Original subtitles

Bank angle. Bank angle.

It takes only 25 seconds

for Sriwijaya Air Flight 182 to spiral out of the sky...

Terrain. Pull up.

- ...and into the Java Sea.

- The airplane's acceleration was nearly approaching

the speed of sound on the way down.

The forces just literally shattered the airplane.

- All 62 people onboard are dead.

- As the investigator-in-charge, I have the responsibility

to answer to the families what caused this accident.

- When investigators examine the flight data...

- It all started here.

- ...they discover an issue never flagged by the airline.

- So the system allowed a defect to slip through the cracks.

- Looks like it.

- It's actually quite startling.

- Whoa.

- I just don't understand

how they could have missed that.

Mayday, Mayday.

Pull up.

It's shortly after two in the afternoon

at Soekarno-Hatta International Airport in Jakarta, Indonesia.

Sriwijaya Air Flight 182

is finally taxiing towards the runway.

Departure was delayed almost an hour because of a monsoon.

- It looks like it's letting up even more.

- Good thing.

- The pilot flying today is 54-year-old Captain Afwan.

34-year-old First Officer Diego Mamahit

is monitoring instruments.

- The captain and the first officer

were both very experienced pilots.

They had thousands and thousands of hours,

both flying and on this airplane itself.

- The cabin is only half full due to the COVID pandemic.

All of the 56 passengers are Indonesian nationals.

Flight 182 will turn northeast from Jakarta,

fly over the Java Sea

to reach its destination of Pontianak,

on the island of Borneo.

- In Indonesia, air travel is a mainstay of transportation.

Because there are so many islands,

customers use air transportation

as a routine means of getting from one place to another.

- The crew performs last-minute checks before takeoff.

- Auto-throttle.

- Armed.

- Flaps.

- Five.

- Stabilizer trim.

- Set.

- They're flying a 26-year-old Boeing 737-500.

- In an island archipelago like Indonesia,

the 737 series airplanes is perfect.

It operates well on and off of shorter runways.

It was built for short-haul flights.

It is very on for 737s

to fly 8, 10, 12 legs in a day.

It's a workhorse.

- Sriwijaya 182, runway two five right,

cleared for takeoff.

- Runway two five right, cleared for takeoff,

Sriwijaya 182.

- Ready?

- Ready.

- The crew gets ready for a busy day.

Take-Off thrust set.

- They are scheduled to fly several legs

by the end of their shift.

- Speed increasing...

Eighty knots.

- V-1. Rotate.

V-2. Positive rate.

- Gear up.

- 400. - Flaps one.

- Just after lift-off...

- L-nav.

- ...Captain Afwan engages the autopilot.

- Flaps up.

- Most pilots really enjoy having

the automatic system engaged as soon as possible.

Because, of course, they're not actually

hand-flying at that point,

so they have a little bit more awareness

of what's going on with the airplane.

- Heading select.

- Two minutes into the flight,

the Captain adjusts the plane's course,

and the autopilot turns the plane east

towards its destination.

In the cabin, passengers settle in

for the 90-minute flight.

As the plane continues its ascent,

the Captain switches the engine power setting

from takeoff thrust to climb thrust.

- Jet engines, like any other engine,

sustain more wear at very high power settings.

So once you get airborne, you reduce

to a climb thrust setting

so that you're reducing wear on the airplane.

- Uh, Captain?

- Almost three minutes into the flight,

the first officer spots something concerning.

- It looks like it might get rough ahead.

- You always try to give the passengers

the smoothest ride that you can.

So we don't fly through thunderstorms.

- Let's turn a bit further east to be safe.

Check if heading zero seven five is open.

- Yes, Captain.

Request heading zero seven five degrees

to avoid weather, Sriwijaya 182.

- Sriwijaya 182,

heading zero seven five approved.

- Zero seven five, Sriwijaya 182.

- The crew is given permission to divert to the right,

around the weather.

But the new route is very busy today.

- Sriwijaya 182, stop climbing at one one zero.

- To avoid other aircraft,

they're instructed to level off at 11,000 feet.

- Stop climbing at one one zero,

copy, Sriwijaya 182.

Captain, change altitude to one one zero.

- One one zero.

