Mayday (2013) s16e04 Episode Script
Deadly Detail
What is going on out there? Everyone, we're about to evacuate the plane.
Remain calm.
I certainly knew that with both engines on fire, it was not gonna go well.
157 passengers rush to escape a burning 737.
Let's go! Let's go! It goes up like a bomb.
In the struggle to explain the inferno, the smallest parts come under intense scrutiny.
The analysis leads to a stunning discovery.
Where is it? It was a true breakthrough in the investigation.
The failure that doomed China Airlines Flight 120 is putting more lives in danger every day.
We really didn't anticipate that there's a risk and it bit us.
China Airlines Flight 120 is on final approach for landing.
Ladies and gentlemen, we're about to begin our descent into Okinawa Naha Airport.
Please give the flight attendants your full cooperation as they prepare the cabin for landing.
The captain is 47-year-old Yu Chien-Kou.
What's the weather for approach? The ceiling is 8,000 feet.
Winds at eight knots.
The first officer is 26-year-old Tseng Ta-wei.
The pilots have more than 8,500 hours of flight experience between them.
- Almost straight down the pipe.
- Yes, sir.
Landing this Boeing 737 should be routine.
The 737 is probably the most popular airframe in the world.
It's flown by most pilots as they start out in their careers.
It's a short-range domestic airplane.
Flight 120 is a one-hour journey from Taiwan to the southern Japanese island of Okinawa.
This morning, there are 157 passengers and eight crew on board.
Put your tray up and fasten your seatbelt.
Jim Caruso is a medical examiner for the US Navy, stationed in Okinawa.
He and his family are on the last leg of a long trip home from vacation.
The family was returning from Brisbane, Australia.
We had done probably 12 or 14 days on vacation and we were hoping to be home for lunch.
Living in Okinawa has given the Carusos the chance to travel through much of Asia.
We got to see China, Hong Kong, mainland Japan, Korea.
We had made use of our location to experience the area.
Naha Airport sits at the southern end of Okinawa, on the shore of the East China Sea.
The pilots reconfigure their plane as they slow down and descend for landing.
Let's go to flaps 25.
Flaps 25.
They deploy flaps from the wing's back edge, along with slats from the front edge.
These devices keep the plane airborne at lower speeds.
When we start configuring, we begin to put out flaps and slats, which extend the area of the wing and give us more lift and allow us to fly slower.
And, of course, the landing and touchdown itself are the most complicated part of the flight.
They're now less than a minute from the runway.
OK, honey.
You have to remain in your seat.
I think everybody was looking forward to landing, getting off the airplane and getting back to regular life.
30, 20, 10.
It's a textbook landing.
Flaps up.
Once you're landed, you figure you're home free.
The taxi is usually routine.
After landing checklist.
Speed brakes.
All that's left for the China Airlines pilots is to park the plane.
Engine start levers.
Engine start levers, cut off.
With the engines off, they can finally relax.
The pilot is relieved.
He's no longer at risk.
A catastrophic event after you're parked is almost non-existent.
Seatbelts.
Seatbelts off.
The biggest challenge ahead of you from there is making sure you can get through customs.
No-one ever expects anything to go wrong, especially once the engines are turned off.
But one passenger has noticed that something's not right.
My wife was next to a woman who made some sort of exclamation towards the engine on the right side.
(SPEAKING IN FOREIGN LANGUAGE) What's going on? There was some smoke coming from that engine.
That was the first sign that something was out of the ordinary.
What is going on out there? Anti-ice, off.
- Start switches, off.
The pilots are finishing the shutdown - checklist.
Transponder TCAS.
Hey! What is this? What's happening? Just when they thought they were safely parked Cockpit, ground.
Number two engine fire.
.
.
a radio call alerts them to an urgent danger.
Their plane is on fire.
Attention, crew on station.
Attention, crew on station.
Bringing the flight attendants to their station tells them that what might likely be next, would be an emergency evacuation.
Dynasty 120, we are calling a fire truck.
Remain stand-by.
Uh, we have a wheel fire, please.
(SPEAKING IN FOREIGN LANGUAGE) Cabin crew, prepare for evacuation.
Prepare for evacuation.
Everyone, remain calm.
We're about to evacuate the plane.
Remain calm.
Fear begins to spread throughout the cabin.
Outside, the fire is getting worse.
The engine on my side also started smoking and flaming.
So, now, we had both wings on fire.
And at that point, people began to panic.
Remain calm! No pushing! I had no idea, at that point, how things would play out.
But I certainly knew that with both engines on fire, it was not gonna go well.
Parking brakes.
Speed brakes.
It's that lever.
The pilots know they need to get their passengers off the plane before flames reach the fuel tanks.
But they can't open the cabin doors yet.
Engine fire warning switches.
Override.
They must follow an evacuation checklist.
We want the pilots to grab the list, simply read it and do it.
No wondering what step is next, because the sequence of the steps are very important.
Pull and rotate.
Everybody, remain calm.
Do not bring your luggage or personal belongings.
Seconds feel like hours as the crisis escalates.
Finally, the pilots are ready to open the doors.
Evacuation required now.
Required.
No pushing.
No pushing.
Please keep moving forward.
But it will take time for all 157 passengers to make it to the exit.
George Ishizaki is watching the unfolding disaster from inside the airport terminal.
I just happened to have my camcorder with me.
I thought, "Oh, my god.
What is happening?" Keep moving forward.
With the fire growing more intense, time is running out.
Let's go! Let's go! We were quite a ways back from any exit, since the over-wing exits were useless.
So my focus was really to get the kids moving forward and off the aircraft.
- (SPEAKING IN FOREIGN LANGUAGE) - Go ahead.
Go ahead, alright? Jim Caruso stays behind to help other passengers get off the burning plane.
I don't actually remember hesitating.
It may have been a little difficult to make that decision, since the kids were already moving forward.
Hey, no pushing.
Keep moving forward.
The smoke actually started building and then that's when everything started happening really quickly.
Jim Caruso is separated from his family.
The heat and smoke are getting worse.
He hears a cry for help.
(SPEAKING IN FOREIGN LANGUAGE) The woman behind me pointed towards the overhead bin.
I was concerned if she was pointing towards flames coming in.
