Original subtitles

DR. LIU (English Dub): The plane was sinking deeper and deeper.

NARRATOR: In the heart of one of Asia's busiest cities,

rescuers rush to pull air crash survivors to safety.

INVESTIGATOR 2: Nothing wrong with this actuator.

NARRATOR: Taiwan's Aviation Safety Council

confronts some urgent questions about TransAsia Flight 235.

PETER: What were the flight crew doing?

Were there engineering issues involved in this event?

How on earth did it end up in this situation?

INVESTIGATOR 1: Take a look at this.

NARRATOR: A video surfaces that makes the disaster in Taipei

notorious worldwide.

PETER: It's quite harrowing because you're seeing the

final moments of a tragic event unfolding before your eyes.

INVESTIGATOR 2: What was happening on that plane?

♪ ♪

NARRATOR: Taipei, capital city of Taiwan.

Near its center, amidst soaring towers, lies Songshan Airport.

The next plane scheduled for departure this morning

is TransAsia Flight 235.

The TransAsia cabin crew is waiting for a

last-minute addition to the passenger list.

FLIGHT ATTENDANT: Welcome aboard. Row 19D midway down, aisle seat.

NARRATOR: Dr. Liu Chau-Hui has made it.

DR. LIU (English Dub): It just so happened that particular flight

had a few open seats.

I was supposed to be on the later flight,

but I decided to get on the earlier one.

DR. LIU: Yeah. Is this me?

ANNOUNCEMENT: Ladies and gentlemen, make sure your seat backs

and tray tables are in their full upright positions.

Ensure your seat belt is securely fastened.

NARRATOR: There are three highly-trained pilots in the cockpit.

The first officer is Liu Tzu-Chung.

He has almost 7,000 hours of flight time.

FO. LIU: Oil pressure.

CAPT. LIAO: Check.

NARRATOR: Captain Liao Chien-Tsung is a former military pilot.

There's also a third pilot who's an observer on today's flight.

FO. LIU: Forty-five starter off.

CAPT. LIAO: Start lights off.

NARRATOR: TransAsia 235 is a commuter flight from Taipei

to the Taiwanese island of Kinmen,

just off the coast of mainland China.

Scheduled flight time is approximately one hour.

FLIGHT ATTENDANT: Would you like a paper?

DR. LIU: Oh, thank you.

NARRATOR: Dr. Liu Chau-Hui is returning home to Kinmen,

where he runs a medical practice.

DR. LIU (English Dub): I usually took TransAsia

because their service was quite good.

When I'd get on the plane, I'd like to grab a paper

and catch up on the day's events.

FLIGHT ATTENDANT: The cabin's ready, sir.

CAPT. LIAO: Okay. Roger, thanks.

FO. LIU: Songshan ground, TransAsia 235 request taxi.

AIR TRAFFIC CONTROLLER: TransAsia 235, runway one-zero,

taxi via whiskey.

FO. LIU: Okay. Whiskey to one-zero.

NARRATOR: The ATR 72-600 is the latest, most advanced version

of the European commuter plane.

Its Pratt & Whitney turboprop engines

are extremely powerful and fuel-efficient.

PETER: It's a very popular aircraft, particularly because

it has attractive operating economics.

It's commonly used in short-haul regional airline operations.

NARRATOR: The pilots' digital displays create

what's known as a glass cockpit.

PETER: When people refer to a glass cockpit aircraft,

they're referring to not only the displays

but what often we're talking about is

an advanced-technology aircraft

with sophisticated automation capabilities.

FO. LIU: The electronic checklists switch automatically.

Once you complete certain parts it'll switch forward.

NARRATOR: The first officer briefs his colleague

on the cockpit's technology.

Hung Ping-Chung is an experienced pilot

who's learning this computerized system.

SO. HUNG: Can you do it manually?

FO. LIU: Well, you can, but when starting the engine,

for example, it'll go to the next page

once you close the bleed valves.

♪ ♪

NARRATOR: Songshan Airport sees six million passengers a year.

For air traffic controllers, that means

handling about 100 flights a day.

