Original subtitles

639 pieces of wreckage are recovered from the scene.

Six hundred and thirty-nine pieces

that only deepen the mystery of a deadly plane crash.

All right, a little bit more to the right. There!

But when investigators bring up the 648th piece of China Airlines Flight 611,

they get their answer.

There was definitely a eureka moment on the dock.

It would be scrutinized more closely than any other piece of debris.

On this single piece of wreckage,

investigators would find the one clue that would tell them

why a modern jetliner with 225 people on board shattered in mid-air.

Mayday! Mayday!

Thirty feet.

Speed is low, sir, watch it.

Did you feel that?

May the 25th, 2002.

Gears up.

A China Airlines 747 lifts off from Taiwan's capital, Taipei.

Taipei approach, Dynasty 611 airborne passing 1,600.

Dynasty 611, Taipei approach radar

contact climb and maintain flight level 260.

Two, six, zero. Dynasty 611.

Autopilot B, engage.

China Airlines is Taiwan's national airline.

There are 225 people on board Flight 611.

Today's flight is a short one.

One hour and 40 minutes across the Taiwan Strait to Hong Kong.

This route is one of the most widely-traveled on the planet.

It makes so much money,

it's called The Golden Route.

Ladies and gentlemen, the fasten seatbelt sign

has been turned off.

For your safety, we do recommend that you keep

your seatbelt fastened at all times while seated.

Minutes after taking off,

Flight 611 climbed steadily above the Taiwan Strait.

The plane's autopilot controls the ascent.

And, then, 20 minutes after taking off,

at an altitude of almost 35,000 feet...

At Taipei Area Control, the flight vanishes from radar.

Dynasty 611, Taipei. Dynasty 611, Taipei.

I've got a plane off radar.

China Airlines 611.

It's last known return was East 119 decimal 67,

North 23, decimal 98.

Taiwanese authorities quickly launch one of the largest rescue missions

in that country's aviation history.

I gave a clear order that the priority

would be searching for whoever was still alive.

Then bodies, and then, only then, wreckage.

More than 1,000 people take part.

Fishing boats, the Coast Guard, and Taiwan's military race out to sea.

Flight 611 was 55 kilometers from the Taiwanese shore,

just north of the Penghu Islands when it disappeared.

Rescuers find debris floating in the Taiwan Strait.

The first thing we saw

was a great amount of wreckage,

including landing gear wheels, napkins, knives, and forks.

Wreckage from the plane is spread far and wide.

Some items are found on land more than 100 kilometers away in central Taiwan.

As the rescue effort continues, Taiwan's Aviation Safety Council

begins its investigation into the crash of the 22-year-old plane.

747-200, delivered August 2nd, 1979.

Kay Yong is the managing director of the ASC.

He'll be leading the investigation.

We're setting up a command post on Penghu Island. Let's go.

China Airlines have had a very, very poor safety record.

As a matter of fact, it was considered one of the worst in the world.

Typically, it had, like, one major accident every four years.

This particular investigation was, by far, the most difficult one.

And one of the reasons why was it's... it's in the ocean floor.

The search for survivors goes on around the clock.

There were 225 people on the airplane.

Nobody is found alive.

The bodies are taken to the Penghu Islands to be identified and examined.

Since the accident involved an American-made plane,

the NTSB joins the investigation.

A team of investigators is dispatched to Taiwan,

They'll be led by John DeLisi in Washington.

We have a very good working relationship with the ASC,

The Aviation Safety Council, of Taiwan.

So we knew that they would ask for

and welcome our assistance in the investigation.

Wreckage that's found floating

is also brought to the Penghu Islands.

Investigators need to know how one of the world's most successful planes,

on one of the world's most-traveled routes, simply fell out of the sky.

Well, Boeing 747 is the world's most popular jumbo jet,

and it's flown millions of people, probably billions of miles.

So it... We were very concerned.

Good morning. I'm anxious to see what you have.

Sophisticated ground based-radar

tracked Flight 611 throughout its short journey.

It should provide investigators with a much clearer picture of the flight

than the radar at Air Traffic Control.

Kay Yong gets the first major clue in this case.

The radar tracked the plane as it climbed on course to 35,000 feet.

