All language subtitles for Air.Disasters.S10E04.Deadly.Detail.1080p.PMTP.WEB-DL.AAC2.0.H.264-maldini_track3_[eng]

JIM: What is going on out there?

FLIGHT ATTENDANT:
Everyone, we're about
to evacuate the plane.

Remain calm.

JIM: I certainly knew
that with both engines on fire

it was not going to go well.

NARRATOR: 157 passengers
rush to escape a burning 737.

JIM: Let's go, let's go!

KIT: It goes up like a bomb.

♪

NARRATOR: In the struggle
to explain the inferno,

the smallest parts come
under intense scrutiny.

The analysis leads to
a stunning discovery.

INVESTIGATOR: Where is it?

BOB: It was a true breakthrough
in the investigation.

NARRATOR: The failure that
doomed China Airlines Flight 120

is putting more
lives in danger every day.

KIT: We really didn't
anticipate that there's a risk,

and it bit us.

Flight attendant:
LADIES AND GENTLEMEN,
WE ARE STARTING OUR APPROACH.

Pilot: WE LOST BOTH ENGINES!

Flight attendant:
PUT THE MASK OVER YOUR NOSE.

EMERGENCY DESCENT.

Pilot: MAYDAY, MAYDAY.

Flight attendant:
BRACE FOR IMPACT!

Controller: I THINK I LOST ONE.

Man: INVESTIGATION STARTING
INTO THIS TRAGEDY...

Man: HE'S GONNA CRASH!

♪

NARRATOR: China
Airlines Flight 120

is on final
approach for landing.

CPT. YU: Ladies and gentlemen,

we're about to begin our descent
into Okinawa Naha Airport.

Please give the flight
attendants your full cooperation

as they prepare
the cabin for landing.

NARRATOR: The Captain is
47-year-old Yu Chien-kou.

CPT. YU: What's the
weather for approach?

FO. TSENG: The ceiling is 8,000
feet. Winds at eight knots.

NARRATOR: The first officer
is 26-year-old Tseng Ta-wei.

The pilots have more than 8,500
hours of flight experience

between them.

CPT. YU: Almost
straight down the pipe.

FO. TSENG: Yes, sir.

NARRATOR: Landing this
Boeing 737 should be routine.

KIT: The 737 is probably
the most popular airframe

in the world.

It's flown by most pilots as
they start out in their careers.

It's a short-range
domestic airplane.

NARRATOR: Flight 120 is a
one-hour journey from Taiwan

to the southern
Japanese island of Okinawa.

This morning,
there are 157 passengers

and eight crew on board.

FLIGHT ATTENDANT:
Please put your tray up
and fasten your seat belt.

NARRATOR:
Jim Caruso is a medical
examiner for the U.S. Navy

stationed in Okinawa.

He and his family are on the
last leg of a long trip home

from vacation.

JIM: The family was returning
from Brisbane, Australia.

We had done probably 12
or 14 days on vacation,

and we were hoping
to be home for lunch.

NARRATOR: Living in Okinawa has
given the Carusos the chance

to travel through much of Asia.

JIM: We got to see China, Hong
Kong, mainland Japan, Korea.

We had made use of our location
to experience the area.

NARRATOR: Naha Airport sits
at the southern end of Okinawa,

on the shore of
the East China Sea.

The pilots reconfigure
their plane as they slow down

and descend for landing.

CPT. YU: Let's go to flaps 25.

FO. TSENG: Flaps 25.

NARRATOR: They deploy flaps
from the wing's back edge,

along with slats
from the front edge.

These devices keep the
plane airborne at lower speeds.

KIT: When we start configuring,

we begin to put
out flaps and slats,

which extend the area of
the wing and give us more lift

and allow us to fly slower.

And of course the
landing and touchdown itself

are the most
complicated part of the flight.

NARRATOR: They're now less
than a minute from the runway.

JIM: Okay, honey. You
have to remain in your seat.

JIM: I think everybody was
looking forward to landing,

getting off the airplane and
getting back to regular life.

AUTOMATION: 30, 20, 10.