(SPEAKING IN FOREIGN LANGUAGE) I looked up and I saw a pair of crutches.
Everybody was just sliding down the slides and once they got on the ground, they were just scrambling.
Once the smoke and fire started building, the cabin became rather warm.
I do recall some of the windows actually cracking from the heat.
Finally, they make it to the exit.
The plane has been burning for close to three minutes.
It could explode at any moment.
Captain, all passengers are evacuated.
You're the last ones.
We got to get out of here.
Typically, the captain will stay until everybody's off and he will verify that the airplane is empty.
The pilots have put their passengers' safety first.
But now, it may be too late for them.
We're gonna have to climb out through the window.
- You first.
- Yes, sir.
All 737 cockpits are equipped with an emergency escape rope.
It's designed to help pilots exit through the side window.
But it's no easy manoeuvre.
Exiting the airplane is more difficult than it sounds.
It's a relatively small window.
Going down the rope has a risk.
- Then - Whoa! Whoa! Whoa! You felt a huge kaboom.
I've never felt anything like that.
We actually could feel the ground shake.
Passengers run to safety as a fiery explosion engulfs the plane they just escaped.
The fate of the pilots is still unknown.
As I looked back after the first explosion, I recall crew members fast roping, as it were, out of the cockpit.
The force of the blast overpowers the first officer.
He dropped down from the height of the cockpit window, onto the ground.
Incredibly, he's able to get up and away from the flames.
The captain quickly follows.
It was good that he did that, because the fire just gutted the airplane.
More explosions rock the airport.
The fuselage, I guess, melted.
The back half just kind of fell to the ground.
Finally, fire trucks arrive on scene.
Everybody had exited the aircraft at that point and was gathering in the terminal.
It was a huge relief to have the kids and my wife and I together.
We certainly were looking back at the aircraft again, in amazement.
Fire on an airplane can quickly become lethal.
Incredibly, on Flight 120, all 165 people on board have escaped unharmed.
I've never heard of any evacuation where somebody wasn't hurt.
To get this many people off in such a dire circumstance, in a very short period of time with no injuries, is miraculous.
If there's a next time, passengers may not be so lucky.
Pressure to figure out what happened falls on an international team of air crash investigators.
OK, let's get to work! They need to explain how an airliner that had landed safely and turned off its engines, suddenly burst into flames.
We have no clue.
We do not know what happened.
We tried to find out from the wreckage that remained still on the apron.
Normally, fires occur in-flight, perhaps during taxi, sometimes.
But rarely in a parking spot after the engines are shut down.
The challenge for investigators is most of the evidence will be destroyed by the fire.
Across the globe, there are more than 5,000 Boeing 737s in service.
There's a 737 taking off and landing every three or four seconds in the world.
If the plane has a design flaw that somehow leads to uncontainable fire, countless passengers could be at risk.
We were aware that the 737 is probably the most popular airliner out there.
So there's a reason, once an accident occurs, to try to figure out what happened pretty darn quickly.
The search for Flight 120's black boxes begins immediately.
One of our main goals, initially, is to try to find the cockpit voice recorder and the flight data recorder.
These are important because a lot of times, they tell us what happened.
But investigators know that after such an intense fire, there's a chance the black box data will be lost.
They need other leads.
Good investigators don't rely totally on flight data recorders, for instance, or cockpit voice recorders, because they can be destroyed.
So we rely on witnesses to tell us their impression of what happened.
Well, we taxied off the runway, down the apron, to our assigned parking spot.
Once we parked, we shut off the engines and some time after that, we heard the aircraft was on fire.
We needed to know what type of fire it was, what the ignition source would be, what the fuel source would be.
Those were the areas of our main questioning, right off the bat.
I radioed the controller, letting him know we had a wheel fire.
Investigators know that if a wheel caught fire on Flight 120, there's more than one possible cause.
A deflated tire can result in burning rubber.
Overheated brake pads could potentially ignite hydraulic fluid.
In a wheel well of an aircraft, there are a lot of hydraulic lines going to the landing gear assemblies and things like that.
Hydraulic fluid is very flammable.
If a hydraulic leak occurred and it happened to drip onto a hot brake, for instance, well, there you go.
- Hey, what is this? - We have a wheel fire.
If the pilots are right about where the fire started, investigators should be able to find proof.
They examine the plane's right side wheel well and landing gear assembly.
They find scorched wreckage, but not enough to convince them that this is where the fire began.
Once we were able to closely examine that part of the aircraft, we were very confident that a wheel well fire, per se, did not occur.
The seat of the fire seemed to be forward and a little bit to the right of the wheel well area.
It seems the pilots were mistaken about the origins of the fire.
Where it started remains a mystery.
Solving that mystery may have just become easier.
Investigators have recovered the plane's black boxes.
The Japanese team, they retrieved both the CVR and FDR.
Let's get working on the FDR immediately.
On modern 737s, the flight data recorder has thousands of parameters, data bits that come in to the recording device itself.
It will take time to download and verify all the data.
Meanwhile, the charred fire scene continues to challenge investigators.
With all this heat damage, it's nearly impossible to tell where the fire started.
They're almost certain the fire began on the right side of the plane, as witnesses reported - but where exactly? Wait a sec.
Scorched wires provide a promising new lead.
What do you think? Did an electrical fire destroy Flight 120? Serious electrical failures are rare, but not unheard of.
In 1998, the cockpit of Swissair Flight 111 began filling with smoke shortly after take-off.
The pilots tried to make an emergency landing in Halifax, Canada.
They never made it.
Their plane disappeared into the Atlantic Ocean, killing all 229 people on board.
Investigators found that an electrical fault in the entertainment system almost certainly sparked the fire that doomed the plane.
OK, let's see what we got.
If the fire aboard Flight 120 was caused by faulty wiring, investigators may now be able to confirm it.
They've successfully downloaded the black box data.
Any electrical problem or failure in any on-board system should show up in the data.
Almost every system on the aircraft is recorded.
Its status is recorded.
So we looked very quickly through these hundreds of electrical possibilities and we found nothing.
It wasn't electrical.
The analysis comes up empty.
At that time, we can rule out some wheel fire or some other electrical fire.
Investigators turn their attention to the aircraft's right engine.
