All language subtitles for When.Big.Things.Go.Wrong.S01E02.Hidden.Flaws.1080p.AMZN.WEB-DL.DDP5.1.H.264-BurCyg_track3_[eng]

ANNOUNCER: This program is
rated PG, and contains

ANNOUNCER: This program is
rated PG, and contains

ANNOUNCER: This program is
rated PG, and contains

mature subject matter.

Viewer discretion is advised.

NARRATOR:
An airplane loaded with
passengers is going down...

ATC: He's coming down real fast.

I remember hearing a lot
of screaming,

a lot of panic
and a lot of chaos.

MAN: But what caused it
to crash?

This wasn't a bomb,
it wasn't a bird strike.

What happened up there
at 37,000ft

that rendered
this airplane uncontrollable.

SIAN: Now... engineers
unlock the clues

to the world's
biggest disasters...

... to find out what happens
when big things go wrong.

These are the ultimate fears
that keep structural engineers
awake at night.

MAN: Oh, my God!

NARRATOR: Dawn.
Denver Stapleton
International Airport.

Thousands of passengers
wait to board flights.

Among them, is sports caster
Jerry Schemmel.

You know it seemed
like a normal day,
it really did.

I remember getting
to the airport about
six o' clock in the morning

and we found out
our flight was cancelled.

And so we got put on
standby status

and finally maybe close
to six hours after
originally supposed to fly,

got on United Flight 232
that took off to Chicago.

NARRATOR: At 1.45 pm,
Jerry heads to his seat.

We were the last
to board the aircraft,

I remember walking that plane
thinking to myself
"Well this is a big plane."

NARRATOR: Almost 20 years
after its launch,

the DC-10 remains
one of the largest
passenger jets in the sky.

It's also highly distinctive.

The DC 10 is
one of the most iconic airplanes
of the '70s and 80's

because of its characteristic
three engine structure,

it's got two engines under
the wing and one over the tail.

NARRATOR: Today,
as United flight 232
leaves Denver,

it's carrying 296 passengers
and crew.

But none of them know
they are heading for disaster.

(CLOCK TICKING)

First hour was routine,
it really was.

it was a smooth flight,

I remember that everything
seemed normal,

nothing out of the ordinary
at all.

(CLOCK TICKING)

JERRY: The flight attendants
were picking up the lunch

and the trays and all that,
I'm thinking,
it's a normal flight.

NARRATOR: Seconds later...

I thought a terrorist
had planted a bomb,

it's been detonated
and we're going down

and everybody is gonna die here
in the next whatever it takes
to hit the ground.

I remember hearing screaming,
a lot of panic, a lot of chaos.

NARRATOR: But the explosion
is only the start
of their ordeal.

The blast damages
critical flight controls.

(CLOCK TICKING)

NARRATOR: By a stroke of luck,
on board is Denny Fitch

a flight instructor
who has clocked
over 23,000 hours flying

including in a DC10.

He helps the two pilots regain
some control of the plane.

Denny Fitch and Captain Haynes
have to reinvent the wheel

in order to land this plane.

It can only turn to the right
and so as they're circling

they're going down at elevation.

That means they have
only one shot to get it right.

NARRATOR: The crew aims
for Sioux City, Iowa.

JERRY: Captain Haynes
is on the PA system,

he said I want everybody
to understand
this is going to be rough.

This is not gonna be a landing
where we're gonna land safely

and you're gonna
walk off the plane,

this is going to be a crash
landing.

NARRATOR: Against all odds,
they line up with the runway.

I got in that brace position
right away,

and I just waited and waited,

and thinking to myself,
man 30 seconds is a long time.

(CLOCK TICKING)

NARRATOR: The DC 10
is descending at 255MPH,
twice as fast as it should be.

I was not ready
for how hard we hit.

It just sort of felt like
we dropped out of the sky
and hit the ground.

(CLOCK TICKING)

NARRATOR: The airplane's wing
hits the runway first...

Fuel ignites.
the aircraft breaks in two...

The biggest section
skids off the runway

ending up upside-down
in a cornfield.

