Original subtitles

[narrator] With over 100,000 flights departing each day

from airports around the world,

the aviation industry has cemented itself

into our daily lives.

[Rob] Aviation is often quoted as the safest form of transport,

but whenever there is an accident, sadly,

they're often examples of fatal engineering.

Japan, 1985.

520 people died when Japan Airlines Flight 123 encountered

a terrifying and unprecedented technical problem.

It's a single blow that causes a chain reaction of disaster.

Four years later, England, 1989.

An engine failure and insufficient pilot training

resulted in the death of 47 passengers.

If you're gonna shut down an engine, you need to make

sure that you're shutting down the right one.

In the summer of 1996, off the coast

of New York, TWA Flight 800 explodes 12 minutes

after takeoff due to a terrifying and unprecedented

chemical phenomenon aboard a commercial airliner.

All it would take was a spark to turn the central wing tank

into a bomb.

Were these accidents the result of unavoidable circumstances?

Or were they examples of fatal engineering?

[electronic theme music playing]

Wednesday, July 17, 1996. It's 8:19 pm.

[suspenseful music playing]

TWA's flight 800 takes off from New York, bound for Paris,

with 230 passengers and crew on board.

-[suspenseful music playing] -[engine roaring]

[pilot over radio] TWA's lifeguard 800 heavy,

eight thousand, two hundred climbing on one thousand.

This aircraft has been in service for 25 years,

logging over 93,000 flight hours.

[Rob] You could call it a real veteran with an impressive track record,

but on this particular day, none of those passengers

will reach their final destination.

[suspenseful music intensifies]

Just 12 minutes later, disaster would strike.

As air traffic control attempts to reach out to flight 800,

they receive only silence.

As the TWA Boeing climbs to its cruising altitude,

people on the ground and an airline pilot

aboard a nearby aircraft

see the plane explode in midair over the Atlantic Ocean,

some 15 kilometers from Long Island.

[explosion blasting]

[Tower] Eastwind 507, you reported an explosion.

Is that correct, sir?

[pilot] Yes, sir, about five miles out.

[Tower] TWA 800 -- [indistinct].

-[pilot] I think that was him. -[Tower] I think so.

What happened?

What caused the deaths of the 230 people on board?

[Shini] Though many on the ground have suspected terrorism,

claiming to have seen missiles directed up towards Flight 800.

The reality is perhaps far more terrifying.

Right now, the Coast Guard, the National Transportation

Safety Board, the FAA, and the FBI are on the scene

of the crash.

Using massive search equipment, they located the wreck

at a depth of 37 meters.

In the wreckage, they retrieved the cockpit

voice and flight data recorders.

[indistinct speaking over radio]

These two orange boxes are the final moments of TWA 800.

They offer to the investigators a valuable first clue

and point them in a surprising direction.

[Michel speaking French]

It's a strange occurrence that might provide a key clue.

The malfunctioning fuel quality indicators might be

the smoking gun.

Additionally, the cockpit recorder reveals two unusual

aircraft sounds, sounds that pilots and mechanics

can't interpret.

It's 8:31 p.m., the time when the flight recordings stop,

the moment the plane explodes.

Eventually, the experts manage to bring to the surface almost

500,000 pieces of wreckage,

95% of the aircraft,

and reconstructed it in this Long Island hangar.

It is here that they will come to understand the drama

that has played out in this aircraft.

[speaking French]

And what they discovered was that the explosion

that occurred could not have come from an external object.

This explosion started on the inside and blew out.

[Shini] The fuselage of the aircraft had been bent outwards

around the wing center section of the aircraft.

The center section of the aircraft is the area

between the wings.

This is one of the strongest sections,

with the fuselage connected to the wings through structural

elements like spanwise beams and spars.

This section also houses a critical component involved

in the accident.

In a large aircraft, like the Boeing 747,

you need a huge amount of fuel to fly the massive distances

that they do.

And the majority of that fuel is stored within the wings

and within what's called a central fuel tank, which sits

in between the wings within the fuselage itself.

This is the largest of all fuel tanks on the 747.

The central wing tank can carry almost 50,000 liters of fuel.

But on this particular day, it's almost empty.

[speaking in French]

That central fuel tank didn't need to be full.