NARRATOR: It's a
textbook landing.

CPT. YU: Flaps up.

JIM: Once you're landed
you figure you're home free.

The taxi is usually routine.

CPT. YU:
After landing checklist.

FO. TSENG: Speed brakes.

NARRATOR: All that's left for
the China Airlines pilots

is to park the plane.

FO. TSENG: Engine start levers.

CPT. YU: Engine
start levers cut off.

NARRATOR: With the engines
off they can finally relax.

KIT: The pilot is relieved.
He's no longer at risk.

A catastrophic
event after you're parked

is almost non-existent.

FO. TSENG: Seat belts.
CPT. YU: Seat belts off.

JIM: The biggest challenge
ahead of you from there

is making sure you
can get through customs.

No one ever expects
anything to go wrong,

especially once the
engines are turned off.

NARRATOR: But one
passenger has noticed

that something's not right.

JIM: My wife was next to a woman

who made some
sort of exclamation

towards the engine
on the right side.

FEMALE PASSENGER:

JIM: What's going on?

JIM: There was some
smoke coming from that engine.

That was the first
sign that something

was out of the ordinary.

JIM: What is going on out there?

FO. TSENG: Anti-ice,
off. Start switches, off.

NARRATOR:
The pilots are finishing
the shut-down checklist.

FO. TSENG: Transponder T-CAS.

CPT. YU: Hey! What is this?

FO. TSENG: What's happening?

NARRATOR: Just when they thought
they were safely parked...

GROUND CREW: Cockpit,
ground. Number 2 engine fire.

NARRATOR: ...a radio call alerts
them to an urgent danger.

Their plane is on fire.

FO. TSENG:
Attention, crew on station.

Attention, crew on station.

KIT: Bringing the flight
attendants to their station

tells them that what
might likely be next

would be an
emergency evacuation.

RADIO CALL: Dynasty 1-2-0,
we are calling a fire truck.

Remain on standby.

FO. TSENG: We have
a wheel fire. Please.

FEMALE PASSENGER:

FO. TSENG: Cabin crew,
prepare for evacuation.

Prepare for evacuation.

♪

FLIGHT ATTENDANT:
Everyone, remain calm.

We're about to evacuate
the plane. Remain calm.

NARRATOR: Fear begins to
spread throughout the cabin.

Outside, the fire
is getting worse.

JIM: The engine on my side also
started smoking and flaming.

So now we had
both wings on fire.

And at that point
people began to panic.

FLIGHT ATTENDANT:
Remain calm! No pushing!

JIM: I had no idea at that point
how things would play out,

but I certainly knew that
with both engines on fire

it was not going to go well.

FO. TSENG: Parking brakes.
Speed brakes. It's that lever.

NARRATOR: The pilots know they
need to get their passengers

off the plane before
flames reach the fuel tanks.

But they can't open
the cabin doors yet.

CPT. YU: Engine fire
warning switches. Override.

NARRATOR: They must
follow an evacuation checklist.

KIT: We want the pilots to
grab the list, simply read it

and do it.

No wondering what step is next,

because the sequence of
the steps are very important.

CPT. YU: Pull and rotate.

FLIGHT ATTENDANT:
Everybody remain calm.

Do not bring your
luggage or personal belongings.

NARRATOR: Seconds feel like
hours as the crisis escalates.

Finally, the pilots are
ready to open the doors.

FO. TSENG: Evacuation
required now. Required.

♪

FLIGHT ATTENDANT: No
pushing. No pushing.

Please keep moving forward.

NARRATOR: But it will take
time for all 157 passengers

to make it to the exit.

George Ishizaki is
watching the unfolding disaster

from inside the
airport terminal.

GEORGE: I just happened to
have my camcorder with me.

I thought, oh my
god, what is happening?

FLIGHT ATTENDANT:
Keep moving forward.

NARRATOR: With the
fire growing more intense,

time is running out.

JIM: Let's go. Let's go!

JIM: We were quite a
ways back from any exit

since the over-wing
exits were useless.

So my focus was really to
get the kids moving forward

and off the aircraft.