One hundred and twelve people
die in the crash.

It's one of America's
deadliest air disasters.

This wasn't a bomb,
it wasn't a bird strike.

Something happened up there
thousands of feet up

that rendered
this airplane uncontrollable.

What brought down this DC10?

And could it happen again?

NARRATOR: The roots
of this mystery lie in events

before the plane
even hits the runway...

It's 1965.

With the economy booming,
air-travel is growing fast

and passenger numbers
are doubling every ten years.

In response McDonnell-Douglas
design the massive DC10

to carry more customers.

The first design proposals
for the DC10

were for a wide-bodied
double decker airliner

with four engines capable
of carrying 550 passengers.

But that was just too ambitious,
too aggressive,

it was paired down
into what we see.

Which is the three engines,
a single level

and it was a very very
useful plane.

NARRATOR: The DC-10
is a state-of-the art aircraft

and its construction calls
for the latest materials.

One very strong metal
in particular...

Titanium.

For high stress applications
requiring a strong metal,

there's no substitute
for titanium.

While the strength of steel
in on a par with titanium,

it weighs 45 percent more.

Titanium appears almost
indestructible.

NARRATOR: It's perfect
for jet-engine parts...

Like a fan disc.

Set deep inside the engine,

a fan disc produces
most of the thrust
needed for flight.

Spinning at 3,800 revolutions
per minute,

it experiences immense stress
when in use.

So it has to be tough.

To construct aviation components
out of titanium,

you have to start
with a raw material.
This is called a billet.

NARRATOR: These are huge pieces
of metal alloy,

forged in extreme heat.

Before shipping,
each billet undergoes

ultrasonic inspection
to look for any defects.

If there are defects
within the billet,

those defects get carried along
into whatever component
you're manufacturing.

NARRATOR: In a factory mistake,
one billet
escapes the safety check.

And the first clue
to the United 232 disaster
lies within it.

It's a flaw no bigger
than a grain of sand.

Hidden just below the surface
of the 7000-pound billet.

It's then sent to Ohio,
where it's disk.into a fan

And fitted
into the most critical part
of the airframe...

The tail-engine
of the Sioux City jet.

A deadly crack now lies
in the heart of the plane.

No-one knew
that this microscopic anomaly
was in this fan disc.

NARRATOR: Even the smallest
defects can bring down
the biggest machines.

As space shuttle engineers
discover in Florida, in 1986.

NARRATOR: Like the DC-10,

a weakness lies within
the 1.2- billion-dollar
spacecraft.

ARCHIVE: T minus three minutes
and counting

NARRATOR: January 28th,
and the Challenger shuttle
prepares for blast off.

ARCHIVE: Gimbal checks
now complete.

On board, seven crew members,
including high- school teacher,
Christa McAuliffe.

ARCHIVE: T minus two minutes
and counting

She's the first US civilian
selected to go into space.

Key to lift-off, rocket boosters
on both sides of the shuttle,

packed with 500 tons
of explosive fuel.

NARRATOR: Rubber O-rings,
just a quarter
of an inch thick,

are all that seal
in the highly flammable gas.

ARCHIVE: Ninety seconds
and counting.

A "O" ring is squishy
so that, when you press on it,

it deforms and fills
all the microscopic gaps

between the two materials
you're pressing together.

And that now,
does not allow any gas
to get out or any liquid.

ARCHIVE: T minus 45 seconds
and counting.

Sounds of pressure
and water system now armed.

Because the O Rings
are basically a form of rubber

you've got to be careful
when it comes to temperature.

If it's too cold it changes
how that material reacts.

NARRATOR: O-rings work best
at temperatures
above 64 degrees.

But on launch day,
it's a chilly 36 degrees.

Take a donut, right?
As soon as you buy a donut,

it's nice and squishy.
It's soft.

It's at room temperature.

Stick the donut
in the refrigerator overnight.

Now pick it up,
it's crispy, right?

It's just like more brittle
and it's tough.

ARCHIVE: T minus 30 seconds,
we've had a go
for auto sequence start.