There was enough fuel in other fuel tanks around the aircraft.

The central fuel tank on this flight only had about 2%

of its maximum capacity.

It contains only 300 gallons kerosene.

Kerosene is partly chosen due to the fact that as a fuel,

if you took a match to it and tried to light it as

a liquid, it's just gonna put the match out.

It's not that volatile as a liquid, but as a vapor,

it becomes much more volatile.

All that was needed to create it was a heat source and time.

And that heat is not far away.

Beneath the central wing tank lie elements responsible

for the drama to come.

[speaking in French]

In summer, temperatures in New York can exceed

30 degrees Celsius.

On July 17, 1996, TWA Flight 800 was originally scheduled

to take off at 7 p.m.

However, it was delayed at the gate,

with its passengers already on board.

A fleet service vehicle, which helps to load and unload

aircraft between flights, has broken down,

blocking the aircraft at the gate.

Meaning that it wouldn't be able to pull back

to go out to the runways and take off.

Secondly, there was some confusion around

passengers' luggage.

As a result, the plane remains grounded.

But throughout the wait for takeoff, the cabin remains

air conditioned for the comfort of the passengers.

[Shini] What seems like a fairly routine, though frustrating,

inconvenience has created a deadly situation

in the plane's center wing tank.

Soon, it will develop into a fatal disaster.

July 17, 1996.

TWA Flight 800 was originally scheduled

to take off at 7 p.m.

However, it was delayed at the gate,

with its passengers already on board.

Nobody knows it, but two of the three air conditioning

motors are heating up the 1,000 liters of kerosene

in the center wing tank.

This action creates an unprecedented situation,

terribly dangerous for the entire aircraft

and its passengers.

That central fuel tank, with a small amount of fuel

in it, is getting warmer and warmer and warmer.

Though the aircraft's center wing fuel tank was only loaded

with 300 gallons of fuel for the flight to Paris,

there was another substance slowly building up inside it

that would prove fatal.

This substance is known as fuel vapor, and in a kerosene tank,

it's an extremely dangerous gas.

[Michel speaking French]

[Shini] All it would take was a spark

to turn the central wing tank into a bomb.

8:02 p.m.

TWA 800 is finally cleared to leave its gate.

It receives its departure clearance and joins the queue

of aircraft awaiting takeoff.

Between its arrival and departure, the aircraft has

been on the ground for two hours and 45 minutes,

with two of its three air conditioning motors operating

at maximum capacity.

8:19 p.m., the pilot sets the engines to full power

to take off from the end of the runway.

[tower] TWA 800... Climb and maintain one-three thousand.

[captain] TWA's 800 heavy climb and maintain one-three thousand..

This is when a spark is introduced.

The flight recordings show that 10 minutes after takeoff,

at precisely 8:29 p.m., the captain of TWA 800

commented on the abnormal movements of the fuel gauges.

He is then cut off when air traffic control asked him

him to climb to 15,000 feet.

Unfortunately, he never reaches this altitude.

The jittery gauges in front of the captain reflect what's

going on in the central tank.

The hot, dense fuel vapor disturbs the seven

probes inside.

[Michel speaking French]

These electric components operate safely within close

proximity to volatile substances like jet fuel.

Even if there was a spark, it wouldn't have enough energy

to ignite a combustion of fuel.

But that wiring was also bundled with other cabling

and other wiring systems within the aircraft.

And those wires had larger currents running through them.

This grouping of cables provide the final element to complete

this explosive cocktail.

What's believed to have happened was that those little

crackles that were heard by the captain and the flight crew

up in the cockpit...

with a short circuit and some of those cabling systems

that required a larger current, there's your spark,

the third element needed for combustion.

Fuel,

oxygen, spark.

The rest is inevitable.

The time is 8:31 p.m.

As the plane reaches an altitude of 13,800 feet,

the fatal cocktail explodes.

A massive explosion takes place within the central wing tank...

blowing out that central part of the aircraft, a key part

for its structural integrity.

The plane starts to buckle, and the front of the aircraft

tears itself away from the back.

The cockpit, with a few rows of seats behind,

plummets down into the ocean.

[Shini] The rest of the plane continued in the air, the wings still

connected to what remained of the aircraft's fuselage.