AIR TRAFFIC CONTROLLER: TransAsia 235, runway one-zero,

wind one-zero-zero degree niner knots, cleared for takeoff.

FO. LIU: Okay. Cleared for takeoff.

Cabin crew, prepare for takeoff.

DR. LIU: Have a great flight.

FLIGHT ATTENDANT: Thank you. Enjoy your flight.

NARRATOR: Just before 11 in the morning, Flight 235 gets rolling.

FO. LIU: Engine instrument check normal.

CAPT. LIAO: V-1. FO. LIU: V-1.

CAPT. LIAO: Rotate.

♪ ♪

NARRATOR: The captain engages the autopilot

and sets his desired airspeed and altitude.

PETER: As soon as the aircraft has taken off,

they're going through a series of checklist items.

CAPT. LIAO: Gear up.

FO. LIU: Gear up.

PETER: I know they've got a particular climb profile,

and they're executing the after takeoff checks

and the initial climb checks to make sure

that all the systems are performing as required.

NARRATOR: Flight 235 climbs out over Metropolitan Taipei,

a densely packed city of more than seven million people.

Seconds later... the Master Warning sounds.

PETER: The Master Warning is indicative of

an emergency situation requiring an immediate response.

NARRATOR: TransAsia 235 has lost an engine.

The captain disengages the autopilot.

CAPT. LIAO: I have control. FO. LIU: You have control.

NARRATOR: In the cabin, engine noise suddenly drops.

The pilots need to get their plane back on the ground.

CAPT. LIAO: Heading mode.

NARRATOR: The captain wants a heading back to the airport.

FO. LIU: We're below 2500 feet. Turn to heading... it's...

CAPT. LIAO: Come on.

FO. LIU: Zero, zero-niner-five.

CAPT. LIAO: Check.

PETER: When you lose an engine in a twin-engine aircraft,

you need to be able to maintain your climb performance

and you need to be very careful that your airspeed

does not decay or reduce too much during that climb.

FO. LIU: Okay, engine flameout check.

CAPT. LIAO: Check.

NARRATOR: Speed and climb-rate are dropping fast.

FO. LIU: Watch the speed.

AUTOMATION: Stall. Stall.

NARRATOR: The stall warning means the plane is flying

too slowly to maintain lift.

PETER: The stall warning at low altitude is

a critical situation that no pilot ever wants to end up in.

NARRATOR: Flight 235 is less than a mile from the runway.

♪ ♪

NARRATOR: Passengers can now see that they're no longer climbing.

CAPT. LIAO: Terrain ahead.

SO. HUNG: You are low!

PETER: The stick shaker is a tactile alerting system

where the control column shakes or vibrates very noticeably.

It's a very salient cue to pilots

to indicate that you must intervene

to prevent the aircraft from entering a stall.

♪ ♪

NARRATOR: The situation is critical.

PETER: It's a highly stressful event.

FO. LIU: Tower, TransAsia 2-3-5, Mayday. Mayday.

Engine flameout.

NARRATOR: Songshan controllers fear the worst,

a crash in the middle of the city.

♪ ♪

FO. LIU: Engine flameout both sides.

SO. HUNG: How is this possible?

♪ ♪

NARRATOR: Flight 235 is now only 500 feet

above the streets of Taipei.

PETER: The crew were surrounded by high-density housing,

highrise apartment blocks, a heavily populated area.

You're really between a rock and hard place.

SO. HUNG: Impact! Brace for impact!

CAPT. LIAO: Oh no! Pull up!

AUTOMATION: Terrain. Terrain. CAPT. LIAO: Oh no!

♪ ♪

NARRATOR: All controllers can see is that Flight 235

has dropped off the radar.

They have no idea if anyone has survived.

AIR TRAFFIC CONTROLLER: Suspend all takeoff and landing operations.

Begin emergency procedures.

NARRATOR: After hitting an elevated highway in downtown Taipei,

TransAsia Flight 235 is sinking in the Keelung River.

DR. LIU (English Dub): I could feel something was off.

I thought to myself: Why is there water where my shoes are?