- The Boeing 737 continues its right turn.

Three and a half minutes into the flight...

- Approaching one one zero.

- ...it nears the target altitude.

- One one zero.

- In the cabin, the passengers begin to sense

the plane banking left.

It continues until the plane is on its side.

Back in Jakarta, the Controller realizes Flight 182

is suddenly going off course, and radios the crew.

- Sriwijaya 182, what's your heading?

- She gets no response.

At that moment, Flight 182 is diving towards the Java Sea

at an incredible speed.

Terrain.

- Captain do some...

- Captain Afwan is desperately

trying to regain control of the plane.

Captain! Captain!

- But his efforts fail.

- The airplane's acceleration was nearly approaching

the speed of sound on the way down.

The forces just literally shattered the airplane.

- A little more than four hours after Sriwijaya

Air Flight 182 disappears from radar,

search and rescue teams reach the plane's last

reported coordinates,

11 nautical miles northwest of Jakarta,

over the Java Sea.

The teams find only an oil slick,

small pieces of debris, and human remains.

The Boeing 737 has disintegrated

and all 62 people on board are dead.

With over 700 aviation fatalities in the last decade,

Indonesia is already considered one of the deadliest

aviation regions in the world.

- This accident needed to be resolved fairly quickly.

People needed to understand it to gain confidence

of flying in that region.

- Divers soon discover that most of the wreckage

is buried in mud 50 feet below the surface.

- The scope of the wreckage was very wide

and it was monsoon season in Indonesia

with heavy rain and strong wind,

so it was challenging for us to recover the wreckage.

- It's up to the team of investigators

from Indonesia's National Transportation Safety Committee,

the KNKT,

to find out why the 737 plunged into the sea.

The KNKT's Lead investigator,

Ray Nurcahyo,

reviews video of the crash site of Flight 182,

looking for the first clues as to what went wrong.

- Nurcahyo. Hey, Ony.

Yeah, I'm looking at the video now.

The pieces are really small.

What's the distribution area of the wreckage?

Mm-hmm.

80 meters by 110 meters.

Okay. Alright, thanks.

- When I saw the debris, I was quite shocked.

Even the strongest part of the aircraft,

such as engines, it's destroyed.

So my impression was that the impact speed

was very high.

- Because pieces of the plane are buried in thick mud

at the bottom of the sea, it will be impossible to recover

the parts that might reveal the cause of the crash.

Searchers concentrate on finding the plane's

two black boxes instead.

- The black box contained the information of how

the aircraft was flying,

how the aircraft system performs,

and the conversation of the pilots in the cockpit.

It will be very difficult for us to determine

the cause of the accident without the black box.

- Okay, let's pull up the radar track.

- Until the black boxes are found,

investigators must rely on the evidence

they do have, like Flight 182's radar track.

- Everything looks fine so far.

They turn right toward the destination....

It deviates left...

...and drops like a rock.

- Flight 182 descended more than 10,000 feet

in only 25 seconds.

- Both pilots were experienced pilots.

So to be involved in such catastrophic accident

showed that something serious happened

that pilot could not handle.

- So did the crew give any indication

they had problems with the plane?

- None.

Investigators contact the controller

for insight.

- But they requested a heading change,

to avoid weather.

Request heading zero seven five degrees

to avoid weather, Sriwijaya 182.

- Sriwijaya 182, heading zero seven five approved.

- Zero seven five Sriwijaya 182.

- Flying in Southeast Asia and Indonesia

is always challenging.

The weather is very tropical, which means that thunderstorms,

monsoon rains are a matter of routine.

- Okay. Let's see what they flew into.

- Did weather conditions play a role in the accident?

- They will pull all the meteorological data

available to see if there are any external forces

being applied to the airplane, such as windshear.

- So this is a storm here.

- They examine satellite images of the weather conditions

at the time of the crash.

- Add the flight path...

They were definitely flying around the bad weather,

not into it.

But some cloud cover.

- The pilot did not fly in the storm cloud,

however, they were still in a cloud

that prevent them to see the horizon.

- Heading select.

- Without more evidence,

it will be hard to know if the heavy clouds

played a role.

Three days after the crash,

the search for the black boxes is successful.