[speaking French]

It took four years and $35 million to complete one

of the largest air investigations in history.

Following the accident,

modifications were made to the aircraft's internal wiring

to prevent such a scenario from happening again.

[Rob] Firstly, the wiring was reconfigured so that no longer

would you have those low current wires bundled

with higher current.

The chance of a spark and an energy being transferred

into the fuel tanks was eliminated.

Secondly, regulations were introduced to make sure

that never again would you be allowed to take off

with a small amount of fuel that could easily turn into a vapor.

And finally, increased insulation was installed

between the air conditioning units and the central fuel tank.

The flight of TWA 800 turned into one

of the world's greatest air disasters.

But what happens when you combine new aircraft

engineering design with old ways of thinking, human error

can often also be the cause of fatal engineering.

On January the 8th, 1989, British Midlands flight 92

takes off from London Heathrow on its way to Belfast

in Northern Ireland,

a flight it would have done many times before.

[Shini] This flight would be flown by a brand new aircraft and had

been delivered to British Midlands Airways one month

prior to that date, Boeing's brand-new 737-400.

Major changes from previous versions of the 737

include its modern dashboard with the introduction

of digital functions and its revolutionary

new CFM56 engines.

When the 126 passengers and crew board Flight 92,

they have no doubt about the reliability of this aircraft.

However, they will never reach their destination.

27 minutes after takeoff, this masterpiece

of aeronautical engineering loses the use

of one of its engines.

Diverted for an emergency landing, it crashed 900 meters

from the runway at East Midlands Airport,

South of Nottingham, in the small town of Kegworth.

[sirens wailing]

Despite the violence of the impact that kills

47 people, 74 passengers and crew miraculously survived

this terrible crash.

I was suspended upside down, just with my safety belt

holding me on and my wife just down below me.

The captain is among the survivors.

Injured in his back and legs, he is hailed for his courage

and decision making.

[speaking French]

To understand this, we need to go back 30 minutes

before the crash.

8:52 p.m.

British Midland Flight 92 departs from Heathrow Airport

in London.

13 minutes after takeoff, precisely at 9:05 p.m.,

as the plane nears its cruising altitude, a worrying phenomenon

occurs on board.

[Rob] The pilots and a number of the passengers realize

that something's not quite right.

There's some vibrations that feel more than what you'd

normally expect, and you can feel it in the aircraft.

What they don't know is that there's a problem in one

of the two engines.

The CFM56 is made up of two inseparable elements that will

be the key components in this deadly accident.

[speaking French]

The essential component for making an aircraft fly

is the fan.

It is made up of 38 blades, each 1.5 meters long.

These blades turn and they draw in a huge amount of air

and thrust it out the back that propels the engine forward.

But as the investigation will reveal, one of the blades will

be the source of the problem.

Blade number 17 has suffered a crack and it's shifted

its position slightly within the configuration.

Not only does Blade 17 crack,

but as the engine continues to rotate, it begins to twist.

As a result, the gap between this blade and the one adjacent

to it widens, allowing more air to pass at that point

through the engine.

As the fan continues to rotate at a speed of 20,000

revolutions per minute, this excess airflow

destabilizes the fan and threatens the proper

functioning of the engine.

[speaking French]

That blade, having shifted just a few millimeters, is now

touching the outer casing of the cowling

that contains the engine.

As passengers look through the windows, they see sparks

coming from the left engine.

Then they experience a second terrifying event,

smoke in the cabin.

[speaking French]

At this point, everyone understands

that the situation is abnormal, and there is

a problem with the aircraft.

The passengers begin to panic.

The captain and his copilot are highly experienced.

They have over 16,000 flight hours between them,

including 1,000 hours on the Boeing 737.

Critically, however, only 76 of those hours

are on this new model of the 737.

Only one day of training was required by the manufacturer

to obtain their certification to fly the Boeing 737-400.

This included all the new features of the aircraft,

as well as the nuances of the aircraft

in emergency situations.

Relatively new to the Boeing 737-400, they're about to make

several fatal assumptions and miscalculations.

The two pilots understand that there is an issue with

one of the engines and begin to assess the situation.

They decide to shut down the engine that's causing

these vibrations.

