flights may be "slow" to take off.
"If you are watching, if you are at an airport, check with your airline, it depends on [if they] have crews available," he said.
"We are going to try to move as many of those as we can tonight if we have capacity.
"If not, we are going to start tomorrow morning with our airline partners to move those aircraft but is going to take us some time to unwind what has happened this afternoon."
Mullin: No evidence of cyberattack
US Homeland Security Secretary Markwayne Mullin has just been asked whether there's any truth to rumours the incident was related to a cyberattack.
"There's nothing completely certain right now; it doesn't appear that way," he says, adding that a team has been activated to investigate the matter.
"When we start looking at cyber threats, cyberattacks, typically somebody's going to raise their hand up and say, 'Hey, we did that'. There's no chatter. We haven't seen any footprints … of people that have got into the system. It appears this was mechanically driven, however, we are still looking."
Mullin says the incident does indicate a national security risk and a national emergency.
He and Duffy are pushing for Congress to appropriate more funding to upgrade the FAA's "old" communications systems, which they say failed and caused the issues today.
US nationwide flight ground stop order has been lifted: Duffy
Transportation Secretary Sean Duffy says authorities opened up the airspace at 8:15pm local Eastern Time, about half an hour ago.
Done out of an 'abundance' of caution, transportation secretary says
Transportation Secretary Sean Duffy is now speaking.
He says the issue was picked up about 3:30pm eastern time in North America.
"We experienced instability for our radar and communications in our centres across the country," he said.
He said they began having inconsistencies in the data from the radars in their communications in planes.
"We have procedures for this, our pilots are well trained, our controllers are well trained," he said.
"At the point we issued a ground stop we had over 5,300 planes in the air … last time I looked we had 400.
"We didn't lose all telecoms, we didn't lose all radar, but that instability, out of an abundance of caution, we did the ground stop."
Mullin says things 'working ... in the right direction'
US Homeland Security Secretary Markwayne Mullin and Transportation Secretary Sean Duffy have just walked into the White House press room to provide a briefing of the situation.
Right out of the gate, Mullin says he wants to make clear this incident is not related to yesterday's Microsoft outages.
He says the government is "moving at an unprecedented pace" to resolve the issue.
"Right now, things seem to be working ... in the right direction," he says.
US flights ground stop order about to be lifted: Reuters
We're seeing reports from Reuters that an update on today's ground stop order in the US is imminent.
The news agency is citing a US official who says the halt order for departing flights across the country is about to be lifted.
Reuters also says the US Federal Aviation Administration is also reporting the cancellation of the earlier stop order.
We're still waiting to hear from US Homeland Security Secretary Markwayne Mullin and Transportation Secretary Sean Duffy at the White House.
We'll provide you with further details as they come.
What our readers on the ground are saying
I'm sitting in an airport lounge at DFW. The mood is hopeful, but nothing is moving
- Jason
I'm on the Bay Area Rapid Transit BART train in San Francisco heading to SFO airport to get my flight tonight to Melbourne via Fiji. Looks like my flight is still On Time. All other Fiji Airway flights out of SFO appear delayed or cancelled!.Hopefully mine takes off on time so I don't miss my connection!
- Paul
On a plane waiting to disembark at Chicago's OHare airport for 2 hours. We have been told they have run out of places to park planes.
- Brendon
Aussie currently stuck at LAX, I was meant to fly to JFK at 12:36pm and our plane got grounded as it was on the runway about to take off. No real updates have been provided by American Airlines or LAX- my flight keeps getting moved. I am now meant to board at 7pm but this gets pushed back every hour
- Ariella
Flights delayed here in Tokyo also
- Jill Babicci
Thank you for sharing, everyone!
We've got our fingers crossed for you that you won't be in for a long day (or night)!
We will keep you updated with the latest information as it comes to hand, but also be on the lookout for information from your airlines and travel agents.
