Original subtitles

A passenger jet that's supposed

to be flying south of Kathmandu crashes

to be flying south of Kathmandu crashes

into a mountain north of it.

Terrain.

Pull up.

It's false, it's false.

It's false, it's false.

Oh, my god!

Investigators are baffled.

Investigators are baffled.

It immediately created some mysteries

as to why the airplane got to a place that was not expected.

as to why the airplane got to a place that was not expected.

Air China 1-2-9, are you able to land?

A plane that should be high above a mountain

slams into it instead.

slams into it instead.

Ah!

The investigation uncovers

The investigation uncovers

a shocking series of mistakes.

Why didn't they turn here?

But they just keep going, and then

But they just keep going, and then

they crash into the mountain.

And a jetliner goes down in a high altitude forest.

The crash reveals a technological blind spot

that could have prevented the tragedy.

that could have prevented the tragedy.

The common thread is a combination

of loss of situational awareness and lack

of loss of situational awareness and lack

of understanding of where you are in relation to the terrain.

Ladies and gentlemen, we are starting our approach.

Ladies and gentlemen, we are starting our approach.

We lost both engines.

Emergency responding.

Mayday, mayday.

Brace for impact!

Brace for impact!

Thai Airways Flight 311

cruises over Nepal just above the peaks

cruises over Nepal just above the peaks

of the mighty Himalayas.

The pilot flying is Captain Preeda Suttimai.

His first officer is Phunthat Boonyayej.

His first officer is Phunthat Boonyayej.

Combined, they have close to 30,000 flying hours.

Combined, they have close to 30,000 flying hours.

I will never get tired of seeing these mountains.

Kathmandu is a popular tourist destination.

Kathmandu is a popular tourist destination.

It's a mountainous airport, and a lot of tourists

fly in just for that, for the scenery.

fly in just for that, for the scenery.

The flight's 99 passengers

left Bangkok, Thailand, and are bound for Nepal's capital

left Bangkok, Thailand, and are bound for Nepal's capital

Kathmandu on an Airbus A310.

Kathmandu on an Airbus A310.

The approach requires navigating above some of the world's

highest mountains and then making

a steep descent to the runway.

a steep descent to the runway.

Kathmandu, Thai 311.

Request descent.

Request descent.

Thai 3-11, you have negative traffic.

You are cleared for descent.

Thai 3-11, request 0-2.

Thai 3-11, request 0-2.

Thai 3-11, confirm requesting 0-2.

Thai 3-11, confirm requesting 0-2.

Confirm.

The pilots are expecting

to make the usual straight-in approach

from the south to runway 0-2.

from the south to runway 0-2.

That will keep them clear of the mountains north of the airport.

But then...

Kathmandu, Thai 3-11.

Kathmandu, Thai 3-11.

We cannot make a approach now.

We will need to turn back to Romeo

and climb to one, 8,000 feet, and start our approach again.

and climb to one, 8,000 feet, and start our approach again.

They realize they're too close to the runway

They realize they're too close to the runway

to safely commence the descent.

The pilots will need to circle back

to the south of the airport and make a second approach.

to the south of the airport and make a second approach.

You would be challenged at doing a circling approach

in a mountainous environment.

in a mountainous environment.

It's one thing to do it without any obstacles.

It's another thing to do it surrounded by mountains.

It's another thing to do it surrounded by mountains.

Using the flight management system,

the first officer enters the navigational waypoint called

the first officer enters the navigational waypoint called

Romeo to restart their approach.

But the system won't lock in a flight path to Romeo.

But the system won't lock in a flight path to Romeo.

It disappeared.

It's Romeo 27, isn't it?

It's Romeo 27, isn't it?

Row me oh.

The pilots keep trying to program the Romeo waypoint.

The pilots keep trying to program the Romeo waypoint.

Thick clouds limit their view from the cockpit.

Thick clouds limit their view from the cockpit.

Then...

Pull up.

Airspeed low.

Airspeed low.

Sink rate.

Pull up.

Turn back, turn back.

It's false, it's false.

It's false, it's false.

Pull up.

Pull up.

Obstacle, obstacle.

Pull up.

Oh, my god!

Thai 3-11, please report your position.

Thai 3-11, please report your position.

The search for Thai Airways Flight 311

begins immediately.

Nepal sets up a royal commission of local and

international investigators.

international investigators.

This is the airport.

Flight 3-11 was coming in from the south here.

Until the airplane is found, it's difficult to figure

out what might have happened.

And the search, of course, started in the south

because it came in from the south.

Where is this thing?