FEMALE PASSENGER (In distress):

JIM: Go ahead. Go
ahead, all right?

NARRATOR: Jim Caruso stays
behind to help other passengers

get off the burning plane.

JIM: I don't
actually remember hesitating.

It may have been a little
difficult to make that decision

since the kids were
already moving forward.

FLIGHT ATTENDANT: Hey, no
pushing. Keep moving forward.

GEORGE: The smoke
actually started building, and

that's when everything started
happening really quickly.

♪

NARRATOR: Jim Caruso is
separated from his family.

The heat and smoke are getting
worse. He hears a cry for help.

FEMALE PASSENGER:

JIM: The woman behind me pointed
towards the overhead bin.

I was concerned if
she was pointing towards

flames coming in.

FEMALE PASSENGER:

JIM: I looked up and I
saw a pair of crutches.

GEORGE: Everybody was
just sliding down the slides,

and once they got on the ground
they were just scrambling.

♪

JIM: Once the smoke
and fire started building,

the cabin became rather warm.

I do recall some of the
windows actually cracking

from the heat.

NARRATOR: Finally,
they make it to the exit.

♪

The plane has been burning
for close to three minutes.

It could explode at any moment.

FLIGHT ATTENDANT:

Captain, all
passengers are evacuated.

You're the last ones.

CPT. YU: We
gotta get out of here.

KIT: Typically, the captain
will stay until everybody's off

and he will verify
that the airplane is empty.

NARRATOR: The pilots have put
their passengers' safety first.

But now it may be
too late for them.

CPT. YU: We're going to have to
climb out through the window.

You first.

FO. TSENG: Yes, sir.

NARRATOR: All 737
cockpits are equipped

with an emergency escape rope.

It's designed to help pilots
exit through the side window,

but it's no easy maneuver.

KIT: Exiting the airplane is
more difficult than it sounds.

It's a relatively small window.
Going down the rope has a risk.

♪

Then...

WITNESS: Oh.
Whoa. Whoa. Oh my god!

GEORGE: You felt a huge kaboom.

I've never felt
anything like that.

JIM: We actually could
feel the ground shake.

♪

NARRATOR: Passengers run to
safety as a fiery explosion

engulfs the plane
they just escaped.

The fate of the
pilots is still unknown.

JIM: As I looked back
after the first explosion,

I recall crew members
fast-roping, as it were,

out of the cockpit.

NARRATOR: The force of the blast
overpowers the first officer.

GEORGE: He dropped down from the
height of the cockpit window

onto the ground.

NARRATOR: Incredibly, he's
able to get up and run away

from the flames. The
captain quickly follows.

GEORGE: It was
good that he did that,

because the fire
just gutted the airplane.

NARRATOR: More
explosions rock the airplane.

GEORGE: The
fuselage I guess melted.

The back half just
kind of fell to the ground.

NARRATOR: Finally, fire
trucks arrive on the scene.

JIM: Everybody had exited
the aircraft at that point

and was
gathering in the terminal.

It was a huge
relief to have the kids

and my wife and I together.

We certainly were looking
back at the aircraft again

in amazement.

NARRATOR: Fire on an airplane
can quickly become lethal.

Incredibly, on Flight
120, all 165 people on board

have escaped unharmed.

KIT: I've never
heard of any evacuation

where somebody wasn't hurt.

To get this many people off
in such a dire circumstance

in a very short period of time
with no injuries is miraculous.

♪

NARRATOR: If
there's a next time,

passengers may not be so lucky.

Pressure to figure
out what happened falls

on an international team
of air crash investigators.

THOMAS: Okay. Let's get to work.

NARRATOR: They need to
explain how an airliner

that had landed safely
and turned off its engines

suddenly burst into flames.

THOMAS: We have no clue.
We do not know what happened.

We tried to find out from
the wreckage that remained

still on the apron.

BOB: Normally
fires occur in-flight,

perhaps during taxi sometimes,

but rarely in a parking spot
after the engines are shut down.

THOMAS: The challenge
for the investigator is,

most of the evidence will
be destroyed by the fire.