♪ ♪

NARRATOR: Those lucky enough to survive the crash

are now at risk of drowning.

DR. LIU (English Dub): I remember very clearly, I saw a woman who

I thought was an air hostess. I told her not to be afraid.

DR. LIU: It will be okay.

NARRATOR: The water level starts to rise.

DR. LIU (English Dub): The plane was sinking deeper and deeper.

The temperature was very cold. I couldn't hear anything.

The water had drowned out all sounds.

NARRATOR: Then, passengers are relieved to hear

a welcome sound.

Rescuers are on the way.

First responders climb onto the fuselage

and start pulling people from the wreckage.

DR. LIU (English Dub): I just wanted the doors to open quickly

so that I could escape.

NARRATOR: The swift current of the Keelung River means

that shocked survivors won't be safe

until rescuers can get them to the riverbank.

The city of Taipei has never seen

an aviation accident like it.

Of the 58 people on Flight 235, only 15 make it out alive.

All three pilots are dead.

♪ ♪

Investigators from Taiwan's Aviation Safety Council

are anxious to start collecting evidence at the scene.

STEVEN (English Dub): The most important thing for us

is to retrieve the black boxes.

However, we have to wait for the search and rescue to finish

before we can go in.

NARRATOR: For now, they have to be patient.

But a stunning piece of evidence has already surfaced.

INVESTIGATOR 1: Take a look at this. It just came in.

INVESTIGATOR 2: Can you put it up here for me?

What?

What was happening on that plane? Play it again.

PETER: It was quite extraordinary that the final

sequence of events was captured by

the dash cam footage in the motor vehicle.

It's quite harrowing because you're seeing the final moments

of a tragic event unfolding before your eyes.

INVESTIGATOR 2: Freeze it. Freeze it.

STEVEN (English Dub): We were obviously really shocked,

wondering why the plane was flying in this way.

INVESTIGATOR 1: What do you think? Left engine? Control surfaces?

THOMAS: When you watch the video clip,

you know there's something wrong about the engine.

The prop seems very slow.

INVESTIGATOR 2: You can see the propeller blades.

They couldn't have been going at full speed.

THOMAS: I thought either the aircraft lost one engine

or either the flap or the aileron jammed during takeoff.

INVESTIGATOR 2: We need to study that wreckage.

♪ ♪

NARRATOR: Salvage crews pull what remains of Flight 235

from the Keelung River.

THOMAS: We recovered everything.

I think we finished the wreckage recovery

around noon-time the second day.

NARRATOR: There's no telling which piece of wreckage

might hold an important clue.

Investigators wonder if the flight control system

shows any sign of a malfunction.

THOMAS: So we have to examine that part of the wreckage.

INVESTIGATOR 2: Nothing wrong with this actuator.

THOMAS: We cannot find anything wrong with the actuator,

the linkage of the control.

We cannot find any abnormal situation

for the flight control system.

INVESTIGATOR 1: Control system seems fine.

NARRATOR: A search for any pre-impact failures

in the plane's hydraulic system also comes up empty.

INVESTIGATOR 2: Nothing wrong with the hydraulics.

Is this the left engine?

INVESTIGATOR 1: Yes.

NARRATOR: Investigators know from the dash cam video

that the plane was banked steeply to the left.

A mechanical fault with the left engine

seems like the next most obvious suspect.

INVESTIGATOR 2: We need to take a look inside. Get the borescope.

STEVEN (English Dub): From a borescope examination,

we can see whether or not the compressor and turbine

are damaged on the inside.

Since the turbine rotates with extremely high speed,

if it is even slightly damaged

it will be completely destroyed.

NARRATOR: But the borescope examination yields no new clues.

STEVEN (English Dub): The examination showed that

everything was in place, and all the moving parts

were still capable of moving.

INVESTIGATOR 2: Left engine completely operational. Ah. Strange.

NARRATOR: They need to explore other possibilities.

INVESTIGATOR 2: What about the right engine?

Let's go take a look.

NARRATOR: They study the right engine,

and what they find is mystifying.

INVESTIGATOR 2: Look at the blades. They're feathered.

