AMNA NAWAZ: Welcome to the "News Hour."

Air travel across the country is at a standstill tonight after the Federal Aviation Administration issued a rare nationwide ground stop, citing extraordinary circumstances and reasons of safety.

Runways across the country were emptied tonight, and hundreds of flights have been impacted so far.

A short time ago, Homeland Security Secretary Markwayne Mullin told reporters he did not believe this was tied to a specific attack.

MARKWAYNE MULLIN, U.S.

Homeland Security Secretary: I want to make sure we say this again.

There's no reason for the public to be afraid or scared for your loved ones.

This isn't another 9/11.

I just can't repeat that enough.

People are making that assumption because that's the last time we had a nationwide ground stoppage.

This is a telecommunication outage.

This is much different.

AMNA NAWAZ: It's just the third time in recent decades that there's been a nationwide grounding.

The last time was in January of 2023 after the failure of a pilot communications system.

Information is still very limited, but let's try to answer what we can.

Our aviation correspondent, Miles O'Brien, is here for just that.

Miles, welcome back, and thanks for joining us.

These kinds of nationwide ground stops are extremely rare.

I know you have been talking to your contacts.

Do we know what's behind this moment?

MILES O'BRIEN: Well, there's a lot of speculation right now, Amna.

We should characterize that, that no one really knows for sure, or at least is not saying so.

But what you have is a systemwide problem in a system that is built on redundancy, and so you have to wonder what the single-point failures could be and why those exist.

There are 22 regional en route centers that manage aircraft at cruise altitude passing across the country.

They are connected to each other by simple landlines, kind of old-fashioned landlines, and there's some speculation that that system of connecting those en route centers has failed.

Now, what caused that?

Could that have been some sort of hacking event potentially?

Or could it have something to do with the modernization of the system, which we all know relies on floppy disks and paper strips and spinning radars which go back to the 1940s?

So, what the FAA is trying to do is attach a rocket booster to a horse and buggy.

And that's where you start realizing the vulnerabilities in a system that should have layer upon layer redundancy on them.

AMNA NAWAZ: I mean, Miles, just to give people a sense of the scope of this ground stop, take a look at this flight tracker graphic.

This is showing all the flights across the U.S.

and in the region there halted.

Those are yellow.

Those are not moving.

And so, Miles, tell us about this communications outage as the secretary alluded to there.

Obviously, some folks are asking, could this have something to do with the massive Microsoft outage that we have been talking about?

And does it potentially give way to other vulnerabilities here?

MILES O'BRIEN: Well, that's just it.

It shouldn't be that vulnerable.

And if it is possible to take down one layer, there should be at least another layer.

This is a function once again, Amna, of kicking the can down the road, as Congress and Washington has done for years and years, on infrastructure in the air.

This is a system that is bursting at the seams.

Travel is at an all-time record, in spite of the cost of it.

You know what it's like getting on these planes, and we're still using systems that date back many decades.

This -- it is high time that we got serious about investing in this system and creating something that is more resilient, more redundant, and God forbid we end up with a situation where we have a mishap.

Fortunately, everybody's safe, extremely inconvenienced, but at least everybody is safe through all this.

And that is a testament to the heroic air traffic controllers who work in this system, antiquated as it is, heroically every day to make it work.

AMNA NAWAZ: That is our aviation correspondent, Miles O'Brien, with the very latest.

Miles, thank you so much.

Appreciate your time.

MILES O'BRIEN: You're welcome, Amna.