Original subtitles

CAPT. WIYOGO: Come on, climb! Climb! Climb!

NARRATOR: An Airbus A300 veers fatally off course.

CAPT. WIYOGO: No! No! Nooooo!

[Crash]

SANTOSO: It was the biggest human loss in Indonesian history.

ROBERT: It really was overwhelming.

SANTOSO: These are two pieces we need to find.

SANTOSO: The task was to find the black box.

NARRATOR: As investigators begin to examine the evidence...

AIR TRAFFIC CONTROLLER: Indonesia 152, turn right heading zero-four-six.

SANTOSO: Here, right on course.

NARRATOR: ... each new clue is more perplexing than the last.

ROBERT: That's go-around power.

SANTOSO: We cannot figure it out.

ROBERT: The impact point was nowhere near

where we would expect the aircraft to be.

ROBERT: Where did they think they were going?

We just didn't understand that.

[♪ theme music ]

♪

NARRATOR: There are 222 passengers on board

Garuda Indonesia Flight 152.

They're on their way to the city of Medan

on the Indonesian island of Sumatra.

CAPT. WIYOGO: Let's stay on autopilot as long as we can.

FO. ZUWALDI: Yes, sir.

NARRATOR: Captain Rachmo Wiyogo has been flying in Indonesia

for nearly twenty years.

He's very familiar with today's flight path.

CAPT. WIYOGO: For missed approach, climb straight ahead

to 2,500 and contact ATC.

You don't have to write this down. Just relax.

FO. ZUWALDI: Yes. Okay, sir.

NARRATOR: Tahta Zuwaldi has only recently upgraded

from flight engineer to first officer.

The plane they're flying is an Airbus A300,

one of the most reliable commercial airliners in the sky.

Flight 152 left the Indonesian capital of Jakarta

nearly ninety minutes ago.

Headed northwest, it is expected to arrive at its destination

in about half an hour.

ATIS: Surface winds calm. Visibility 400 meters.

NARRATOR: An automatic weather report alerts the crew

to one factor about their flight that's not routine.

ATIS: Present weather: smoke.

NARRATOR: Forest fires in Sumatra have sent

a thick blanket of smoke across all of Southeast Asia.

It's wreaking havoc on people's health and on air traffic.

DAVID: Smoke is limiting visibility to a degree

that would make the descent and the approach

really quite difficult -- not impossible,

but really quite difficult.

NARRATOR: The cabin crew of Flight 152 begins preparing

for the upcoming descent.

On the ground, it's a busy afternoon

for Medan air traffic controllers.

FO. ZUWALDI: Indonesia 152 requesting descent clearance.

NARRATOR: They're handling flights from several domestic airlines,

including Merpati, Bouraq and Garuda Indonesia.

AIR TRAFFIC CONTROLLER: Confirming descent to flight level one-four-zero.

NARRATOR: The controller clears Garuda 152 to begin its descent.

FO. ZUWALDI: Descending to flight level one-four-zero,

Indonesia 152.

NARRATOR: Medan Airport has just one runway.

Right now, the controller has a Bouraq Airlines flight

ready to take off.

He needs to slow the approaching Garuda flight

until that plane clears the runway.

AIR TRAFFIC CONTROLLER: Indonesia 152, descend to 3,000 feet

for runway zero-five. Reduce speed two-two-zero.

FO. ZUWALDI: Reduce speed to two-two- zero knots, Indonesia 152.

Seat belt, no smoking.

NARRATOR: Less than fifteen minutes from the airport,

Flight 152 descends through 10,000 feet.

CAPT. WIYOGO: It's smoky here below 10,000.

FO. ZUWALDI: Oh yeah.

DAVID: The pilot would never have been able to get

any external visual cues.

He would have been flying entirely on instruments.

♪

NARRATOR: The reduced visibility puts added pressure

on the controllers.

DAVID: If there is smoke all the way down to the ground,

the controller knows the pilot is going to encounter problems.

They're gonna need all the help they can get,

and the controlling should be very accurate.

NARRATOR: The captain adjusts the power to his engines.

AIR TRAFFIC CONTROLLER: Merpati 152, turn left

heading two-four-zero to intercept runway zero-five.