NARRATOR: Across the globe,
there are more than 5,000

Boeing 737s in service.

KIT: There's a 737
taking off and landing

every three or four
seconds in the world.

NARRATOR: If the
plane has a design flaw

that somehow leads
to uncontainable fire,

countless
passengers could be at risk.

BOB: We were aware that the 737

is probably the most
popular airliner out there.

So there's a reason
once an accident occurs

to try to figure out what
happened pretty darn quickly.

♪

NARRATOR: The search for
Flight 120's black boxes

begins immediately.

BOB: One of our
main goals initially

is to try to find the
cockpit voice recorder

and the flight data recorder.

These are important,
because a lot of times

they tell us what happened.

NARRATOR: But
investigators know that

after such an intense fire

there's a chance the
black box data will be lost.

They need other leads.

BOB: Good investigators
don't rely totally

on flight data
recorders, for instance,

or cockpit voice recorders
because they can be destroyed.

So we rely on witnesses
to tell us their impression

of what happened.

CPT. YU: Well, we
taxied off the runway

down the apron to our
assigned parking spot.

FO. TSENG: Once we parked,
we shut off the engines,

and some time after that we
heard the aircraft was on fire.

BOB: We needed to know
what type of fire it was,

what the
ignition source would be,

what the fuel source would be.

Those were the areas of our main
questioning right off the bat.

FO. TSENG: I radioed the
controller letting him know

we had a wheel fire.

NARRATOR: Investigators know
that if a wheel caught fire

on Flight 120, there's
more than one possible cause.

A deflated tire can
result in burning rubber.

Overheated brake
pads could potentially

ignite hydraulic fluid.

BOB: In a wheel
well of an aircraft

there are a lot
of hydraulic lines

going to the landing gear
assemblies and things like that.

Hydraulic fluid
is very flammable.

If a hydraulic leak occurred
and it happened to drip

onto a hot brake for
instance, well, there you go.

CPT. YU: Hey. What is this?
FO. TSENG: We have a wheel fire.

NARRATOR:
If the pilots are right
about where the fire started,

investigators should
be able to find proof.

They examine the
plane's right side wheel well

and landing gear assembly.

They find scorched wreckage,
but not enough to convince them

that this is
where the fire began.

BOB: Once we were
able to closely examine

that part of the aircraft,

we were very confident
that a wheel well fire per se

did not occur.

The seat of the fire
seemed to be forward

and a little bit to the
right of the wheel well area.

NARRATOR: It seems
the pilots were mistaken

about the origins of the fire.

Where it started
remains a mystery.

♪

Solving that mystery may
have just become easier.

Investigators have recovered
the plane's black boxes.

THOMAS:
The Japanese team retrieved
both the Boeing's CVR and FDR.

THOMAS: Let's get
working on the FDR immediately.

BOB: On modern 737s,
the flight data recorder

has thousands of parameters,

data bits that come in to
the recording device itself.

It will take time to download
and verify all the data.

♪

NARRATOR: Meanwhile,
the charred fire scene

continues to
challenge investigators.

THOMAS: With all this heat
damage it's nearly impossible

to tell where the fire started.

NARRATOR: They're
almost certain the fire began

on the right side of the
plane as witnesses reported.

But where exactly?

THOMAS: Wait a sec.

NARRATOR: Scorched wires
provide a promising new lead.

THOMAS: What do you think?

NARRATOR: Did an electrical
fire destroy Flight 120?

Serious electrical failures
are rare, but not unheard of.

In 1998, the cockpit
of Swissair Flight 111

began filling with
smoke shortly after takeoff.

The pilots tried to
make an emergency landing

in Halifax, Canada.
They never made it.

Their plane disappeared
into the Atlantic Ocean,

killing all 229 people onboard.

Investigators found
that an electrical fault

in the entertainment system

almost certainly sparked
the fire that doomed the plane.

THOMAS: Okay.
Let's see what we got.

NARRATOR: If the
fire aboard Flight 120

was caused by faulty wiring,

investigators may now
be able to confirm it.