The flight data recorder has been found.

They also find the cockpit voice recorder's

locator beacon.

But the CVR itself has disintegrated

and the critical memory card is missing.

They will need to continue sifting through the mud

to find it.

Will the flight data be enough

to determine why the pilots lost control of Flight 182?

It will take us two to five days

to read the record.

Hopefully, everything will be fine

and the mystery of this incident can be unveiled.

Within days of finding

Sriwijaya Air Flight 182's flight data recorder,

investigators review the plane's flight parameters.

- Look at that.

The thrust levers should always be moving together.

But they split,

causing the right engine to stay at full power

and the left moved to idle.

- The team discovers the thrust levers

powering the left and right engines

were at significantly different settings.

- Finding the thrust lever split

was a breakthrough to the investigations.

It answer our questions

why the aircraft deviate from the flight path

and dive in such ways.

- That amount of split...

will push a plane on its side.

- There was a lot more thrust on the right side

of the airplane than the left side of the airplane.

- But what could have caused the thrust levers to split?

- It all started here,

when they change from Take-Off mode

to Climb mode.

- Two-and-a-half minutes into the flight,

the Captain switches the autopilot

and auto-throttle settings to reduce engine power.

- Less power is needed,

so the auto throttle should be pulling both thrust levers back,

but the right one doesn't budge.

- To reach the lower combined engine power,

the auto-throttle pulls the left thrust lever

much further back than normal

to compensate for the stuck right thrust lever.

- Clearly, something was preventing it

from coming back, whether the auto-throttle

was not commanding it properly,

or was there something mechanical holding the throttle

from not coming back?

- But even if the auto-throttle caused an asymmetry,

pilots are trained to deal with this kind of issue.

- During the investigations, one of our question was:

Why such significant differences

between left and right thrust lever

resulting in the catastrophic event?

- A minute after the split starts,

the plane starts rolling left.

And then it takes about 15 seconds

before the pilot disengages the auto-pilot

and takes control.

That's not the only strange thing.

- Instead of leveling the plane,

the captain turned it into a steeper left bank.

Bank angle. Bank angle.

- Why would the captain turn the control wheel the wrong way?

I see.

It looks like the control wheel was holding right.

- The autopilot held the control wheel right

to fight the left roll.

With the right engine creating more thrust,

it caused the plane to bank to the left.

The autopilot fought to level the plane,

but it ultimately failed.

- Maybe when the captain looks at the control wheel,

he thinks the plane is turning right.

- The captain grabs the control wheel,

disengages the autopilot, and turns left.

- But of course, this was exactly

the opposite action that they should have taken.

- The left turn quickly becomes an irreversible left roll.

Bank angle. Bank angle.

- Bank angle! Captain!

- Eight seconds before plunging into the water,

the captain tries to salvage the situation.

Captain! Captain!

- Captain Afwan finally pulls the right thrust lever to idle,

but it's too late.

- What would have been a minor overbank condition

resulted in a loss of control in flight

that resulted in a loss of the airplane.

- Why did the pilots end up in this situation

in the first place?

- Investigators still need to find out what caused

the right thrust lever to jam at takeoff power.

But with most of the plane's wreckage

still on the bottom of the sea,

they'll have to look elsewhere for clues.

The investigation into the crash

of Sriwijaya Air Flight 182

now focuses on the Aircraft Maintenance Log

to explain why the aircraft's right thrust lever

didn't move back.

- So, you've got the records now?

- Yeah, but it's going to take a while to get through these.

- The records date back to 2012,

the year Sriwijaya Air leased the then

18-year-old Boeing 737.

- Aircraft Maintenance Logs are a great source of history

that lets you recreate the overall health

of the airplane and ensure that it's being maintained correctly.

- After every flight, a technician checks

the maintenance log.

It lists issues the pilot reported during the flight,

and the action taken to address them..

- The plane flew an average of seven flights per day.

It adds up to over 10,000 pages.

Okay, let's get to it.

- It will take time to review each record.

Meanwhile, the victims' families are desperate for answers.

- As the investigator-in-charge, I have the responsibility

to answer to the families and the public

what caused this accident.

Such tragic accidents need a good explanation

for the family to understand why they lost their loved ones.