As the search continues,

investigators interview the air traffic controller,

hoping for any kind of lead.

hoping for any kind of lead.

We don't have radar here, so can't help you

with the airplane's location.

I just rely on what the pilots tell me.

I just rely on what the pilots tell me.

The nonradar environment, they have a mental picture.

And that picture is really painted by the words

And that picture is really painted by the words

that the pilot reports to them.

They don't have an exact location.

Almost like working blindfolded.

Almost like working blindfolded.

Kathmandu, Thai 3-11.

Kathmandu, Thai 3-11.

We cannot make approach now.

We will turn back to Romeo and climb to one, 8,000 feet,

We will turn back to Romeo and climb to one, 8,000 feet,

to start our approach again.

To redo the approach, they would have

to turn back towards the south.

to turn back towards the south.

48 hours after Flight 311

48 hours after Flight 311

disappeared, villagers report finding aircraft debris

to the north of Kathmandu.

to the north of Kathmandu.

The reported crash site is nowhere near

the area they'd been searching south of the airport.

the area they'd been searching south of the airport.

North of Kathmandu, the Himalayan peaks soar

to a height of 20,000 feet.

to a height of 20,000 feet.

For that reason, almost all planes

approach the airport from the south, where the mountains

approach the airport from the south, where the mountains

are closer to 8,000 feet.

are closer to 8,000 feet.

Send out the helicopters.

Tell them to start searching to the north of the airport.

Later that day, 27 miles north of Kathmandu,

search crews find the remains of Thai Airways Flight 311.

search crews find the remains of Thai Airways Flight 311.

The point of impact is a steep rock

The point of impact is a steep rock

face more than 11,000 feet up the side of a remote mountain.

None of the 113 people on board survived.

None of the 113 people on board survived.

It immediately created some mysteries

as to what might have happened or why

the airplane got to a place that was not expected.

the airplane got to a place that was not expected.

The level of destruction was enormous.

The level of destruction was enormous.

You couldn't tell that you had an Airbus A310.

You couldn't tell that you had an Airbus A310.

You couldn't even tell you had two engines.

The location of the crash puzzles investigators.

The location of the crash puzzles investigators.

The plane should never have been this far north of the runway.

The plane should never have been this far north of the runway.

So why was it there?

So why was it there?

It's hard to tell what we're even looking at here.

Incredibly, the team is able to retrieve the plane's

Incredibly, the team is able to retrieve the plane's

flight data recorder and cockpit voice recorder

from the fragments of debris.

Investigators hope they'll provide

Investigators hope they'll provide

crucial evidence that will reveal how the plane ended up

so far off course.

so far off course.

OK.

Start it up.

While the FDR is being processed,

investigators analyze the cockpit voice recorder.

investigators analyze the cockpit voice recorder.

Lots of clouds.

Thai 3-11, Kathmandu.

Go ahead.

Would you request for runway 0-2, please?

Thai 3-11, request 0-2.

Thai 3-11, request 0-2.

Everything seems normal until they begin

Everything seems normal until they begin

to restart their approach.

Thai 3-11, report 2-5 DME.

Thai 3-11, report 2-5 DME.

Wait a minute.

Kathmandu to Thai 3-11.

Kathmandu to Thai 3-11.

Confirm runway 0-2 available.

Wait a minute.

Stop.

Stop.

The pilot talking to the controller

is not the first officer.

It's the captain.

It's the captain.

Why was the captain speaking with the controller?

As the pilot flying, the captain should have focused

As the pilot flying, the captain should have focused

solely on flying the plane, not communicating

with air traffic control.

with air traffic control.

In this case, I noticed that the captain was, in many cases,

taking over the radio transmission work.

taking over the radio transmission work.

The CVR reveals another surprising detail.

The CVR reveals another surprising detail.

Dammit.

The flaps cannot be extended.

The flaps would not extend to full configuration,

which for the Kathmandu approach, is essential.

which for the Kathmandu approach, is essential.

The recording leads investigators to ask

some troubling questions.

Did malfunctioning flaps and a distracted pilot

Did malfunctioning flaps and a distracted pilot

send the plane into the path of a mountain?

Investigators listening to the cockpit voice recorder for Thai

Airways Flight 311 learned that the pilots were concerned

Airways Flight 311 learned that the pilots were concerned

with an issue with their flaps.

Dammit.

The flaps cannot be extended.

But just as suddenly as the problem with the flaps

But just as suddenly as the problem with the flaps

began, it resolves itself.

Back to normal now.

Can we make a left turn to Romeo?

Can we make a left turn to Romeo?

Understand.

Operation normal.

And you'd like to make an approach?