Then, suddenly, Flight 611's signals split apart.

The break up is quite graphic.

Right when the event happened, it appeared as if there were

three or four sizable pieces of wreckage that were getting radar returns

that then began to drift and scatter as they fell to the earth.

So that told us that the airplane broke up in flight.

Investigators now must turn their attention

to finding out what caused that breakup.

There's all kinds of theories about,

you know, what seems to be happening on that particular aircraft.

We knew that something massive had happened,

happened suddenly without warning.

It doesn't take long for the media to consider a sinister possibility,

that Flight 611 was shot down.

- China and Taiwan have a combative relationship. -

China has fired missiles towards Taiwan in the past.

There's suspicion in the media that China shot down Flight 611.

There were a lot of theories about, you know, the...

It was shooting down by enemy fire.

Only eight months earlier, a Siberia Airlines flight

with 78 people on board was shot down over the Black Sea.

It was accidentally hit by a missile fired from Ukraine during a training exercise.

On the day of the China Airlines crash,

China was conducting military exercises in the Taiwan Strait.

But officials there insist no missile was launched towards Flight 611.

None of the wreckage recovered so far

has any of the telltale signs of being hit.

And there's no evidence on radar that there was ever a missile heading for Flight 611.

Once the evidence began to come in,

it very quickly ruled out a missile,

much the same way that it ruled out it being a mid-air collision.

There were no other objects in the air near the airplane.

Few things would cause a plane to break up in mid-air.

One of the big ones is a bomb.

Medical examiners check the bodies that have been recovered

for burn marks and shrapnel.

They find none.

The plane's metal skin would be torn and curled in a very particular way

if there had been a bomb on board.

Investigators find no such damage on any of the pieces.

But to rule out a bomb, they'll have to find more wreckage.

I think that'll be it for floating wreckage.

The team from the NTSB arrives in Taiwan.

Good morning. I'm Clint Crookshanks from the NTSB.

Good to see you, gentlemen. I'm afraid we still don't have much.

Clint Crookshanks is a structural engineer who knows the 747 intimately.

I didn't have any preconceived notions.

This was my first major accident working for the NTSB.

We are not getting much from the floating debris.

In flight break-up, that's all we know.

Taiwan's Civil Aeronautics Authority doesn't take any chances.

They ground all of China Airlines' 747-200 series planes

until they can be inspected for mechanical flaws.

This puts added pressure on investigators to find out what happened.

Thank you for bringing these.

To the NTSB, this accident seems to have a lot in common

with one of the world's most-studied plane crashes.

That of TWA Flight 800 six years earlier.

Like the China Airlines flight, it broke into pieces while still climbing.

That plane crashed into the Atlantic

shortly after taking off from New York.

TWA Flight 800 was the biggest investigation the NTSB has ever done.

Lasted about four years.

The painstaking investigation uncovered a design flaw with the 747.

Wiring near one of the plane's fuel tanks

could spark and ignite the fuel in the tank.

Investigators conclude

that's what likely caused the crash.

Investigators are struck by similarities between the two flights.

Both were 747s.

Both disintegrated without warning while still climbing.

Both flights took off in very hot weather.

The heat may have caused Flight 800 to explode.

That plane sat on the tarmac with its air-conditioning running.

Investigators believe hot air from the air conditioner overheated the plane's fuel.

The early evidence is pointing to a repeat of TWA Flight 800.

So it looks really very, very similar.

So, therefore, the... our immediate focus

was, essentially, the central fuel tank.

Three weeks after the crash, the Jan Steen,

a sophisticated salvage vessel, arrives in the Taiwan Strait.

It's equipped with divers, a diving chamber,

and a remote-operated submarine complete with sonar and video cameras.

The NTSB were tasked with manning the recovery vessel

and watching video screens from the ROV.

Using sonar,

investigators have located the wreckage of Flight 611 deep underwater.

All right, to the right a bit.

Clint Crookshanks knows all the pieces that make up a 747.

But he's never seen them like this.

It was really quite a shock when I first saw pieces on the floor of the ocean.

With only the lighting of the ROV to guide you,

you would notice something that looked like an airplane part.

The ROV would then circle around the part, looking at it from all angles.

