This Boeing 737 barreling down the runway on its belly right before smashing into that wall and going up in flames.

Mike Valerio is on the scene. He's out front.

It is the unmistakable outcry of grief heard throughout South Korea's Muan International Airport.

Families unable to absorb the anguish of the Jeju Air catastrophe.

Hundreds of relatives huddling in the departure hall, waiting for news of whether their loved one's remains are found.

A friend of a couple killed in the crash said he came here to confirm for himself his friends of 30 years are simply gone.

I have nothing to say, but it's tragic, he told us. I watch the news all day, and for now, they say bird strike could be the cause.

I'm so shocked and hurt, I cannot even put it into words.

Now, so many people have chosen to stay. They're not going anywhere, and that's seen, evidenced by all of these tents that go from here pretty much to the end of the terminal.

They go back three tents to the edge of the check-in counters.

You see food deliveries throughout the day. Let's keep going this way.

And the echoes of grief.

The scenes inside are just a short drive from the cataclysmic crash site.

The tale of the doomed airliner still jutting above the field, a mountain in the middle of the debris.

More than a thousand people now mobilized to sift through pieces of the plane.

The crash scene is absolutely harrowing.

Just a few steps away, you can see where the doomed Jeju Air jetliner careened through the embankment and burst into flames.

And more than a day later, you can still see forensics teams in their white suits combing through the debris along with members of the police force as well as members of the South Korean military.

Now, to my right, you can see soldiers looking through the fields and around them.

To give you an idea of the force of this crash, a full football field away from where we're standing, you can see mangled, twisted chairs thrown from the jetliner.

A representative of the victims' families urging an even larger response.

What I want to request from the government is to increase the manpower so that the recovery can be carried out more swiftly.

I hope my siblings, my family can be recovered and returned to us, even if only 80 percent intact.

For now, Muan remains the epicenter of a nation in mourning.

The weight of unspoken farewells and quiet desperation made unbearable an absence of answers.

So, Brianna, as we zoom in and show you what's happening now that the sun has come up here, New Year's Eve in South Korea, why this investigation is so critical, not just to South Korea, but everybody watching at home, the rest of the world.

Investigators are trying to figure out if this was perhaps a problem specific to this plane, specific to the circumstances of the day.

Or, Brianna, if perhaps a bird strike caused a possible chain reaction that might have disabled the lifeblood of this plane, the hydraulic system, the mechanical system that is in charge of the brakes, the flaps on the plane, the landing gear.

And if that second possibility is indeed the case, that is something that will be absolutely critical for airlines around the world to know since so many of us fly on these Boeing 737-800s, Brianna.

Certainly. Mike Valerio, thank you for the report from Muan, South Korea.

Out front now, retired Captain Tammy Jo Schultz.

She was the pilot of Southwest Flight 1380, which landed safely after the left engine on the Boeing 737 exploded mid-flight.

Captain Schultz, thanks for being with us.

We see, in this case in South Korea, the plane skidding with the landing gear apparently still up, flaps apparently undeployed by all appearances there.

The pilot reporting that bird strike that we're looking at a video of, we've now learned, right before the crash.

What do you think overall happened here?

Because it seems that a bird strike ultimately should be survivable.

Right. Brianna, thank you for having me.

And first of all, I would like to extend my condolences to the families that are hurting today.

And bird strikes are not, singularly, they are not an accident in waiting.

We see the bird strike, what we can presume is a bird strike with a puff of smoke coming out of the engine.

And these engines, these CFM56 engines are tested with frozen birds thrown into them.

And so we don't see smoke coming out of the engine afterwards.

We can assume that the engine, I mean, it chewed it up and spit it out.

Now, if they did have to shut down that engine, 737s are built so redundant, it can fly on one engine.

So the electrical system, the hydraulic system, all of them have backups, if not duplicate, triplicate.

So that would not in itself cause a problem.

Even if the bird strike took out a hydraulic system, if it took out an electrical system, they're redundant.