And you'd like to make an approach?

Affirm, affirm.

But the delay in extending the flaps

meant that the pilot couldn't descend toward the airport

meant that the pilot couldn't descend toward the airport

in time to make a safe landing.

We can't land at this time.

We have to make a left turn back to Romeo

and start our approach again.

and start our approach again.

But other air traffic coming in from the south

prevented Flight 311 from turning left.

prevented Flight 311 from turning left.

Thai 3-11, we have negative traffic at or above flight

level 1-5-0 within our jurisdiction

level 1-5-0 within our jurisdiction

except Royal Nepal at 2-0-6.

except Royal Nepal at 2-0-6.

You are cleared for descent.

Then something perplexing happens.

The controller goes silent.

Answer, please.

Answer, please.

Answer, please.

Flying north toward mountains

and with traffic to his left, the captain makes a decision...

and with traffic to his left, the captain makes a decision...

without waiting for ATC clearance.

without waiting for ATC clearance.

We'll climb and turn to the right.

He begins turning right,

back toward the start of his approach south of the airport.

back toward the start of his approach south of the airport.

Moments later, investigators hear a strange question

from the first officer.

from the first officer.

Are we going north?

The recording exposes a troubling inconsistency.

It seems the captain intended to turn

south, away from the mountains.

Yet minutes later, they're still flying

Yet minutes later, they're still flying

north toward the mountains.

Terrain, terrain.

Pull up.

Pull up.

Turn back, turn back.

It's false, it's false.

Pull up.

Pull up.

Oh, my god!

Oh, my god!

Is that the data from the FDR?

Great.

Great.

Fortunately, the flight data has been recovered.

And investigators have their first chance to analyze

And investigators have their first chance to analyze

the plane's flight path.

What the team finds raises more questions.

What the team finds raises more questions.

And right here, they're looping around to restart

their approach, right?

their approach, right?

All right.

But they just kept turning.

Instead of turning 180 degrees,

straightening out, and heading south to Romeo,

straightening out, and heading south to Romeo,

Flight 311 turns a full 360 degrees

Flight 311 turns a full 360 degrees

and continues heading north.

It just doesn't make any sense.

Fire it up.

Fire it up.

In search of answers, they

turn to a flight simulator.

turn to a flight simulator.

The captain just took over communications

with the controller.

Yeah, OK.

In terms of simulator testing, the one thing

that it allows the investigators to do

that it allows the investigators to do

is replicate what happened and understand

what the crew would see or any other problems

that they would face.

that they would face.

Kathmandu, Thai 3-11.

Confirm runway 0-2 available.

Confirm runway 0-2 available.

At this point, they know the captain is flying

the aircraft, monitoring the instruments,

the aircraft, monitoring the instruments,

and communicating with the controller,

all on one of the steepest, most difficult descents in aviation.

all on one of the steepest, most difficult descents in aviation.

OK, there is a lot going on here right now.

OK, there is a lot going on here right now.

Dammit.

The flaps cannot be extended.

The time spent resolving the flaps

issue creates a delay.

They can no longer make the straight-in landing.

They can no longer make the straight-in landing.

Only choice is to circle back and do another approach.

Only choice is to circle back and do another approach.

The captain can program

the flight computer to take the plane to a selected heading.

the flight computer to take the plane to a selected heading.

In this case, that means turning to the left,

but there's a problem.

This controller said there's traffic to the left.

This controller said there's traffic to the left.

To avoid the traffic, the captain decides

to adjust the autopilot.

to adjust the autopilot.

We'll climb and turn to the right.

To make the turn, he rotates

To make the turn, he rotates

the heading knob to the right.

Watch your turn. You're starting to level off.

- Oh. - Here, right.

He's trying to do too many things at once.

He's asking to go to a point.

He's trying to fly the airplane on the autopilot.

He's trying to fly the airplane on the autopilot.

And he's starting to lose the 3D picture that he

has in his head, where he is.

has in his head, where he is.

Investigators make a critical discovery.

Investigators make a critical discovery.

The distracted pilot makes a fatal mistake.

He turned it one too many times and did a full circle.

He turned it one too many times and did a full circle.

Investigators now understand how the crew, facing

Investigators now understand how the crew, facing

nearly zero visibility and thick clouds,

had no idea they were actually turned

had no idea they were actually turned

back toward the mountains.

Pilots are trained to fly using only their instruments.

Pilots are trained to fly using only their instruments.

Why did these pilots fail to notice their mistake?

Why did these pilots fail to notice their mistake?

Take a look at this.

Take a look at this.

There are no cardinal points on the compass.