Crookshanks' job is to help the Taiwanese

identify specific airplane parts among the wreckage.

I think it takes a different kind of mind

to be able to look at a mangled part

and kind of straighten it out in your head

to really determine where it comes from on the airplane.

All right, a little bit more to the right.

All right, go back.

There! Okay, that's definitely a piece of wing. Let's mark it.

Once a piece is identified,

its GPS coordinates get recorded.

The GPS mapping tells investigators

that the debris is spread out over 325 square kilometers.

It will be difficult to track down specific pieces of the plane.

Twenty-five days after the crash of Flight 611,

the plane's two black boxes have been found.

One contains voice recordings of conversations in the cockpit.

The other, data from the plane's flight computer.

Either could hold the clues that will reveal what happened

during the final minutes of the flight.

If the answer is on the tape, investigators may not have to bring up

more wreckage to the surface.

The data is critical.

Everybody ready?

Investigators begin with the plane's cockpit voice recorder.

They hope that the pilots will have said something to each other

about an emergency on board.

Welcome aboard China Airlines.

The recording begins about 10 minutes before the plane took off.

- Twenty. - Preparations for the flight sound normal.

- Okay, after start checklist. - After start, anti-ice.

The crew checks all their systems

and runs through standard checklists.

Off. Off.

It was a very, very experienced crew.

Both the captain and the fli... and the first officers were quite seasoned.

Dynasty 611, runway 06,

wind 050 at nine are cleared for take-off.

Cleared for takeoff. Dynasty 611.

Take off.

- 80. - Check.

Vee one.

Rotate.

- CO-PILOT: [ON RADIO] Flap five. One-one green.

CO-PILOT: Okay, flap up.

Investigators listen to more than conversations.

They also want to hear if the plane itself was making any unusual sounds.

Noises on the cockpit voice recorder can either be audible spoken words

that are recorded by a microphone,

or they can be structural discrepancies that are picked up

by the microphone.

If anything, though, this cockpit is unusually quiet.

Uni Air 608, reduce speed...

The captain seems relaxed.

The microphones pick up the sound of controllers

talking to other planes.

Trans Asia 536 fly heading 050.

In the moments before the disaster, nothing seems wrong.

There are no unusual sounds.

Now descend and maintain 250.

The final words spoken in the cockpit are from Captain Yi Ching-Fung.

Two thousand.

He calls out the distance to their cruising altitude.

That's followed by the sound of a chime...

...alerting the crew that they are nearing 35,000 feet.

And then the cockpit microphone picks up the sound of the plane breaking apart.

Half a second later, the recording stops.

The cockpit voice recorder indicated that the...

the conversation of the cockpit crew were totally normal,

and all of a sudden, just... just dying.

The recorders told us that something happened,

but it wasn't enough to tell us exactly what it was yet.

Many things had been ruled out by then, but we didn't have the golden nugget.

We didn't have the real piece of evidence

that told us what initiated the breakup of the 747.

After the disappointment of the voice recorder,

studying the wreckage becomes the only option for investigators.

They focus their efforts on items that can either

prove or disprove the link to TWA Flight 800.

So we play a lot of focus on the wreckage observation,

examination of the center fuel tank.

On July the 12th, 48 days after the crash...

Okay, whoa, whoa.

Little to the left, please.

Success.

All right.

That's definitely the central fuel tank.

Okay, let's mark that. Let's bring that up.

The tank joins the sea of wreckage piling up at the pier.

Investigators study it closely for any evidence that it exploded.

If it did explode like the TWA tank, it would be curled and twisted.

And the metal would be bent outwards.

But this fuel tank is different.

And we found the central field tank was relatively intact.

And it's crumpled inwards.

Unlike the tank from the TWA flight, there's no soot.

There would be if the jet fuel inside had ignited.

So, at that time, we pretty much ruled out

it was the cause of the center fuel tank.

The wreckage recovered so far has also forced investigators

to abandon another theory,

that a bomb brought down the plane.

None of the wreckage showed any evidence of sooting,

any kind of explosive damage.

The China Airlines crash was neither a repeat of TWA Flight 800,

nor a deliberate bombing.

Investigators are running out of leads.

