Original subtitles

(crashing noises)

NARRATOR: Japan Airlines Flight 123 crashes into a mountain,

killing 520 people.

It's the deadliest single aircraft accident in history.

SCHLEEDE: We were working in this terrible carnage. I get chills thinking about it.

NARRATOR: Investigators immediately suspect an act of terror.

Right now it's a bomb. That's what the crime guys are telling us.

NARRATOR: But the wreckage tells a different story.

INVESTIGATOR 1: There's no fire damage. No shrapnel damage?

NARRATOR: What they soon discover…

It was the only thing holding the two sides together.

NARRATOR: …threatens to ground

one of the most popular commercial jets on the planet, the 747.

SCHLEEDE: We were concerned that we had a structural flaw in the airplane,

and others were worried, too.

(tense music)

(theme music plays)

MAN (over radio): Mayday! Mayday!

(alarm blaring)

GPWS: Pull up.

(indistinct radio chatter)

NARRATOR: It's 6:10 p.m. at Tokyo's Haneda Airport.

Japan Airlines Flight 123 is ready for departure.

SASAKI: Number one engine start.

NARRATOR: In the left-hand seat is 39-year-old First Officer Yutaka Sasaki,

training to become a 747 Captain.

(engines powering on) I'll handle the radios while you fly.

NARRATOR: The Captain is Masami Takahama, a former military pilot,

who joined Japan Airlines 20 years ago.

The flight plan calls for a right turn out.

Haneda ground, Japan Air 1-2-3. Request taxi. Charlie 7.

Thank you, sir.

NARRATOR: Today's flight is full, with 509 passengers on board.

It is the start of the Obon holiday.

(speaking Japanese)

(translation) Obon is a Buddhist event about the ancestors' spirits.

It happens in summer.

People in the city go back to their hometown with families to celebrate.

(continues speaking Japanese)

NARRATOR: Twenty-six-year-old Yumi Ochiai is an off-duty flight attendant.

Hi. So glad to have a break for the holiday.

(speaking Japanese)

(translation) Yumi Ochiai was like many young Japanese,

she wanted to see the world.

Working for the airlines allowed her to do that.

(continues speaking Japanese)

(engines powering up)

V-1.

Rotate.

NARRATOR: Thirty minutes before sunset, Flight 123 lifts off.

- Positive rate. - Gear up.

Very nice.

NARRATOR: Flight 123 is one of dozens of 747s carrying passengers throughout Japan.

(inaudible dialogue)

To this day, the 747 is the most iconic jetliner ever built.

When it debuted in the '70s,

it was by far the biggest commercial plane that had ever flown.

And every pilot wanted to fly this plane.

NARRATOR: To meet growing demand for cheap travel within Japan,

Boeing designed the 747 SR, a special version of the jumbo jet.

SMITH: The 747-SR, or Short Range, was an unusual variant,

in that it was designed for high-density, short-haul operations.

The Minister of Transportation was on the last leg.

I hope you gave him a smooth flight.

NARRATOR: Assisting on tonight's trip is Flight Engineer Hiroshi Fukuda.

He's flown on 747s since they were introduced to Japan Airlines in the 1970s.

SMITH: These earlier 747s required three pilots,

the third pilot being a flight engineer

who sat behind the captain and first officer,

controlling all of the airplane's systems and subsystems

that were later consolidated

into the more computerized, two-pilot airplanes that we have today.

Through 10,000. Flight level 2-4-0 selected.

NARRATOR: It's an hour-long flight from Tokyo to Osaka,

one of Japan's busiest domestic routes.

Eleven minutes into the flight,

Japan Airlines 123 approaches its cruising altitude.

Okay, 1,000 feet to go and we'll level off.

Yes, sir.

NARRATOR: As they near 24,000 feet,

the crew settles in for what's expected to be a smooth flight.

(explosion) (rumbles)

Whoa. (alarm wails)

SMITH: If an airplane is suddenly displaced by some violent force,

the autopilot can suddenly kick off.

Then the pilots now have to take control and physically steer the airplane again.

Something exploded?

I'm squawking 7700.

SMITH: Putting 7700 into the transponder

is a way of broadcasting an urgent situation.

Was that a gear door?

TAKAHAMA: Check gear. What about the engines?

All engines are good.

SMITH: When something unusual or sudden happens,

pilots are trained to stop, analyze,

evaluate the situation before simply reacting.