CAPT. WIYOGO: Number one always lags behind a bit,

so keep an eye on it for me. FO. ZUWALDI: Okay.

AIR TRAFFIC CONTROLLER: Indonesia 152, do you read?

FO. ZUWALDI: Indonesia 152. Say again?

AIR TRAFFIC CONTROLLER: Okay. Turn left heading two-four-zero,

two-three-five now to intercept runway zero-five.

FO. ZUWALDI: Roger, left heading two-three-five, Indonesia 152.

NARRATOR: The plane below has now taken off. The runway is clear.

AIR TRAFFIC CONTROLLER: Bouraq 683, turn left heading one-two-zero.

Indonesia 152, traffic clear. Descend to 2,000 feet.

FO. ZUWALDI: Descending to 2,000 feet, Indonesia 152.

NARRATOR: If it weren't for the heavy smoke,

passengers would be able to see the ground by now.

DAVID: They had very limited visibility.

Anybody who's driven a car in fog

will know what I'm talking about.

AIR TRAFFIC CONTROLLER: Indonesia 152, turn right heading zero-four-six.

FO. ZUWALDI: Turn right heading zero-four-six, Indonesia 152.

CAPT. WIYOGO: Flaps 8.

FO. ZUWALDI: Speed check. Flaps 8.

CAPT. WIYOGO: The cockpit is hot. See what you can do. It's so hot.

FO. ZUWALDI: It's set to cool, sir. It should be fine.

NARRATOR: Any second now, the controller expects

to see Flight 152 turn onto final approach.

♪

CAPT. WIYOGO: What?

NARRATOR: The Airbus has somehow become

dangerously close to the ground.

CAPT. WIYOGO: Come on, climb! Climb! Climb!

NARRATOR: The crew struggles to raise the plane's nose

and gain altitude.

But the 130-ton jet takes time to respond,

time they don't have.

[Chaos]

CAPT. WIYOGO: No!

[Screaming]

No! No! Noooo! Noooooo!

[Crash]

♪

NARRATOR: Locals rush to the crash site,

seventeen miles from Medan airport.

It's soon clear there's nothing they can do to help.

All 234 people onboard the flight are dead.

This is the deadliest aviation accident in Indonesia's history.

The entire nation wants answers.

MARDJONO: We should come to the answer on not only what happened,

how it happened but also why it happened.

NARRATOR: Investigators soon join the throngs

of police and locals already at the crash site.

SANTOSO: Let's see how far back this wreckage goes.

NARRATOR: Santoso Sayogo is a key member of the investigative team,

and the accident has affected him personally.

SANTOSO: I knew both the captain and first officer

for a long, long time.

When you found out that your two friends

was the victim of the accident,

it's quite a shocking experience.

ROBERT: Santoso! We'll need to secure the site somehow.

NARRATOR: The Air Accidents Investigation Branch

sends Rob Carter to assist with the investigation.

ROBERT: The site was chaotic. There were lots of people around,

some in uniform but it didn't seem like very many.

There was no overall control.

Lots of people doing different things, very little

that seemed to be related to accident investigation.

The smell was almost overpowering at that stage,

coupled with the heat and the humidity and the pollution.

It really was overwhelming.

NARRATOR: The chaotic scene is an immediate concern for Carter.

He's worried the lack of security

could compromise the investigation.

ROBERT: A tremendous number of local people

were going over the wreckage in different ways

and they were carrying pieces away.

We worried that they might be carrying away bits of aircraft,

which we'd be really interested in.

NARRATOR: If authorities can't gain control of the site

and protect valuable evidence, the truth about what happened

to Garuda Indonesia Flight 152 may never be known.

♪

SANTOSO: Okay, good.

The left engine was found here.

ROBERT: Excellent.

NARRATOR: The wreckage from Flight 152 lies

seventeen miles southwest of Medan airport.

The compact nature of the crash zone tells investigators

that the plane was in one piece when it hit the ground.

ROBERT: It looked as if we had most of, if not all,

of the aircraft within an area 120 by 80.

That's pretty compact.

NARRATOR: The wreckage tells investigators something else as well --

something they can't explain.