White House address expected shortly
We're seeing a note from the White House that US Homeland Security Secretary Markwayne Mullin and Transportation Secretary Sean Duffy will soon speak to the media.
We will keep you up to date with what is said at their press conference, as it comes to us.
📷: Inside US airports and planes
The outage has now been underway for about four hours.
Here is what it looks like at American airports and on planes.
Why are planes still taking off at some airports?
Flight Radar 24 shows plenty of planes in the sky over the US. And a good number of those are recent departures of passenger flights from US airports. It's a funny-looking shutdown if, indeed, there still is one in place.
- Dax
Flightradar App is showing flights in the US departing. I've just watched two planes depart JKF in the last 5 mins, one to Brussels, the other to London.
- Brooke
I just watched Singapore Airlines flight SQ11 depart from LAX bound for Tokyo.
- Russ
We've been getting plenty of comments about how international flights appear to still be on the move.
It's true — international departures have been running on a case-by-case consideration, so it's not surprising to see some still taking off.
We've seen flights taking off on both the east and west coast, bound for Europe and Asia respectively.
The US Federal Aviation Administration has not clarified which states are clear to permit departures, though.
ABC presenter's son stranded in New Orleans as plane ticket prices 'shoot up'
William McDonald told ABC Radio Brisbane he is three weeks into a trip across the US with a friend and is stuck at Louis Armstrong New Orleans International Airport.
He says the price of flights has been shooting up.
"My friend I think has just tried to buy tickets that are normally probably $US200 and now they're up to like $US1,000," he says.
William, the son of ABC radio presenter Bill McDonald, hopes the issue is something that can be resolved soon.
"But then they said it could be seven hours, it could be 12 hours, it could be 24 hours," he says.
"So very unhelpful time frame and I don't really know what I'm working with here at the moment."
He says the line at the information desk is "pretty extensive".
"There's a few frustrated people … everyone's just sort of waiting to hear about what's going on, just any information, because apart from the seven to 24-hour time frame we've been given, that's all we have."
Trump hoses down suggestions of cyberattack
US President Donald Trump has just spoken with Fox News.
He says it does not appear that the communications issue was caused by a cyberattack or AI.
We'll let you know if he says more, as it comes to us.
Grounding planes was the right call, expert says
Shawn Pruchnik is an associate professor at the aviation department at Ohio State University, a former pilot and an accident investigator.
Speaking to ABC News, he says the decision by the FFA to ground all planes was the right one.
"We have this significant problem of airplanes at higher altitudes that cannot communicate with air traffic control, so the solution to that is less airplanes up there," Pruchnik says.
"Keep everyone down, let everyone land."
He says it is too early to know what caused the communication issue.
"Something broke maybe, a cyberattack, installing this new AI system that they're trying out, a software update … those are the types of the things at the top of the list that need to be investigated," Pruchnik says.
"Some of those are more serious and difficult to fix."
He says the planes still in the air will be able to land safely.
"We are trained as pilots to be able to approach an airport and land without radio communication … it is a little more high risk but there is less airplanes up there to worry about and we have collision protection in airplanes," he says.
Stranded Australian reports 'hundreds stuck in airport queues in New York'
Trish Crabb is among the Australians caught up in the flight cancellations in the US.
She said she and her husband were due to fly from JFK Airport in New York to Miami, when they learned their flight had been grounded.
"The line-up is huge, at least 200 people in front of me and that's just for our Delta flight," Ms Crabb said.
She said the couple, who are holidaying in the US, were due to fly to Miami, before travelling to Fort Lauderdale by car to board a cruise.
"My husband is going to try and find us a hotel room somewhere close by, and hopefully we will be able to get a flight out at some stage," she said.
Ms Crabb said everyone was "very calm" and most people were "taking it in their stride".
Any connection with yesterday's Microsoft outage?
Seems interesting timing with the Outlook outage yesterday. Any connection?
- Scott
Hi Scott,
There's no apparent connection wit