Now, that in itself isn't a big deal.

It happens fairly regularly.

When something's wrong with an engine,

you can shut it down.

The aircraft, like the Boeing 737-400, can fly safely

on one engine.

But if you're gonna shut down an engine, you need

to make sure that you're shutting down the right one.

British Midland Flight 92

departs from Heathrow Airport in London.

The pilots can clearly see on their instruments

that something is wrong.

However, they are not used to the brand-new digital screens

on the dashboard.

The pilots can clearly see

that something's wrong with the left-hand engine.

Their instrumentation is showing it.

They can also feel the vibrations.

However, as strange as it may seem, the pilots will make

a mistake that will prove fatal.

[engine whirring]

[speaking French]

The left-hand engine that's causing

vibrations is now the only thing providing

thrust, keeping the plane in the sky.

The flight continues flying on a single failing engine.

However, they do not yet realize their mistake.

When they shut down the working engine, the cockpit gauges

return to normal.

The vibrations and the smoke stop.

[speaking French]

[Rob] And so it feels to the cockpit that everything is fine.

The right decision has been made, and we're going to land

in East Midlands Airport off of the power from one engine.

At this point, they still have time to realize their mistake

and restart the engine, but they take no

further action.

The passengers can clearly see that smoke,

and flames and sparks are still coming out from this engine.

As flight 92 aligns with the runway, the throttle is

pushed forward, increasing the power demanded

from the left engine.

That is the turning point.

[speaking French]

It is 9:18 p.m.

The flames and vibrations reappear.

During the investigation, part of the outer casing

of blade 17, as well as fragments from blades 4 and 5,

were found during flight 92's final approach

to East Midlands Airport.

Blade 17, which had already suffered fatigue damage

and came loose within the engine's fan, had possibly

been ingested by the engine, released from a trapped

position, damaging other fan blades as it's drawn

through the engine.

[speaking French]

It becomes clear they will not make it to the runway.

They're forced to make the decision that no pilot ever

wants to make. Forced to make a crash landing.

Between the plane and the runway is one of the busiest

motorways in the UK, the M1, and the plane's heading

straight for it.

The pilots don't have many options.

In fact, they only have two choices.

[speaking French]

The pilot chooses to crash onto the slope near the highway.

30 minutes after taking off from London, the captain makes

the most dreaded announcement a commercial pilot can make.

Captain Hunt uses the intercom to ask passengers to prepare

for a crash landing.

Some passengers manage to get themselves

into the brace position. Others do not.

Violent vibrations inside the cabin cause the overhead

compartments to open, and luggage falls

onto the terrified passengers.

The plane loses thrust and begins to dive.

The plane makes contact with the ground on one side

of the motorway, crashing through fields and some trees,

crosses the motorway.

[Shini] The forward section splits and continues onwards

up the embankment, while the tail of the plane separates

and folds up on top of the midsection

and the passengers in the main cabin section of the aircraft.

British Midland Flight 92 crashes just 900 meters

from the runway of East Midlands Airport.

Miraculously, no one on the highway is injured.

You might argue that this was a case of fatal engineering

because of the errors that occurred in that left-hand

side engine, the cracks, the movement

of the turbine blades that caused the fire

and the vibrations.

But in this case, the pilot made the wrong decision.

[speaking French]

Because of this fatal error, 47 people died, and 74

will carry the lasting effects of their severe injuries.

This avoidable tragedy caused a shockwave throughout

the aviation industry.

Due to Captain Hunt and First Officer McClelland's

relative inexperience in the Boeing 737-400

under such dire circumstances and Boeing's

inadequate pilot training, recommendations were made

to ensure all pilots are thoroughly prepared

before taking control of a new aircraft variation.

[Rob] Undoubtedly, the catalyst for the British Midlands

aircraft disaster was a fault within the engine.

But what happens when your engines are working fine,

but you lose the ability to control the plane in the air?

We're in Japan at Tokyo's Haneda Airport

on August 12, 1985.

Japan Airlines flight 123 departs for Osaka.

It's 6:12 p.m.

This is a 54 minute flight, so a relatively short flight.

But in Japan, the number of people wanting to make

this flight is huge.