They've successfully
downloaded the black box data.

Any electrical problem or
failure in any onboard system

should show up in the data.

BOB: Almost every system
on the aircraft is recorded.

Its status is recorded.

So we looked
very quickly through

these hundreds of
electrical possibilities

and we found nothing.

THOMAS: It wasn't electrical.

NARRATOR: The
analysis comes up empty.

THOMAS: At that time we
can rule out some wheel fire

or some other electrical fire.

NARRATOR: Investigators
turn their attention

to the aircraft's right engine.

In flight, the
CFM-56 power plant

generates internal
temperatures of more

than 2,000 degrees Fahrenheit,
hotter than molten lava.

Could an engine fire
have sparked the inferno?

BOB: We of course looked at
the engines very carefully,

the right engine especially

because there was a lot
of fire damage around it.

It was fairly easy to
look inside the engine

and examine the
core, so to speak,

where all the damage in an
engine failure usually occurs.

And we found nothing wrong.

The engine was damaged
externally but not internally,

so we eliminated it
as a possible factor.

THOMAS: What could have
burned this entire plane down?

NARRATOR: The
investigation has hit a wall.

The cause of the catastrophic
fire remains unknown,

while every day thousands
of 737s continue to fly.

There's growing
pressure on investigators

to find the answer.

BOB: We knew we had a little bit
of detective work ahead of us

and we pressed on.

♪

NARRATOR: The video
capturing the fiery destruction

of China Airlines Flight 120

could provide
investigators with clues

to what started the fire.

THOMAS: Whoa.

NARRATOR: The footage
reveals just how quickly

the flames spread
through the passenger jet.

But for investigators, the
most important clue is missing.

The recording hasn't
captured the critical moment

the fire started.

THOMAS: From the
video, we can only understand

there was fire and
the location of the fire

and it seems that something
was feeding to the fire.

But we cannot understand why.

♪

NARRATOR: Investigators
widen the search for leads.

THOMAS: What did you see?

NARRATOR: The effort pays off
when an airport ground worker

provides a critical detail.

BOB: A ramp worker on the
right side of the aircraft

said very distinctly
that he saw a liquid

running down the
leading edge of the right wing

before the fire broke out.

THOMAS: Thanks.

NARRATOR: Fluid leaking
from this part of the wing

of the aircraft can be
only one thing: jet fuel.

The 737 holds
4,390 gallons of fuel,

much of it in tanks located

inside the plane's
two massive wings.

BOB: When we figured out that an
actual fuel leak had occurred,

it was a breakthrough,

a true breakthrough
in the investigation.

We now needed to
know why it originated.

THOMAS: We know the fuel
was leaking, but from where?

A fuel line?

NARRATOR: Finding solid evidence
amongst the burnt remains

of the plane's fuel
system won't be easy.

The Boeing 737-800
has high-pressure pumps

inside the wing.

They deliver 200 gallons of
fuel per hour to the engine.

All that fuel flows
through flexible pipes.

Could one of those
fuel pipes be the culprit?

BOB: Fuel lines are
probably in a sense

the most vulnerable
part of a fuel system.

They take bends and
sometimes they're exposed

where they could get knocked
or punctured by something.

So we tried to trace the entire
fuel system of the aircraft.

♪

NARRATOR: It's another dead end.

THOMAS: It
wasn't the fuel lines.

NARRATOR: None of the
fuel lines are ruptured.

BOB: We had a
lot of fire damage,

but the fuel lines that we
examined seemed to be intact

and functional.

NARRATOR: Investigators
still can't explain the fire.

They know enough fuel
leaked from the plane

to feed the flames, but they
don't know where it came from.

BOB: Once we
eliminated fuel lines per se

as a possible problem,

pretty much the only
thing out in that area

that could have gone wrong is
a leak in the fuel tank itself.

NARRATOR: The plane's fuel tanks
are made from aluminum alloy

and designed to withstand
the rigors of flight for years.

They should never crack or leak.

Examining them

presents one of the most
difficult challenges yet.

They hope a tool called a
borescope will do the trick.