NARRATOR: Feathered is a propeller's failsafe position.

When a propeller engine loses power in flight,

the blades automatically rotate parallel to the air stream

to reduce drag.

PETER: What an auto-feather does,

it changes the pitch of the blades

to reduce the drag on the blades

to make sure that the airplane's flying performance

is not degraded.

NARRATOR: The discovery only deepens the mystery.

INVESTIGATOR 2: Why would the right engine be feathered

when the dash cam video clearly shows the plane

banking to the left?

INVESTIGATOR 1: It doesn't make any sense.

INVESTIGATOR 2: Let's have a look.

THOMAS: When we discovered a feather of the propeller, we

know there should be something wrong about the engine.

INVESTIGATOR 2: Anything?

INVESTIGATOR 1: Nothing at all.

STEVEN (English Dub): Both engines yielded normal results after examination.

They were both fine.

INVESTIGATOR 1: There's nothing wrong with this engine either.

INVESTIGATOR 2: If both engines were operational,

why did this plane crash?

NARRATOR: Investigators now have two related questions to answer.

What caused the right engine's propeller to feather?

CAPT. LIAO: Terrain ahead!

NARRATOR: And why did the plane bank violently to the left

just before impact?

NARRATOR: At a Songshan Airport hangar, Taiwanese investigators

still have no explanation

for the crash of TransAsia Flight 235.

Video of the turboprop's fatal plunge into the Keelung River

has spread worldwide.

But clues to what caused the crash are in short supply.

INVESTIGATOR 1: Hello? Okay. Thank you. Sir, the FDR data's in.

INVESTIGATOR 2: All right. Let's have a look.

NARRATOR: Investigators hope the plane's flight data recorder

can tell them more.

♪ ♪

The FDR records dozens of performance parameters,

including fuel flow, engine temperature and propeller speed.

FO. LIU: Okay, engine flameout check.

CAPT. LIAO: Check.

NARRATOR: Investigators already know that

the right side propeller feathered before impact.

FO. LIU: Watch the speed.

♪ ♪

INVESTIGATOR 2: Let's see the operating systems of engine two.

NARRATOR: Perhaps the flight data can tell them why.

THOMAS: When we go through the data, for engine number two

we find some parameters were normal like oil pressure,

engine temperature, fuel flow.

INVESTIGATOR 2: The engine's completely fine.

NARRATOR: But one other piece of data

seems to tell a different story.

INVESTIGATOR 2: Take a look at this.

The torque is all over the place.

THOMAS: One parameter, the torque value, fluctuated.

NARRATOR: Torque is a measure of an engine's power

to spin the propeller.

It increases and decreases during flight,

but it's not supposed to fluctuate.

INVESTIGATOR 2: Why is it doing that? Pass me the schematic.

NARRATOR: They dig deeper, studying how

the Pratt & Whitney engine measures torque.

THOMAS: So we tried to find out the design logic

for the system.

INVESTIGATOR 2: What's the connection between the torque

and the feathered propellers?

NARRATOR: They learn that the engine's auto-feathering system

includes an electronic torque sensor.

It measures how much twisting force the engine is producing.

Extremely low torque indicates that the engine has failed.

So a low reading triggers the system to feather the propeller.

But they know the engine did not fail.

There seems to be only one way

to explain the unusual torque data.

INVESTIGATOR 2: Maybe the sensor is sending a faulty reading,

triggering the auto-feathering unit.

NARRATOR: They suspect the problem was not

with the engine itself but with the sensor measuring torque.

THOMAS: We figured out that that probably will be

the signal problem between the torque sensor and the receiver.

INVESTIGATOR 2: Send the sensor to the lab so we can analyze it.

NARRATOR: If they're right about the torque sensor failing,

then they'll finally have solved

the mystery of the feathered propeller.

But investigators are no closer to understanding

another mysterious aspect of this crash.

Why did a two-engine plane

with a feathered propeller on the right side

end up banking to the left?

Searching for an answer, they return to the flight data.

INVESTIGATOR 2: What do the parameters of the left engine say?

Can you show me the fuel flow, please?