Look at this.

NARRATOR: Sixteen seconds after the explosion,

the pilots realize the cabin is losing pressure.

SMITH: If an airplane depressurizes at anything over 20,000 feet or so,

now suddenly you don't have oxygen to breathe.

WARNING SYSTEM: Put on your oxygen mask, fasten seat belts.

We are making… (shouts of panic)

NARRATOR: The emergency masks provide only 15 minutes of oxygen,

just enough oxygen for an emergency descent to below 10,000 feet.

Something exploded.

(grunts)

Right turn. (yells) Right turn!

(Sasaki grunts) Tokyo, Japan Air 1-2-3, having trouble.

Request return back to Haneda.

- Descend and maintain 220. Over. - Roger. Right heading zero, nine zero.

NARRATOR: The pilots of Flight 123 attempt a sharp turn back to Haneda Airport,

now 70 miles behind them.

- Don't bank so much. - SASAKI (grunting): Okay.

The R-5 door is broken. We're making an emergency descent.

TAKAHAMA: Don't bank so much!

Hydraulic pressure has dropped.

NARRATOR: While the crew tries to determine why the cabin depressurized,

they face an even more serious problem with the hydraulic systems.

(grunting)

(speaking Japanese)

SUZUKI: Without the hydraulic pressure,

it's very difficult to move the control surfaces.

(continues speaking Japanese)

(Sasaki grunting)

Don't bank so much, it's manual!

NARRATOR: The decrease in hydraulic pressure

is making it difficult for the first officer

to stop the dangerously steep right turn.

- Turn it back! - It won't go back.

TAKAHAMA: Hydraulics are all out.

SMITH: Nobody in that cockpit had ever seen a complete hydraulics failure.

There was no checklist, no procedure for how to deal with that.

Descend.

NARRATOR: The pilots are unsure if their control inputs are doing anything.

What's going on?

He's not turning back to Haneda.

NARRATOR: Air traffic controllers are puzzled

by Flight 123's erratic flight path.

Why isn't he descending?

Japan Air 123, confirm, you were declaring an emergency?

TAKAHAMA (over radio): Affirmative.

CONTROLLER: Request nature of your emergency.

- TAKAHAMA: Uncontrollable. - Uncontrollable. Roger. Understood.

Put your heart into it. (Sasaki grunts)

SMITH: If you've lost pitch control, elevator control,

an airplane will fall into an oscillating series of climbs and descents, a phugoid.

The plane will pitch up until it runs out of speed.

It will then nose down into a descent. It will pick up speed and momentum.

As the wings begin to generate more lift, the plane will again begin a climb.

(grunts)

NARRATOR: The pilots try using engine power to turn the airplane towards Haneda.

(engines roar)

SMITH: By increasing power on the left side, the plane would turn to the right.

Increasing power on the right side, the airplane would turn to the left.

(engines increase)

NARRATOR: It works. The 747 starts a slow turn to the right.

WARNING SYSTEM: We are making an emergency descent.

Put on your oxygen masks, fasten seat belts…

OCHIAI: Don't worry, the pilots have turned us back.

We will be arriving in Haneda soon, okay?

WARNING SYSTEM: Fasten seat belts.

NARRATOR: Still at 22,000 feet,

the captain can see Haneda in the distance, 81 miles away.

Can you hold? (Sasaki grunts)

SMITH: The crew reflexively thought, "Let's get this plane back to Haneda."

And why Haneda and not somewhere closer? Because they were familiar with Haneda.

NARRATOR: Haneda is within reach, but the plane's erratic behavior is worsening,

and the pilots are at breaking point.

(grunting)

WARNING SYSTEM: Put on your oxygen masks, fasten seat belts…

NARRATOR: In the cabin, emergency masks are running out of oxygen.

WARNING SYSTEM: Put on your oxygen masks, fasten seat belts.

We are making an emergency descent.

(tense music)

SASAKI: I don't understand what's happening!

NARRATOR: For 14 minutes, the crew of Japan Airlines 123

has been struggling to control their 747.

They can't get the plane to descend.

SASAKI: Gear down.

SMITH: Lowering the landing gear,

dumping all of that machinery down into the airstream

will slow a plane down by vastly increasing the amount of drag,

helping it to descend.