A close look at the cockpit compass

reveals a possible explanation.

reveals a possible explanation.

The instrument lacks the usual direction

markers, N, S, E, W, indicating north, south, east,

markers, N, S, E, W, indicating north, south, east,

and west headings.

I think if there had been a big N on top of the compass

I think if there had been a big N on top of the compass

for the whole time, it might have made a difference.

Are we going north?

Are we going north?

We will turn back soon.

And then, only many miles north of the airport,

And then, only many miles north of the airport,

does the first officer say, hey, my display

says I'm north of the airport.

But by then, it's too late.

But by then, it's too late.

Terrain, terrain.

Turn back, turn back.

Turn back, turn back.

Ah!

No!

The accident underscores the need

for more advanced air traffic control technology

at Kathmandu's airport.

at Kathmandu's airport.

In an environment like Kathmandu, radar was essential.

In an environment like Kathmandu, radar was essential.

And radar was put into Kathmandu so this... this

would not happen again.

The disaster also reinforces the importance

The disaster also reinforces the importance

of teamwork among pilots.

I'm flying the airplane.

I'm flying the airplane.

You're doing this.

You communicate with me.

I communicate with you.

And we, as a team, maximize to a greater extent

And we, as a team, maximize to a greater extent

than the individual capability everything we can do,

including knowing situational awareness

including knowing situational awareness

and escaping when we have to.

10 years later, a plane

crashes into a mountain it should have flown high above...

crashes into a mountain it should have flown high above...

Must go around! Pull up!

Pull up!

...in a tragedy that is a simple matter of bad timing.

...in a tragedy that is a simple matter of bad timing.

No!

Terrain, terrain.

Terrain, terrain.

Pull up.

Air China Flight 129 has been in the air

Air China Flight 129 has been in the air

for almost two hours.

Captain Wu Xinlu heads the Chinese flight crew.

Captain Wu Xinlu heads the Chinese flight crew.

He has more than 6,000 flying hours.

He has more than 6,000 flying hours.

18 degrees, dew point 1-6.

First Officer Gao Lijie has more than 1,200

First Officer Gao Lijie has more than 1,200

hours flying the Boeing 767.

Expect radar vectors to left downwind.

Expect radar vectors to left downwind.

The most junior member of the team

is Second Officer Hou Xiangning.

is Second Officer Hou Xiangning.

There was a third pilot in the cockpit, a second officer,

who was doing the radio calls.

who was doing the radio calls.

And that was because of his proficiency in English.

Flight 120 is flying southeast

Flight 120 is flying southeast

from Beijing to Gimhae International

Airport in Busan, South Korea.

Airport in Busan, South Korea.

It should be on the ground in less than 30 minutes.

It should be on the ground in less than 30 minutes.

Good morning.

With you now.

15 minutes before landing,

15 minutes before landing,

the crew contacts the airport's approach controller.

Air China 1-2-9, Gimhae approach.

Air China 1-2-9, Gimhae approach.

Fly heading 1-9-0.

Descend to 6,000.

Descend to 6,000.

In this case, the copilot started the approach.

He was actually the pilot flying.

The captain was really monitoring

The captain was really monitoring

his altitude because the captain is a nonflying pilot.

Air China 1-2-9, turn left, heading 1-6-0.

Air China 1-2-9, turn left, heading 1-6-0.

Descend to 2,600.

Descend to 2,600.

Visibility is not very good.

Gimhae Airport is near Korea's

Gimhae Airport is near Korea's

southern coast, an area known for unpredictable weather.

Visibility is spotty as the passenger jet

descends through thick clouds.

I don't think there was anything unique

I don't think there was anything unique

about this particular day.

There were clouds.

There was rain.

Runway in sight.

But strong winds are making the current landing

But strong winds are making the current landing

approach difficult. So the controller

gives Flight 129 new landing instructions.

gives Flight 129 new landing instructions.

Air China 1-2-9, Contact Tower 118.1.

Air China 1-2-9, Contact Tower 118.1.

Circle west.

Circling approach is a visual approach.

The pilot has to maintain sight of the runway the entire time.

The pilot has to maintain sight of the runway the entire time.

The wind is too strong.

It's very hard to fly.

The thick clouds obscure

The thick clouds obscure

the tower controller's view.

Cleared to land Runway 1-8.

Cleared to land Runway 1-8.

Reduce speed.

OK.

The controller can't see the incoming 767.

The controller can't see the incoming 767.

Air China 1-2-9, are you able to land?

Let's go around!

Let's go around!

Pull up!

Pull up!

Ah!