As more wreckage is identified and recovered,

investigators find an intriguing clue.

It's discovered when they examine a series of small vents from Flight 611.

All commercial jetliners have dozens of these vents near the floor.

They're essentially pressure release valves.

They're called dado panels,

and there's only one reason for them to open.

If the cargo area underneath the passengers

were to suddenly decompress, the pressurized air above

would exert so much force on the floor

that it could collapse and damage vital fight controls.

That's precisely what happened to a Turkish Airlines flight in 1974.

The pilots couldn't control their plane after their cargo door blew out.

We've lost it!

If the floor on that flight hadn't collapsed,

the pilots may have been able to save the plane.

After that accident, the NTSB recommended

that manufacturers install many more relief vents

between a passenger plane's upper and lower levels.

If there is decompression in the cargo area,

the dado panels open automatically

and release the pressure on the floor.

There were 65 dado panels on the China Airlines flight.

Nineteen of them were recovered from the ocean.

Four recovered panels were in the open position.

It tells investigators that there must have been

a sudden loss of pressure beneath the passenger cabin.

But it doesn't tell them what caused it.

The dado panels lead investigators closer

to solving the mystery of this crash.

But it's just a small piece of a much bigger puzzle.

There are hundreds of pieces of wreckage to be examined for clues.

Kay Yong now wonders if a few of those pieces

might be able to tell him where the decompression originated.

I've been reading about the trajectory analysis you did on Flight 800.

I'd like to try it.

Ballistic trajectory analysis is a technique

that US investigators used to figure out how TWA Flight 800 disintegrated.

It's impossible to do without specialized computers.

We figured that, because it disintegrated in the mid-air,

the ballistic analysis from which they,

NTSB, did in TWA 800 could be very, very useful to us,

to help us to analyze the trajectory of the flying debris.

The analysis is based on a simple fact.

The pieces that came off the plane first would be the first to hit the water.

If investigators can figure out which pieces those were,

they'll know where the trouble began.

Radar that had been tracking the plane as it climbed

also ended up tracking pieces of debris as they fell.

The salvage workers have recorded the precise location

of those same pieces of wreckage.

Their logs could match a specific piece to its radar track.

Investigators know the wind speed on the day of the crash,

and they can obtain precise information about ocean currents.

The last piece of the puzzle comes from the plane's flight data recorder.

The plane's altitude, speed, and direction at the time of the break-up.

As they're brought to the dock,

every single piece of wreckage has been logged and numbered for identification.

Three-two-seven.

Kay Yong selects 18 pieces of wreckage for the computer analysis.

Some from the front, some from the middle,

and some from the back of the plane.

One-nine-nine.

Along with all the other data, he'll feed information

about each item's weight and shape into the computer.

Five-two-six.

Based on where the pieces fell, the computer should be able to calculate

which of those 18 pieces was the first to come off the plane.

Can we see when each one of those items separated from the aircraft?

All of the data paints a telling picture of what happened at 35,000 feet.

Kay Yong gets to see how Flight 611 broke up from beginning to end.

The tail came off first.

Along with the dado panels, it's a very important clue.

So that pretty much indicating that something happened in the back of the aircraft,

rather than something happened in the forward part.

Investigators are now keen to recover items from the rear of the plane.

Hundreds of pieces of wreckage are piling up at the pier on the Penghu Islands.

The NTSB sends metallurgist Frank Zakar

to Taiwan to examine the wreckage.

I was walking along the yard where the wreckage was placed,

and, at that time, I walked up to item 640.

I noticed that there were some peculiar areas of interest

that I wanted to look at a little bit further.

With this battered piece of metal, investigators have struck gold.

There was definitely a eureka moment on the dock

that was, hey, we might have something here.

Hey, it's Frank. I think we found your golden nugget.

Item number 640 would give investigators

a revealing glimpse into the past,

and lead them to conclude that the crash of Flight 611

actually began 22 years earlier.

Let's get as many pictures as we can.

The massive piece of fuselage that has caught Frank Zakar's attention

is exactly what investigators have been searching for.

It includes a piece of the belly, the side wall, and the rear cargo door.

It's from the back of the plane,

precisely where the analysis told them the break-up had begun.

This piece of wreckage was highly unusual.

