Original subtitles

High above the Himalayas,

High above the Himalayas,

the windshield of Sichuan Airlines Flight 8633 cracks.

It's on the inside.

It's on the inside.

That's not good.

And then gives way completely.

And then gives way completely.

It's almost like having a bomb explode right beside you.

The decompression forces the first officer

The decompression forces the first officer

halfway out of a plane.

In freezing temperatures and rapidly

running out of oxygen, the captain needs to find a way

to get his plane to safety.

Useful consciousness is probably about 40 seconds.

Useful consciousness is probably about 40 seconds.

The lives of everyone on board

now rests in the hands of one man.

now rests in the hands of one man.

I'm just so, so cold.

Ladies and gentlemen,

we are starting our approach.

we are starting our approach.

We lost both engines.

...the load.

Emergency descent.

Mayday, Mayday.

Brace for impact!

Brace for impact!

I think I lost one.

Investigations starting...

It's going to crash.

It's going to crash.

High above Central China, Sichuan Airlines Flight

High above Central China, Sichuan Airlines Flight

8633 reaches cruising altitude.

8633 reaches cruising altitude.

Level at 3, 2, 1.

Roger.

Roger.

45-year-old Captain Liu Chuanjian

is a highly experienced former military pilot

is a highly experienced former military pilot

and a flight instructor.

We're approaching an area of turbulence.

We're approaching an area of turbulence.

It shouldn't be too rough.

It shouldn't be too rough.

First officer Shu Rui Chen is 27 years old

and has five years of flying experience, four of them

and has five years of flying experience, four of them

with Sichuan Airlines.

They're flying an Airbus A319.

They're flying an Airbus A319.

The A319 is part of the Airbus A320 series, just a little bit

shorter, a little bit lighter, but with still two very

shorter, a little bit lighter, but with still two very

powerful engines.

Very well suited for taking a heavy load out

Very well suited for taking a heavy load out

of a high altitude airport where your weight and balance is

extremely critical.

There are 119 passengers on board.

Many catch up on lost sleep after an early morning

departure.

departure.

It should be a smooth ride from here to Lhasa.

The plane took off from Chongqing Airport.

It's a two hour and 40 minute flight to Lhasa, tucked

It's a two hour and 40 minute flight to Lhasa, tucked

in the Himalayan Mountains.

They're flying into Lhasa, which

is one of the most demanding airports in the world.

is one of the most demanding airports in the world.

It's not a dangerous airport if you follow the rules

and you watch the weather carefully.

and you watch the weather carefully.

Captain Liang Peng is the second in command.

I'll be back well before landing.

I'll be back well before landing.

See you then.

He's been a pilot for 10 years.

Today, he'll assist with a high-altitude landing in Lhasa,

Today, he'll assist with a high-altitude landing in Lhasa,

which involves more challenging procedures.

This particular flight had three pilots...

a captain, a first officer, and a secondary captain...

a captain, a first officer, and a secondary captain...

because the aircraft is landing at a higher elevation airport,

and those require specific procedures.

and those require specific procedures.

When you're flying into a high-altitude airport,

you're worried about performance issues,

and you're also concerned about the approach path

through the mountains.

All three of the pilots involved here

were very experienced with high altitude, captain especially.

There are five flight attendants on board,

among them Binan, who's been with Sichuan Airlines

for 11 years.

for 11 years.

6 minutes after reaching cruising altitude,

6 minutes after reaching cruising altitude,

flight 8633 crosses onto the Tibetan Plateau, the largest

flight 8633 crosses onto the Tibetan Plateau, the largest

and highest plateau on Earth.

The altitudes are way above 20,000 feet,

The altitudes are way above 20,000 feet,

not just with the peaks but the plateau itself.

Change of control.

Change of control.

Sichuan 8633 reporting crossing Mikos Bravo 213.

Sichuan 8633 reporting crossing Mikos Bravo 213.

To control.

Roger.

Sichuan 8633 at Mikos Bravo 213.

Sichuan 8633 at Mikos Bravo 213.

Not a cloud in the sky.

Not a cloud in the sky.

40 minutes into the flight...

The windshield is cracked.

Do you have the checklist?

Just as First Officer Shu finds the checklist,

Just as First Officer Shu finds the checklist,

the situation deteriorates.