- We found something.

- After several weeks of searching maintenance logs,

investigators discover an alarming pattern.

- The accident aircraft enters Sriwijaya's fleet

in the spring of 2012

and crashes in 2021.

On November 7, 2013,

a pilot reports an auto-throttle malfunction.

From then until five days before the accident flight,

there are 64 more reports of auto-throttle malfunctions.

That's a lot.

- And none of the reports are very detailed.

- In fact, not a single pilot report

mentions the thrust levers splitting.

- The auto-throttle system was routinely written up

as either "unserviceable" or "causing problems".

There was not a lot of specific information.

- How'd they follow up?

- They tried a number of things.

Most of the time, they only cleaned the connectors

on the auto throttle computer,

checked the computer systems,

the bare minimum.

- When maintenance gets back a report

that the auto-throttle malfunctioned,

their first action is to verify

if the computing system is working or not.

- To do that, technicians disconnect

the auto-throttle computers from the system,

clean the electrical connectors

and then re-attach them.

They then perform a computer test in the cockpit

that detects and diagnoses faults.

- So they'd clean the connectors,

do a test, get a "no faults" result,

and consider the case closed.

- But the auto-throttle problems kept on happening.

- The quick fix work such as cleaning

and reconnecting is not the correct action

for the problem. The line maintenance engineers

should go to the next step to fix the problem.

- Did they try anything else?

- Yes.

From 2014 up until a week before the accident flight,

they replaced various computers and other components.

And then they would do the same test,

get a "no faults" report,

and put the plane back in service,

only for the same auto-throttle problem

to pop up again within a few weeks or less.

- So why wasn't the computer test catching the problem?

- Because the test has limits.

- The post maintenance test only checked

the auto-throttle system's computers and power supply.

- It wasn't capable of finding any faults

in the auto-throttle mechanical systems,

like the cable to the engines.

- They were doing what I would consider

limited troubleshooting.

They were utilizing the flight management computer,

but interrogating a very small portion of the system.

- We double-checked the logs to see if they ever inspected

the cabling all the way to the engines.

- And? - They never did.

- Was there a persistent mechanical malfunction

that Sriwijaya's maintenance department failed to detect?

With much of Flight 182's shattered wreckage

still sitting on the floor of the Java Sea,

the Indonesian investigators come up with a novel way

of finding the answer.

- Does Sriwijaya have any other 737-500s like this one?

- Let me check.

They do.

Same age. Entered the fleet the same time.

- Let's check its logs and see if it's plagued

with similar issues.

- Could the examination of a similar Sriwijaya plane

explain why Flight 182's right thrust lever jammed?

Investigators turn their attention

to another 737-500

under maintenance in Sriwijaya Air's fleet

to understand why the right thrust lever

of Flight 182 might have jammed.

- Well, we can't recreate the computer test.

But we can still check out the thrust lever.

There's resistance.

When we know that it is hard

to move the thrust lever, that means there's an obstacle

or a friction on the cables.

- Okay. Let's see what's going on.

- The investigators check the inner workings

of the throttle assembly.

- Whoa.

It's been awhile since anyone cleaned this out,

if ever.

Let's check the condition of the cables.

- Looking at the thrust lever mechanisms

in one particular area is not enough.

You have to look at where it's originating from

and where it's going to. In this case,

from the flight deck into the engine.

- Pass that up here.

- They examine the cables running down from the cockpit

and through the equipment bay to see if they can find

something that could cause thrust levers to jam.

- When you're in the electronic and equipment bay,

you're doing two things: You're visually inspecting,

and you're also feeling for anything

that could be binding or sticky.

- Check out the dried lubricant.

Add some dirt and some rust,

that's a recipe for cable binding.

- Binding prevents the thrust lever

from being pushed or pulled.

It's like it's pinched.

- So, the planes are the same type,

the same age,

maintained in the same ways.

It follows that the accident plane

would have the same problem.

- The team assumes that the cable

for the right thrust lever bound,

preventing it from moving.

To compensate, the autopilot had to keep

pulling back the left lever.

What's unclear is why Sriwijaya

let the throttle system deteriorate so badly.

- You never let an airplane go with binding or friction.