The debris field shows that the plane was flying

away from the airport when it slammed into a hillside

southwest of the runway.

It's exactly opposite from the direction

they should have been flying.

ROBERT: One of the things that seemed so strange was

where the impact point was.

It was nowhere near where we would expect the aircraft to be

for the proper sort of approach into the airport.

We just didn't understand that.

SANTOSO: These are two pieces we need to find.

NARRATOR: They hope the plane's flight recorders

can help clear up the mystery.

SANTOSO: They should be in this area here. Okay, let's go.

MARDJONO: Our principle is find the black box,

and the clues and the evidence are there.

NARRATOR: Investigators fear the boxes may have been

carried off by looters.

They recruit hundreds of local people to search for them.

ROBERT: We were really looking very strongly for

the cockpit voice recorder, flight data recorder

really to fill in any sort of detail on how this had happened.

NARRATOR: At the same time, they gather information

from the air traffic controller,

the last person to have communicated with Flight 152.

AIR TRAFFIC CONTROLLER: They approached from the southeast.

I was trying to bring them in this way,

a left turn and a right turn

that gets them into runway zero-five.

NARRATOR: The controller suspects the captain

somehow misinterpreted his instructions

and missed the final turn.

AIR TRAFFIC CONTROLLER: He didn't understand which way to turn.

He made a left turn here instead.

But without the cockpit recording and the flight data,

it's impossible to say why the plane turned the wrong way.

Perhaps there was a mechanical failure

or some other last minute crisis.

SOERJANTO: We could not determine why the captain

make the aircraft turning to the left.

This is a very interesting. This is... it's a big puzzle.

NARRATOR: With no sign of the black boxes, investigators

gather air traffic recordings made in the tower.

It's hoped they can shed some light on why the plane turned

away from the airport instead of towards it.

ROBERT: We were still wondering whether it could be

some sort of systems failure, possibly even

some sort of mild structural failure,

some distracting aspect for the pilots.

It really left that pretty wide open.

SANTOSO: Roll tape.

AIR TRAFFIC CONTROLLER: Confirming descent to flight level one-four-zero.

NARRATOR: The air traffic recordings capture

only the radio calls between the pilots and the controller.

AIR TRAFFIC CONTROLLER: Indonesia 152, descend to 3,000 feet

for runway zero-five.

NARRATOR: They're not as helpful as a CVR recording, which

would reveal all sounds and conversation inside the cockpit.

AIR TRAFFIC CONTROLLER: Reduce speed to two-two-zero.

SANTOSO: He needs to get Bouraq 683 airborne.

NARRATOR: But investigators listen closely for any clue

as to why the A300 veered so badly off course.

At first, the communication seems completely normal.

AIR TRAFFIC CONTROLLER: Merpati 152, turn left heading

two-four-zero to intercept runway zero-five

from the right side.

NARRATOR: But then, the controller uses the wrong call sign.

SANTOSO: You have Merpati 152, and now he's got Garuda 152.

NARRATOR: Records show that earlier in the day,

the controller was talking to a Merpati flight

with the same number, one five two.

It seems that now he's mixed up the two call signs.

DAVID: Instead of Garuda 152, he said Merpati 152.

The Garuda pilot didn't pick this message up

for obvious reasons.

AIR TRAFFIC CONTROLLER: Indonesia 152, do you read?

FO. ZUWALDI: Indonesia 152. Say again?

DAVID: Then suddenly the controller realized

that he'd given the wrong call sign,

so he called up for a second time.

AIR TRAFFIC CONTROLLER: Okay. Turn left heading

two-four-zero... two-three-five now

to intercept runway zero-five.

SANTOSO: Left heading two-three-five.

FO. ZUWALDI: Roger, left heading two-three-five, Indonesia 152.

NARRATOR: It appears the misunderstanding is quickly cleared up.

SANTOSO: The controller says they made that turn.

NARRATOR: After the brief moment of confusion,

the Garuda flight is exactly where it should be.

FO. ZUWALDI: On heading two-one-five, Indonesia 152.

SANTOSO: That puts them about here, right on course.

One more right turn and he's lined up with the runway.

AIR TRAFFIC CONTROLLER: Indonesia 152, turn right heading zero-four-six.