In flight, the CFM56 power plant generates internal temperatures of more than 2,000 degrees Fahrenheit - hotter than molten lava.
Could an engine fire have sparked the inferno? We, of course, looked at the engines very carefully.
The right engine especially, because there was a lot of fire damage around it.
It was fairly easy to look inside the engine and examine the core, so to speak, where all the damage in an engine failure usually occurs.
And we found nothing wrong.
The engine was damaged externally, but not internally.
So we eliminated it as a possible factor.
What could have burned this entire plane down? The investigation has hit a wall.
The cause of the catastrophic fire remains unknown while every day, thousands of 737s continue to fly.
There's growing pressure on investigators to find the answer.
We knew we had a little bit of detective work ahead of us and we pressed on.
The video capturing the fiery destruction of China Airlines Flight 120 could provide investigators with clues to what started the fire.
Whoa.
The footage reveals just how quickly the flames spread through the passenger jet.
But for investigators, the most important clue is missing.
The recording hasn't captured the critical moment the fire started.
From the video, we can only understand there was fire and the location of the fire and that it seems that something fed in to the fire.
But we cannot understand why.
Investigators widen the search for leads.
What did you see? The effort pays off when an airport ground worker provides a critical detail.
A ramp worker on the right side of the aircraft said, very distinctly, that he saw a liquid running down the leading edge of the right wing before fire broke out.
Thanks.
Fluid leaking from this part of the wing of the aircraft can be only one thing - jet fuel.
The 737 holds 4,390 gallons of fuel, much of it in tanks located inside the plane's two massive wings.
When we figured out that an actual fuel leak had occurred, it was a breakthrough, a true breakthrough in the investigation.
We now needed to know why it originated.
We know the fuel was leaking, but from where? A fuel line? Finding solid evidence amongst the burnt remains of the plane's fuel system won't be easy.
The Boeing 737-800 has high-pressure pumps inside the wing.
They deliver 200 gallons of fuel per hour to the engine.
All that fuel flows through flexible pipes.
Could one of those fuel pipes be the culprit? Fuel lines are probably, in a sense, the most vulnerable part of a fuel system.
They take bends and sometimes, they're exposed where they could get knocked or punctured by something.
So we tried to trace the entire fuel system of the aircraft.
It's another dead end.
It wasn't the fuel lines.
None of the fuel lines are ruptured.
We had a lot of fire damage, but the fuel lines that we examined seemed to be intact and functional.
Investigators still can't explain the fire.
They know enough fuel leaked from the plane to feed the flames, but they don't know where it came from.
Once we eliminated fuel lines, per se, as a possible problem, pretty much the only thing out in that area that could have gone wrong is a leak in the fuel tank itself.
The plane's fuel tanks are made from aluminium alloy and designed to withstand the rigors of flight for years.
They should never crack or leak.
Examining them presents one of the most difficult challenges yet.
They hope a tool called a borescope will do the trick.
It's a small camera that can peer into tight spaces.
It gives them a unique view inside the plane's right-wing fuel tank.
What it reveals changes the entire course of this investigation.
Whoa.
Did you look at that? All of a sudden, clear as a bell, we saw this bolt sticking out of the fuel tank itself.
Where the bolt came from is a complete mystery, but it has ruptured the tank right where the ground worker spotted leaking fuel.
It's hard to describe how significant this was.
I mean, this was the core of the investigation.
Now we knew what happened, the rest of the investigation was trying to figure out why this occurred.
A punctured fuel tank was the cause of one of the most infamous air crashes in history.
A supersonic Air France Concorde burst into flames on take-off after running over a piece of metal debris on the runway.
Did a similar scenario lead to the total destruction of China Airlines Flight 120? OK.
We need to cut into this wing.
Investigators need to get a closer look at the mysterious bolt that made a hole in the fuel tank.
The investigator in charge said, "Yep, now's the time to start "cutting into that thing.
" OK, got it.
Now, they need to figure out where the bolt came from.
They study schematics of the 737 wing structure.
We went back to the drawings and went back to things like maintenance records to try to figure out exactly what it was.
They soon get their answer.
A downstop assembly.
The downstop assembly is part of the slat mechanism on the wing's leading edge.
- Let's go to flaps 25.
- Flaps 25.
Pilots extend flaps and slats during every take-off and landing.
The downstop is fixed to the end of a track that slides back and forth.
The device prevents the slats from moving too far forward.
The downstop is there, quite frankly, to stop it when it reaches its maximum deployment length.
If it didn't exist, then there would be no way to retain the slat on the aircraft.
Investigators have identified the piece that penetrated the fuel tank.
They know it's not from another plane, like the runway debris that caused the Concorde disaster.
But they have other important questions that need answers.
We had the assembly.
We knew it punctured the tank.
Our next step was trying to figure out how this could possibly have occurred.
Investigators pour over Boeing service documents to learn more about downstop assemblies on the 737.
They make a surprising discovery.
This has happened before and it's happened more than once.
There'd been two previous instances of this device coming apart and causing minor fuel leaks.
This was the first instance of an actual destructive fire.
In both previous instances, parts from a downstop assembly punctured a fuel tank, just like on Flight 120.
Clearly, they knew it was a problem.
Boeing was so concerned about the problem, it issued a special work order to secure the downstop assembly on all 737s worldwide.
The solution that Boeing had recommended was to remove the nut from this particular device and install some thread-hardening material and then you reinstall the nut.
It hardens in place.
What if the work order on this plane was never completed? Investigators review the Boeing work orders.
If the plane that burned in Okinawa was never fixed, that could explain the accident.
We tried to figure out, when is the last time anybody touched that assembly.
But according to the records, the proper work was carried out very recently.
We discovered that this particular component, this downstop, had been manipulated only a couple of weeks or so prior to the accident.
It just doesn't make sense.
Investigators can see that the nut on the downstop assembly is still attached.
It seems that the work order to replace it was completed just as the records show.
So, what went wrong? That's the weird part that we wanted to figure out at that time.
They examine the downstop assembly from Flight 120.
They check all the component parts.
Finally, they spot something.
We decided to count parts and, lo and behold, a washer was missing.
Where is it? There's supposed to be a washer right behind the nut.