It's something that every line maintenance engineer

or technician understands, that you have to isolate

the problem and not accept any form of binding

or friction in a control surface.

- Okay, thanks for your time.

- Investigators interview officials from Sriwijaya Air

to determine why the airline did not address

the cable-binding in the plane's throttle system.

- Well, that was enlightening.

- How so?

- Management didn't think the auto-throttle issues

occurred frequently enough to warrant a grounding

or an inspection.

So they never knew that the cables

weren't moving properly.

- How could 65 malfunctions

not be considered frequent enough?

- Because...

it didn't meet the regulations' definition

of a "repetitive defect".

- According to the Indonesian Ministry of Transportation,

for an issue to be considered a repetitive defect,

it must occur three times over fifteen flights

on the same aircraft.

None of Sriwijaya Flight 182's auto-throttle issues

met that condition.

- So the system allowed a defect to slip through the cracks.

- It looks like it.

- It just seems strange that the thrust levers

could split so much without some warning kicking in.

Does the airplane have some failsafe mechanism

for preventing thrust lever asymmetry?

- I'll look into it.

- The 737 was unique

by having independent thrust lever controls

for the left and the right engines.

And so, that inherently provided for failure modes

that could cause one thrust lever to be driven

differently from the other.

- You were right.

737 Classics have a system

that disconnects the auto-throttle.

- The system is called the Cruise Thrust Split Monitor

or CTSM.

It detects any significant difference in thrust

between the left and right engines.

- The CTSM is designed to disconnect the auto-throttle

before the split gets to be so much

that the autopilot can't fight it.

- Was the CTSM working properly?

- Okay. The auto-throttle is supposed to disconnect

under these three conditions:

The flaps are less than 12.5 degrees,

the difference in power between the two engines

is at least 700 pounds,

and either spoiler is extended

more than 2.5 degrees

for more than 1.5 seconds.

- Flight spoilers are surfaces on the wings

that work in tandem with the ailerons

to control an airplane's bank.

Did flight 182's flight parameters

meet the conditions to automatically

disconnect the auto-throttle?

- Okay, so...

their flaps were at zero.

- Condition one, met.

- And the difference in power between the engines...

hits 700 pounds

early in the flight.

- Condition two, met.

- The spoiler hit 2.5 degrees

for one-and-a-half seconds here.

- Condition three, met.

- Except the auto-throttle disengages 30 seconds

after the spoilers met their condition.

- Investigators now know the CTSM,

the plane's last line of defense

against the thrust asymmetry,

activated too late.

- The CTSM should have disconnected the autopilot

and the auto-throttle.

Had the alarm sounded on the auto-throttle disconnect,

the flight crew members' attention would have been turned

to the thrust levers,

and they would have seen the split.

- So,

why did it take 30 seconds

for the spoiler to trigger the CTSM?

- The wreckage won't give us that answer.

- Even though the debris at the bottom of the sea

could not tell us about the flight spoiler,

we tried to find the evidence somewhere else.

- Investigators search the maintenance records

of the crashed 737

for evidence that would explain

why the spoiler malfunctioned.

- Anything?

- Nothing.

And it looks like there was no requirement to check it.

- We found that there was no instruction

from the aircraft manufacturer

to inspect the flight spoiler system

unless there was an abnormality.

- As a result, the investigators have no way to determine

what exactly caused the critical 30 second delay.

- Here's the thing,

even though the auto-throttle disengaged

30 seconds later than it should have,

it doesn't explain why the pilots

never caught the thrust asymmetry in the first place.

- We need that CVR.

- Hearing what happened inside the cockpit

may be the only way to explain why the crew

was late responding to the split thrust.

- Captain!

Nearly three months after the accident,

the investigation gets a big break.

Divers find the memory card

from Sriwijaya Air Flight 182's cockpit voice recorder.

We did it systematically

and thank God, last night at 8 o'clock, we found it.

- Will the CVR explain why the pilots failed to notice

the split in the thrust levers,

and why the captain turned the plane the wrong way?

- Okay, let's start here

when the thrust levers begin to diverge.

Let's see if they notice it.

Request heading change to zero seven five

degrees to avoid weather, Sriwijaya 182.

Sriwijaya 182,

heading zero seven five approved.