And so Japan Airlines regularly use a Boeing 747, crammed full

with 500 passengers, shifting people

between Tokyo and Osaka.

Specifically designed for the Japanese market,

this Boeing 747-SR46

is the largest airliner of its time, it can accommodate

up to 550 passengers.

With 524 passengers and crew members aboard, it is nearly

full when it takes off from Tokyo Airport.

[Rob] Twelve minutes into this particular flight,

something goes devastatingly wrong with the aircraft,

and it never makes its destination in Osaka.

An explosion occurs at the rear of the plane,

depressurizing the cabin, and destroying both the tail's

rudder and hydraulic systems, making the aircraft

uncontrollable, a nightmare for every passenger.

For over 30 minutes, the pilots fight

with the aircraft, repeatedly informing ground

crews that they have lost control.

-[pilot yelling over radio] -[engine roaring]

[alarms beeping]

At 6:56 p.m., 44 minutes after its takeoff, the plane crashes

into the slopes of Mount Osutaka,

100 kilometers from Tokyo.

[suspenseful music playing]

The crash results in 520 deaths.

Never has an aviation disaster involving a single aircraft

claimed so many victims.

Incredibly, rescue teams managed to find four survivors

within the wreckage of the plane.

[Shini] But was such a tragic loss of life avoidable?

Were warning signs missed?

Was flight 123 a case of fatal engineering?

[Rob] In order to understand what's happened here,

we need to go back in time seven years back.

When, on one occasion, when this plane was taking off,

it suffered a tail strike.

In aviation, a tail strike refers to the moment when

the tail of the aircraft touches the ground

during takeoff or landing.

This is what happened on June 2nd, 1978,

at Osaka Airport.

[speaking French]

As an airplane climbs higher, it enters a zone where the air

is thinner, colder, and unsuitable for the human body.

To maintain a comfortable atmosphere for the people

on board, the cabin is kept at normal pressure.

It is pressurized with air taken from the aircraft's

engines and pumped into the cabin.

This disc-shaped bulkhead is the essential shield

that separates the pressurized rear cabin from the tail

of the aircraft, which is not pressurized.

[Shini] Without this bulkhead, pressure would be lost through

the back of the aircraft and would be unable to maintain

a suitable atmosphere at a plane's cruising altitude.

This is why all repairs must be done meticulously,

but in this case, it was not.

Once the repair was finished, inspectors discovered

an alarming situation.

There were significant gaps between parts of the new

bulkhead that threatened its proper functioning.

To solve this major issue, engineers decided to install

a junction to serve as a seal between the two parts involved.

However, the junction plate was difficult to install due

to the curvature of both the plate and the bulkhead.

Boeing engineers decided to cut the plate to install it

and used half as many rivets as needed, a choice that would be

fatal for Japan Airlines Flight 123.

[speaking French]

And over a period of time, those repairs started

to suffer cracks and started to become unstable.

On this flight, that instability became disastrous.

It was a ticking time bomb.

August 12, 1985.

The Japan Airlines Boeing 747 has been in flight

for 12 minutes and is approaching

its cruising altitude of 24,000 feet.

[Shini] As passengers and crew settled into the flight,

a loud boom thunders through the plane.

Over time, cracks in the weakened area of the bulkhead

created an air gap that disrupted the balance

of the cabin's pressurization.

The bulkhead could not withstand this influx of air.

Inevitably, it explodes.

Suddenly, the cabin is no longer pressurized.

It is exposed to the atmosphere and the air pressure

at the altitude where the plane found itself, which is much

lower than what we find when we're on earth.

As such, there's not as much oxygen.

The oxygen masks drop from the overhead compartments.

The captain realizes the cabin is undergoing rapid

depressurization and that the passengers' lives are at risk.

[captain speaking Japanese over radio]

He descends to a lower altitude so the air becomes breathable

for those on board and requests an emergency landing

at Tokyo Airport.

[captain speaking Japanese on radio]

[tower speaking Japaense]

[Rob] The crew knows something has happened, but they can't see

the entirety of the plane.

They don't know exactly the extent of the damage that's

been caused by this loud bang, this explosion somewhere

in the aft of the plane.

[speaking French]

This photo was taken during that hellish flight

by a witness on the ground.