INVESTIGATOR 1: That all seems fine.

INVESTIGATOR 2: The propeller speed.

NARRATOR: According to the data, the left engine

was in perfect working order.

STEVEN (English Dub): Engine number one's performance was always good.

All its statistics were normal.

INVESTIGATOR 2: The power lever angle.

NARRATOR: But when they check the throttle settings,

they make a stunning discovery.

INVESTIGATOR 2: Unbelievable.

THOMAS: When we go through the FDR data, we find that the

power of the number one engine was gradually being reduced,

reduced and eventually being shut off.

INVESTIGATOR 2: The left engine was manually shut down.

NARRATOR: Investigators know the ATR 72

is not equipped with an auto-throttle system.

The throttles can only be moved by hand.

INVESTIGATOR 2: It had to have been shut down by one of the pilots.

THOMAS: So we start to wondering why the pilot

would shut down the good engine.

STEVEN (English Dub): Honestly, at the beginning,

we did not understand how this could happen.

INVESTIGATOR 1: That's crazy.

♪ ♪

INVESTIGATOR 1: Let's take a look at the circuit board.

NARRATOR: Investigators examine the torque sensor

from the right engine of TransAsia Flight 235.

They're looking for any defect that could have caused

the propeller to feather in flight.

STEVEN (English Dub): The lab used precise testing methods.

They made a cross-section of the circuit board

and looked at its image.

♪ ♪

INVESTIGATOR 1: Take a look at this. It's a broken solder.

NARRATOR: They discover microscopic faults in the circuit board.

PETER: And that was related to the soldering joints

in a particular circuit board being compromised

for reasons that were difficult to establish.

It was possibly related to some form of manufacturing defect

or something of that nature.

THOMAS: And that would be enough to stop

the transmission of the signal.

NARRATOR: With a broken circuit board,

the torque sensor couldn't do its job.

Even though the engine was turning,

the sensor couldn't detect any torque.

So the system automatically feathered the propeller.

PETER: The brain of the system thought that torque

had reduced below a pre-determined value,

which I think is about 18%,

and that is what triggered the auto-feather.

FO. LIU: Okay, engine flameout check.

CAPT. LIAO: Check.

NARRATOR: Finally, they understand

why the right side propeller feathered.

But they still haven't explained the crash.

The ATR 72 has two engines.

Losing propeller thrust in one of them

should not have been a catastrophic event.

THOMAS: They are designed to fly only with one engine.

CAPT. LIAO: Terrain ahead.

AUTOMATION: Terrain. Terrain. Pull up.

PETER: Pilots train for engine out operations regularly.

Typically, it's bread and butter for an airline pilot

to deal with an engine failure on a multi-engine aircraft.

NARRATOR: To figure out why 43 people died,

investigators must now answer a much more difficult question.

THOMAS: We still have number one engine produce power normally,

but for some reason the pilot decided

to shut down the good engine.

FO. LIU: Watch the speed.

THOMAS: We had to find out why.

NARRATOR: Investigators turn to the cockpit voice recording.

INVESTIGATOR 1: Okay. Ready? Let's hear what we got.

FO. LIU: Oil pressure?

CAPT. LIAO: Check.

THOMAS: The accident flight is very short,

less than three minutes.

So we listened to the CVR starting from

the takeoff roll to the end of the flight.

FO. LIU: Before taxi Checklist. Propeller brake?

CAPT. LIAO: Off.

FO. LIU: Nose wheel steering?

CAPT. LIAO: On.

FO. LIU: Procedure complete.

INVESTIGATOR 1: Checklist complete.

So far they're following procedure to a T.

THOMAS: You have to make your procedure very clear.

INVESTIGATOR 2: Let's see what happens closer to takeoff.

FO. LIU: Engine instrument check normal.

CAPT. LIAO: V-1. FO. LIU: V-1.

CAPT. LIAO: Rotate.

AIR TRAFFIC CONTROLLER: TransAsia 235, contact approach

on one-one-niner-decimal seven. Good day.

INVESTIGATOR 2: What's that sound?

INVESTIGATOR 1: It must be the engine two fault warning.