Air China Flight 129 crashes

Air China Flight 129 crashes

into the side of Mount Dotdae just

three miles from the runway.

three miles from the runway.

Of the 166 people on board, only 37 survive.

Of the 166 people on board, only 37 survive.

The crash site was horrible.

It was truly a miracle that they were

It was truly a miracle that they were

able to find a number of survivors

from such a massive crash.

from such a massive crash.

Korean Air accident investigators

Korean Air accident investigators

arrive on the scene along with American investigators

from the National Transportation Safety Board.

from the National Transportation Safety Board.

You could tell the whole area had been cleared out

by the impact of the whole aircraft,

by the impact of the whole aircraft,

and pieces were spread all over the place.

and pieces were spread all over the place.

I was surprised that anybody survived.

Let me borrow those.

Let me borrow those.

From the crash site, investigators

can see the airport nearly three miles away.

can see the airport nearly three miles away.

There is no simple explanation why Flight 129 hit

terrain so far from the runway.

terrain so far from the runway.

What are they doing here, when they should

be all the way down there?

be all the way down there?

What would cause them to get this low this far out?

He should have been well above this terrain.

He should have been well above this terrain.

You wondered, why did this guy hit a hill?

Investigators concentrate

Investigators concentrate

on what the crash site can tell them about the accident.

Debris is scattered for hundreds of yards down the hillside.

Debris is scattered for hundreds of yards down the hillside.

Normally, when an incident occurs,

Normally, when an incident occurs,

the wreckage and debris tend to stay within the area

of their initial impact point.

of their initial impact point.

The positioning of the fuselage

gives the team its first clue.

gives the team its first clue.

The back of the plane must have landed

first, meaning the pilot was pulling

up as the plane hit the ground.

up as the plane hit the ground.

This suggests the crew made a last-ditch effort

to clear the mountain.

Investigators are faced with a troubling question.

Investigators are faced with a troubling question.

In the midst of a routine landing,

why did the pilots fly so low?

why did the pilots fly so low?

To understand why Air China Flight 129 crashed

To understand why Air China Flight 129 crashed

into the side of a mountain, puzzled investigators

look at the airliner's speed, altitude,

look at the airliner's speed, altitude,

and heading parameters obtained from the flight data recorder.

Around here, they should be circling in for a landing.

But they just keep going.

But they just keep going.

Then they crash into the mountain.

Why didn't they turn here?

How were they supposed to do this approach?

How were they supposed to do this approach?

The landing procedure for a circling approach

to Busan requires pilots to use a cockpit chronometer,

to Busan requires pilots to use a cockpit chronometer,

a type of stopwatch.

Flight crews time maneuvers to the precise second

using headings and visual landmarks

as references, a challenging task in thick clouds.

as references, a challenging task in thick clouds.

So gear down here.

Then they're supposed to do a 45-degree turn for 20 seconds

Then they're supposed to do a 45-degree turn for 20 seconds

here.

Then they're supposed to make a 45-degree turn for 20 seconds

Then they're supposed to make a 45-degree turn for 20 seconds

here.

You time it out 20 seconds.

You turn parallel to the runway, and then you

make what's called a base turn, a 180-degree turn,

make what's called a base turn, a 180-degree turn,

and land on the runway.

Here, they should see the end of the runway.

Here, they should see the end of the runway.

20 seconds later, they should have made their base turn.

20 seconds later, they should have made their base turn.

Investigators realize the pilot

got off to a bad start making his approach.

got off to a bad start making his approach.

The flight recorder showed that the pilot

did not execute his first turn.

did not execute his first turn.

He's supposed to make a left turn to begin

the circling approach, and he's supposed

to do that aggressively.

to do that aggressively.

He didn't turn with a steep enough bang.

What were the pilots thinking?

What were the pilots thinking?

Let's start from the very beginning of their approach.

The team hopes the cockpit voice recorder

The team hopes the cockpit voice recorder

will answer that question.

Air China 1-2-9, you may approach.

Air China 1-2-9, you may approach.

Fly heading 1-9-0.

Descend to 6,000.

Roger.

Up till now, they think they're coming in here.

But the controller changes it to here.

But the controller changes it to here.

The crew's plan for a straight-in approach

is changed to a circling approach

is changed to a circling approach

that will take them to the other side of the airport.

We are using Runway 1-8 right.

So they immediately acknowledged

their circling approach.

their circling approach.

But it soon becomes clear that they

missed a critical step.

missed a critical step.

So we exit on this side taxiway?

What's it called?

Charlie 6.

Charlie 6.

After we land, we can leave directly

using taxiway Charlie 6.

using taxiway Charlie 6.