It illustrates the horrifying tragedy of Japan Airlines

Flight 123, carrying 524 passengers and crew.

Unbelievably, the tail is missing from this aircraft.

The tail will be found in Sagami Bay, 60 kilometers

from Tokyo Airport.

When the partition exploded, the air pressure inside

the cabin rushed toward the tail of the plane.

This extremely violent decompression is the trigger

for the worst case scenario.

[speaking French]

[Rob] Without those two controls, as the pilot, you have very

little input to dictate the movement of the aircraft.

6:28 p.m.

Four minutes after the partition rupture and the loss

of cabin pressure, the captain informs air traffic

control that the plane is uncontrollable.

They are given permission to land at nearby airports.

[tower speaking Japanese on radio]

[captain responding in Japanese]

However, the aircraft begins to perform maneuvers

that are, at once, dangerous and terrifying.

The phenomenon is known as phugoid motion.

It occurs when the aircraft repeatedly gains and loses

altitude in several phases.

The plane comes down through gravity, builds up speed,

the lift in the wings increases, and the plane

goes up again.

As it goes up, it loses its speed, and so gravity

dictates that it comes down, almost like it's

on a roller coaster.

6:48 p.m.

JAL flight 123 is now only 7,000 feet above the mountain

ranges of the Japanese Alps.

The mountains are getting closer, and the crew

desperately tries to find a way to control the plane,

as the flight controls are no longer responding.

When the bulkhead ruptured and the pressure exploded

in the tail of the aircraft, it wasn't just the vertical

stabilizer and rudder that were destroyed.

The tail also contains components of another critical

system onboard the aircraft, the hydraulic system.

[Shini] The Boeing 747, like most planes, uses a series

of hydraulics to power flaps on both the tail and the wings

of the plane.

By tilting these flaps with ailerons, the pilot can

then control airflow around the plane,

and therefore the plane's direction and speed.

However, when the explosion of the pressurization bulkhead

tore off part of the tail, it also damaged hydraulic

system pipes located there.

The fluid they contained, vital for the system

to function, gradually began to leak out.

Within 60 to 90 seconds following the explosion

at the rear of the aircraft, hydraulic pressure was

completely lost.

6:50 p.m.

The crew of JAL flight 123 has lost control of the aircraft

for 26 minutes.

[speaking French]

[Rob] No matter how hard he tries,

his efforts will be unsuccessful.

For 30 minutes, the pilots fight courageously

to keep this 260-ton aircraft in the air, a 30-minute

nightmare for everyone on board, during which passengers

record their final moments.

[speaking French]

6:55 p.m.

43 minutes after takeoff, the airports of Haneda

and Yokota confirm they are ready to receive

flight 123 for an emergency landing.

[captain speaking Japanese over radio]

The crew on board confirms the message,

but it's their last transmission.

Despite the heroic efforts of the pilot, inevitably

the plane crashes.

-[pilot yelling] -[engine roaring]

-[alarm beeping] -[yelling continues]

And it crashes into a mountain ridge.

[Shini] The plane continued forward with the passengers

in this section experiencing forces greater than 10 to 20 G.

[explosion rumbles]

According to onboard seismic sensors, it is 6:56 p.m.

when the plane the plane makes its final movements

on the ground, and the debris settles

into its final position.

What we know is that there were no survivors in the front

of the aircraft, but there were dozens of survivors

in the rear.

Despite the power of the impact, some passengers

have survived.

However, they are in a remote area

in the Osutaka Mountain Range,

over 1,600 meters above sea level in the middle

of the night.

They have to wait 12 hours before rescue teams reach

the crash site, 12 hours that will be fatal

for the majority of the survivors.

Only four would survive until the following morning.

In addition to the four survivors, the rescue teams

find a camera.

On it were photos from the final moments

inside Flight 123.

[speaking French]

Aviation is often quoted as the safest form of transport,

and the statistics play that out.

But whenever there is an accident, sadly,

they're often examples of fatal engineering.

After the accident, Boeing took steps to modify the hydraulic

systems of its planes in order to prevent such a tragic

scenario from happening again.

This disaster also served as a true lesson on the importance

of aircraft maintenance, a lesson for the entire

aviation industry.