It doesn't work. The gear won't go down. (Sasaki groans)

Let's try the alternate.

In an emergency situation, like a hydraulic failure,

the crew can lower the landing gear with gravity.

However, once the gear is down, it cannot be pulled back again.

- Lower! - Yes! Yes!

Gear coming down.

SMITH: Really, they're just trying desperation moves here,

trying to find the right configuration to stabilize the plane as best they can.

- TAKAHAMA: Keep the nose down. - Yes.

NARRATOR: With the landing gear down, the aircraft begins to slow.

We are descending now.

NARRATOR: Fifteen minutes after the incident began,

Japan Airlines 123 is finally losing altitude.

The gamble has paid off.

SMITH: It's not in what I would call controlled flight,

but it's a steadier condition than it was in,

and it's descending now into lower altitudes

where passengers can breathe again.

Hold it here.

SASAKI (grunts): We're over Lake Sagami.

NARRATOR: Just ahead, the pilots see the familiar lights of Tokyo.

(grunts)

But the captain's optimism vanishes when the plane suddenly banks hard to the left.

This may be hopeless.

Lower the nose more.

- Request radar vectors to Haneda. - Roger, understood.

Keep heading zero, nine, zero for runway 2-2.

Whoa. (grunts)

NARRATOR: As the plane descends below 10,000 feet, the situation worsens.

(grunts)

TAKAHAMA: It's uncontrollable again. Watch out for the mountain.

SMITH: So then, it suddenly begins descending at a high rate of speed

directly towards the mountains.

NARRATOR: Japan Airlines 123 is flying directly away from Haneda airport,

heading straight towards high terrain north of Mount Fuji.

- Right turn or we will hit the mountains! - (yells) Yes!

NARRATOR: Nine minutes after lowering the landing gear,

the plane has descended 15,000 feet.

Where did he go?

NARRATOR: Flight 123 drops below the peaks of the surrounding mountains,

out of range of Tokyo's radar.

TAKAHAMA: Max power. (Sasaki grunts)

NARRATOR: Incredibly, the pilots are able to arrest the dramatic dive.

SMITH: The plane begins a very abrupt pitch up,

so much so that now they're very worried about the airplane stalling

at the top of that climb.

NARRATOR: When the airspeed drops to 108 knots, the stick shaker activates.

FUKUDA: Increase power.

(grunts) Not good. We're stalling.

SMITH: The plane slows to a 108 knots,

which is beyond the stall margin for a 747.

How they didn't just drop out of the sky at that point, I'm not sure.

We are losing altitude. Raise the nose!

NARRATOR: The flight crew is exhausted.

For 25 minutes, they have fought for control

as they continue to fly away from Haneda Airport.

(grunts)

Flaps?

SMITH: The first officer suggests deploying the flaps,

which may help them stabilize the airplane,

allow them to fly at a slower speed without stalling.

- Extend the flaps. - Flaps coming out.

SMITH: Because the normal hydraulic deployment is obviously unavailable,

when flaps are deployed electrically, they come out very, very slowly.

NARRATOR: For more than a minute, Flight 123 flies almost normally.

(yells) Left turn!

NARRATOR: As the crew attempts a left turn back to Haneda,

the plane banks hard to the right.

(engines whirring)

Japan Air 1-2-3, request position.

CONTROLLER: Your position is 45 miles northwest of Haneda.

NARRATOR: Unknown to the pilots,

the flaps on each wing are extending at different speeds.

SMITH: What's happened is the flaps on the left side

have come down faster than the flaps on the right side.

This has caused the left wing to produce a lot more lift,

which is turning the plane hard to the right.

TAKAHAMA (yells): The nose!

NARRATOR: The uneven flaps make the situation worse.

The nose!

NARRATOR: Four thousand feet from the ground,

Japan Airlines 123 is dropping fast, losing 15,000 feet a minute.

TAKAHAMA: Raise the nose. Raise the nose! (Sasaki grunts)

WARNING SYSTEM: Quite soon, we will be making an emergency landing.

(whimpers)

NARRATOR: The pilots use all their strength to regain control.

I can't hold it much longer!

- NARRATOR: But nothing works. - Flaps up! Flaps up!

TAKAHAMA: Flaps up!

GPWS: Sink rate.

- TAKAHAMA: Raise the nose! - GPWS: Pull up.