One of the procedures is to run your finger lightly over it

and see if you can feel any bumps and trying to figure out,

and see if you can feel any bumps and trying to figure out,

is this an external or an internal crack?

It's on the inside.

It's on the inside.

That's not good.

A crack on the inner pane

makes the windshield vulnerable to shattering.

makes the windshield vulnerable to shattering.

So it says here, "Descend to a lower altitude."

The windshield of an aircraft

actually has several layers of glass,

actually has several layers of glass,

and this was the inner pane that was cracked.

The safe thing to do is divert to a safe landing zone.

The safe thing to do is divert to a safe landing zone.

It's what we call a precautionary emergency,

but it's still very important.

I have control of the radios.

Chengdu, Chengdu, Sichuan 8633.

Chengdu, Chengdu, Sichuan 8633.

We have a malfunction.

Requesting descent to a lower altitude.

Sichuan 8633 descend to flight level 280.

Sichuan 8633 descend to flight level 280.

28,000 feet.

28,000 feet.

I'm turning back.

I have a cracked right windshield.

Sichuan 8633, got it.

Confirm, you have a broken windshield?

Confirm, you have a broken windshield?

Affirmative

Sichuan 8633, confirm, will you divert to Chongqing?

Sichuan 8633, confirm, will you divert to Chongqing?

Negative.

We must diert to Chengdu.

The window crack is severe.

The window crack is severe.

Confirm, you will divert to Chengdu.

As the pilots begin their descent...

As the pilots begin their descent...

Affirmative.

We...

...the cracked windshield

...the cracked windshield

explodes, sucking the first officer

partially out of the window.

The sound and fury of losing a windshield

is something that almost like having

a bomb explode right beside you without it

a bomb explode right beside you without it

doing you any physical damage.

It is soul shaking, to say the least.

It is soul shaking, to say the least.

All of the high pressure wants to go to the low pressure area.

So anything that isn't attached is

So anything that isn't attached is

going to want to escape to that hole, including a human being.

going to want to escape to that hole, including a human being.

Sichuan 8633, Roger.

Descend and maintain flight level 280.

As the aircraft dives toward the mountains,

As the aircraft dives toward the mountains,

the first officer hangs on at 32,000 feet above the Earth.

the first officer hangs on at 32,000 feet above the Earth.

When the first officer was pulled forward,

he impacted the side stick, and that pushed the aircraft down

and to the right.

and to the right.

This flight is over high terrain.

So it has a much higher probability of impacting

So it has a much higher probability of impacting

terrain more quickly.

On the ground, the controller notices

On the ground, the controller notices

a sudden shift in altitude.

Sichuan 8633?

Sichuan 8633?

With no time to review all the warnings,

With no time to review all the warnings,

the captain returns to basics.

He begins to fly the plane manually.

There were a number of different warnings happening

There were a number of different warnings happening

at the exact same time.

But the most important thing is to fly the airplane.

But the most important thing is to fly the airplane.

Focus on maintaining a safe altitude.

Captain Liu regains some control

and levels the plane.

But he's facing oxygen deprivation

from the rapid decompression.

In the case of an explosive decompression

at cruise altitude, hypoxia will set in fairly quickly.

at cruise altitude, hypoxia will set in fairly quickly.

The mask is stowed in a compartment behind the pilot

The mask is stowed in a compartment behind the pilot

on the left, and Captain Liu can't

reach it with his right hand.

His left hand must remain on the side stick.

His left hand must remain on the side stick.

At about 31,000 feet, the time of useful consciousness

is probably about 40 seconds for a healthy individual.

is probably about 40 seconds for a healthy individual.

This is something that you can't play around

with because it is lethal.

with because it is lethal.

The captain can't get his first officer back in.

The captain can't get his first officer back in.

He's on his own.

The former fighter pilot knows, if he can't make

a rapid descent, there's no hope of saving his passengers

a rapid descent, there's no hope of saving his passengers

and his helpless first officer.

and his helpless first officer.

Immediately after Flight 8633's cockpit

Immediately after Flight 8633's cockpit

windshield shatters, Captain Liu tries

to return to Chengdu Airport.

This is an incredibly stressful situation.

The first officer has been partially

The first officer has been partially

sucked out of the aircraft.

The captain needs to get down to breathe,

but the mountains are higher than that breathable oxygen.

but the mountains are higher than that breathable oxygen.