PETER: When the Master Warning first activated,

they were approximately about 1200 feet above ground level.

INVESTIGATOR 2: They're flying an ATR 72/600.

It shouldn't be a huge problem.

THOMAS: If they followed procedure, do everything correctly,

they should be able to fly back to land without any problem.

INVESTIGATOR 1: This is a crucial moment.

Let's hear what they're gonna do next.

CAPT. LIAO: I have control.

NARRATOR: Investigators hear the sound of the autopilot turning off.

INVESTIGATOR 1: He's disengaging the autopilot.

He shouldn't be doing that.

PETER: It's hard to understand why the pilot flying

disconnected the autopilot during an emergency situation.

He just made a difficult situation worse.

INVESTIGATOR 2: Keep playing.

FO. LIU: Okay, engine flameout check.

CAPT. LIAO: Check.

PETER: Their attention will be directed to

the engine warning display, which in the ATR 72

clearly indicates which engine has failed.

THOMAS: There's a checklist procedure on the screen.

You follow it step by step.

NARRATOR: But instead of following the emergency checklist...

FO. LIU: Watch the speed.

NARRATOR: ... the captain does something inexplicable.

CAPT. LIAO: Pull back number one.

INVESTIGATOR 2: The captain is starting to shut down engine one

without fully understanding

what the computer system is telling him.

NARRATOR: Both engines are capable of producing power.

But because the right engine has feathered, it has lost thrust,

behaving like a car in neutral.

When the captain pulls back the left throttle,

he leaves himself with no thrust from either engine.

PETER: He didn't seem to fully appreciate

that that had ultimately resulted

in number one engine being shut down.

INVESTIGATOR 2: How could he do such a thing?

NARRATOR: Investigators have discovered

from the cockpit voice recorder

that the captain of Flight 235

shut down the plane's only working engine.

INVESTIGATOR 2: Why didn't the first officer stop him?

NARRATOR: They continue listening to the recording,

trying to understand why the captain's mistake

wasn't corrected in time.

CAPT. LIAO: I will pull back on engine one throttle.

INVESTIGATOR 2: He can't just say he's gonna shut down the engine.

NARRATOR: Pilots are supposed to run a cross-check,

where one pilot verifies the actions of the other.

PETER: When the pilot flying shut down the operative engine,

he did so very quickly

without discussing it with the pilot monitoring.

INVESTIGATOR 1: He's acting before even

confirming what the emergency is.

THOMAS: When there is a warning come up,

the procedure says you identify the problem before you act.

FO. LIU: No, wait a second. Cross-check.

PETER: The pilot monitoring, to his credit,

did try to stop the pilot flying

from manipulating the engine number one power lever,

and he announced he wanted a cross-check.

But there was no definitive confirmation from

the pilot flying that the problem was engine number two.

CAPT. LIAO: Heading mode.

NARRATOR: Instead, the captain interrupts the first officer

to ask for a new heading.

FO. LIU: We're below 2500 feet.

CAPT. LIAO: Come on!

FO. LIU: Zero. Zero-niner-five.

CAPT. LIAO: Check.

INVESTIGATOR 2: The first officer did tell the captain to wait.

He knows that the captain

was pulling back on the wrong engine,

and when he did try to question it

the captain just confirmed what he was doing.

PETER: All of a sudden they've got a dual engine failure,

and the pilot monitoring I think has been caught off guard,

and he's not really sure what's gone on.

CAPT. LIAO: Restart the engine.

FO. LIU: I can't restart the engine!

CAPT. LIAO: Oh, wow. I shut off the wrong engine.

PETER: The pilot flying clearly has an epiphany

that they're in very dire trouble.

CAPT. LIAO: Restart the engine.

FO. LIU: I can't restart the engine!

CAPT. LIAO: I shut off the wrong engine.

STEVEN (English Dub): It's very sad.

When I heard him say, "I shut off the wrong engine,"

I was completely devastated.

NARRATOR: By the time the captain realizes his mistake,

it's too late.

SO. HUNG: Impact! Brace for impact!