What do the flaps tell you here, Captain?

Right. If per chance, they did have to shut down an engine, would be one of the reasons they didn't use flaps 40, which is the full flap setting.

But it looks like without having all the information at our fingertips, it should have been landed with a flaps 40 setting to slow down.

They did a great touchdown.

Without gear, we don't know why the gear were not coming down.

All three not coming down is quite unusual.

And if they had had a chance to go through their checklist and try the manual unlock and drop of the gear, we don't know that yet.

But they did a touchdown with gear up.

It looked fine.

Some of the negative things that happened here were the short approach that had them flaps up going much faster than normal and landing about halfway down the runway.

So they gave up quite a bit of their landing space.

That coupled with the barricade that was built at the end of the runway for the localizer lights.

That design is not something I've seen in the U.S. or near international flying.

So that was kind of the perfect storm in this situation.

Yeah, it's really upsetting.

That could be the thing that ultimately made the difference, even if there were a series of other issues.

Captain Schultz, thank you so much for being with us.

It is certainly, we feel for the families as well.

It's just horrible what they're going through.

Thank you.

Certainly.

Thank you, Brianna.

We're hearing from one of the two survivors of the deadly plane crash in South Korea.

Hospital officials say the flight attendant, only referred to by his surname Lee, told doctors, quote,

We're also hearing from officials on the ground that the plane's black boxes have been recovered.

The video shows the Boeing 737 skirted along the runway on its belly before crashing into a wall and going up in flames.

While the cause of the crash is still being investigated, officials say pilots shouted,

The fiery crash killing 179 people and leaving two crew members as the lone survivors.

Now, for those families of those on board,

Won International Airport has become a place of mourning as they await to hear about their loved one's remains.

I want to bring in retired United Airlines Captain Kit Darby and former senior NTSB investigator Greg Feith.

Kit, I want to start with you.

The plane's two black boxes have been recovered, one of which has been partially damaged.

We're told. How long does it take to process?

And are you concerned if it's damaged that it could affect really telling the full story here?

Well, we certainly want to know the full story from both black boxes.

It depends on the extent of the damage.

Could be a quick repair or it could be months if we have to put it back together piece by piece.

Kit, I think the biggest question is obviously why this happened.

The plane appeared to crash land on the runway without any landing gear and officials, as I just noted, said the pilot made a mayday call shouting bird strike.

What do you make of the reporting about the bird strike and the reporting the landing gear may not have been down at all?

Well, from the video, the gear wasn't down, the flaps weren't out, the spoilers weren't deployed on the landing.

This was a very complex situation.

Actually, beyond most training events, you might land with no flaps, but not the combination of events here.

So the bird strike, you know, in my experience, would not normally lead to any gear or flap problems.

We'll have to see what happened to understand how this airplane made a gear up, flaps up, no spoilers on landing, landing on a runway that was marginal in length.

A very, a very tense situation.

Yeah. And underscoring just how many questions remain right now.

Greg, Southwest Airlines, which also flies Boeing aircraft, put out a statement saying, quote, we are engaged with the FAA and Boeing and will take any steps they recommend as the investigation unfolds.

What's an investigation like this mean for airlines here in the U.S.?

Well, there are a couple of things, Phil.

One, the NTSB and the FAA are in route to South Korea to help with the investigation.

Because we are the state of manufacture, that is Boeing is here.

We have a responsibility, especially with the FAA, for continued airworthiness of that aircraft.

So it's going to be incumbent upon the investigators to find out if there is any kind of mechanical malfunction or failure that could be systemic in this aircraft.

Or was this a maintenance related issue or was this a crew performance issue?

It's evident that whatever happened, there was a high sense of urgency to get the airplane on the ground.

They aborted the first approach, circled back around in a teardrop, tried to land on the opposing runway.

But as Kit said, they didn't have the gear, the airplane really configured for landing.

Yet it probably was configured on the initial approach.