To get out of the mountains quickly,

the captain puts the Airbus into a sharp descending left turn.

the captain puts the Airbus into a sharp descending left turn.

In a emergency situation, the pilot's

In a emergency situation, the pilot's

going to maneuver the aircraft outside what would normally

going to maneuver the aircraft outside what would normally

be an acceptable envelope.

Shu, can you get back on your own?

Shu, can you get back on your own?

I can't let go of the control stick!

After the first officer is sucked out of the windscreen,

After the first officer is sucked out of the windscreen,

he's trying to get back into the aircraft.

he's trying to get back into the aircraft.

61 seconds after the windshield

explodes, the pressure between the internal and external air

explodes, the pressure between the internal and external air

equalizes.

Once the pressure equalizes between the flight deck

Once the pressure equalizes between the flight deck

and the exterior of the aircraft,

the first officer is able to bring

the first officer is able to bring

himself back into the aircraft.

Shu!

Shu!

Shu!

You OK?

Get your harness!

With the pressure equalized,

With the pressure equalized,

the Airstream reverses and an ice-cold wind comes rushing in.

the Airstream reverses and an ice-cold wind comes rushing in.

Your mask too!

High winds hamper the first officer's efforts.

High winds hamper the first officer's efforts.

If you're flying at 30,000 feet,

it could be 40 degrees below zero.

it could be 40 degrees below zero.

So you have not only the extreme cold.

You also have the extreme pressure

You also have the extreme pressure

of the wind coming in at you.

With the first officer safely back inside,

With the first officer safely back inside,

the captain accelerates his descent

to the airport 71 miles away.

Can you reach the transponder?

Can you reach the transponder?

Liu wants to notify air traffic

control of their emergency.

control of their emergency.

When an aircraft squawks 7700 on the transponder,

When an aircraft squawks 7700 on the transponder,

it identifies the air traffic controllers

in the area something is wrong and that aircraft

in the area something is wrong and that aircraft

needs priority.

Sichuan 8633, what is the nature of your emergency?

Sichuan 8633.

Sichuan 8633.

Tibet 9832, Chengdu.

Tibet 9832, Chengdu.

The controller contacts other pilots for help.

Tibet 9832.

Tibet 9832.

Go ahead.

Could you call Sichuan 8633 on the frequency?

They've got an emergency.

They've got an emergency.

Let's see if you can get through.

All right.

All right.

Sichuan 8633, this is Tibet 9832.

Chengdu control is calling you.

Chengdu control is calling you.

In the cabin, the relief captain retrieves

his electronic flight bag.

his electronic flight bag.

The electronic flight bag on the aircraft

provided the crew with the escape

provided the crew with the escape

routes they could fly to get to lower

altitudes in the mountains.

altitudes in the mountains.

Give me a hand with the navigation!

Copy.

Your mask.

I'm good for now.

I'm good for now.

I can't let go of the controls.

Altitude is 23,700.

Altitude is 23,700.

As the plane nears the lowest

altitude it can fly over mountainous terrain,

altitude it can fly over mountainous terrain,

the captain levels off.

Speed... 297 knots.

Speed... 297 knots.

The cabin has oxygen masks.

Binan is in charge.

Shu!

Can you hear me?

Are you hurt?

I'll perform the FO duties.

I'll perform the FO duties.

With first officer Shu too injured to assist,

relief captain Liang takes over his duties.

relief captain Liang takes over his duties.

Got the escape chart?

On it.

On it.

Captain Liang checks the charts for the safest

Captain Liang checks the charts for the safest

route over the mountains.

Chengdu is 63 miles away.

Chengdu is 63 miles away.

Continue descent at 500 feet per minute,

then level at 22,000 until we clear the mountains.

then level at 22,000 until we clear the mountains.

C... copy.

I'll call the altitudes.

I'll call the altitudes.

The second in command can see that the captain

is handling this, but there are things that have to be done.

is handling this, but there are things that have to be done.

And one of them is making sure that they don't go too low.

The Airbus reaches 23,400 feet

and is nearly out of the mountains.

and is nearly out of the mountains.

You can do it.

I'm just so, so cold.

Captain Liu is fearless.

But at this altitude, he risks hypothermia,

But at this altitude, he risks hypothermia,

and the airport is still 60 miles away.