FO. LIU: Pull up! CAPT. LIAO: Noooo!

PETER: Unfortunately, neither crew member

actually followed the standard set of procedures

for dealing with an engine flameout after takeoff.

NARRATOR: Investigators now have

an even more puzzling question to answer.

INVESTIGATOR 2: Why didn't the captain understand what he was doing?

NARRATOR: The captain's failure to recognize the situation

and react properly ended up costing 43 lives.

He thought that the left engine had failed

when the aircraft was clearly telling him it was

the right engine that had a problem.

How could the captain have gotten things so wrong?

INVESTIGATOR 2: What was this captain's background?

NARRATOR: When they dig into the captain's history,

they make a disturbing discovery.

INVESTIGATOR 1: The captain failed one of his key training components.

PETER: The pilot flying's training records had indicated

that he was prone to being a bit anxious.

CAPT. LIAO: I have control.

FO. LIU: You have control.

PETER: Feeling a little bit overwhelmed in emergency situations

and had a tendency to prematurely respond

or act in that situation.

CAPT. LIAO: Pull back number one.

♪ ♪

INVESTIGATOR 1: He was also fired from his last job.

NARRATOR: Although the captain was an accomplished military pilot,

his civilian record is raising questions.

INVESTIGATOR 2: Maybe he wasn't used to the ATR 72/600.

NARRATOR: The records soon confirm that hunch.

Liao Chien-Tsung had logged relatively few hours

in TransAsia's newest commuter plane.

PETER: The captain in the left-hand seat had

approximately 5,000 hours total time,

and he had about 250 hours on the ATR 72/600.

FO. LIU: Wait a second. Throttle!

CAPT. LIAO: Number one feather shut-off.

NARRATOR: The ATR 72-600 is known for its advanced technology.

Investigators now wonder if this aircraft,

with its computerized glass cockpit, was too complicated

for a relatively inexperienced pilot to manage in a crisis.

CAPT. LIAO: Restart the engine.

FO. LIU: I can't restart the engine!

PETER: They can often be overwhelmed

with the huge volume of information.

They also have to consider the nature of the automation

and the modes that are presented to them.

So it's more challenging.

CAPT. LIAO: I shut off the wrong engine.

NARRATOR: Did information overload lead to the deaths

of 43 people in one of Taiwan's worst air disasters?

NARRATOR: Investigators need to know if the advanced technology

designed to help pilots in the ATR 72/600

may instead have contributed to the crash of Flight 235

by confusing the TransAsia captain.

INVESTIGATOR 2: Okay. Ready to fly out of Taipei?

INVESTIGATOR 1: Let's do it.

NARRATOR: To try to find out, they program a flight simulator

using the flight data from the downed plane.

THOMAS: We have weather information. We have FDR data.

We have CVR data. So we put those together

to duplicate the condition of the accident.

NARRATOR: The data lets investigators fly the exact same flight:

the same speeds, same climb rate,

and, 37 seconds into the flight, the same cockpit alarm.

INVESTIGATOR 1: That's the warning. Engine two flameout.

NARRATOR: The plane's computer instantly identifies

which engine has lost thrust.

INVESTIGATOR 2: Check autopilot armed. Run the checklist.

NARRATOR: The automated checklist pops up.

Clear, concise and easy to follow.

INVESTIGATOR 1: Up trim on engine one.

Auto feather on number two.

INVESTIGATOR 2: Check.

INVESTIGATOR 1: Engine two flameout confirmed.

INVESTIGATOR 2: Confirm. Secure engine number two.

NARRATOR: The checklist calls for the pilot monitoring

to reduce power in the feathered engine to idle.

The other pilot guards the working engine.

PETER: Then you would bring a condition lever

into the fuel shut-off détente,

which removes fuel from the engine.

INVESTIGATOR 1: Condition lever to fuel shut-off.

INVESTIGATOR 2: Check.

PETER: And then the engine will be secured and shut down.

INVESTIGATOR 2: Engine number two secured.

NARRATOR: Now powered by just one engine,

the plane keeps climbing safely on autopilot.