It wasn't what we were seeing on all the other pieces.

And it immediately drew our attention,

and drew the focus of the investigation.

The way most of the metal is torn

suggests it ripped apart violently in mid-air.

Aerodynamically, as an airplane's moving through the air,

if it's... if it were to break apart,

just the force of the incoming air at over 500 miles per hour

will just break up perfectly good structure.

That's what we call an overload fracture.

So most of the pieces that came up early

were just indicative of that kind of overload.

When metal breaks due to overload or overstress, it comes apart at an angle.

But the fractured edges of piece number 640 aren't angled,

they're flat.

What do you think?

It's definitely not overstress. It's metal fatigue.

Fatigue fractures happen when metal is stressed

repeatedly over time until it breaks.

It looks very different from a stress fracture.

Typically, a metal fatigue crack will have a flat appearance.

It'll be very smooth.

That's exactly the kind of crack

that investigators observe on piece number 640.

That tells them it didn't break off the plane suddenly

as it fell from the sky.

This piece separated from the plane over time.

Had it caused the deaths of 225 people?

There was much more work that needed to be done.

A detailed analysis of the piece had to be done

in order to see if this, in fact, was the smoking gun.

There's something else about this piece that stands out.

It has a metal patch on it.

It's called a doubler plate.

It's the equivalent of a patch on a punctured tire.

It's not unusual to find numerous doubler plates on older planes like this one.

A doubler plate is like a patch that you put over fuselage skin.

If there were to be a tear,

or a blemish, a crack identified,

you'd want to repair the fuselage back to its original strength.

And one way to do that is to put a doubler plate,

or a patch right over the existing structure.

At some point, this section of the 747 had been repaired.

Investigators need to know why it was fixed and how that was done.

We're looking for repair to the aft lower lobe.

Whatever it was, it was big.

Investigators sift through 22 years of documents.

But the records are sketchy.

Finding details on one particular repair could take time.

There's something about this particular doubler

that catches Frank Zakar's attention.

The outside of the fuselage contained longitudinal streaks

that appeared to emanate from between the doubler plate and the skin.

Something is leaking from underneath the metal patch.

Was there a possibility that the skin had broken, cracked?

And was there any fuel or air coming out from between the doubler and the fuselage?

And that warranted further examination.

Let's cut it from here...

to here.

And send this piece to Chung-Shan.

In order to see what's underneath the doubler,

a large section of piece 640 is sent to a lab.

No evidence has been found of structural or mechanical problems

with Boeing's 747-200 airplanes.

Taiwanese aviation officials have no reason to keep the planes on the ground.

The Chung-Shan Institute of Science and Technology is a military research facility.

It's at the forefront of Taiwan's space program.

This is where investigators take a section of piece number 640

for a closer examination.

The NTSB's Frank Zakar finds a telling clue on the crack itself.

When I looked at the fracture surface,

I found that this one specific area was covered with aluminum oxide,

pretty much similar to rust on a car.

Years of exposure to oxygen changes the color of metal.

The discoloration tells investigators that this particular crack

at the rear of the airplane has been there for a very long time.

Then, when the doubler is finally removed,

investigators get a look at the aluminum skin underneath.

They're intrigued by what they see.

When we disassembled the doubler plate from the skin,

we noticed that there was some fairly long gouge marks.

This is beyond the kind of damage a doubler is meant to patch.

That was an "aha" moment, that we... we might have something here.

The search of the plane's documents also pays off.

The records contain a very short reference to a mishap 22 years earlier,

when this plane was only six months old.

Speed is low sir, watch it.

Its tail scraped the runway while landing.

- Did you feel that? - It happens when a plane

lands or takes off at too steep an angle.

It's called a tail strike.

Dynasty 009, Hong Kong tower.

We observed smoke and sparks from your tail on landing.

Roger, Hong Kong Tower. We'll have that looked at.

Tail strike, sir. I better log that.

It is a relatively common occurrence. It's not a good thing.

Some airplanes even have what's called a bumper in that portion of the fuselage,

so that if the tail ever does get too close to the ground,

instead of sacrificing skin from the fuselage,

you might have the sacrificial bumper that will take that wear.

Tail strike damage is routinely repaired.