- Zero seven five, Sriwijaya 182.

Approaching one one zero.

One one zero.

- Not a word about the thrust levers.

So now...

...the plane is starting to roll left.

- It's what the investigators don't hear that stands out.

- They don't notice. - They're not paying attention

to the aircraft.

- This is the time when the pilots should have time

to monitor the aircraft.

- The FDR shows the pilots had several indications

that things were going wrong on Flight 182.

If they had monitored their primary flight display,

they would have noticed that they were in a left bank

instead of a right one.

If they had looked at the control column,

they would have seen that it didn't return to center

after commanding the right turn.

And most importantly,

if they had checked their thrust levers,

they would have realized that they were split.

- These are three major breakdowns

in the way the airplane is supposed to be operating,

any one of which should have drawn the attention

of either flight crew member.

- They gave all responsibility for flying the plane

to the auto-throttle and the autopilot.

- Auto-throttle.

- Armed.

- It's what investigators call

the "ironies of automation".

- Flight crews become more and more confident

that the automatic system is gonna fly

the airplane safely.

And so, the pilot's not really thinking

that the airplane is going to be in any kind of difficulty.

- So, when did they finally clue in

to the fact that they were banking left instead of right?

- Okay, let's hear more.

Set standard.

Sriwijaya 182, climbing to altitude

one three zero, roger.

- One three zero? - One three zero.

Bank angle. Bank angle.

Bank angle. Bank angle.

Bank angle. Bank angle.

- They seem confused.

- They're totally unaware of their situation

because they're flying in clouds but not looking

at their instruments.

It's the bank angle warning that clues them in.

- The crew was clearly startled.

They didn't understand what was going on.

Bank angle. Bank angle.

Terrain. Pull up.

- The captain hears the bank angle warning,

looks at his control wheel,

sees it deflected right, and then turns it left,

making the situation worse.

- Did the first officer provide any assistance to the captain?

- Bank angle!

Captain!

Captain! Upset! Upset!

Pull up. Bank angle.

Bank angle.

Bank angle. Bank angle.

- The First Officer isn't helping at all.

He's completely forgotten all his procedures.

Bank angle. Bank angle.

- The co-pilot did not provide significant information

to the captain.

The aircraft attitude,

whether left or right or pitching down or

pitching up as described in the procedures.

- Even after the auto-throttle disengages,

it still takes the captain 10 seconds

to bring the right thrust lever back to idle.

If the auto-throttle disengaging doesn't prompt him to do that,

what does?

- It was the overspeed warning.

Fifteen seconds into the dive,

the plane is accelerating to near the speed of sound.

It's on the verge of breaking up,

so the cockpit's overspeed warning sounds.

- With the overspeed condition,

that's when he finally realizes

that both engines need to be at idle

and they make that correction.

- He finally corrects the asymmetry,

but it's too little, too late.

- If the aircraft flying higher,

maybe 30,000 feet,

the aircraft might have recovered.

In the final report,

released more than a year-and-a-half after

the crash, investigators highlight

the many failings that contributed

to the crash of Flight 182.

Chief among them was the failure of the pilots

to pay attention to what their plane was telling them

during the flight.

What happened was the sense of confidence

and complacency towards the automation system

may have caused poor monitoring and awareness

of other instruments and activities.

The report also highlights the failure

of maintenance, both at the line and management levels,

in recording a history of auto-throttle malfunctions.

- For them not to take the time

to take the aircraft out of service

and effectively troubleshoot it

in today's era is just not heard of.

You have to ensure that you're upholding safety

and you're taking every action

to troubleshoot and inspect the airplane.

- It was tragic that no pilot reported thrust lever split

in their failures. They always reported them

as auto-throttle issues.

But they didn't say the words "thrust lever split."

If the pilots don't report the problem accurately,

nobody's gonna fix it.

- Sriwijaya Air committed to improving its training

for both pilots and maintenance engineers.

But today, the airline is a much smaller operation.

Its fleet consists of four aircraft.

Only one of its 737-500s is still in use.

This accident gave the world a valuable lesson

that simple problems could lead to a catastrophe.

It is our hope that this kind of incident

will never happen again in the future.

Subtitling: difuze