NARRATOR: Engineers flag
their concerns
about the O-rings performance

in the cold
and try to stop the launch.

But NASA proceeds anyway.

ARCHIVE: The SRB hydraulic
power units have started.

The first evidence
of a potential abnormality

is in the form of black smoke
that's just puffing out

right above a seal
where an O Ring would be.

INAUDIBLE RADIO: T minus 10...

That's an indication
that high pressure gas
is getting through that seal

and as the gas gets through,
it starts to open up even more.

ARCHIVE: Three. Two. One.

And lift off on the 25th
space shuttle mission,

and it has cleared the tower.

Challenger go with
throttle up.

NARRATOR: Nobody
in mission control
spots the smoke.

Challenger has passed
the point of no return.

Disaster is inevitable.

You end up with a major failure,

where the fuel
was blowing out of the sides

and the whole
thing blew apart.

(EXPLOSION)

NARRATOR: The world
watches in horror.

ARCHIVE: Obviously
a major malfunction.

We have no down link.

NARRATOR: One of the most
complex machines ever built,

brought down
by a quarter inch part.

Like Challenger,
the Sioux City DC-10

is fatally compromised
by a hidden mistake.

In a highly engineered
piece of equipment
like an airplane,

the very small details
really matter

and it only takes
one tiny little failure
to cause a catastrophe.

NARRATOR: Coming up.
Other clues to why it
crashed...

The thought of all three failing
at once

was inherently possible,

but was waved off
as not gonna happen.

NARRATOR: And later,
a Dakota train crash shows

what can happen
when warning signs are ignored.

NARRATOR: When big things
go wrong,

engineers must find out why.

In the case
of the Sioux City plane.

One clue is a microscopic
defect in the fan disk.

These cracks are virtually
invisible to the untrained eye

and they are extremely hard
to detect to the trained eye.

NARRATOR: But the plane flies
for 17 years without incident.

So what else
could explain this disaster?

All aircraft undergo
regular maintenance

and the Sioux City DC-10
is no exception.

Its three jet engines
clock up 42,000 flight hours,

and with each flight,
the tail engine edges closer
to failure.

Every time
the engine was started

the crack would grow
a little bit more
from the cavity,

just a fraction.

We call it a fatigue crack

and it's started to grow
and progress

over the lifetime
of the engine.

DR. HENRY: Now this crack
starts spreading

and starts growing and getting
deeper and deeper
into the material,

weakening this component.
And you have no idea.

NARRATOR: Engineers
carry out six major inspections

during the aircraft's lifetime,
but every time they miss
the flaw.

It was so small
that it wasn't really considered

and the whole system
was designed
to detect these larger cracks

and these larger anomalies.

In this instance
it was just so small

that it went undetected
during the ultrasonic testing
of that time.

NARRATOR: By the final
inspection in 1989,

just months before the crash,

the cavity in the engine
has grown into a crack
about half an inch long.

And it's still missed.

There would come a point
where it had grown enough,

that one more start of
the engine would result in it
breaking and smashing out.

NARRATOR: Now every flight
is a potential disaster.

Unseen cracks can grow
and may eventually snap.

When they do, they create
havoc.

As the drivers of two huge
freight trains discover.

NARRATOR:
On the North Dakota plains...

A train's axle has slowly grown
a micro-crack over 11 years.

Just like with the DC10,

routine inspections
and maintenance
have failed to spot it.

And when it breaks,
disaster strikes, causing
a catastrophic collision.

NARRATOR: Two billion tons
of freight moves

across America's rail-lines
every year.

And all that cargo
calls for big trains.

December 30th, 2013,
a 104-car train travels west,

through the city of Casselton.
Loaded with grain.

The steel axle
of one of the cars
has a tiny fatigue crack.

Hidden in the metal
since it was manufactured
over a decade ago.

One and a quarter inches long,
the crack is growing

and, as it weakens,
the axle begins to bend.

Imagine you gotta piece of rope
and deep inside the rope

is like a little shard of glass.

And so now as you start
using the rope

and you're working
with the rope,

you're moving it around
and that little shard of glass

is gonna start cutting the
tendons of that rope,

making it weaker and weaker,
but you can't tell

cause you're looking
at the outside of the rope.