- TAKAHAMA: Power! - GPWS: Terrain. Pull up.

(grunts) GPWS: No sink.

(somber music)

NARRATOR: Japan Airlines Flight 123 has crashed into a mountain

in a remote area northwest of Tokyo.

When rescuers reach the crash site the next morning, they find devastation.

Only the left wing and rear section of the aircraft are recognizable.

As rescuers examine the tail section, they make an astonishing discovery.

There are four survivors.

SMITH: To have made it out and to have survived the next 15 or so hours

under the wreckage in the wilderness, I don't know how it happened, but it did.

NARRATOR: Five hundred and twenty people have died.

The deadliest single plane crash in history.

Japan's Air Accident Investigation Commission, or AAIC,

is soon joined by experts from the NTSB and Boeing.

We were working down there in this terrible carnage,

and family members had already been brought up to the mountain

and they built little altars.

And that's… I get chills thinking about it.

NARRATOR: One of the survivors is Yumi Ochiai, the off-duty flight attendant.

INVESTIGATOR 1: She's able to talk?

NARRATOR: Though injured, Yumi is able to speak to investigators.

Yumi, can you tell me what you remember?

We were ascending when something exploded behind me.

NARRATOR: Investigators discover that 12 minutes into the flight,

over Sagami Bay, there was an explosion.

The survivor's account gives investigators their first big clue.

(wind gusting)

(speaking Japanese)

After the sound of the explosion, Mrs. Ochiai saw a white fog,

and this white fog is a result of a sudden decompression.

(continues speaking Japanese)

NARRATOR: Immediately after decompression,

the flight attendant describes seeing a hole in the fuselage.

INVESTIGATOR 1: Thank you.

NARRATOR: Based on the survivor's account, investigators are immediately suspicious.

Right now it's a bomb. That's what the crimes guys are telling us.

NARRATOR: Japan is already on high alert.

Two months before the crash, a bomb detonated at Narita Airport

on the same day that an Air India 747 fell from the sky off the coast of Ireland.

SCHLEEDE: There was all kinds of concern, internationally, and in Japan

that we had a terrorist group trying to blow airplanes out of the sky.

Let's keep an open mind and look for something else.

Well, even if you think it might be a bomb, that's speculation.

The 747 was one of the more popular airplanes in service at this time

and we were worried that if it was something else,

it might ground the airplanes.

INVESTIGATOR 1: Make sure we catalog everything.

NARRATOR: With the black boxes sent off for analysis,

investigators examine the wreckage in an aircraft hangar.

Let's test for explosive residue near the back.

I had this package of glass bottles and cotton swabs and tweezers

and alcohol and water, and diligently swabbed the aft lav walls

and sent the samples back to the company in Seattle.

NARRATOR: To reconstruct the final 30 minutes of the flight,

they turn to the radar track.

- Almost 24,000 feet over Sagami Bay. - INVESTIGATOR 1: Yeah.

NARRATOR: As investigators zero in on how and where the incident began,

- they get a break. - Hey. That's our plane.

NARRATOR: A witness on the ground took a photo of the plane during the incident.

INVESTIGATOR 2: A piece of the tail missing.

INVESTIGATOR 1: The vertical stabilizer is pretty much gone.

NARRATOR: Losing a vertical fin has never happened to an airliner this big before.

SMITH: The airplane had lost most of its tail.

And it makes sense that investigators were focused

on the possibility of an in-flight explosion, a bomb.

INVESTIGATOR 2: A missing tail, and Yumi Ochiai said there was a hole behind her.

It all adds up. But we need the tail to prove it.

NARRATOR: The day after the crash of Japan Airlines Flight 123,

part of the missing tail is found floating in Sagami Bay south of Tokyo.

So what do you think?

NARRATOR: Investigators examine the tail,

looking for any clues that point to a bombing.

There's no fire damage.

- No shrapnel damage? - NARRATOR: But that's not what they find.

PURVIS: Nothing really looks like bomb damage.

There's a lot of telltale signs. I saw none of that.

NARRATOR: Until they get the swab results back from the lab,

they can't rule out a bomb entirely.

So you were the controller that handled Japan Air 123, right?

Correct.

NARRATOR: Investigators speak to the controller

who was in contact with the crew for 32 minutes.

Did the pilots say anything about what happened to the plane?

Right from the start, they said it was uncontrollable.