Could a single missing washer have played a role in the accident? It seems unlikely, but investigators can't rule it out.
They need to find the washer.
We thought initially that the washer may have somehow gotten inside the fuel tank, but that's not the case at all.
We examined very carefully, the rest of the wing, and we found that particular washer in the leading edge assembly of the wing, just laying in there, loose.
The washer is a fit.
Recovering the missing washer raises a puzzling question.
The nut was on there and it was torqued down correctly, but there was no washer on it at all.
How did the washer become detached from the bolt, but not the nut? If the nut is still on the bolt, why is there something between that fell off? It seems like an impossibility and yet somehow it happened.
The Flight 120 fire investigation heads to Taiwan and the headquarters of China Airlines.
Investigators hope to shed some light on the mystery of the detached washer.
I appreciate you making the time.
We went to China Airlines to ask them to demonstrate how they do the maintenance work.
Do you think you can show me how you completed this repair on the downstop assembly? Sometimes, maintenance records don't tell you the true story.
They can tell you that according to somebody, a maintenance procedure had been done correctly.
But to get a better story, you have to actually watch the procedure being done.
A mechanic demonstrates how he performs the downstop repair.
You won't be able to see much of what I'm doing.
Performing maintenance on this particular downstop is a little tricky.
The mechanic is gonna be in a very restricted visual area, so he's going to have to work with his hands.
He's gonna have to feel the apparatus.
After applying glue, you put the bolt into place.
You can imagine that you're under the wing and you cannot see it.
Sorry.
I just dropped it.
Don't worry.
It's easy to pick up again.
- It's an eye-opening demonstration.
- And that's how it's done.
Thank you.
You have been very helpful.
It's not very easy for them to confirm they finished their job and everything is in order there.
Records show that the work order repair was the only time mechanics ever serviced the downstop in the history of the accident airplane.
There's only one possible explanation for how the washer found in Okinawa came loose.
It fell off during the maintenance procedure in Taiwan.
It could have just slipped off the gentleman's fingers when he was trying to install it.
It could have stuck to the nut and then fallen off just before he touched them together.
A lot of things could have happened.
The bottom line is, the washer was not there.
But understanding what happened to the washer still leaves investigators scratching their heads.
The downstop assembly had a well-tightened nut that was also glued to the bolt.
How could it fall out? And how did this piece start a raging fuel fire that destroyed a 70 million airplane? Alright, now let's test it without a washer.
Investigators experiment with the suspicious part from Flight 120 to see how it performs without the washer.
The design of this assembly requires each component to play a specific role.
So any piece that is not reinstalled is critical.
They make a stunning discovery.
The small washer is the only thing preventing the unit from falling out of its mount.
Without the washer, it fails.
We discovered that the nut and the bolt were smaller than the rest of the assembly and that the washer was a required item.
This is an example of an intact downstop assembly.
You take the nut off, you take the washer off, put the nut back on, like they did in Taiwan, and now, you'll note that the assembly itself is pretty ineffective.
It falls apart without much problem at all.
Finally, it's clear why the downstop assembly was able to fall out of the slat track.
How it punctured the fuel tank is the final piece of the puzzle.
But investigators believe the design of the slat mechanism itself may hold the answer.
When the engineers are designing these aircraft, they take into consideration maximum space utilisation.
And for the design of a leading-edge slat, they came up with something called a can.
The slat can is the area inside the wing that houses the moving track.
The can is a void that extends into the fuel tank and allows for the device that operates the slat to move in and out.
The space inside the slat can is tight, just big enough for the sliding track.
A foreign metal object taking up any space inside the can would be an accident waiting to happen.
It would render the entire assembly not only non-functional, but dangerous.
China Airlines Flight 120.
157 passengers, eight crew.
Investigators believe they finally understand the sequence of events that led to a devastating fuel fire in Okinawa.
It all begins weeks before the accident with a botched repair to a critical component.
A single missing washer turns a downstop into a hidden danger - a bolt that can work its way loose over time.
Washers really aren't supposed to hold things together.
But this washer did, because of its design.
Six weeks after the failed repair Please give the flight attendants your full cooperation as they prepare the cabin for landing.
.
.
a routine descent into Okinawa requires the pilots to deploy the flaps and slats as usual.
Inside one of the track cans on the right wing, the loosened downstop is just barely holding on.
Touchdown is enough of a jolt to finally knock the downstop out of its track.
Flaps up.
The unsuspecting crew soon retracts the flaps and slats.
The plane's powerful hydraulics move the slat track back into the can.
But now, the downstop bolt is in the way.
The track pushes it to the back of the can and then straight through, puncturing the right-wing fuel tank.
The hole in the fuel tank caused the leak.
The plane would have been carrying thousands of litres of fuel.
As the plane taxis, the engine exhaust is powerful enough to disperse the leaking fuel.
It can't come into contact with the hot tailpipe or brakes.
After landing checklist.
But once the pilots park and shut down the engines, the situation instantly becomes much more dangerous.
- Engine start levers.
- Engine start levers cut off.
The leaking fuel starts dripping directly onto the scorching-hot tailpipe.
What is going on out there? The leaking jet fuel ignites on contact.
The speed of the development of the fire is incredible.
Obviously, fuel burns very well and it goes up like a bomb.
Everybody, remain calm.
The cabin crew's professional conduct gets 157 passengers off the plane in just one minute and 42 seconds.
The Naha Airport fire leads investigators to a striking realisation.
The repair that was ordered actually caused the fire.
It was kind of ironic.
The Taiwanese maintenance procedure was to prevent an accident and, in essence, the procedure had a lot to do with why this particular accident happened.
It's a great study in unintended consequences.
We really were trying to fix a problem.
We really didn't anticipate that every time we handle a maintenance piece like this, there is a risk, and it bit us.
In the wake of the Naha Airport inferno, aviation authorities around the world order the inspection of the entire fleet of 737s.
In the US alone, 21 planes are found to have the same defect, all of them at risk of a catastrophic fuel leak and fire.
Boeing takes immediate action.
It redesigns the downstop mechanism and ensures that the improved part is installed on each and every plane.
Boeing made the changes necessary to ensure that the accident didn't occur again.
It took a little time, as it normally does, to get to the final resolution of it, but they did what they needed to do.