The computerized systems have helped

the pilots avoid disaster, exactly as designed.

PETER: It's quite manageable. The crew can continue the flight,

climb to a safe altitude, reconsider their options.

INVESTIGATOR 2: Now we just have to fly

back to the airport and land. I have an idea.

Let's see what happens if we just let the plane fly itself.

Reset from the start.

INVESTIGATOR 1: Resetting.

THOMAS: When we do the simulator test, we try to find out

what will happen if the pilots do nothing.

NARRATOR: Incredibly, the simulation shows that

even if there had been no pilot input at all,

the plane would not have crashed.

THOMAS: The aircraft will continue climb

and then fly with no problem.

So I think the aircraft was designed to handle

that situation, as long as we don't do anything wrong.

NARRATOR: Any doubts about the glass cockpit have now been erased.

The advanced systems of the ATR 72-600

did not lead to the crash of Flight 235.

There must have been some other factor.

Investigators study reports from previous incidents

where similar mistakes were made.

They suggest an intriguing possibility.

INVESTIGATOR 2: Interruptions and multi-tasking.

NARRATOR: Investigators know the captain's workload was high.

Taking manual control of the plane distracted him

from running a cross-check with his first officer.

INVESTIGATOR 2: He's multi-tasking.

FO. LIU: Watch the speed!

INVESTIGATOR 2: He could have been suffering from change blindness.

PETER: Change blindness, people are focused or fixated on

another item or area of interest,

and so they miss what would be considered

a very distinguishable change in the environment,

but they don't perceive it.

CAPT. LIAO: I will pull back engine one throttle.

INVESTIGATOR 2: Even when all the systems were telling him

it was engine two, his perception told him

he was doing the right thing. Change blindness.

NARRATOR: The first officer even tried to warn him.

FO. LIU: No, wait a second. Cross-check.

NARRATOR: It seems the captain was blind to the clear warning

that his right engine had feathered.

Investigators finally understand

what went wrong aboard TransAsia Flight 235.

A microscopic crack in a circuit board

disabled an engine sensor

that led the system to wrongly determine

that the right engine had failed.

But that in itself wouldn't have caused the plane to crash.

INVESTIGATOR 2: This was a series of mistakes on the part of the captain.

When engine two feathered, the captain reacted

before he had properly assessed the situation.

NARRATOR: The captain should have followed a checklist.

CAPT. LIAO: I have control.

NARRATOR: Instead, he turned off the autopilot

and reduced power in the wrong engine.

CAPT. LIAO: I will pull back engine one throttle.

INVESTIGATOR 2: All we know for sure is he shut down

their only working engine.

By the time he realizes, it's too late.

CAPT. LIAO: Restart the engine.

FO. LIU: I can't restart the engine!

CAPT. LIAO: Wow. I shut off the wrong engine.

♪ ♪

INVESTIGATOR 2: Why did TransAsia hire this pilot?

NARRATOR: Investigators dig into

TransAsia's corporate background...

INVESTIGATOR 1: Check this out.

NARRATOR: ... trying to understand how a pilot

with such a poor record ever got through the door.

INVESTIGATOR 1: And this.

INVESTIGATOR 2: This company's been expanding rapidly.

NARRATOR: What they find paints a picture

of a growing company struggling to compete

with bigger players in the competitive Asian market.

PETER: A more regional operator like TransAsia Airways

appears to have struggled to certainly

recruit and retain the sort of expertise that airlines seek.

NARRATOR: The crash of Flight 235 would be

the last accident for TransAsia Airlines.

In November 2016, the company ceased operations

and went out of business.

PETER: There's a multitude of reasons that the board

decided to shut down the airline.

But there's an inescapable conclusion that

the adverse or poor safety performance of the airline

certainly had an economic impact on the airline.

NARRATOR: Even though TransAsia Airlines no longer flies,

air crash investigators hope that the tragedy of Flight 235

will serve as an important safety reminder

to pilots at other airlines around the world.

THOMAS: We all understand that pilots, they're human.

Humans make mistakes.

So that's why we design the standard operating procedures.

And the basic important thing is for people

just follow the procedure.