Stop.

They're talking about what to do after they land.

They're talking about what to do after they land.

But they never did a proper briefing

for the actual landing, let alone

what they had to do to execute their final approach.

what they had to do to execute their final approach.

When that didn't happen, somebody is supposed to speak

up and say, hey, Captain or First Officer,

up and say, hey, Captain or First Officer,

we didn't do approach briefing.

That's crew coordination.

The missed briefing helps explain why the crew

made the mistake of turning much less

than the required 45 degrees.

than the required 45 degrees.

Timing.

Wait, where's my stopwatch?

Wait, where's my stopwatch?

A circling approach demands precise timing

A circling approach demands precise timing

of the turning maneuvers.

Here's where they start the timer.

Here's where they start the timer.

Timing.

The captain must begin his final turn

in exactly 20 seconds.

in exactly 20 seconds.

They had to fly the aircraft away from the airport, and then

a turn onto final, and then land in the opposite direction.

a turn onto final, and then land in the opposite direction.

The wind is too strong.

It's very hard to fly.

I have control.

Investigators are stunned by what they hear.

Investigators are stunned by what they hear.

In the middle of the 20-second timer,

he decides to take control.

That's crazy.

It confused the first officer, made the division of duties

It confused the first officer, made the division of duties

uncertain.

They didn't know what person was supposed to do what.

They didn't know what person was supposed to do what.

A critical mistake...

the captain fails to tell the first officer

the captain fails to tell the first officer

to monitor the chronometer.

The U-turn back to the runway should

begin at the 20-second mark.

begin at the 20-second mark.

But with the captain now flying, and the first officer still

looking through the clouds for the runway,

looking through the clouds for the runway,

they don't initiate the turn.

Do you have the runway in sight?

No, I can't see out.

No, I can't see out.

Turn!

Turn now!

Then why he didn't say, let's get out of here,

Then why he didn't say, let's get out of here,

let's miss the approach, we don't understand that.

The captain continues to descend

The captain continues to descend

for almost 30 seconds before the first officer finally

speaks up.

speaks up.

Must go around!

Pull up!

Pull up!

Ah!

But it's too late.

But it's too late.

No!

Pull up!

Pull up!

Terrain, terrain.

Terrain, terrain.

Terrain, terrain.

Pull up.

This is a botched approach.

You never fly into a cloud on a circling approach.

You never fly into a cloud on a circling approach.

If you do, you should be initiating a go around

to get out of that situation.

to get out of that situation.

Why did these experienced pilots

attempt a visual approach in the worst possible conditions?

attempt a visual approach in the worst possible conditions?

The cause of this accident are basically human factors.

There was poor crew coordination.

There was poor crew coordination.

There was poor communications intracockpit and between

the tower and the cockpit.

the tower and the cockpit.

In the aftermath of the Flight 129 disaster,

Air China classifies Gimhae as a special airport.

Air China classifies Gimhae as a special airport.

All pilots are now taught how the area's

challenging mountainous terrain can affect takeoffs, landings,

challenging mountainous terrain can affect takeoffs, landings,

and go arounds.

If you're worried about visibility, if you're worried

If you're worried about visibility, if you're worried

about the mountainous terrain, don't do a circling approach

unless you're absolutely sure you can keep the runway

unless you're absolutely sure you can keep the runway

environment in sight.

You have to be on your best game when

you fly in mountainous terrain.

you fly in mountainous terrain.

But when a jet goes down in the mountains

of Alsace, investigators observe how even the most sophisticated

of Alsace, investigators observe how even the most sophisticated

navigational equipment can't guarantee

navigational equipment can't guarantee

disasters will be averted.

Air Inter Flight 148 has just taken off from Lyon, France.

Air Inter Flight 148 has just taken off from Lyon, France.

1-2-4, decimal 9-0-5.

Thank you.

Thank you.

Captain Christian Hecquet and First Officer Joel

Cherubin are experienced pilots with more than 12,000

Cherubin are experienced pilots with more than 12,000

flying hours between them.

The flight is a short, one-hour hop

between Lyon, France and Strasbourg

between Lyon, France and Strasbourg

in the mountainous Alsace region.

The French airline prides itself on quick turnarounds

The French airline prides itself on quick turnarounds

between cities.

And crews are encouraged to avoid delays.

And crews are encouraged to avoid delays.

We were famous for our very short turnaround.

And the faster we flew, the better wages we got.

And the faster we flew, the better wages we got.

But the pilots, already under time pressures,

But the pilots, already under time pressures,

receive an unwelcome communication

from Strasbourg Airport, which changes their plans.

from Strasbourg Airport, which changes their plans.