SANTOSO: There it is. Clear as day.

FO. ZUWALDI: Turn right heading zero-four-six, Indonesia 152.

SANTOSO: Okay, stop there.

They definitely understood turn right.

NARRATOR: How the flight went so horribly wrong

in the final few moments is baffling.

SANTOSO: It's in the exact opposite direction they were told.

Why?

SANTOSO: The ATC give instruction,

"Indonesia 152 turn right onto heading zero-four-six."

But the aircraft turned to the left.

At that stage we do not have any clue at all.

NARRATOR: Investigators need the CVR if they hope to figure out

what exactly went on in the cockpit of Flight 152.

♪

A week after the crash of Garuda Indonesia Flight 152,

devastating scenes of loss and suffering

underscore the accident's human toll.

Indonesians from all walks of life

want to know what caused this deadly tragedy.

♪

SANTOSO: They have to be somewhere.

Let's go back to where we started and look again.

Let's go. Come on. Let's go.

NARRATOR: There's still no sign of the plane's black boxes.

Investigators are beginning to worry that

the answers so many people are hoping for may never be found.

ROBERT: We've got to find them.

ROBERT: It was very frustrating not having

the cockpit voice recorder and the flight data recorder.

They are really crucial to understanding the subtleties

of an aircraft accident.

♪

NARRATOR: The terrible conditions at the accident site aren't helping.

MARDJONO: At that time, it was rainy season,

and you can imagine how wet it was and slippery as well.

NARRATOR: Despite the setbacks, the team presses on.

ROBERT: Let's see if we can figure out what this plane was doing.

NARRATOR: They collect key pieces of wreckage,

including flight instruments from the cockpit.

Soerjanto Tjahjono of the

National Transportation Safety Committee

hopes those instruments will tell him

how the plane was performing.

SOERJANTO: We could not find the black boxes,

so we used anything from the cockpit like the gauges,

any instrument in the cockpit.

NARRATOR: Many of the gauges on this version of the Airbus

are electronic, which means that when they lose power they

display their final readings like a snapshot in time.

ROBERT: When electrical power goes off, the instrument freezes.

NARRATOR: Those readings provide valuable insight

into the final moments of Flight 152.

ROBERT: There it is. It looks like one-point-five-five-two.

That's go-around power.

They were trying to fly out of trouble.

ROBERT: The engine instruments showed us that the engines

were actually at a very high level of thrust

at the point that they lost electrical power.

NARRATOR: The finding reveals that the pilots

saw the danger ahead and tried desperately

to get their plane to climb.

ROBERT: The crew had responded by increasing the engine thrust

when they realized they were close to the ground.

NARRATOR: As the evidence begins to add up,

the likelihood of a mechanical failure aboard Garuda 152

looks increasingly remote.

ROBERT: It sure seems like the aircraft was under control.

ROBERT: Putting it all together, the instruments seemed

to indicate to us that the aircraft was what we call

"a going concern" when it hit that ridge,

that it was some sort of controlled flight into terrain.

DAVID: Controlled means that there's nothing wrong

with the airplane.

[Crash]

And yet it plows into a mountainside.

♪

NARRATOR: It's been twenty-six days since the crash of Flight 152.

Investigators still have no explanation for its mysterious

final turns and fatal impact.

But then they get their first big break.

SANTOSO: Well, well, well.

NARRATOR: It turns out that the plane's

voice and data recorders were not carried off by looters,

but they were almost completely hidden from sight

in the dense Indonesian forest.

SANTOSO: It was a surprise for us to find that

the two black box were sitting there for 26 days

until we found it in very soft soil and entangled

with the root of the falling tree.

SANTOSO: Let's hope they hold some answers.

NARRATOR: They rush the boxes to a lab where technicians

will work to recover cockpit sounds and conversation

along with detailed aircraft performance data.

The long wait for the most crucial evidence is almost over.

SANTOSO: We tried to concentrate first on the FDR

and try to figure out the flight path of the aircraft.

NARRATOR: When investigators plot the newly found data,

they see that it finally rules out any chance

of a mechanical failure.

ROBERT: So left away from the airport

and then a right turn smack into the mountains.