Captioned by Ai-Media ai-media.
tv
Remain calm.
I certainly knew that with both engines on fire, it was not gonna go well.
157 passengers rush to escape a burning 737.
Let's go! Let's go! It goes up like a bomb.
In the struggle to explain the inferno, the smallest parts come under intense scrutiny.
The analysis leads to a stunning discovery.
Where is it? It was a true breakthrough in the investigation.
The failure that doomed China Airlines Flight 120 is putting more lives in danger every day.
We really didn't anticipate that there's a risk and it bit us.
China Airlines Flight 120 is on final approach for landing.
Ladies and gentlemen, we're about to begin our descent into Okinawa Naha Airport.
Please give the flight attendants your full cooperation as they prepare the cabin for landing.
The captain is 47-year-old Yu Chien-Kou.
What's the weather for approach? The ceiling is 8,000 feet.
Winds at eight knots.
The first officer is 26-year-old Tseng Ta-wei.
The pilots have more than 8,500 hours of flight experience between them.
- Almost straight down the pipe.
- Yes, sir.
Landing this Boeing 737 should be routine.
The 737 is probably the most popular airframe in the world.
It's flown by most pilots as they start out in their careers.
It's a short-range domestic airplane.
Flight 120 is a one-hour journey from Taiwan to the southern Japanese island of Okinawa.
This morning, there are 157 passengers and eight crew on board.
Put your tray up and fasten your seatbelt.
Jim Caruso is a medical examiner for the US Navy, stationed in Okinawa.
He and his family are on the last leg of a long trip home from vacation.
The family was returning from Brisbane, Australia.
We had done probably 12 or 14 days on vacation and we were hoping to be home for lunch.
Living in Okinawa has given the Carusos the chance to travel through much of Asia.
We got to see China, Hong Kong, mainland Japan, Korea.
We had made use of our location to experience the area.
Naha Airport sits at the southern end of Okinawa, on the shore of the East China Sea.
The pilots reconfigure their plane as they slow down and descend for landing.
Let's go to flaps 25.
Flaps 25.
They deploy flaps from the wing's back edge, along with slats from the front edge.
These devices keep the plane airborne at lower speeds.
When we start configuring, we begin to put out flaps and slats, which extend the area of the wing and give us more lift and allow us to fly slower.
And, of course, the landing and touchdown itself are the most complicated part of the flight.
They're now less than a minute from the runway.
OK, honey.
You have to remain in your seat.
I think everybody was looking forward to landing, getting off the airplane and getting back to regular life.
30, 20, 10.
It's a textbook landing.
Flaps up.
Once you're landed, you figure you're home free.
The taxi is usually routine.
After landing checklist.
Speed brakes.
All that's left for the China Airlines pilots is to park the plane.
Engine start levers.
Engine start levers, cut off.
With the engines off, they can finally relax.
The pilot is relieved.
He's no longer at risk.
A catastrophic event after you're parked is almost non-existent.
Seatbelts.
Seatbelts off.
The biggest challenge ahead of you from there is making sure you can get through customs.
No-one ever expects anything to go wrong, especially once the engines are turned off.
But one passenger has noticed that something's not right.
My wife was next to a woman who made some sort of exclamation towards the engine on the right side.
(SPEAKING IN FOREIGN LANGUAGE) What's going on? There was some smoke coming from that engine.
That was the first sign that something was out of the ordinary.
What is going on out there? Anti-ice, off.
- Start switches, off.
The pilots are finishing the shutdown - checklist.
Transponder TCAS.
Hey! What is this? What's happening? Just when they thought they were safely parked Cockpit, ground.
Number two engine fire.
.
.
a radio call alerts them to an urgent danger.
Their plane is on fire.
Attention, crew on station.
Attention, crew on station.
Bringing the flight attendants to their station tells them that what might likely be next, would be an emergency evacuation.
Dynasty 120, we are calling a fire truck.
Remain stand-by.
Uh, we have a wheel fire, please.
(SPEAKING IN FOREIGN LANGUAGE) Cabin crew, prepare for evacuation.
Prepare for evacuation.
Everyone, remain calm.
We're about to evacuate the plane.
Remain calm.
Fear begins to spread throughout the cabin.
Outside, the fire is getting worse.
The engine on my side also started smoking and flaming.
So, now, we had both wings on fire.
And at that point, people began to panic.
Remain calm! No pushing! I had no idea, at that point, how things would play out.
But I certainly knew that with both engines on fire, it was not gonna go well.
Parking brakes.
Speed brakes.
It's that lever.
The pilots know they need to get their passengers off the plane before flames reach the fuel tanks.
But they can't open the cabin doors yet.
Engine fire warning switches.
Override.
They must follow an evacuation checklist.
We want the pilots to grab the list, simply read it and do it.
No wondering what step is next, because the sequence of the steps are very important.
Pull and rotate.
Everybody, remain calm.
Do not bring your luggage or personal belongings.
Seconds feel like hours as the crisis escalates.
Finally, the pilots are ready to open the doors.
Evacuation required now.
Required.
No pushing.
No pushing.
Please keep moving forward.
But it will take time for all 157 passengers to make it to the exit.
George Ishizaki is watching the unfolding disaster from inside the airport terminal.
I just happened to have my camcorder with me.
I thought, "Oh, my god.
What is happening?" Keep moving forward.
With the fire growing more intense, time is running out.
Let's go! Let's go! We were quite a ways back from any exit, since the over-wing exits were useless.
So my focus was really to get the kids moving forward and off the aircraft.
- (SPEAKING IN FOREIGN LANGUAGE) - Go ahead.
Go ahead, alright? Jim Caruso stays behind to help other passengers get off the burning plane.
I don't actually remember hesitating.
It may have been a little difficult to make that decision, since the kids were already moving forward.
Hey, no pushing.
Keep moving forward.
The smoke actually started building and then that's when everything started happening really quickly.
Jim Caruso is separated from his family.
The heat and smoke are getting worse.
He hears a cry for help.
(SPEAKING IN FOREIGN LANGUAGE) The woman behind me pointed towards the overhead bin.
I was concerned if she was pointing towards flames coming in.
(SPEAKING IN FOREIGN LANGUAGE) I looked up and I saw a pair of crutches.