NARRATOR: Around 2.08pm,
it finally snaps.

Broken pieces of steel
tumble under the train

and derail
some of the cars behind.

But the train is so long
its driver has no idea.

And coming the other way,
another train,

pulling the worst
possible cargo.

Over two million gallons
of combustible crude oil.

By the time
the driver of the oil train
sees the derailed car,

it's too late.

You've got metal wheels
in contact with a metal rail,

so you've got
plenty of friction
and a source for a spark,

and a spark goes off
and lights the whole thing up.

NARRATOR: The fireball spews
toxic gasses
and burns for 24 hours.

It's sheer luck
that nobody dies
in this disaster.

Coming up...
More clues uncovered.

The pilots don't know
what's going on,

but something is very,
very wrong with the aircraft.

NARRATOR: And more
shocking disasters
when big things go wrong.

NARRATOR: A DC10 aircraft
has crashed,

killing half those on board.

The survivors start to come
to terms with their ordeal.

I don't even know what happened,

I didn't even know
we were upside down
until I let go of my seatbelt.

We went to the wing
and slid down
into the corn field.

To be unscathed is a miracle.

NARRATOR: Investigators now
examine the wreckage
looking for answers

but with vital components
strewn across Iowa,

it's a difficult task.

MAN: That whole
fan area is missing!

NARRATOR: The next piece
to the puzzle
lies somewhere surprising.

NARRATOR: In 1968
when planning the DC-10,

its manufacturers,
McDonnell-Douglas,

consider the growing
domestic market.

With the right plane,
a fortune could be made.

The company needs a plane
with longer range
than two-engined jets,

but with lower operating costs
than its four-engined rivals.

The engines of the time,
the jet engines,

didn't have enough thrust
to only use 2.

The optimal solution then
is to have three engines,

but where do you put
the third engine?

You can't have two engines
on one side
and one on the other.

So, the solution
was to put the third engine

on top of the airplane
in the tail.

The engines on the DC10
were the General Electric
CF6 turbofan engine,

this engine had a very good
reputation in aviation

as being safe, reliable,
and all around a great engine.

NARRATOR: The CF6 engine
seems like a winner,

with innovations in both power
and fuel efficiency.

With three of these engines,
DC10's can range 3500 miles.

And at a greatly reduced
fuel cost.

But could this drive
for efficiency
come with a downside,

creating a fatal weak point
in the plane?

Sometimes, saving money
can cost lives...

as a London
neighborhood learns.

NARRATOR: A tower block burns
through the night...

And horrified residents
can only stand by and watch.

How could this happen
to a recently renovated
apartment building...

Grenfell Tower. London, England.
Built in 1974.

While modernizing
the building,

aluminum weather-proof
sidings are fitted

in place of expensive
zinc sidings.

But there is a major problem
with this aluminum siding.

This actually had plastic
or polyethylene inside of it.

So, the majority of it
is combustible, it's flammable.

NARRATOR: There's also
a two-inch gap

between the aluminum siding
and the insulation.

The perfect funnel
to fuel a fire.

It's a really bad design, right?

Because now, what you've done
is you've got a little gap,
air gap.

So, it's like you've wrapped
the entire building
in a sheath that's combustible.

And you've given
just enough space
for air to get in there

and feed the flames.

NARRATOR: In the early hours
of Wednesday June 14th,

a refrigerator catches fire
on the fourth floor.

Firefighters arrive
in ten minutes.

But the blaze spreads
too fast.

Once you get this thing started

once the air can get in
and fuel it
there's no going back.

NARRATOR: The fire takes hold
and burns all night long.

As the sun comes up,
the scale of the tragedy
becomes clear.

It could've easily
been avoided.

It emerges that fire-resistant
sidings for the whole building

would have only
cost another $400,000.

Now for that amount saved
72 lives were lost.

NARRATOR: Coming up...
The unthinkable happens
to the DC-10...

There is no way
that all of the hydraulics

should ever fail all at once,
that's impossible.