NARRATOR: It clearly shows that the pilots

deliberately commanded that fatal turn.

ROBERT: Where did they think they were going?

Can you bring me the descent profile, please?

SANTOSO: After we got the FDR, some questions got some answers.

NARRATOR: The data also shows that the plane was

in a steady descent until it hit a treetop...

at about 1,500 feet.

ROBERT: So why didn't they level off at 2,000 feet?

AIR TRAFFIC CONTROLLER: Indonesia 152, traffic clear.

Descend to 2,000 feet.

NARRATOR: The crew was not cleared to descend

any lower than 2,000 feet. They should have held that altitude.

♪

ROBERT: So here we were somehow with the aircraft

hitting a tree about 500 feet below its last cleared altitude.

[Crash]

That was a real mystery.

NARRATOR: Investigators now know the pilots turned

in a direction opposite to the controller's instructions

and dropped below their assigned altitude.

What they still don't know is why.

They hope the cockpit voice recorder can provide an answer.

SANTOSO: Let's start with turn number one... here.

♪

FO. ZUWALDI: Indonesia 152 requesting descent clearance.

NARRATOR: For Santoso Sayogo, the job of listening

to the recording comes with an extra burden.

SANTOSO: I knew both pilots, the captain and the first officer,

and I personally can recognize whose voice

are coming from the CVR.

It's not easy listening to the tape.

AIR TRAFFIC CONTROLLER: Merpati 152, turn left heading two-four-zero

to intercept runway zero-five from the right side.

SANTOSO: Okay, that's the confused call sign.

CAPT. WIYOGO: Number one always lags behind a bit,

so keep an eye on it for me.

FO. ZUWALDI: Okay.

NARRATOR: The tape reveals that the Garuda pilots

don't respond to the first instruction

because they don't think it's for them.

AIR TRAFFIC CONTROLLER: Indonesia 152, do you read?

FO. ZUWALDI: Indonesia 152. Say again?

AIR TRAFFIC CONTROLLER: Okay. Turn left heading two-four-zero...

two-three-five now to intercept runway zero-five.

NARRATOR: The controller repeats himself.

FO. ZUWALDI: Roger, left heading two-three-five, Indonesia 152.

NARRATOR: The crew then makes the turn as instructed.

CAPT. WIYOGO: Why so far out? SANTOSO: So far out?

NARRATOR: And yet the recording leaves investigators

with a disturbing impression.

FO. ZUWALDI: 152, heading two-three-five.

Confirm that we are clear of the mountainous area.

SANTOSO: He doesn't sound sure of where he is.

ROBERT: There seemed to be some degree of confusion

between the pilots and the air traffic controller

as to where the aircraft was.

AIR TRAFFIC CONTROLLER: Confirm, sir. Continue turning left heading two-one-five.

SANTOSO: They're on course. A right turn toward the runway is next.

AIR TRAFFIC CONTROLLER: Indonesia 152, turn right heading zero-four-six.

FO. ZUWALDI: Turn right heading zero-four-six, Indonesia 152.

SANTOSO: They turned left instead.

NARRATOR: What investigators hear next

makes the left turn even more baffling.

CAPT. WIYOGO: Flaps 8.

FO. ZUWALDI: Speed check. Flaps 8.

NARRATOR: Even though the crew is turning away from the airport,

they're configuring their plane as though heading towards it.

SANTOSO: Why would you extend flaps while turning away from the airport?

What if he thinks he is turning towards the airport?

What if he thinks he's here?

He believes he has to turn left to get to the runway.

NARRATOR: Feeling he may be close to a breakthrough,

Santoso Sayogo reviews the airport approach chart.

DAVID: The charts lay out what the normal approach is,

and the pilots normally expect to fly that.

NARRATOR: He discovers that Garuda 152 wasn't on the standard approach.

The standard approach to Medan is from the left side, which

involves making a final left turn to line up with the runway.

But because there was an aircraft departing,

the Garuda captain was instructed to approach

from the right side of the runway,

requiring something he wasn't used to --

a right turn before landing.

DAVID: The controller took them in a direction

which was not what they would have expected

according to the approach charts.

But there shouldn't really have been a problem with that.