Everybody was just sliding down the slides and once they got on the ground, they were just scrambling.
Once the smoke and fire started building, the cabin became rather warm.
I do recall some of the windows actually cracking from the heat.
Finally, they make it to the exit.
The plane has been burning for close to three minutes.
It could explode at any moment.
Captain, all passengers are evacuated.
You're the last ones.
We got to get out of here.
Typically, the captain will stay until everybody's off and he will verify that the airplane is empty.
The pilots have put their passengers' safety first.
But now, it may be too late for them.
We're gonna have to climb out through the window.
- You first.
- Yes, sir.
All 737 cockpits are equipped with an emergency escape rope.
It's designed to help pilots exit through the side window.
But it's no easy manoeuvre.
Exiting the airplane is more difficult than it sounds.
It's a relatively small window.
Going down the rope has a risk.
- Then - Whoa! Whoa! Whoa! You felt a huge kaboom.
I've never felt anything like that.
We actually could feel the ground shake.
Passengers run to safety as a fiery explosion engulfs the plane they just escaped.
The fate of the pilots is still unknown.
As I looked back after the first explosion, I recall crew members fast roping, as it were, out of the cockpit.
The force of the blast overpowers the first officer.
He dropped down from the height of the cockpit window, onto the ground.
Incredibly, he's able to get up and away from the flames.
The captain quickly follows.
It was good that he did that, because the fire just gutted the airplane.
More explosions rock the airport.
The fuselage, I guess, melted.
The back half just kind of fell to the ground.
Finally, fire trucks arrive on scene.
Everybody had exited the aircraft at that point and was gathering in the terminal.
It was a huge relief to have the kids and my wife and I together.
We certainly were looking back at the aircraft again, in amazement.
Fire on an airplane can quickly become lethal.
Incredibly, on Flight 120, all 165 people on board have escaped unharmed.
I've never heard of any evacuation where somebody wasn't hurt.
To get this many people off in such a dire circumstance, in a very short period of time with no injuries, is miraculous.
If there's a next time, passengers may not be so lucky.
Pressure to figure out what happened falls on an international team of air crash investigators.
OK, let's get to work! They need to explain how an airliner that had landed safely and turned off its engines, suddenly burst into flames.
We have no clue.
We do not know what happened.
We tried to find out from the wreckage that remained still on the apron.
Normally, fires occur in-flight, perhaps during taxi, sometimes.
But rarely in a parking spot after the engines are shut down.
The challenge for investigators is most of the evidence will be destroyed by the fire.
Across the globe, there are more than 5,000 Boeing 737s in service.
There's a 737 taking off and landing every three or four seconds in the world.
If the plane has a design flaw that somehow leads to uncontainable fire, countless passengers could be at risk.
We were aware that the 737 is probably the most popular airliner out there.
So there's a reason, once an accident occurs, to try to figure out what happened pretty darn quickly.
The search for Flight 120's black boxes begins immediately.
One of our main goals, initially, is to try to find the cockpit voice recorder and the flight data recorder.
These are important because a lot of times, they tell us what happened.
But investigators know that after such an intense fire, there's a chance the black box data will be lost.
They need other leads.
Good investigators don't rely totally on flight data recorders, for instance, or cockpit voice recorders, because they can be destroyed.
So we rely on witnesses to tell us their impression of what happened.
Well, we taxied off the runway, down the apron, to our assigned parking spot.
Once we parked, we shut off the engines and some time after that, we heard the aircraft was on fire.
We needed to know what type of fire it was, what the ignition source would be, what the fuel source would be.
Those were the areas of our main questioning, right off the bat.
I radioed the controller, letting him know we had a wheel fire.
Investigators know that if a wheel caught fire on Flight 120, there's more than one possible cause.
A deflated tire can result in burning rubber.
Overheated brake pads could potentially ignite hydraulic fluid.
In a wheel well of an aircraft, there are a lot of hydraulic lines going to the landing gear assemblies and things like that.
Hydraulic fluid is very flammable.
If a hydraulic leak occurred and it happened to drip onto a hot brake, for instance, well, there you go.
- Hey, what is this? - We have a wheel fire.
If the pilots are right about where the fire started, investigators should be able to find proof.
They examine the plane's right side wheel well and landing gear assembly.
They find scorched wreckage, but not enough to convince them that this is where the fire began.
Once we were able to closely examine that part of the aircraft, we were very confident that a wheel well fire, per se, did not occur.
The seat of the fire seemed to be forward and a little bit to the right of the wheel well area.
It seems the pilots were mistaken about the origins of the fire.
Where it started remains a mystery.
Solving that mystery may have just become easier.
Investigators have recovered the plane's black boxes.
The Japanese team, they retrieved both the CVR and FDR.
Let's get working on the FDR immediately.
On modern 737s, the flight data recorder has thousands of parameters, data bits that come in to the recording device itself.
It will take time to download and verify all the data.
Meanwhile, the charred fire scene continues to challenge investigators.
With all this heat damage, it's nearly impossible to tell where the fire started.
They're almost certain the fire began on the right side of the plane, as witnesses reported - but where exactly? Wait a sec.
Scorched wires provide a promising new lead.
What do you think? Did an electrical fire destroy Flight 120? Serious electrical failures are rare, but not unheard of.
In 1998, the cockpit of Swissair Flight 111 began filling with smoke shortly after take-off.
The pilots tried to make an emergency landing in Halifax, Canada.
They never made it.
Their plane disappeared into the Atlantic Ocean, killing all 229 people on board.
Investigators found that an electrical fault in the entertainment system almost certainly sparked the fire that doomed the plane.
OK, let's see what we got.
If the fire aboard Flight 120 was caused by faulty wiring, investigators may now be able to confirm it.
They've successfully downloaded the black box data.
Any electrical problem or failure in any on-board system should show up in the data.
Almost every system on the aircraft is recorded.
Its status is recorded.
So we looked very quickly through these hundreds of electrical possibilities and we found nothing.
It wasn't electrical.
The analysis comes up empty.
At that time, we can rule out some wheel fire or some other electrical fire.
Investigators turn their attention to the aircraft's right engine.