Finally, 12 minutes after the rapid decompression,

Finally, 12 minutes after the rapid decompression,

Flight 8633 clears the towering Tibetan Plateau.

34 miles to the airport.

Get in there, captain.

Get in there, captain.

Captain Liu turns toward the airport.

Altitude is 20,900.

Altitude is 20,900.

C... copy.

C... copy.

They were able to get beyond the mountains.

Then other concerns... do we communicate

with air traffic control?

with air traffic control?

Do we set up for the landing?

Chengdu, Sechuan 8633.

Chengdu, Sechuan 8633.

Mayday, Mayday, Mayday.

Mayday, Mayday, Mayday.

Message received.

Mayday declared.

Sichuan 8633 cleared to descend to flight level 190.

Sichuan 8633 cleared to descend to flight level 190.

Siberia 581, climb to flight level 250, offset 3 miles.

Siberia 581, climb to flight level 250, offset 3 miles.

The controller clears the airspace

around the damaged airplane.

around the damaged airplane.

West China 6271, maintain flight level 160 and offset 3 miles.

West China 6271, maintain flight level 160 and offset 3 miles.

In the cabin, Binan tries to contact the crew.

In the cabin, Binan tries to contact the crew.

The flight attendants are doing their best to ensure

The flight attendants are doing their best to ensure

that the cabin is calm.

Everyone has their supplemental oxygen.

But one of the complicating events

But one of the complicating events

here is they never get into communication

with the flight deck to understand the full scope

with the flight deck to understand the full scope

of the situation.

Flight 8633 is now 28 miles from Chengdu.

Flight 8633 is now 28 miles from Chengdu.

Approaching 19,000 feet.

The captain can breathe a little better now.

The captain can breathe a little better now.

Roger.

Roger!

Hang in there, Shu!

Hang in there, Shu!

Sichuan 8633, cabin depressurization,

Sichuan 8633, cabin depressurization,

flying direct to Chengdu, then descending to 10,500 feet.

flying direct to Chengdu, then descending to 10,500 feet.

Flying direct to Chengdu, then descending to 10,500 feet.

The crew's transmitting in the blind

The crew's transmitting in the blind

because they're trying to tell air traffic

control their intentions.

control their intentions.

But they can't hear anything that air traffic control's

saying because of all of the noise coming

in from that missing window.

in from that missing window.

Look over the warnings.

As the flight makes its way toward the airport,

As the flight makes its way toward the airport,

the pilots assess the state of their aircraft.

The captain knows the windscreen is gone.

He knows that the control panel is gone.

He knows that the control panel is gone.

But he doesn't know exactly what else has

been damaged on the aircraft.

been damaged on the aircraft.

Auto brakes are gone...

anti skids, spoilers, APU.

anti skids, spoilers, APU.

They've all got warnings.

With so many instruments

potentially inoperative, the landing

must be performed manually.

must be performed manually.

This was a highly automated aircraft.

This was a highly automated aircraft.

When you have damage like in this incident,

that automation is taken offline,

and they have to figure out how to land the airplane.

and they have to figure out how to land the airplane.

OK, OK.

Do you want to try the autopilot?

Too risky.

Too risky.

Re-engaging disabled instruments is a gamble Captain

Liu isn't willing to take.

Liu isn't willing to take.

He could lose what little control he has over the plane.

That is great airmanship to just take what he has

That is great airmanship to just take what he has

and work with it, because in an emergency,

you don't know exactly what you're going to get.

you don't know exactly what you're going to get.

Sichuan 8633, orbit to the right and descend 8,800 feet on

QNH 1004 at present position.

QNH 1004 at present position.

You're cleared to land on runway 02.

Flight 8633 makes a 360-degree turn

to lose altitude while preparing for landing.

to lose altitude while preparing for landing.

11,200 feet.

11,200 feet.

Copy!

We're still above our maximum landing weight.

We're heavy by half a ton.

We're heavy by half a ton.

The pilots must factor in the extra weight

of their unused fuel as they prepare to configure

of their unused fuel as they prepare to configure

the plane for landing.

An overweight landing on an Airbus 319 where you can't dump

An overweight landing on an Airbus 319 where you can't dump

fuel means that you've got to be much more careful in terms

fuel means that you've got to be much more careful in terms

of actually touching down.

You may have more difficulty stopping the airplane.

You may have more difficulty stopping the airplane.