Controllers are supposed to confirm the approach path

with the pilots well before they get to the runway.

SANTOSO: How could he not have known which approach he was flying?

Back to 1:27, please.

[Tape rewinding]

AIR TRAFFIC CONTROLLER: Merpati 152, turn left

heading two-four-zero to intercept runway zero-five

from the right side.

NARRATOR: As Santoso Sayogo listens again

to what he thought was a harmless call sign mix-up,

he suddenly realizes that it had major consequences.

FO. ZUWALDI: Indonesia 152, say again.

NARRATOR: When the controller repeats

the approach instructions, he leaves out a critical detail.

AIR TRAFFIC CONTROLLER: Turn left heading two-four-zero...

two-three-five now to intercept runway zero-five.

SANTOSO: He didn't repeat which side they were approaching from.

DAVID: He should have made it clear:

You're not going to come in

from the left-hand side of the runway.

You're going to come in from the right-hand side.

SANTOSO: He thinks he's flown past the airport

when he's told to make this turn.

He's expecting the next turn to be a left turn

but instead he's told to turn right.

NARRATOR: It seems that the captain,

still unable to see the ground through the smoke,

dials in a left turn out of habit.

It is a tragic error that leads to disaster.

But investigators now wonder, why did the first officer

not notice his captain's mistake?

AIR TRAFFIC CONTROLLER: Indonesia 152, turn right heading zero-four-six.

FO. ZUWALDI: Turn right heading zero-four-six, Indonesia 152.

NARRATOR: First Officer Zuwaldi clearly acknowledges

the instruction for a right turn.

Yet seconds later, the plane turns left.

It's almost impossible to understand.

Investigators have established that

the captain of Garuda Indonesia Flight 152 made a fatal turn

after a radio call mix-up left him with

a confused mental picture of the approach he was flying.

DAVID: The vectors, the directions given them

by the air traffic controller, can create a bit of confusion.

Controllers didn't make it clear enough to the pilots

that this was not going to be the standard pattern.

AIR TRAFFIC CONTROLLER: Indonesia 152, turn right heading zero-four-six.

FO. ZUWALDI: Turn right heading zero-four-six, Indonesia 152.

NARRATOR: They focus on the words of the first officer

in an attempt to understand why he didn't

immediately react to the wrong turn.

CAPT. WIYOGO: It's getting hot, isn't it? The cockpit is hot.

See what you can do. It's so hot!

SANTOSO: The captain asked the first officer

to check the air conditioning.

DAVID: The co-pilot turned his eyes upward to the panel

where he checked the air conditioning controls.

NARRATOR: The brief distraction diverts

the first officer's attention from his instruments

at a critical moment.

FO. ZUWALDI: It's set to cool, sir. It should be fine.

DAVID: As a result, the co-pilot missed crucial information

from the instruments.

FO. ZUWALDI: Turn right!

SANTOSO: He looked back.

He was surprised to find the aircraft turning to the left

instead of turning to the right.

CAPT. WIYOGO: Indonesia 152, confirm turning left or right

heading zero-four-six.

AIR TRAFFIC CONTROLLER: Turning right, sir.

FO. ZUWALDI: Sorry, captain. Sorry.

CAPT. WIYOGO: Roger, 152.

AIR TRAFFIC CONTROLLER: 152, confirm you are turning left now.

CAPT. WIYOGO: We are turning right now.

AIR TRAFFIC CONTROLLER: 152, okay. Continue turning left.

NARRATOR: In all the confusion over which way to turn...

CAPT. WIYOGO: Turn left? We are turning right now.

AIR TRAFFIC CONTROLLER: Oh God! Okay.

NARRATOR: ... valuable seconds are lost.

SANTOSO: They're flying straight towards the mountain.

ROBERT: There were many confusing factors for him.

CAPT. WIYOGO: What?

ROBERT: The smoke pollution was certainly one of them.

The confused instructions of air traffic control.

He did not really have a good mental picture

of where the aircraft was and where it was meant to be.

CAPT. WIYOGO: Climb! Climb! Climb!

SANTOSO: The moment they took the wrong turn, they were doomed.

DAVID: It was this uncertainty, lack of clarity

in the captain's head which really let this accident happen.