In flight, the CFM56 power plant generates internal temperatures of more than 2,000 degrees Fahrenheit - hotter than molten lava.
Could an engine fire have sparked the inferno? We, of course, looked at the engines very carefully.
The right engine especially, because there was a lot of fire damage around it.
It was fairly easy to look inside the engine and examine the core, so to speak, where all the damage in an engine failure usually occurs.
And we found nothing wrong.
The engine was damaged externally, but not internally.
So we eliminated it as a possible factor.
What could have burned this entire plane down? The investigation has hit a wall.
The cause of the catastrophic fire remains unknown while every day, thousands of 737s continue to fly.
There's growing pressure on investigators to find the answer.
We knew we had a little bit of detective work ahead of us and we pressed on.
The video capturing the fiery destruction of China Airlines Flight 120 could provide investigators with clues to what started the fire.
Whoa.
The footage reveals just how quickly the flames spread through the passenger jet.
But for investigators, the most important clue is missing.
The recording hasn't captured the critical moment the fire started.
From the video, we can only understand there was fire and the location of the fire and that it seems that something fed in to the fire.
But we cannot understand why.
Investigators widen the search for leads.
What did you see? The effort pays off when an airport ground worker provides a critical detail.
A ramp worker on the right side of the aircraft said, very distinctly, that he saw a liquid running down the leading edge of the right wing before fire broke out.
Thanks.
Fluid leaking from this part of the wing of the aircraft can be only one thing - jet fuel.
The 737 holds 4,390 gallons of fuel, much of it in tanks located inside the plane's two massive wings.
When we figured out that an actual fuel leak had occurred, it was a breakthrough, a true breakthrough in the investigation.
We now needed to know why it originated.
We know the fuel was leaking, but from where? A fuel line? Finding solid evidence amongst the burnt remains of the plane's fuel system won't be easy.
The Boeing 737-800 has high-pressure pumps inside the wing.
They deliver 200 gallons of fuel per hour to the engine.
All that fuel flows through flexible pipes.
Could one of those fuel pipes be the culprit? Fuel lines are probably, in a sense, the most vulnerable part of a fuel system.
They take bends and sometimes, they're exposed where they could get knocked or punctured by something.
So we tried to trace the entire fuel system of the aircraft.
It's another dead end.
It wasn't the fuel lines.
None of the fuel lines are ruptured.
We had a lot of fire damage, but the fuel lines that we examined seemed to be intact and functional.
Investigators still can't explain the fire.
They know enough fuel leaked from the plane to feed the flames, but they don't know where it came from.
Once we eliminated fuel lines, per se, as a possible problem, pretty much the only thing out in that area that could have gone wrong is a leak in the fuel tank itself.
The plane's fuel tanks are made from aluminium alloy and designed to withstand the rigors of flight for years.
They should never crack or leak.
Examining them presents one of the most difficult challenges yet.
They hope a tool called a borescope will do the trick.
It's a small camera that can peer into tight spaces.
It gives them a unique view inside the plane's right-wing fuel tank.
What it reveals changes the entire course of this investigation.
Whoa.
Did you look at that? All of a sudden, clear as a bell, we saw this bolt sticking out of the fuel tank itself.
Where the bolt came from is a complete mystery, but it has ruptured the tank right where the ground worker spotted leaking fuel.
It's hard to describe how significant this was.
I mean, this was the core of the investigation.
Now we knew what happened, the rest of the investigation was trying to figure out why this occurred.
A punctured fuel tank was the cause of one of the most infamous air crashes in history.
A supersonic Air France Concorde burst into flames on take-off after running over a piece of metal debris on the runway.
Did a similar scenario lead to the total destruction of China Airlines Flight 120? OK.
We need to cut into this wing.
Investigators need to get a closer look at the mysterious bolt that made a hole in the fuel tank.
The investigator in charge said, "Yep, now's the time to start "cutting into that thing.
" OK, got it.
Now, they need to figure out where the bolt came from.
They study schematics of the 737 wing structure.
We went back to the drawings and went back to things like maintenance records to try to figure out exactly what it was.
They soon get their answer.
A downstop assembly.
The downstop assembly is part of the slat mechanism on the wing's leading edge.
- Let's go to flaps 25.
- Flaps 25.
Pilots extend flaps and slats during every take-off and landing.
The downstop is fixed to the end of a track that slides back and forth.
The device prevents the slats from moving too far forward.
The downstop is there, quite frankly, to stop it when it reaches its maximum deployment length.
If it didn't exist, then there would be no way to retain the slat on the aircraft.
Investigators have identified the piece that penetrated the fuel tank.
They know it's not from another plane, like the runway debris that caused the Concorde disaster.
But they have other important questions that need answers.
We had the assembly.
We knew it punctured the tank.
Our next step was trying to figure out how this could possibly have occurred.
Investigators pour over Boeing service documents to learn more about downstop assemblies on the 737.
They make a surprising discovery.
This has happened before and it's happened more than once.
There'd been two previous instances of this device coming apart and causing minor fuel leaks.
This was the first instance of an actual destructive fire.
In both previous instances, parts from a downstop assembly punctured a fuel tank, just like on Flight 120.
Clearly, they knew it was a problem.
Boeing was so concerned about the problem, it issued a special work order to secure the downstop assembly on all 737s worldwide.
The solution that Boeing had recommended was to remove the nut from this particular device and install some thread-hardening material and then you reinstall the nut.
It hardens in place.
What if the work order on this plane was never completed? Investigators review the Boeing work orders.
If the plane that burned in Okinawa was never fixed, that could explain the accident.
We tried to figure out, when is the last time anybody touched that assembly.
But according to the records, the proper work was carried out very recently.
We discovered that this particular component, this downstop, had been manipulated only a couple of weeks or so prior to the accident.
It just doesn't make sense.
Investigators can see that the nut on the downstop assembly is still attached.
It seems that the work order to replace it was completed just as the records show.
So, what went wrong? That's the weird part that we wanted to figure out at that time.
They examine the downstop assembly from Flight 120.
They check all the component parts.
Finally, they spot something.
We decided to count parts and, lo and behold, a washer was missing.
Where is it? There's supposed to be a washer right behind the nut.
Could a single missing washer have played a role in the accident? It seems unlikely, but investigators can't rule it out.