It's a small camera that
can peer into tight spaces.

It gives them a unique view

inside the plane's
right wing fuel tank.

What it reveals
changes the entire course

of this investigation.

THOMAS: Whoa.
Would you look at that?

BOB: All of a
sudden, clear as a bell,

we saw this bolt sticking
out of the fuel tank itself.

Where the bolt came
from is a complete mystery,

but it has ruptured the tank

right where the ground
worker spotted leaking fuel.

BOB: It's hard to describe
how significant this was.

I mean, this was the
core of the investigation.

Now we knew what happened.

The rest of the investigation
was trying to figure out

why this occurred.

NARRATOR: A punctured
fuel tank was the cause

of one of the most infamous
air crashes in history.

A supersonic Air France Concorde
burst into flames on takeoff

after running over a piece
of metal debris on the runway.

Did a similar scenario
lead to the total destruction

of China Airlines Flight 120?

THOMAS: Okay. We need
to cut into this wing.

NARRATOR: Investigators
need to get a closer look

at the mysterious bolt that
made a hole in the fuel tank.

BOB: The investigator
in charge said, yep,

now's the time to start
cutting into that thing.

♪

♪

THOMAS: Okay. Got it.

NARRATOR:
Now they need to figure
out where the bolt came from.

They study schematics
of the 737 wing structure.

BOB: We went
back to the drawings

and went back to things
like maintenance records

to try to figure out
exactly what it was.

NARRATOR: They
soon get their answer.

THOMAS: A downstop assembly.

NARRATOR: The downstop assembly
is part of the slat mechanism

on the wing's leading edge.

CPT. YU: Let's go to flaps 25.
FO. TSENG: Flaps 25.

NARRATOR: Pilots
extend flaps and slats

during every
takeoff and landing.

The downstop is fixed
to the end of a track

that slides back and forth.

The device prevents the slats
from moving too far forward.

RODNEY: The downstop is there,
quite frankly, to stop it

when it reaches its
maximum deployment length.

If it didn't exist
then there would be no way

to retain the
slat on the aircraft.

NARRATOR: Investigators
have identified the piece

that penetrated the fuel tank.

They know it's not
from another plane,

like the runway debris that
caused the Concorde disaster.

But they have other important
questions that need answers.

BOB: We had the assembly.
We knew it punctured the tank.

Our next step was
trying to figure out

how this could
possibly have occurred.

♪

NARRATOR: Investigators pore
over Boeing service documents

to learn more about
downstop assemblies on the 737.

They make a
surprising discovery.

THOMAS: This has
happened before,

and it's
happened more than once.

♪

BOB: There'd been
two previous instances

of this device coming apart
and causing minor fuel leaks,

but this was the first instance
of an actual destructive fire.

In both previous instances,
parts from a downstop assembly

punctured a fuel tank,
just like on Flight 120.

THOMAS: Clearly, they
knew it was a problem.

NARRATOR: Boeing was so
concerned about the problem,

it issued a special work order

to secure the downstop
assembly on all 737s worldwide.

RODNEY: The solution
that Boeing had recommended

was to remove the nut
from this particular device

and install some
thread hardening material,

and then you reinstall
the nut. It hardens in place.

THOMAS: What if the
work order on this plane

was never completed?

NARRATOR: Investigators
review the Boeing work orders.

If the plane that burned
in Okinawa was never fixed,

that could explain the accident.

THOMAS: We tried to figure out

when is the last time
anybody touched that assembly.

NARRATOR: But
according to the records,

the proper work was
carried out very recently.

BOB: We discovered that
this particular component,

this downstop,
had been manipulated

only a couple of weeks or
so prior to the accident.

THOMAS: It just
doesn't make sense.

NARRATOR: Investigators
can see that the nut

on the downstop
assembly is still attached.

It seems that the work order
to replace it was completed

just as the records
show. So what went wrong?

THOMAS: That's the weird part
that we wanted to figure out

at that time.

NARRATOR:
They examine the downstop
assembly from Flight 120.

♪

They check all
the component parts.

Finally, they spot something.