Investigators want to know how China Airlines went about fixing the plane.

They could only find a brief mention of the repairs

that were done in the plane's logbook.

That's all there is?

That's all we could find.

There's not a lot of detail in China Airlines' records.

China Airline indicating they could not find any... any of those documents.

And when we start looking for it, we could not find any.

And then they said that they probably got lost.

The documents that do exist show that the day after the tail strike,

- China Airlines did a temporary repair. -

Workers attached a large aluminum plate over the damaged area.

What do we know about the permanent repair?

Doesn't get much better.

A more permanent repair was to be carried out within four months.

This is what we've got.

The maintenance records indicated

that the permanent repair was done

in accordance with Boeing recommendations

in their Structural Repair Manual.

Evidence that we uncovered indicate that the repair was not done

per the Boeing repair manual.

According to the manual,

many of the scratches on the plane were too deep to be repaired.

The entire damaged section should have been cut out and replaced.

You have to follow certain procedures,

and that the Boeing Structural Repair Manual

indicating very clearly what you should do step by step.

22 years later,

investigators can tell that, for some reason,

the damaged piece was not replaced.

The scratches from the tail strike are still there.

China Airlines engineers tell investigators

that the scratched area was too large to cut out,

so they sanded the scratches down instead.

In the event of scratching,

it depends on how deep the scratches are.

If they're not very deep, they can be blended out.

But if the scratches are too deep,

the repair technique that's called for

is to actually cut out all of the scratched material

and then design a doubler patch that's larger, by a big percentage,

of the structure that was originally removed.

The scratches weren't sanded down, or cut out.

They're still there.

Maintenance workers then made one final mistake.

They put the doubler plate right over the scratched material.

The doubler plate that they put on

was not 30 percent larger than the affected area.

In fact, it was barely, maybe not even in certain locations,

larger than the area that was scratched.

Even though the repair wasn't done

according to Boeing's instructions,

the way it was logged made it seem like it was.

So, for 22 years, anyone reading that entry would assume the damaged area

had been cut out, as it should have been.

Pieces were really starting to fall into place now.

Once we saw this piece of structure

- that had the fatigue cracks in it... -

...and we realized that it came from a structural repair that was not done properly...

...that was left to fly for 20 years...

Airborne, passing 1,600.

...things began to make sense.

By covering an improper repair with a doubler,

and then documenting the repair as meeting Boeing standards,

the workers made their mistake impossible to detect.

What was so insidious about this improper repair

was that the doubler plate hid all of the damage.

So, if you weren't there, watching them do this repair improperly,

you wouldn't know that it was done improperly.

You would have assumed that the structure underneath

had been cut out the way it was supposed to.

And every time the plane took off over the next 20 years,

the concealed problem got worse and worse.

The air inside a commercial airplane is pressurized.

As the plane climbs, air is forced into the cabin

to keep the pressure inside the plane greater than the pressure outside.

It's like inflating a tire. The inside air pushes against the plane's skin.

Each time the airplane pressure rises,

pressure builds up inside the fuselage of the airplane.

That crack could open up

for a certain amount of inches or microns or millimeters.

The plane's skin expanded and contracted a little bit every time.

Because they weren't properly repaired, the cracks grew and spread.

Eventually, the crack grew into a stunning 2.3 meters.

If you were charting the crack, you would have seen very slow growth early.

But as time went on, the growth was getting bigger and bigger.

A small scratch had grown into an enormous problem.

Then, in May, 2002, as Flight 611 climbed,

that problem killed 225 people.

As the airplane climbed in altitude, and the fuselage was pressured,

that put enough strain on this growing crack

that it reached its critical length.

And, from there, it just spread like a spider web.

It went in all directions, and it probably looped all the way around the fuselage

to the point where the entire aft section of the airplane

just broke off from the rest of the structure.

The plane went into a steep dive.

The force of the air on what was left of the plane quickly ripped it to pieces.

Investigators know that an unseen crack caused Flight 611 to break apart.

They now discover that China Airlines came heartbreakingly close

to finding that crack and saving 225 lives.

The China Airlines 747, was in regular service for 22 years

following the improper repair to its skin.

It took off and landed more than 20,000 times.