They are told to land on Runway 0-5.

0-5?

No chance.

Captain Hecquet was hoping

Captain Hecquet was hoping

to use Runway 23, an approach that

provides the plane's autopilot with a precise navigational

provides the plane's autopilot with a precise navigational

fix.

But the new runway, 0-5, requires the aircraft

But the new runway, 0-5, requires the aircraft

to circle around for landing.

A new approach could take longer and affect flight time

A new approach could take longer and affect flight time

and delay their turnaround.

If they had warned us in advance... cripes!

If they had warned us in advance... cripes!

Get down fast.

Get down fast.

I hear you.

Picking up on the captain's frustration,

the air traffic controller in Strasbourg offers assistance.

the air traffic controller in Strasbourg offers assistance.

I can take you with the radar to lead you to ANDLO at 5,000.

I can take you with the radar to lead you to ANDLO at 5,000.

The controller will guide the flight crew step

The controller will guide the flight crew step

by step towards ANDLO, an electronic waypoint on the

approach path to Runway 0-5.

approach path to Runway 0-5.

That will help the pilots line up for landing on that runway.

That's good.

That's good.

Oh, yeah.

OK, then.

Turning left to heading.

2-3-0 degrees.

2-3-0 degrees.

Since Runway 0-5 doesn't allow

for a full autopilot approach, the captain

for a full autopilot approach, the captain

must make his own calculation for the angle of descent.

That makes three decimal three degrees.

That makes three decimal three degrees.

3.3 degrees is a normal flight angle that provides

a good slope for landing.

a good slope for landing.

The controller talks Flight 148

The controller talks Flight 148

through the last turn, which will align it with the runway,

now 15 miles away.

Authorized for final approach 0-5.

The captain configures the plane for landing.

Flaps towards two.

Flaps towards two.

Flaps towards two.

Flaps at two.

Gill down.

We have to watch our descent.

We have to watch our descent.

The approach axis.

The first officer notices a problem

with how the plane is lining up horizontally with the runway.

with how the plane is lining up horizontally with the runway.

It was 60.

Check it out.

Check it out.

Right away.

But before the crew can adjust their course...

the A320 has flown into the side of a mountain.

the A320 has flown into the side of a mountain.

The crash is catastrophic.

The crash is catastrophic.

An emergency is declared at Strasbourg Airport.

An emergency is declared at Strasbourg Airport.

I immediately called my two main investigators,

and we organized the go team.

and we organized the go team.

It takes rescuers more than three hours

to get to the crash site, which is located

to get to the crash site, which is located

12 miles from the runway.

Eight passengers have survived.

Eight passengers have survived.

But 87 passengers and crew, including the pilots,

have died.

have died.

A group of international accident investigators

joins the French Accident Investigation Bureau, the BEA,

joins the French Accident Investigation Bureau, the BEA,

in the search for clues to explain the crash.

In the BEA lab, technicians discover

In the BEA lab, technicians discover

that the flight data recorder is completely destroyed.

They try to salvage data from another recorder

They try to salvage data from another recorder

used by maintenance crews.

It's known as a QAR.

It's known as a QAR.

It took about a day to read a second of recording.

It took about a day to read a second of recording.

Their painstaking efforts

could take a month or more.

could take a month or more.

Any additional second recovered

could reveal something that would make a difference.

could reveal something that would make a difference.

In the meantime, the focus of the investigation

In the meantime, the focus of the investigation

shifts to the cockpit voice recorder, which has survived.

Runway 23.

Runway 23.

Otherwise, I can't make...

The recording reveals the captain's

anxiety early in the flight.

anxiety early in the flight.

You are taking 23, then?

Yes!

0-5.

0-5.

What sort of wind are they giving us?

Turn left, steer 90.

While they listen, investigators

While they listen, investigators

also plot the plane's trajectory using radar information.

They discover that as it circled the mountain,

They discover that as it circled the mountain,

the plane began a dangerously steep and rapid descent.

the plane began a dangerously steep and rapid descent.

Store at two.

The voice recording reveals a remark from the crew

about the speed of the descent.

about the speed of the descent.

It comes just 16 seconds before the crash.

It comes just 16 seconds before the crash.

The aircraft was accelerating abnormally.

We have to watch our descent.

We have to watch our descent.

The captain started to realize there was something

wrong with the descent rate.

But then the first officer changes the subject.

But then the first officer changes the subject.

The approach axis.

We're hitting the axis a half point off.

We're hitting the axis a half point off.

There.

It was 60. Check it out.

Where?

Where?