- Hmm. Did they say why? - No.

But they did mention to dispatch something about damage to a door.

The R-5 door is broken. We're making an emergency descent.

Thank you, it's very helpful.

PURVIS: The pilot reported that the door may have come off

and there was a concern that if the door came off,

it may have damaged the airplane.

The right rear door is here. Behind our survivor.

INVESTIGATOR 2: Maybe that's the opening our survivor described?

That would explain the depressurization.

SMITH: There's a precedent there.

In 1974, the cargo door of a Turkish Airlines DC-10 had blown off,

causing instant decompression of the cabin and failure of the cabin floor,

resulting in the loss of flight controls.

A door is big, so it could definitely do damage to the tail.

Enough damage to knock it right off the plane?

NARRATOR: Several days after the crash, the right rear door is found.

It looks like the door was locked, and it was found with the rest of the wreckage.

So it didn't fall off in flight.

- It was a good theory. - INVESTIGATOR 1: I know.

We're missing something.

(fax machine whirring)

We are back to square one.

No trace of explosives found on the wreckage.

NARRATOR: Flight 123 was not brought down by a bomb.

Well, one thing's for sure. Something happened in the back of that plane.

PURVIS: Was there a structural issue? Was there a design issue, even,

which might affect more 747s than just this one?

We really needed to get an answer to that.

We need to reassemble the tail.

NARRATOR: While investigators focus on the rear of the plane,

the Japanese government orders inspections of all 747 tail assemblies.

Around the world, the safety of the 747 is questioned.

There was moves by the Europeans and the Brits to ground the 747,

and that would have had terrible economic impact on the United States.

INVESTIGATOR 1: So from their first emergency call to the crash,

it was almost 32 minutes.

NARRATOR: The team turns to the cockpit voice recorder for clues.

Let's hear it.

- SASAKI (over tape): Be quick. - FLIGHT ATTENDANT (over tape): Thank you.

(chimes)

It sounds normal.

It's just a flight attendant asking for something on the intercom.

(explosions over tape)

(explosions)

Whoa. (alarms wailing)

Something exploded?

We know there was definitely not a bomb, but did you hear that?

Let's roll it back.

(explosions over tape)

Yeah, I heard that.

That was two explosions.

SCHLEEDE: We didn't know what the boom boom was when we heard it on the CVR.

Okay, let's assume that the first explosion was a decompression,

somewhere behind Yumi.

- What about the second one? - Let's just keep listening.

(Sasaki grunts)

TAKAHAMA: Don't bank so much, it's manual!

(Sasaki grunts)

- Turn it back. - (grunts) It won't go back.

TAKAHAMA: Hydraulics are all out.

NARRATOR: The 747 has four hydraulic systems

that control the rudder, elevator, ailerons, flaps, and landing gear.

Two booms and no hydraulics.

INVESTIGATOR 1: Yeah, they had a lot to deal with.

NARRATOR: For investigators, it's an important clue.

If you lose all your hydraulic systems on the airplane,

you don't have any control over the flight controls.

It's no wonder they told ATC they were uncontrollable.

PURVIS: So having gone away from the door,

we began focusing on the aft end of the airplane.

INVESTIGATOR 1: Somehow, they're all connected.

(tense music)

(indistinct)

Let's try to pinpoint the cause of the decompression.

NARRATOR: The team scours the reconstruction

of the tail section of Japan Airlines Flight 123,

looking for evidence of what caused the first explosion.

The United States needed to determine the cause of this accident

because we manufactured the 747.

We were concerned that we had a structural flaw in the airplane

and others were worried, too.

INVESTIGATOR 1: Okay, let's start here, the rear pressure bulkhead.

NARRATOR: The rear pressure bulkhead stands more than four meters high.

Shaped like an umbrella, it acts like a cork in a champagne bottle,

keeping the cabin pressurized.

Any explosion in the rear of the aircraft could explain the sudden depressurization.

SCHLEEDE: That's when we decided we needed to focus on that area,

on the bulkhead and see what happened there.

NARRATOR: The team recovers the rear pressure bulkhead from the crash site,

and painstakingly reconstructs it over several days.

- INVESTIGATOR 1: So this is it, huh? - INVESTIGATOR 2: Yeah.

At 24,000 feet, that's over a quarter million pounds of pressure.

That's a lot of force.