Flaps wiped?

They don't know yet if deploying the flaps

will slow the plane.

will slow the plane.

Flaps one set.

Yes.

Yes.

The flaps are working so far.

Good.

Speed?

Speed?

212 knots.

Reducing to 203.

Reducing to 203.

The pilots slow the engines further.

Binan can sense that the plane is approaching the airport.

Binan can sense that the plane is approaching the airport.

Attention, everyone.

Please remove your masks.

She prepares the cabin for an emergency landing.

Tuck your head in your lap and brace for impact.

Tuck your head in your lap and brace for impact.

Landing gear.

Roger.

Landing gear.

Landing gear.

The plane is slowing.

But the pilots don't know if the landing gear will engage.

Yes!

Landing gear is down.

Clear to land on runway 02 right.

Wind 250 at 2 meters per second.

Wind 250 at 2 meters per second.

RVR greater than 6,500 feet.

We need the whole runway.

We need the whole runway.

Sechuan 8633, runway 02 right.

Sechuan 8633, runway 02 right.

We need the entire runway.

The captain selected that runway to account for the fact

The captain selected that runway to account for the fact

that the aircraft is heavier and therefore is requiring

more stopping distance.

more stopping distance.

10 miles from the airport, the aircraft

is lined up with a runway.

160 knots.

160 knots.

After everything that's happened,

can they keep it on the runway?

50 feet.

40 feet.

40 feet.

The 63-ton plane prepares to touch down.

Engaging thrust reversers.

The thrust reversers, which help the plane slow down,

don't work.

don't work.

The risk is that you're going to run

off the end of the runway if you don't

have your thrust reversers.

have your thrust reversers.

Brakes, brakes!

Captain Liu gives the foot

Captain Liu gives the foot

brakes everything he's got.

They're his last hope of stopping the plane

from overshooting the runway.

from overshooting the runway.

We made it.

Sichuan 8633.

Sichuan 8633.

We have injuries on board and cannot taxi to the gate.

Against tremendous odds,

everyone onboard Sichuan 8633 is safely back on the ground,

everyone onboard Sichuan 8633 is safely back on the ground,

thanks to the pilot's exceptional skills.

Once everyone is able to exit the aircraft safely,

the real work of the investigation began.

the real work of the investigation began.

What evidence can they find that will

help them answer the question, why did this happen?

help them answer the question, why did this happen?

Investigators from the Civil Aviation Administration

Investigators from the Civil Aviation Administration

of China, or CAAC, look into Sichuan

8633's near catastrophe.

8633's near catastrophe.

Good to see you again.

You as well.

You want to look at the cockpit?

That'd be good.

That'd be good.

A French investigator from the Bureau of Air

Accident Investigation and Analysis, or BEA, also

Accident Investigation and Analysis, or BEA, also

joins the team.

OK.

I'll speak with Captain Liu while one of our team

I'll speak with Captain Liu while one of our team

- takes you to the plane. - Great.

Thanks.

The aircraft is made in France.

The BEA, as the investigative agency for that country,

The BEA, as the investigative agency for that country,

would respond to an accident worldwide.

Thank you for coming in.

Thank you for coming in.

Oh, please, have a seat.

Did something strike the windshield of Flight 8633,

Did something strike the windshield of Flight 8633,

causing it to rupture?

It was a clear day.

We were cruising along at 32,100 feet.

We were cruising along at 32,100 feet.

About 10 minutes in, we heard a loud noise

and saw a big mesh crack.

And then?

A few seconds later, another loud noise, and the crack

A few seconds later, another loud noise, and the crack

radiated further.

I touched the glass, and I could tell it was on the inner pane

and it was bad.

and it was bad.

A cockpit windshield is made up

of three layers of glass, two thick inner panes

of three layers of glass, two thick inner panes

and one thin outer pane.

and one thin outer pane.

The windshield is actually a structural part

of the airplane.

They're quite thick.

They're very strong.

Obviously, they're made to withstand your bird strikes

Obviously, they're made to withstand your bird strikes

and other objects like that.

I called ATC to clear dissent.

I called ATC to clear dissent.

You told them the windshield was cracked?

Yes.

Yes.

But before we finished talking, the window exploded,

a decompression happened, and we lost a bunch of instruments.

a decompression happened, and we lost a bunch of instruments.