NARRATOR: And more
big things go wrong.

NARRATOR: Planes crash
for all kinds of reasons...

Pilot error, mechanical
failure, even bad weather.

And like the weather,

there's something else
engineers can't control...

NARRATOR: The engineers
who designed the futuristic-
looking three-engined DC10

are convinced they have
preparednfor every possible
scenario...

With the most
up-to-date safety systems,

including not just one,
but two back-ups to its
vital hydraulics.

The hydraulics
in this type of machine

are essential
to assist the pilot
and the aircrew

in maneuvering
these flight control surfaces

so they don't have to exert,
you know, 200, 300 pounds
of pressure on the yolk.

NARRATOR: These systems
control the plane's movement,

enabling a pilot
to change direction,
altitude or speed.

If that hydraulic system
isn't operating,

it's almost impossible
to make the plane go
in any direction you want.

There are very few applications
of hydraulic systems

that can be
more mission-critical
than aviation hydraulics.

For the very simple reason
that many human lives
are at stake.

NARRATOR: Which is why the DC-10
has three hydraulic systems

when it only needs
one to fly.

The thought of all three
failing at once

was inherently possible
but was waved off
as not gonna happen.

NARRATOR: For an explosion
to take out all three
systems is unthinkable.

There's no way
that all of the hydraulics
should ever fail all at once.

That's impossible.

It was a one
in a billion
catastrophic failure,

the likes of which
no one had ever seen before.

NARRATOR: But that billion
to one bad luck chance
does happen...

As the pilot and passengers
of one of the most famous
aircraft of all time

find out in the skies
near Paris.

NARRATOR: July 2000.
109 passengers
board an Air France Concorde

for a luxurious flight
to New York.

After an hour's delay,
it finally gets clearance
to take off.

MATT: The winds
had changed at that point,

and instead of taxi-ing
to another runway

and creating a further delay
the aircrew elected

to go ahead and take-off
on the first runway.

NARRATOR: But this runway
hasn't been inspected.

ROB: Just five minutes earlier
a DC-10 had taken off
from the same runway.

And as it did so,
it lost a titanium alloy strip.

A small piece of titanium,
the size of a ruler,
not that big.

That day they'd failed
to do a foreign object
and debris, or a FOD check

on the runway
prior to their departure.

So, the piece of metal
went undetected.

NARRATOR: As the Concorde
begins take-off,

the pilots are unaware
of the 16-inch metal strip

lying directly in their path.

And the plane's tires
run right over it.

The Concorde going
down the runway
and hitting that piece,

that strip of metal from a DC 10
is a one in a million chance.

I mean if that had been
off to the left
just a little bit

they would have
completely missed it.

The rubber explodes.
Portions of the tire debris

slam into the fuel tank.

NARRATOR: It breaks a seal
on the tank.

You never want jet fuel to be
leaking out of a plane
that's about to take off.

NARRATOR: There's a spark
in the damaged fuel cell,
and it ignites.

As the plane takes off,
this engine fire becomes
catastrophically destructive,

and the plane crashes.

NARRATOR: All 109 people
on board die in the crash.

Bad luck brought down
one of the most advanced
passenger jets of all time.

NARRATOR: Coming up...
The crew battle
to save flight 232

They've got one shot
to get it down.

NARRATOR: United Airlines 232
is at 37,000ft

on its way to Chicago.

On today's flight,
296 people including
Jerry Schemmel.

We're Just cruising along,
it's a smooth flight,

and I'm starting
to get a little sleepy,

I'm thinking
a little nap might be good.

Didn't really think anything
was out of the ordinary.

NARRATOR: A half an inch crack
in the fan disk of the DC10's
tail engine

has gone unnoticed
for 17 years.

But it's about to reach
breaking point...

I hear this explosion.

The pilots
don't know what is going on

but something is very,
very wrong with the aircraft.

NARRATOR: They quickly realize
the explosion has taken out
the tail engine

It came
from the back of the plane,

you could hear the explosion,
you could feel it,

and you could feel the plane
beginning to drop after that.