NARRATOR: The recording helps explain how Garuda Flight 152

ended up so badly off course.

But it doesn't answer another critical question.

AIR TRAFFIC CONTROLLER: Indonesia 152, traffic clear. Descend to 2,000 feet.

FO. ZUWALDI: Descending to 2,000 feet, Indonesia 152.

NARRATOR: The crew was instructed to descend no lower

than 2,000 feet, and their autopilot

should have kept them at that altitude.

DAVID: They had gone straight through 2,000 feet

and were heading for 1,500, and that was too low.

SANTOSO: How did they end up below 2,000 feet?

ROBERT: Either the autopilot had failed in some way or other,

which is unusual, or the crew had input the wrong altitude.

NARRATOR: Unfortunately for investigators,

the plane's autopilot system was destroyed in the crash.

DAVID: This impact was so severe

they could pick up the bits afterwards,

but they couldn't establish whether there was

something wrong with it on the day.

NARRATOR: Maintenance records show no history

of the autopilot ever failing to maintain proper altitude,

so a malfunction seems unlikely.

And a report from Airbus all but eliminates

the possibility of autopilot failure.

Engineers calculated that the odds of such a failure

are less than one in two billion.

ROBERT: It's almost impossible for it to fail.

FO. ZUWALDI: Descending to 2,000 feet, Indonesia 152.

NARRATOR: Investigators suspect the captain made an error

while entering his minimum altitude.

ROBERT: It was more probably crew missetting

than it was autopilot failure.

CAPT. WIYOGO: Indonesia 152, confirm turning left or right

heading zero-four-six.

AIR TRAFFIC CONTROLLER: Turning right, sir.

FO. ZUWALDI: Sorry, captain. Sorry.

CAPT. WIYOGO: Roger, 152.

NARRATOR: As the aircraft passes below its target altitude

of 2,000 feet...

AIR TRAFFIC CONTROLLER: 152, confirm you are turning left now.

CAPT. WIYOGO: We are turning right now.

NARRATOR: ... the pilots are engaged in

a confusing conversation about which direction to turn.

AIR TRAFFIC CONTROLLER: 152, okay. Continue turning left.

CAPT. WIYOGO: Turn left? We're turning right now.

ROBERT: They were so preoccupied with their turn

they didn't notice their altitude.

SANTOSO: Both pilots didn't realize that

the aircraft already left 2,000 feet.

NARRATOR: By the time the first officer does notice

the dangerously low altitude...

FO. ZUWALDI: We're descending. CAPT. WIYOGO: What?

NARRATOR: ... it's too late.

DAVID: The quality of their monitoring of their instruments

was not up to scratch.

CAPT. WIYOGO: Come on, climb! Climb! Climb!

DAVID: And that's why they got too low

and they hit the high ground.

♪

[Crash]

NARRATOR: It's finally clear how Garuda Indonesia Flight 152

dropped below the minimum safe altitude.

But there are still important questions to answer.

AIR TRAFFIC CONTROLLER: Indonesia 152, traffic clear. Descend to 2,000 feet.

NARRATOR: The controller in Medan had a read-out

of Flight 152's altitude and direction.

If he had recognized the danger and warned the crew,

hundreds of lives could have been saved.

Why didn't that happen?

FO. ZUWALDI: Descending to 2,000 feet, Indonesia 152.

NARRATOR: Investigators need to understand

why the Medan controller never warned the Garuda pilots

of impending danger.

They pour over the technical specifications

from Medan's radar system.

Most advanced radar systems refresh every five seconds.

But they soon discover that the radar in Medan

is far from advanced.

ROBERT: The radar only refreshed every twelve seconds.

♪

DAVID: That means the controller only gets an updated picture

of where the airplane is every twelve seconds.

AIR TRAFFIC CONTROLLER: 152, confirm you are turning left now.

CAPT. WIYOGO: We are turning right now.

DAVID: A lot can happen in twelve seconds.

So when the pilot turned

in completely the wrong direction...

AIR TRAFFIC CONTROLLER: Continue turning left.

DAVID: ... the controller was not seeing

what the pilot was doing...