Did you see anything hit the windshield?

Did you see anything hit the windshield?

No.

There was no mark, no smear, just a big, mesh-like crack.

OK.

Thank you.

If I have more questions, I'll reach out.

If I have more questions, I'll reach out.

Investigators rule out an external strike as the cause

of the windshield's explosion.

of the windshield's explosion.

Thanks for your time.

There's no evidence of lightning strike

or birds or anything else.

or birds or anything else.

So there was nothing to show that that piece

of the windshield was damaged prior to the event.

of the windshield was damaged prior to the event.

Any signs of how the crack started?

Any signs of how the crack started?

Not really.

Almost everything was sucked out of the windshield,

except this...

except this...

the terminal block.

Located at the bottom of the windshield,

the terminal block holds six electrical wires

the terminal block holds six electrical wires

that control the temperature to prevent freezing or fogging.

The team is dismantling it from the frame

so we can take a closer look.

so we can take a closer look.

OK.

The investigators focused on the terminal block

The investigators focused on the terminal block

because it was the only part of the windscreen assembly

that they had left.

Let's download the data now.

While investigators wait for the terminal block

While investigators wait for the terminal block

to be removed from the plane, they

turn to one of the flight's communication systems

turn to one of the flight's communication systems

for leads.

A digital system called ACARS, or Aircraft Communication

Addressing and Reporting System, sends

Addressing and Reporting System, sends

electronic messages between the aircraft and ground stations

during a flight.

during a flight.

ACARS messages coming from the aircraft

can lead the investigators to certain faults that occurred

can lead the investigators to certain faults that occurred

as well as what the aircraft was doing.

It's all here.

Let's locate the first crack.

Here it is...

7:07 AM.

See that?

Anti-ice right windshield.

Huh, interesting.

Huh, interesting.

Investigators discover that,

after the windshield first cracked,

after the windshield first cracked,

there was a warning message.

The anti-ice message gives you an indication that

The anti-ice message gives you an indication that

there is something wrong with the heating

element in the windscreen.

But it doesn't exactly tell you why.

But it doesn't exactly tell you why.

The windshield cracking and the warning

happened almost simultaneously.

happened almost simultaneously.

The investigators had to think there has to be a connection.

Let's check recent flights.

Let's check recent flights.

Has an anti-ice windshield warning

appeared on other flights?

Investigators searched the fleet's history.

Investigators searched the fleet's history.

Check this out.

2009, a warning popped up on a Sichuan Airlines Flight

2009, a warning popped up on a Sichuan Airlines Flight

after takeoff.

In 2009, the warning also appeared on a Jiangsu

Airlines flight as pilots detected smoke near the bottom

Airlines flight as pilots detected smoke near the bottom

of their windshield.

In 2010, the warning lit up on a China Hebei flight

In 2010, the warning lit up on a China Hebei flight

when pilots noticed a burning smell near the windshield.

when pilots noticed a burning smell near the windshield.

Did they determine a cause?

Did they determine a cause?

Overheating in all three cases.

Investigators saw that in related incidents where

Investigators saw that in related incidents where

this kind of warning came up there were certain effects,

burning smells, anything that indicated there

was an overheating happening.

was an overheating happening.

What about the windshields?

Did any of them crack or rupture?

No, it doesn't look like it.

Citron 8633 never reported smoke.

Nor the smell of burning.

The investigators knew there was

a problem with the right windshield heating system.

So what was different about this incident?

So what was different about this incident?

Investigators turned to physical evidence

from Sichuan Airlines 8633's cockpit for clues as to why

from Sichuan Airlines 8633's cockpit for clues as to why

the windshield shattered.

the windshield shattered.

Check out these wires.

The windshield heating system is electrically driven,

The windshield heating system is electrically driven,

and there are several wires through the terminal block

that help drive the system.

One of those wires looked a lot more damaged than the others.

One of those wires looked a lot more damaged than the others.

Huh.

Huh.

It looks like the wire insulation is charred

and the copper wire is melted.

and the copper wire is melted.

The team finds evidence of overheating.

They noticed that one of the wires

They noticed that one of the wires

was very dark, which is a sign of carbonization.

They could see evidence of burning

They could see evidence of burning

heat around the end of it.

Look at the corrosion inside the terminal block.

Investigators also find

Investigators also find

evidence of moisture buildup.