And I thought,
wow this is really serious.

NARRATOR:
Even if one engine fails,

the DC-10 should be able
to fly with the other two.

But this plane
isn't responding.

The pilots are unable
to steer the plane
go up and down

they are basically powerless.

NARRATOR: Exploding shrapnel
from the tail engine

has cut through
all three hydraulic systems.

The odds that all three
hydraulic systems
were to fail at once

was so rare that it wasn't even
in the emergency procedures.

Without these controls
the pilots can't steer the plane
or take it up or down.

NARRATOR: The plane
is descending six times faster
than it should be.

I grabbed my arm rests
and held on.

NARRATOR: In the cockpit,
alarms are blaring.

The plane is now
almost impossible to control.

The first thing that was going
through their heads was,

what the hell happened,
what's going on back there?

(CLOCK TICKING)

NARRATOR: The flight crew
radio Minneapolis
Air Traffic Control

for emergency assistance.

NARRATOR: They're directed
to the nearest airport,

Sioux City, Iowa.

NARRATOR: As the plane descends,

it constantly rolls
to the right,

threatening to turn
upside-down.

If that happens and flips
all the way over

the plane will tumble
to its doom.

(CLOCK TICKING)

NARRATOR: Pilot captain
Al Haynes fights
to level the plane.

The one thing that they do have
control over is the throttles

which provides power
to each of the engines
under the wings.

So, the captain pulls back
on the throttle on one side

and ups the power
on the other side

and this slowly brings
the wings back into alignment.

It works
and the captain regains
a crude form of steering

using just the throttles,
but there's another problem,

the captain now finds
he can only make
right hand turns.

NARRATOR: DC 10
training instructor
Denny Fitch

is sitting in first class.

By coincidence,
he's practiced
this exact scenario

on a flight simulator,

after hearing about a similar
failure in Japan.

He races to the cockpit to help
and takes over the throttles,

as the pilots
figure out their next move.

NARRATOR: The DC10
begins a succession of circles
over Iowa...

With every turn to the right
it drops 1500-feet.

I could feel this plane
taking this right turn,

and we just kept going
that way. And I thought

why are we just continuing
to turn right,

why aren't we
ever levelling off.

(CLOCK TICKING)

Captain Haynes
got on the PA system
and told us

that we'd been given a directive
to make an emergency landing
at Sioux City, Iowa.

He said I want everybody
in their seats,

the seatbelts are fastened,
they're pulled tight

because, he said, we
are in serious trouble.

NARRATOR: Emergency vehicles
scramble for a crash landing.

I think we circled around four
or five times
trying to get to Sioux City.

(CLOCK TICKING)

NARRATOR: At 3.53pm,
the crew put the DC-10
into its final turn.

It's the moment of truth.

JERRY: Captain Haynes
is on the PA system

telling us that he was gonna
give us a command to brace
three seconds before we hit.

He said...

He said I want everybody
to understand
this is going to be rough.

(CLOCK TICKING)

I thought to myself
let's just get this thing
over with

because I'm as ready as I can be
mentally and physically.

I've said my prayers,
I've said my goodbyes
in my own mind.

NARRATOR: A normal DC10
landing speed is 120mph

but this plane is approaching
twice as fast.

And they're almost going
to make the runway
when all of a sudden...

(CLOCK TICKING)

The wing tips and catches.

And the plane just breaks apart
and tumbles.

I'm looking around,
I'm seeing bodies
being thrown about.

Some were out of their
chairs, some were still
strapped in their chairs,

we bounced a couple of times,
we start sliding
and going forward.

The nose of the plane
dug into the runway

and we flipped
over end to end.

The plane broke into big
pieces at that point
and I just held on...

and slid upside down
and backwards
and finally came to a halt.

JERRY: I was getting ready
to run away from the aircraft,

I heard a baby crying
back inside the wreckage

and I followed the cries.

And by this time we were almost
completely full of smoke.

I couldn't see anything
but I could hear the cries.

So I honed in on it

and I realized the crying
was coming from inside
an overhead bin in this plane.