PURVIS: The rear pressure bulkhead has to hold the pressure inside the airplane.

It's got to be very, very strong. It's got to be failsafe.

And it needs to do its job reliably.

Look, this damage here is from the crash.

These rips are from the plane slamming into the mountain, yeah?

SCHLEEDE: One of the things that investigators are trained to do,

and eventually learn to do is to look for anything that's out of the ordinary.

Check this out.

This isn't crash damage. This is a rupture.

Yeah. And a clean one at that. Look, it runs mainly along this line of rivets.

SCHLEEDE: The straight-line fracture

certainly piqued our curiosity as to what this was all about.

NARRATOR: Investigators discover a rupture 41 inches long.

Because of this long, flat area that we saw,

it made us very curious that this thing had ruptured instantaneously

and caused this explosive decompression.

(explosions)

(wind gusting)

NARRATOR: What could have caused the long rupture?

What do you have?

NARRATOR: The team examines a piece of metal from where the rupture occurred.

Striations. Lots of 'em.

NARRATOR: Under close examination,

they discover a web of radiating contours called striations.

They are telltale signs of growing cracks.

SCHLEEDE: Every time a little fatigue progresses, it leaves a mark.

- What they call striations. - It's long-term metal fatigue.

Yeah. Every flight, every time they pressurized the cabin,

those fatigue cracks would have grown.

NARRATOR: If microscopic cracks form under rivets on the pressure bulkhead,

they would continue to grow with the forces of the plane

being repeatedly pressurized.

PURVIS: So once the airplane's in service these cracks start developing.

But they start under the rivet heads where you can't see them

and even once they progress outside,

they're very difficult to see because they're only a few millimeters long.

INVESTIGATOR 2: Why did the cracks form in the first place?

Yeah. The pressure bulkhead is one of the strongest parts of a 747.

SCHLEEDE: The design philosophy for the pressure bulkhead

included a failsafe design.

If this rear pressure bulkhead had a fatigue crack begin,

it would stop 'cause there was a piece called a crack stopper.

NARRATOR: The rear pressure bulkhead consists of five bays.

Each bay is separated by a strap or crack stopper designed to contain a small crack,

preventing it from spreading to other bays.

So why did this rupture spread beyond the crack stopper?

NARRATOR: Investigators dig into the maintenance history of the aircraft.

Maybe this will help.

This plane had a previous accident.

NARRATOR: Seven years earlier, the plane had an incident landing in Osaka.

It suffered a hard tail strike.

"Severe damage to the rear pressure bulkhead."

Keep going.

INVESTIGATOR 1: The bottom of the bulkhead was crushed. Sent for repairs.

PURVIS: In this Osaka incident,

the airplane's tail did hit the runway pretty hard

and it wore through the skin and actually damaged some structure,

including the rear bulkhead.

NARRATOR: Instead of replacing the entire bulkhead,

Boeing engineers decided to replace only the damaged lower half.

Once the repair is made, it should be as strong

or stronger than when the airplane was originally made.

INVESTIGATOR 1: Well, this is the original bulkhead. This is the new bulkhead.

Maybe the repair is the issue.

PURVIS: This kind of cracking in the same area that the repair was,

was really more of a coincidence than we could have imagined.

So how did you fit the new bottom to the top of the bulkhead?

NARRATOR: Investigators look into the 1978 repair more closely.

That was a really big job.

(drill whirring)

NARRATOR: Technicians worked around the clock for eight days inside the plane

to mount and secure a new lower bulkhead to the upper section.

Did you notice anything out of the ordinary?

There was only one small thing.

(grunts) Now just a little higher.

NARRATOR: During the repair, technicians had difficulty

- connecting the upper to the lower pieces. - There's not enough overlap.

What do you mean?

We had trouble fitting the overlap at the nine o'clock position.

NARRATOR: The difficulties with the repair match exactly where the bulkhead failed.

Okay, thanks for your help.

NARRATOR: Investigators are now confident that the repair seven years ago

is connected to the crash.

(sighs) Now we're getting somewhere.

INVESTIGATOR 2: Okay, normally, the top and bottom

are held together with two rows of rivets, yeah?

NARRATOR: Investigators scrutinize the repair job

to Flight 123's pressure bulkhead.

Right, and they did that everywhere, except for right here.

SCHLEEDE: One area of the bulkhead, the skin did not overlap enough.