Water must have seeped in past the window seals.

They discover a sign of moisture and humidity

and even an unusual color you should not

and even an unusual color you should not

see inside a terminal block.

see inside a terminal block.

Moisture inside the terminal block corroded

and damaged the copper wires.

When a current ran through them, arcing occurred, which created

When a current ran through them, arcing occurred, which created

extremely high temperatures.

You're getting temperatures in excess of 400 degrees Celsius.

It's extremely hot.

It's extremely hot.

The investigators had to answer,

was this enough to make the windshield crack?

Investigators dig into the history of the aircraft,

Investigators dig into the history of the aircraft,

looking for a connection between cracked windshields

and overheating.

Got one, an 8340, December 1997.

Got one, an 8340, December 1997.

I found four more...

I found four more...

2001, 2004, 2007, and 2011.

2001, 2004, 2007, and 2011.

Here's another one in 2009.

Here's another one in 2009.

They discover six similar incidents of cracks

in cockpit windshields.

in cockpit windshields.

Every single incident resulted from overheating.

Every single incident resulted from overheating.

The heat built up inside the windshield

and couldn't dissipate.

Which is why the windows cracked.

Which is why the windows cracked.

The team concludes that an overheated

electrical wire inside the windshield

electrical wire inside the windshield

cracked the inner pane of glass on the first officer's side.

cracked the inner pane of glass on the first officer's side.

The aircraft windshield panes are very closely spaced

together, and when one side is overheated,

together, and when one side is overheated,

it spreads those panes apart.

It causes stresses on those panes.

Did the middle pane crack as well, leading

Did the middle pane crack as well, leading

to catastrophic failure?

to catastrophic failure?

How did Sichuan 8633's windshield explode?

How did Sichuan 8633's windshield explode?

We know the first pane cracked.

The middle pane should have maintained loads

The middle pane should have maintained loads

and kept this intact.

But it failed very quickly.

That was a mystery.

That was a mystery.

To determine why Sichuan 8633's windshield blew

To determine why Sichuan 8633's windshield blew

out after cracking, the team undertakes a windshield failure

scenario test.

scenario test.

The mechanism of what happened in flight to that windshield

is unknown because they didn't recover the windshield.

is unknown because they didn't recover the windshield.

What they could do and what they did do

was to do a laboratory test to see if you can

have a catastrophic failure.

have a catastrophic failure.

They install onto a test bench

a cockpit windshield with a cracked inner pane,

a cockpit windshield with a cracked inner pane,

replicating the first crack.

OK, the window's ready.

Camera's now recording.

Now pressurizing.

They subject the cracked

windshield to the same differential

windshield to the same differential

pressure of Flight 8633.

pressure of Flight 8633.

Let's get the shop pin ready.

They have drilled a small hole in the outer pane

through which a shot pin can pass and strike

through which a shot pin can pass and strike

the middle pane to simulate what would

happen if it cracked as well.

All set.

All set.

The test works.

The windshield is blown out of the frame.

Well, there you have it.

Well, there you have it.

The pressure was just too much.

At 32,000 feet, the difference in pressure

At 32,000 feet, the difference in pressure

between the atmosphere outside and the cockpit inside

was approximately 2 tons.

Investigators conclude that the cracked windshield could

not withstand that pressure.

not withstand that pressure.

What we saw from testing is, once you break the inner pane

What we saw from testing is, once you break the inner pane

and the middle pane, the outer pane

cannot withstand the pressure.

It's going to flex the window out,

It's going to flex the window out,

and it's going to depart the aircraft.

Here you go.

Thank you.

Thank you.

Investigators now know how the windshield

was blown from Flight 8633.

was blown from Flight 8633.

But they still don't understand why

the moisture buildup inside the window was undetected.

the moisture buildup inside the window was undetected.

Moisture is insidious.

It's going to find ways to get in.

So now the question is when they were inspected,

So now the question is when they were inspected,

how they were inspected.

because of wind erosion.

Investigators examine the inspection history

Investigators examine the inspection history

of Flight 8633's windshields.

That's right.

Flip the page.

Flip the page.

Last inspection was 32 days before the incident.

And there were no signs of water buildup on the terminal block.

And there were no signs of water buildup on the terminal block.

How come?

Maintenance would have had to remove the entire windshield

Maintenance would have had to remove the entire windshield

to access it.