He refocused the captain's attention

on the lateral situation rather than

on the lateral situation rather than

the vertical situation, which was the main problem,

of course.

But the biggest mystery remains.

But the biggest mystery remains.

What caused the rapid descent in the first place?

After months of work, all flight data from the damaged recorder

After months of work, all flight data from the damaged recorder

becomes available.

The data reveals that the angle of descent

was far greater than the 3.3 degrees

was far greater than the 3.3 degrees

calculated by the captain.

Three decimal three degrees.

Three decimal three degrees.

That's quite a difference.

That's quite a difference.

As he studies the data,

Perries discovers an important clue

Perries discovers an important clue

involving two key numbers...

the plane's vertical speed, 3,300 feet per minute,

the plane's vertical speed, 3,300 feet per minute,

and the intended flight path angle, 3.3 degrees.

and the intended flight path angle, 3.3 degrees.

Coincidence?

Perries uses a flight simulator to test a new theory.

Perries uses a flight simulator to test a new theory.

Can you show me a descent of 3,300 feet per minute?

He believes that the similarity

He believes that the similarity

is more than a coincidence.

On the autopilot, there are two descent modes...

On the autopilot, there are two descent modes...

flight path angle and vertical speed.

flight path angle and vertical speed.

They are both displayed on the same window.

So 3,300 is shortened to 33.

So 3,300 is shortened to 33.

Now, show me a flight angle of -3.3 degrees.

Now, show me a flight angle of -3.3 degrees.

And the problem on this aircraft

was that the two values were visible on the same window

was that the two values were visible on the same window

and controlled by the same knob.

and controlled by the same knob.

Perries suspects the display confused an already

anxious Captain Hecquet.

anxious Captain Hecquet.

The confusion is quite easy between the two modes

if you don't do it carefully.

if you don't do it carefully.

This is his.

If the captain failed to push the mode selector knob,

then entering 33 would not have initiated a safe angle

then entering 33 would not have initiated a safe angle

of descent of 3.3 degrees.

Instead, it would have put the plane

Instead, it would have put the plane

into a deadly rate of descent of 3,300 feet per minute.

into a deadly rate of descent of 3,300 feet per minute.

But when tested in the simulator,

But when tested in the simulator,

this theory still doesn't result in a crash.

We are missing something.

Every approach would overfly this obstacle

Every approach would overfly this obstacle

by a significant margin.

by a significant margin.

To understand why, Parries turns

to an airbus engineer, who explains a little known element

to an airbus engineer, who explains a little known element

of the autopilot's design.

In emergency situations where the A320 needs to change

direction quickly, the autopilot is

direction quickly, the autopilot is

programmed to reverse the plane's direction

at twice the normal rate.

We immediately went back to the data at the...

We immediately went back to the data at the...

the very second at which the descent

was commanded by the crew.

Gear down.

Parries discovers a tragic coincidence.

We found that at this very second, there was turbulence.

We found that at this very second, there was turbulence.

The momentary turbulence caused

the plane to climb slightly.

the plane to climb slightly.

It was during that second that the crew

commanded the plane to descend.

commanded the plane to descend.

It was 60. Check it out.

Where?

The autopilot read this as an emergency

requiring a rapid descent.

requiring a rapid descent.

That could be it.

Parries goes back to the simulator

Parries goes back to the simulator

to test his theory.

Here it comes.

And we got a crash.

And we got a crash.

Perries's theory now explains

fully how the crew's confusion with the autopilot display...

fully how the crew's confusion with the autopilot display...

Three decimal three degrees.

...caused the plane to descend dangerously

...caused the plane to descend dangerously

close to the mountain.

Then, how turbulence, an obscure safety

Then, how turbulence, an obscure safety

feature, and catastrophic timing combined

to bring it even closer.

to bring it even closer.

Half a second before, half a second later, they

wouldn't have the accident.

wouldn't have the accident.

The report will list these causes...

flight deck...

The investigators' conclusions highlight

The investigators' conclusions highlight

weaknesses in the Airbus 320 cockpit design.

Airbus responds immediately.

The main change, which was very quickly made,

The main change, which was very quickly made,

was to change the display window.

With the new design, when

a pilot selects a vertical speed,

the entire four-digit number is displayed.

the entire four-digit number is displayed.

The confusion between an angle and a vertical speed

was no longer possible.

If I hear there's a smoking hole in the side of a mountain,

I'm almost certain to say, OK, we've got a controlled flight

I'm almost certain to say, OK, we've got a controlled flight

into terrain situation.

The common thread is a lack of understanding of where you

are in relation to the terrain.

are in relation to the terrain.