AIR TRAFFIC CONTROLLER: Oh God.

DAVID: ...until it was getting to be too late.

♪

[Crash]

♪

NARRATOR: Investigators are close to fully understanding

the tragic crash of Flight 152.

There's just one last mystery to solve.

Most commercial jets have a cockpit alarm

that sounds when the plane flies too close to terrain.

GPWS: Terrain. Terrain. Pull up. Pull up.

NARRATOR: It's called the Ground Proximity Warning System,

a loud automated voice alerting pilots to danger.

ROBERT: One of the big questions for us was:

Why did the accident happen when the aircraft

was equipped with a Ground Proximity Warning System?

NARRATOR: According to the flight data recorder,

the GPWS on Flight 152 was triggered five times.

The crew should have heard the first warning

thirty-seven seconds before impact.

But when they check the cockpit recording,

they only hear the voice alarm once.

FO. ZUWALDI: Pull up. Pull up. Pull up.

NARRATOR: And it comes just four seconds before impact.

Something's not right.

They send the tape to an audio lab

where sound technicians enhance the quality of the recording.

♪

Listening to the enhanced tape,

investigators make a stunning discovery.

♪

FO. ZUWALDI: Pull up. Pull up. Pull up.

NARRATOR: The alert "Pull up, pull up"

is not the sound of an automated voice.

SANTOSO: It's definitely Zuwaldi, the first officer.

SANTOSO: Then we realized the recorded of "Pull up, pull up"

wasn't from the GPWS, but it was from one of my friends.

NARRATOR: It can mean only one thing.

SOERJANTO: We knew that the GPWS was not working.

NARRATOR: It's ultimately revealed that there is a flaw

in the GPWS that prevents a warning from sounding

when planes are descending

over certain types of mountainous terrain.

SANTOSO: The GPWS never give the warning to the pilot.

ROBERT: Over the years, GPWS has saved countless lives.

It was sad in this case that those lives weren't saved,

and the modern systems, enhanced GPWS

certainly would have worked way better.

NARRATOR: Investigators have finally uncovered

the tragic series of events that led to the loss of 234 lives.

It all starts with a controller

who confuses one call sign for another.

AIR TRAFFIC CONTROLLER: Merpati 152, turn left heading two-four-zero

to intercept runway zero.

CAPT. WIYOGO: Number one always lags behind a bit,

so keep an eye on it for me.

NARRATOR: The mix-up means the crew of Flight 152

never hear a critical instruction to approach the

runway from the right side instead of the usual left.

FO. ZUWALDI: Indonesia 152, say again.

NARRATOR: The captain compounds the problem

when he enters an incorrect altitude into the autopilot.

AIR TRAFFIC CONTROLLER: Indonesia 152, traffic clear. Descend to 2,000 feet.

FO. ZUWALDI: Descending to 2,000 feet, Indonesia 152.

NARRATOR: The error keeps the autopilot from holding the plane

at 2,000 feet as the crew expects.

♪

Thick smoke from forest fires obscures the view

of landmarks on the ground.

Thinking the runway is to his left,

the captain turns away from the airport towards mountains.

AIR TRAFFIC CONTROLLER: 152, confirm you are turning left now.

CAPT. WIYOGO: We are turning right now.

AIR TRAFFIC CONTROLLER: 152, okay. Continue turning left.

NARRATOR: In the confusion over the turn, no one notices

that the Airbus is dropping dangerously close to the ground.

Ultimately, the warning that should alert them to the danger

never sounds.

CAPT. WIYOGO: What? Come on, climb! Climb!

FO. ZUWALDI: Pull up! Pull up! Pull up!

CAPT. WIYOGO: No! No! No! No! No! Nooooo!

♪

NARRATOR: In their final report, Indonesian investigators

call for improved communications training for pilots

as well as upgrades to Medan's radar system.

They also advise against using the same flight number

for more than one plane on the same route.

ROBERT: I think what really hit home to me about this accident

and the loss of so many lives was how avoidable it was.

SANTOSO: At the end of the investigation, we were surprised

that there were so many human errors

that happened one after another.

DAVID: All of these things came together

to make an accident very much more likely.

If you took away any one of those factors,

the accident might not have happened.