Boeing had to design a patch, a repair. It was called a splice.

NARRATOR: Without enough space for two rows of rivets in the overlap,

a separate splice plate is attached over the area.

But only one row of rivets showed signs of metal fatigue.

It's hard to tell how the repair was done.

We knew that there was supposed to be a splice plate there.

But it was evident to me that there was just one row of rivets taking up the load.

It didn't look right.

They used two different splice plates.

And by using two different splice plates, it compromised the repair.

NARRATOR: Investigators discover the repair team

cut the splice plate in two, perhaps for easier installation.

The lower plate helped secure the overlap. The upper plate did not.

SCHLEEDE: That one row of rivets was insufficient to sustain the loads

and eventually fatigue cracks started and the hull section failed.

The fracture followed the gap between the two splice plates.

SMITH: This particular 747-SR had accumulated over 18,000 cycles

in its 12-year career with JAL. That's just an astonishing number.

(engines powering up) V1.

Rotate.

SMITH: Each one of those cycles, each one of those takeoffs and landings

meant pressurization and depressurization cycles.

PURVIS: The rear bulkhead now had a weak spot.

It was sort of like a ticking time bomb ready to fail.

That's it. That's gotta be it.

SCHLEEDE: It's what investigators call the golden nugget.

We found the, "Aha, that's the cause."

PURVIS: There is no question that, if done correctly,

the repair would not have failed.

NARRATOR: Investigators have discovered what caused the rapid decompression,

but they still need to understand why the tail detached.

INVESTIGATOR 1: The bulkhead ruptures here.

And all that pressurized cabin air has gotta go somewhere.

Now, the shock wave flows up the tail

and it must have just popped off like a champagne cork.

The first boom was the failure of the bulkhead…

(explosions)

…and the second one was after the vertical tail pressurized and it failed.

(alarms wailing)

(wind gusting)

Hey. Check this out. All four hydraulic lines run through the tail section.

INVESTIGATOR 1: So when the decompression happens,

not only do they lose a chunk of that tail, they lose all those lines as well.

SCHLEEDE: In this case, all four hydraulic lines went up the vertical fin.

So that was a poor design.

SMITH: It was just considered so unlikely, so inconceivable

that all four systems would in some way be disabled.

But that's exactly what happened.

NARRATOR: It's a design flaw

that rendered the rest of the plane's flight controls useless.

- TAKAHAMA: Don't bank so much. - (grunts) Okay.

TAKAHAMA: (yells) Don't bank so much.

Hydraulic pressure has dropped.

NARRATOR: Without any hydraulics to control elevators, rudder, or ailerons,

Flight 123 flew an erratic flight path for 32 terrifying minutes.

GPWS: Sink rate. Pull up.

- TAKAHAMA: Raise the nose. - GPWS: Terrain.

TAKAHAMA (yells): Raise the nose! (Sasaki grunts)

GPWS: Don't sink.

NARRATOR: The two pilots used all their strength to regain control.

- I can't hold it much longer! (grunts) - NARRATOR: But nothing worked.

- (yells) Flaps up. Flaps up! - GPWS: Sink rate. Pull up.

FUKUDA (yells): Flaps up!

- TAKAHAMA: Raise the nose! - GPWS: Pull up. Terrain.

- TAKAHAMA: Power! - GPWS: Pull up.

NARRATOR: What began as a repair seven years earlier,

set the stage for a devastating crash…

that took the lives of 520 people,

the worst single aircraft accident of all time.

INVESTIGATOR 1: The initiation and propagation of the fatigue crack…

NARRATOR: A series of recommendations takes direct aim

at the original 747 design.

Operators are ordered to install a cover in the tail

to protect the vertical fin against a bulkhead decompression.

INVESTIGATOR 1: …the improper repair that was…

NARRATOR: Emergency cut off valves are also recommended

to prevent a total loss of hydraulic pressure.

SCHLEEDE: One way they can do this

is to put what they call fuses in a hydraulic system.

If you cut the line, the hydraulic fluid would be trapped in the rest of the line,

and they were installed on the 747.

NARRATOR: Today, hydraulic fuses are used on almost every commercial airliner.

PURVIS: This accident was a watershed moment in aviation safety.

It pointed out a lot of areas that not only the 747,

but other airplanes flying, could be improved,

right then and for the future, and for future designs.