They need to find the washer.
We thought initially that the washer may have somehow gotten inside the fuel tank, but that's not the case at all.
We examined very carefully, the rest of the wing, and we found that particular washer in the leading edge assembly of the wing, just laying in there, loose.
The washer is a fit.
Recovering the missing washer raises a puzzling question.
The nut was on there and it was torqued down correctly, but there was no washer on it at all.
How did the washer become detached from the bolt, but not the nut? If the nut is still on the bolt, why is there something between that fell off? It seems like an impossibility and yet somehow it happened.
The Flight 120 fire investigation heads to Taiwan and the headquarters of China Airlines.
Investigators hope to shed some light on the mystery of the detached washer.
I appreciate you making the time.
We went to China Airlines to ask them to demonstrate how they do the maintenance work.
Do you think you can show me how you completed this repair on the downstop assembly? Sometimes, maintenance records don't tell you the true story.
They can tell you that according to somebody, a maintenance procedure had been done correctly.
But to get a better story, you have to actually watch the procedure being done.
A mechanic demonstrates how he performs the downstop repair.
You won't be able to see much of what I'm doing.
Performing maintenance on this particular downstop is a little tricky.
The mechanic is gonna be in a very restricted visual area, so he's going to have to work with his hands.
He's gonna have to feel the apparatus.
After applying glue, you put the bolt into place.
You can imagine that you're under the wing and you cannot see it.
Sorry.
I just dropped it.
Don't worry.
It's easy to pick up again.
- It's an eye-opening demonstration.
- And that's how it's done.
Thank you.
You have been very helpful.
It's not very easy for them to confirm they finished their job and everything is in order there.
Records show that the work order repair was the only time mechanics ever serviced the downstop in the history of the accident airplane.
There's only one possible explanation for how the washer found in Okinawa came loose.
It fell off during the maintenance procedure in Taiwan.
It could have just slipped off the gentleman's fingers when he was trying to install it.
It could have stuck to the nut and then fallen off just before he touched them together.
A lot of things could have happened.
The bottom line is, the washer was not there.
But understanding what happened to the washer still leaves investigators scratching their heads.
The downstop assembly had a well-tightened nut that was also glued to the bolt.
How could it fall out? And how did this piece start a raging fuel fire that destroyed a 70 million airplane? Alright, now let's test it without a washer.
Investigators experiment with the suspicious part from Flight 120 to see how it performs without the washer.
The design of this assembly requires each component to play a specific role.
So any piece that is not reinstalled is critical.
They make a stunning discovery.
The small washer is the only thing preventing the unit from falling out of its mount.
Without the washer, it fails.
We discovered that the nut and the bolt were smaller than the rest of the assembly and that the washer was a required item.
This is an example of an intact downstop assembly.
You take the nut off, you take the washer off, put the nut back on, like they did in Taiwan, and now, you'll note that the assembly itself is pretty ineffective.
It falls apart without much problem at all.
Finally, it's clear why the downstop assembly was able to fall out of the slat track.
How it punctured the fuel tank is the final piece of the puzzle.
But investigators believe the design of the slat mechanism itself may hold the answer.
When the engineers are designing these aircraft, they take into consideration maximum space utilisation.
And for the design of a leading-edge slat, they came up with something called a can.
The slat can is the area inside the wing that houses the moving track.
The can is a void that extends into the fuel tank and allows for the device that operates the slat to move in and out.
The space inside the slat can is tight, just big enough for the sliding track.
A foreign metal object taking up any space inside the can would be an accident waiting to happen.
It would render the entire assembly not only non-functional, but dangerous.
China Airlines Flight 120.
157 passengers, eight crew.
Investigators believe they finally understand the sequence of events that led to a devastating fuel fire in Okinawa.
It all begins weeks before the accident with a botched repair to a critical component.
A single missing washer turns a downstop into a hidden danger - a bolt that can work its way loose over time.
Washers really aren't supposed to hold things together.
But this washer did, because of its design.
Six weeks after the failed repair Please give the flight attendants your full cooperation as they prepare the cabin for landing.
.
.
a routine descent into Okinawa requires the pilots to deploy the flaps and slats as usual.
Inside one of the track cans on the right wing, the loosened downstop is just barely holding on.
Touchdown is enough of a jolt to finally knock the downstop out of its track.
Flaps up.
The unsuspecting crew soon retracts the flaps and slats.
The plane's powerful hydraulics move the slat track back into the can.
But now, the downstop bolt is in the way.
The track pushes it to the back of the can and then straight through, puncturing the right-wing fuel tank.
The hole in the fuel tank caused the leak.
The plane would have been carrying thousands of litres of fuel.
As the plane taxis, the engine exhaust is powerful enough to disperse the leaking fuel.
It can't come into contact with the hot tailpipe or brakes.
After landing checklist.
But once the pilots park and shut down the engines, the situation instantly becomes much more dangerous.
- Engine start levers.
- Engine start levers cut off.
The leaking fuel starts dripping directly onto the scorching-hot tailpipe.
What is going on out there? The leaking jet fuel ignites on contact.
The speed of the development of the fire is incredible.
Obviously, fuel burns very well and it goes up like a bomb.
Everybody, remain calm.
The cabin crew's professional conduct gets 157 passengers off the plane in just one minute and 42 seconds.
The Naha Airport fire leads investigators to a striking realisation.
The repair that was ordered actually caused the fire.
It was kind of ironic.
The Taiwanese maintenance procedure was to prevent an accident and, in essence, the procedure had a lot to do with why this particular accident happened.
It's a great study in unintended consequences.
We really were trying to fix a problem.
We really didn't anticipate that every time we handle a maintenance piece like this, there is a risk, and it bit us.
In the wake of the Naha Airport inferno, aviation authorities around the world order the inspection of the entire fleet of 737s.
In the US alone, 21 planes are found to have the same defect, all of them at risk of a catastrophic fuel leak and fire.
Boeing takes immediate action.
It redesigns the downstop mechanism and ensures that the improved part is installed on each and every plane.
Boeing made the changes necessary to ensure that the accident didn't occur again.
It took a little time, as it normally does, to get to the final resolution of it, but they did what they needed to do.
Captioned by Ai-Media ai-media.
tv