BOB: We decided to count
parts, and lo and behold,

a washer was missing.

♪

THOMAS: Where is it?

NARRATOR: There's supposed to be
a washer right behind the nut.

Could a single missing washer

have played a role in the
accident? It seems unlikely.

But investigators
can't rule it out.

They need to find the washer.

BOB: We thought
initially that the washer

may have somehow
gotten inside the fuel tank,

but that's not the case at all.

We examined very
carefully the rest of the wing,

and we found that
particular washer

in the leading edge
assembly of the wing,

just laying in there loose.

THOMAS: The washer is a fit.

NARRATOR:
Recovering the missing washer

raises a puzzling question.

BOB: The nut was on there and
it was torqued down correctly,

but there was no
washer on it at all.

How did the washer
become detached from the bolt

but not the nut?

THOMAS: If the nut
is still on the bolt,

why is there something
between that fell off?

NARRATOR: It seems
like an impossibility,

and yet somehow it happened.

The Flight 120 fire
investigation heads to Taiwan

and the
headquarters of China Airlines.

Investigators hope
to shed some light

on the mystery of
the detached washer.

THOMAS: I appreciate
you making the time.

THOMAS: We went
to China Airlines

to ask them to demonstrate how
they do the maintenance work.

THOMAS: Do you think you
can show me how you completed

this repair on the
downstop assembly?

BOB: Sometimes maintenance
records don't tell you

the true story.

They can tell you that
according to somebody,

a maintenance procedure
had been done correctly.

But to get a better story,

you have to actually
watch the procedure being done.

NARRATOR: A
mechanic demonstrates

how he performed
the downstop repair.

MECHANIC: You won't be able
to see much of what I'm doing.

RODNEY: Performing maintenance
on this particular downstop

is a little tricky.

The mechanic is going to be in
a very restricted visual area.

So he's going to have
to work with his hands.

He's going to have
to feel the apparatus.

MECHANIC: After applying glue,
you put the bolt into place.

♪

THOMAS: You can imagine
that you're under the wing

and you cannot see it.

MECHANIC: Sorry. I just
dropped it. Don't worry.

It's easy to pick up again.

NARRATOR: It's an
eye-opening demonstration.

MECHANIC: And
that's how it's done.

THOMAS: Thank you. You
have been very helpful.

THOMAS: It's not very
easy for them to confirm

they finished their job and
everything is in order there.

♪

NARRATOR: Records show
that the work order repair

was the only time mechanics
ever serviced the downstop

in the history of
the accident airplane.

There's only one
possible explanation

for how the washer
found in Okinawa came loose.

It fell off during the
maintenance procedure in Taiwan.

BOB: It could have just slipped
off the gentleman's fingers

when he was
trying to install it.

It could have stuck to
the nut and then fallen off

just before he
touched them together.

A lot of things
could have happened.

The bottom line is,
the washer was not there.

♪

NARRATOR: But understanding
what happened to the washer

still leaves investigators
scratching their heads.

The downstop assembly
had a well-tightened nut

that was also glued to the
bolt. How could it fall out?

And how did this piece
start a raging fuel fire

that destroyed a
$70 million airplane

and threatened the
lives of 165 people?

♪

THOMAS: All right. Now
let's test it without a washer.

NARRATOR:
Investigators experiment
with the suspicious part

from Flight 120 to see how
it performs without the washer.

RODNEY: The design of this
assembly requires each component

to play a specific role.

So any piece that is not
reinstalled is critical.

NARRATOR: They make
a stunning discovery.

The small washer
is the only thing

preventing the unit from
falling out of its mount.

THOMAS: Without
the washer, it fails.

BOB: We discovered
that the nut and the bolt

were smaller than
the rest of the assembly

and that the washer
was a required item.

This is an example of an
intact downstop assembly.

You take the nut off.
You take the washer off.

Put the nut back on,
like they did in Taiwan,

and now you'll note
that the assembly itself

is pretty ineffective.

It falls apart
without much problem at all.

♪

NARRATOR: Finally, it's
clear why the downstop assembly

was able to fall
out of the slat track.