I find the latch,
open the latch, lift the lid

and just sort of scooped
the baby with one arm

and as soon as I grabbed her
she stopped crying.

And then I just turned around
headed for the opening
and got outside the plane.

NARRATOR: Emergency crews
swarm over the wreckage.
112 die.

They find the three
flight-crewand Denny
unconscious, but alive.

Miraculously 184 passengers
and crew survived the impact.

I looked back and I could
see the wreckage
from where I'd come out of.

And it was at that point
that it hit me how bad this was,

because I knew we were
in a big plane.

I'm thinking,
this is a terrible disaster.

NARRATOR: The footage
shocks the nation.

And with some 400 DC-10's
still flying

the aviation industry
is desperate to figure out
what went wrong.

But Investigators
face a monumental task.

Debris is spread across -Iowa.
And a vital piece of the puzzle
is missing.

NARRATOR: When big things
go wrong,

the causes can be obvious.

NARRATOR: But other times
engineers have to search
for answers.

ARCHIVE: You can really see
what is missing

that whole fan area is missing.

NARRATOR: One vital piece
of evidence

in the fatal Sioux City crash
is missing.

The fan disc
is not at the debris site

and could be anywhere
in Iowa.

ARCHIVE: The obstacle
is 20 square miles
of farmland.

The key part still missing
used to be in this
empty casing.

The shell that held
engine number 2 and the fan
that pushed air to it.

NARRATOR: Months go by
and despite a $50,000 reward
the fan disk remains lost.

They searched high and low
for this fan disk.

the search was extensive,
farm land over the mid-west,

and further,
hidden by corn and crops.

It didn't turn up until later
when a farmer was harvesting

and they literally
ran into a fan disk.

NARRATOR: Now investigators
have the final piece to learn

what caused United Airlines
Flight 232 to crash.

And seen through the eyes of
an engineer,

the clues are clear...

Cutting costs...

The third engine
on the tail section
is a disaster waiting to happen.

NARRATOR: A hidden flaw...

We call it a fatigue crack.

NARRATOR: Missed signs...

Maintenance teams failed
to pick up this crack
time and time again.

NARRATOR: And sheer bad luck...

The thought of all three failing
at once was waved off
as not gonna happen.

NARRATOR: As a result
of the Sioux City crash,

investigators would make
31 sweeping recommendations

to improve inspections
and airline safety.

MATT: Several of them revolving
around redundancy
and hydraulic systems,

the protection
of these hydraulic systems

and then refined manufacturing
and inspection processes
for these fan disks.

NARRATOR: But why, in 1989,
faced with
such a catastrophic failure

of its hydraulic systems,
didn't United 232
simply fall from the skies?

You have a huge piece of metal
that is largely uncontrolled.

How do you bring that down
and land it
with only the engines?

NARRATOR: The answer lies
in the quick thinking

of the pilots,

Denny Fitch and the crew.

It was apparent to us
that we had lost
all of our hydraulic fluid

and when I asked Dudley
for the procedure for that...

he said there isn't one.

So we made it up
as we went along.

I've heard pilots,
many of them over the years,

that went into a simulator,
put in to a DC-10,

same conditions we had,
number 2 engine explodes,

hydraulics go out,
and they say every single time

that plane nose dives to
ground and the computer said
everybody's dead.

We have a lot of experience here
and it showed up in the cockpit.

There is no substitute
as far as I am concerned
in experience

and we had it and it shows
that experience
is very important...

NARRATOR: The heroic actions
of the pilots on flight 232

undoubtedly saved Jerry
and the other survivors.

Proving when big things
go wrong, people can step in.

Accidents will happen.
Planes will go wrong.

And when they do
it is the actions of one
or two people

that can save hundreds.

When I look at it today,
31 plus years later,

I think we could not have
had a better crew
inside that cockpit

to give us a shot
at making this thing work

and not everybody dying.

We overcame the odds
because we had a group
of four people in that cockpit

that did all they could,
to try to save lives.

I don't know if it could have
gone any better than it did.

I thank them personally,
and I still do in my mind
every day

for their heroic efforts
inside that cockpit.