And Greg, how big could an investigation like this become?

And I guess you mentioned the U.S. investigators heading over.

How do investigators from different countries here work together on this?

It's really a synergistic process because you're bringing various levels of expertise.

Here, we're bringing Boeing, we're bringing the FAA.

There is a joint program with the engine manufacturer.

Of course, the Koreans, the South Koreans will be the lead investigative authority.

All this information will be ferreted out.

It's all about developing the facts, conditions, and circumstances, putting them into context and really understanding where the whole process of this accident started.

The fact that they hit this wall, it's not a wall.

It's actually the stanchion for the localizer antenna for the instrument approach system.

So the question there, that's what really caused the catastrophic damage and the significant fatalities.

And the question is, why did the airport have that kind of system there?

It was supposed to be frangible.

Yeah, the scale of what investigators are looking at is certainly wide.

Kit Darby, Greg Feith, thanks so much for your time. I appreciate it.

You're looking at video of a passenger jet crash landing at an airport in South Korea yesterday, only moments before it burst into flames, killing all but two people on board.

For more on what we're learning right now about the tragic sequence of events, CNN's Richard Quest is joining us.

Richard, first of all, what are you learning from the video taken just before that deadly crash?

We now know from various reports, air traffic control messages and discussions that there was a bird strike.

The plane was coming into land. There was a bird strike. The pilot declared an emergency, a mayday.

He then turned the aircraft, we're not sure as how far from the runway, and then attempted his crash landing in the opposite direction.

By that stage, the plane was going fast. The gear wasn't down, and that's another thing we don't know the reason why.

The plane landed heavy, very far down the runway, and ran off the end of the runway and into the wall, or the beam, as it was, that was holding the navigation instrumentation.

Wolf, what we know now, and what I know your guests next are going to be talking about, is why was the pilot unable to land, not lowering the landing gear?

What was it after the bird strike that was so imperative to get the plane on the ground immediately?

And then secondary to that, what's becoming clear is that this might have been entirely survivable for those on board, because if you look at the way the plane touched down, it was textbook in terms of the wings were level, the way it was being managed, but for that concrete beam holding the instrument lights and the instrumentation right at the end of the runway.

Wolf, it was when the plane hit that that it exploded, and at that point, the casualties and the fatalities occurred.

Yeah, that was a Boeing 737, and the landing gear did not go down, clearly a problem.

So what happens next, Richard, in this investigation?

It focuses very tightly on two things.

Firstly, after the bird strike, what was wrong with the aircraft that meant the pilot was unable to lower the landing gear, unable to use any of the control surfaces, it would seem, the flaps, the thrust deployers, the spoilers, anything that would have slowed the plane down, and why did he have to land it so fast?

Second, after that, Wolf, and this will be crucial, could this have been survivable?

Do airports need to look at those things that are beyond the runway?

This plane, by the way, ran about six, 700 feet beyond the end of the runway.

Now, there could have been gravel pits, there could have been emergency arrest material, all sorts of things.

Instead, there was this beam holding of instruments, which was concrete.

I think that longer term, because we'll find out what happened with the actual plane itself, but longer term, the big issue is going to be how to make it safer when planes do run off the end of the runway.

They have to learn the lessons of what happened wrong in this case to make sure it doesn't happen again.

Richard Quest, thank you very, very much.

I want to turn to our aviation analyst, Miles O'Brien and David Soussi right now.

David, Richard referenced this, if there was in fact a landing gear malfunction, is there anything that could have made this a slower, safer landing?

Well, what the challenge was is that when they were initially heading up the runway to the north, they were fighting headwinds. There was a southwest wind, 16 to 18 knots, which is a pretty heavy wind.

So when they made that turn to come back around, they had increased their speed by twice that amount.

They lost the headwind and they gained the tailwind.

So they gained 30 knots almost immediately as soon as they turned around.

And now that aircraft is coming back much faster than when they were going to the north.

So a couple of things on the landing gear.