How it punctured the fuel tank

is the final
piece of the puzzle.

But investigators believe

the design of the slat mechanism
itself may hold the answer.

RODNEY: When the engineers
are designing these aircraft,

they take into consideration
maximum space utilization

and for the design
of a leading edge slat

they came up with
something called a can.

NARRATOR: The slat can
is the area inside the wing

that houses the moving track.

RODNEY: The can is a void
that extends into the fuel tank

and allows for the
device that operates the slat

to move in and out.

NARRATOR: The space
inside the slat can is tight,

just big enough
for the sliding track.

Any foreign metal object taking
up any space inside the can

would be an
accident waiting to happen.

BOB: It would
render the entire assembly

not only
non-functional but dangerous.

♪

THOMAS: China
Airlines flight 1-2-0,

157 passengers, eight crew.

NARRATOR: Investigators
believe they finally understand

the sequence of events that
led to a devastating fuel fire

in Okinawa.

♪

It all begins weeks
before the accident

with a botched repair
to a critical component.

A single missing washer turns a
downstop into a hidden danger,

a bolt that can work
its way loose over time.

BOB:
Washers really aren't supposed
to hold things together,

but this washer did
because of its design.

NARRATOR: Six weeks
after the failed repair...

CPT. YU:
Please give the flight
attendants your full cooperation

as they prepare
the cabin for landing.

NARRATOR: A routine descent into
Okinawa requires the pilots

to deploy the flaps
and slats as usual.

Inside one of the track
cans on the right wing,

the loosened downstop
is just barely holding on.

Touchdown is enough of a jolt

to finally knock the
downstop out of its track.

CPT. YU: Flaps up.

NARRATOR: The
unsuspecting crew soon retracts

the flaps and slats.

The plane's powerful
hydraulics move the slat track

back into the can. But now the
downstop bolt is in the way.

The track pushes it to
the back of the can and then

straight through, puncturing
the right wing fuel tank.

THOMAS: A hole in the
fuel tank caused the leak.

The plane would
have been carrying

thousands of liters of fuel.

NARRATOR: As the plane
taxis, the engine exhaust

is powerful enough to
disperse the leaking fuel.

It can't come in contact with
the hot tail pipe or brakes.

CPT. YU:
After-landing checklist.

NARRATOR: But once the pilots
park and shut down the engines,

the situation instantly
becomes much more dangerous.

FO. TSENG: Engine start levers.

CPT. YU: Engine
start levers cut off.

NARRATOR: The
leaking fuel starts dripping

directly onto the
scorching-hot tail pipe.

PASSENGERS:

JIM: What is going on out there?

NARRATOR: The leaking
jet fuel ignites on contact.

KIT:
The speed of the development
of the fire is incredible.

Obviously fuel burns very well,
and it goes up like a bomb.

FLIGHT ATTENDANT:
Everybody remain calm.

NARRATOR: The cabin
crew's professional conduct

gets 157
passengers off the plane

in just one
minute and 42 seconds.

♪

The Naha Airport
fire leads investigators

to a striking realization.

THOMAS:
The repair that was ordered
actually caused the fire.

BOB: It was kind of ironic.

The Taiwanese maintenance
procedure was to prevent

an accident, and in essence
the procedure had a lot to do

with why this
particular accident happened.

KIT: It's a great study
in unintended consequences.

We really were
trying to fix a problem.

We really didn't anticipate that

every time we handle a
maintenance piece like this

there is a risk. And it bit us.

NARRATOR: In the wake of
the Naha Airport inferno,

aviation
authorities around the world

order the inspection of
the entire fleet of 737s.

In the US alone, 21 planes are
found to have the same defect,

all of them at risk of a
catastrophic fuel leak and fire.

Boeing takes immediate action.

It redesigns the
downstop mechanism

and ensures that the
improved part is installed

on each and every plane.

KIT: Boeing made
the changes necessary

to ensure that the
accident didn't occur again.

It took a little
time, as it normally does,

to get to the
final resolution of it,

but they did what
they needed to do.

♪