Over the years, mechanics would have scrutinized the plane.

There's regular inspections per the Boeing maintenance program

that have to be performed on the airplane.

But the massive crack forming at the rear of the plane was never detected.

Another accident in another country

almost led China Airlines to discover the hidden damage.

In 1988, the roof peeled off an aging Boeing 737 owned by Aloha Airlines.

As a result of that incident,

the Federal Aviation Administration

laid out an inspection procedure for older planes.

Airlines around the world were forced to inspect their planes

much more diligently for corrosion and cracks.

The regulation called for airlines

to re-evaluate all existing repairs to a plane's structure.

Indications on this airplane were that if they had looked

at the maintenance records and compared it to the repair,

they would have had to remove the repair and redo it.

China Airlines took the first steps

of the new procedure in 2001, a year before the accident.

The airline identified and photographed

thirty-one different doublers on the 747,

including the one over the catastrophic crack.

Those pictures show investigators

that China Airlines overlooked a vital clue

that could have warned them of the looming danger.

We examined the photographs that China Airlines took of the repair

and noticed that there was some issues

that may have warranted further investigation.

Investigators see a dark brown stain on the outside of the plane.

It's the same mysterious staining

that led Frank Zakar to suspect there was a hole behind the doubler

when he first saw it on the pier.

So why hadn't this stain raised alarms before the crash?

For years, passengers on China Airlines' doomed 747 were allowed to smoke.

They filled the pressurized air with nicotine.

The smoke was being forced out through the crack at the rear of the plane.

Over time, that smoke left a nicotine stain on the outside of the plane.

It was very vivid.

Any experienced maintenance engineer

would be able to spot it right immediately.

Smoking hadn't been allowed on China Airlines

for seven years before the crash.

It tells investigators that the crack in the plane

had been there for at least that long.

But instead of investigating the source of the staining...

We need to conduct the new inspection when we do our next major check.

...China Airlines scheduled the second part of the FAA's procedure,

a detailed inspection of the repaired areas.

And that would be the 7-C check,

currently scheduled for November the 2nd, 2002.

But the 747 never made it to November 2nd, 2002.

It came apart over the Taiwan Strait

five months before the inspection

that would have, undoubtedly, uncovered its hidden flaw.

Investigators want to prevent a similar accident from ever happening again.

They recommend that aviation agencies around the world

immediately inspect repairs for any possible hidden damage.

We were no longer gonna accept just a quick write-up

that the repair was done properly.

If the repair didn't have all the necessary documentation

to allow us to know it was done properly,

we were requiring operators to take doubler plates off

and do a visual inspection of the structure underneath.

The National Transportation Safety Board

issues its own recommendations.

The board asks that maintenance personnel

be warned of the consequences of hiding the kind of damage

that could lead to the structural failure of an airplane.

The moral of this story is that the repair has to be done properly.

As a mechanic, when you're doing work on an airplane,

you're not thinking about the people

who might be flying on that fuselage 20 years from now.

But their safety depends on you doing the repair properly.

China Airlines has revised the way its fleet is inspected and maintained.

Its safety record has improved dramatically since the crash of Flight 611.

Investigators also proposed the development of new tools

that would allow mechanics to detect damage behind a doubler.

Such tools are being used today.

Boeing developed a non-destructive procedure

that can find cracks in the fuselage underneath a doubler.

That device uses ultrasound, sound waves that travel through metal.

It can reveal damage underneath a doubler.

It's the same technology that allows doctors to observe a fetus

while it's still inside the womb.

The device would have been able to detect

the crack behind Flight 611's doubler plate.

But the technology has some limitations.

A great number of hours are required just to do

one specific area of the airplane.

But the technology is getting better.

The problems that led to the China Airlines disaster are not going away.

Planes the world over are getting older.

And older planes need to be more thoroughly inspected for cracks.

Six years after the China Airlines crash,

Southwest Airlines in the United States was hit with a record-breaking fine.

$10.2 million for missing inspections designed to find cracks.

The fining of Southwest brings back into focus

how important it is to do maintenance properly on an airplane.

A proper program of maintenance and inspections can be costly.

But, as China Airlines showed,

the price of not maintaining aging planes is even costlier.