They'll look around the edge to see, are the seals intact?

Are the seals degraded?

Are the seals degraded?

You look at components to see is any evidence

of water intrusion, but you don't pull

of water intrusion, but you don't pull

the window out of the frame.

So without fully disassembling the aircraft,

So without fully disassembling the aircraft,

you can't ensure that you don't have water vapor built up.

But that's not all they discover.

But that's not all they discover.

There are no sensors to detect moisture.

You have sensors for controlling

You have sensors for controlling

the temperature of the window.

But there's nothing in there to tell

you that corrosion is present.

you that corrosion is present.

Even though investigators understand

Even though investigators understand

what caused the incident aboard Flight 8633...

You know what I don't get?

You know what I don't get?

...one piece of the puzzle is missing.

Why did so many systems in the cockpit

fail after the windshield exploded?

With the loss of the windscreen

also came a whole list of things that went off.

It was puzzling.

It was puzzling.

They lost the auto brakes, 6 of the 10 spoilers,

the thrust reversers.

the thrust reversers.

Investigators review all the systems

the pilots of Flight 8633 lost after

the pilots of Flight 8633 lost after

the explosive decompression.

Hm.

Hm.

It looks like they were disabled, not damaged.

The team discovers that all the disabled systems

on Flight 8633 are connected to 17 circuit breakers

on Flight 8633 are connected to 17 circuit breakers

on a panel behind the first officer's seat.

Check out all these popped breakers.

Something must have hit the breaker

Something must have hit the breaker

panel during the decompression.

There's damage here.

There's damage here.

This part of the door lines up with the damage.

The damage to the panel

The damage to the panel

is at the same height as the dented cockpit door.

When the windshield ruptured, the explosive decompression

When the windshield ruptured, the explosive decompression

flung open the cockpit door, which smashed the circuit panel

flung open the cockpit door, which smashed the circuit panel

and popped multiple breakers.

It's almost impossible to think that anybody would

It's almost impossible to think that anybody would

immediately recognize that that was

a mechanical response to the door blowing open

and hitting the side panel.

and hitting the side panel.

Investigators finally have

all the pieces of the puzzle.

Moisture seeped into the window seals of the Airbus A319...

Moisture seeped into the window seals of the Airbus A319...

You couldn't ask for a better view.

You couldn't ask for a better view.

...creating a humid environment where

electrical wires overheated to the point of cracking

electrical wires overheated to the point of cracking

the cockpit windshield.

the cockpit windshield.

Sichuan 8633, confirm, will you divert to Chongqing?

Sichuan 8633, confirm, will you divert to Chongqing?

Negative.

We must divert to Chengdu.

The window crack is severe.

The window crack is severe.

The tremendous pressure differential

compounded the existing thermal stress on the cracked panes,

compounded the existing thermal stress on the cracked panes,

leading to the rupture and explosive decompression.

leading to the rupture and explosive decompression.

With his first officer sucked out of the window, Captain

With his first officer sucked out of the window, Captain

Liu's quick thinking, flying skills,

and tremendous courage in the face of oxygen deprivation

and tremendous courage in the face of oxygen deprivation

allowed him to fly the plane out of danger.

The captain didn't suffer from hypoxia.

The captain didn't suffer from hypoxia.

Investigators looked at the surrounding factors

and kind of came to the conclusion that he was

and kind of came to the conclusion that he was

operating purely on adrenaline, basically,

and was able to operate the aircraft safely down

and was able to operate the aircraft safely down

to Chengdu.

You can do it!

You can do it!

The crew endured glacial temperatures

and battled the odds to safely land the damaged plane

and battled the odds to safely land the damaged plane

and save the lives of all 128 people onboard.

and save the lives of all 128 people onboard.

Any accident in incident investigation

is also a learning opportunity.

There were changes that were made by the manufacturer

There were changes that were made by the manufacturer

to tighten up the quality control to make it less

likely that you would have situations that might allow

likely that you would have situations that might allow

moisture to get past the seals.

The crew's handling of the incident earned them

The crew's handling of the incident earned them

accolades around the world.

There have been accidents in the past where the whatever

There have been accidents in the past where the whatever

happened at altitude was survivable but the crew got

so rattled and was so non-communicative

so rattled and was so non-communicative

they end up crashing the airplane on the other end.

This crew did a really excellent job.