Original subtitles

[Narrator] Just minutes after takeoff

from Jakarta, Indonesia...

[Pilot] Lion 6-1-0,

I have no reliable altitude information.

All instruments disagree.

[Narrator] ...pilots fight to control

one of the world's newest airliners,

the Boeing Max 8...

[Instruments Beeping]

They never really figured out

what was going on.

[Narrator] ... and end up crashing into the Java Sea.

[Speaking Indonesian]

[Translated] This was a very serious accident.

What does the tracking data show?

[Narrator] Investigators follow an erratic flight path...

They're off course,

and their altitude's all over the place.

[Narrator] ... a history of maintenance issues...

Did we have problems? You bet we did.

[Narrator] ... and learn about a hazardous piece

of hidden software.

Looks like the MCAS kicked in.

What's that?

[Narrator] What they uncover

shocks the world and grounds an entire fleet.

[John Cox] The 737 Max story

will clearly be a watershed event in aviation history.

[Flight Attendant] Ladies and gentlemen,

we are starting our approach.

[Pilot] We lost both engines!

[Flight Attendant] Put the mask over your nose.

-Emergency descent. -[Pilot] Mayday, Mayday!

[Flight Attendant] Brace for impact!

[Controller] I think I lost one.

Man: ... investigation starting into this tragedy...

Man: He's gonna crash!

[Narrator] It's just after 5:00 a.m.

in Jakarta, Indonesia,

as 181 passengers settle in

for a short domestic flight.

-In the cockpit... -Fuel pumps?

[Narrator] ...First Officer Harvino

performs pre-flight procedures.

Fuel pumps are on.

[Narrator] The captain on this flight

is Bhavye Suneja, who has

more than 6,000 flying hours.

The passengers are onboard the latest version

of the renowned Boeing 737,

known as the Max 8.

David Carbaugh is a former Boeing test pilot.

The Max is the fourth iteration

of the 737,

one of the most successful airliners ever.

And it was basically born out of a need to improve

efficiency and performance.

[Narrator] The Max 8 has quickly become

Boeing's fastest-selling airplane,

with more than 300 already in the skies

and almost 5,000 in the order books.

The one being used on today's flight

was delivered to Lion Air two months ago.

[Flight Controller] Lion 6-1-0, you are cleared

to runway 2-5 left via Sierra Charlie One.

Contact tower when you are in position.

Lion 6-1-0, cleared to runway 2-5 left

via Sierra Charlie One.

All clear, no traffic. Let's run before takeoff.

Flaps?

Flaps five. Five indicated.

[Narrator] Lion Air flight 610

is a 90-minute journey from Jakarta

over the Java Sea

to Bangka island.

The low-cost airline operates hundreds

of these short flights every day.

Indonesia is the fourth most populous country

in the world,

and with 17,000 islands you gotta have

an easy way to do short-range transportation

to get to those places.

And the Max is the ideal airplane

for that kind of operation.

[Controller] Flight 6-1-0

cleared for takeoff, runway 2-5.

Contact Terminal East when airborne.

Lion 6-1-0 cleared for takeoff.

[Engines Rev]

-[Narrator] At 6:20... -Rotate.

the Max 8 lifts off the runway at Jakarta.

[Alarm Beeping]

But immediately there's trouble.

The captain's control yoke starts shaking,

a warning that the plane is about to stall.

Takeoff config.

Okay, but... what?

[Narrator] The pilots can't identify

the source of the problem.

They have no choice but to continue climbing.

The passengers are unaware

that the pilots are dealing with anything unusual.

[Beeping]

[Controller] Lion 6-1-0,

fly heading 2-4-8

and follow standard instrument departure.

[Harvino] Lion Air 6-1-0.

[Narrator] The air traffic controller

has no idea that there's an issue in the cockpit.

The pilots get a warning that their airspeed indicators

do not agree.

Airspeed disagree. What's going on?

Should we request a return to Jakarta?

Landing gear up.

[Controller] Lion 6-1-0,

climb to flight level 2-7-0.

[Narrator] Still unaware of any trouble,

the controller instructs the crew to continue climbing

to 27,000 feet.

Altitude disagree.

[Narrator] The first officer now notices

that the altimeters also show conflicting readings.

Acknowledged. Altitude disagree.

Lion 6-1-0,

confirm our current altitude, please.

Lion 6-1-0, your present altitude is...

900 feet.

[Narrator] The pilots are getting conflicting data

about their altitude and their airspeed.

[Beeping]

Captain Suneja expects his first officer

to carry out the procedure for this situation.

Okay, memory items. Airspeed unreliable.

Uh, what altitude should I request?

Yeah, uh, request, uh...

proceed.

[Narrator] The situation is deteriorating quickly.

Climbing above 1,000 feet,

the pilots are still unsure of their airspeed.

If they fly too slowly,

the plane could stall and fall from the sky.

Request clearance to any holding point.

[Narrator] Captain Suneja wants to get the plane to a point

where he can circle and solve the problem.

Lion 6-1-0, request clearance to some holding point

due to our current condition.

Lion 6-1-0, what's the nature of your problem, please?

We are experiencing a flight control problem.

Lion 6-1-0.

[Beeping]

Where's the...

Airspeed, airspeed...

There's no airspeed unreliable.

It's there.

Got it.

Autopilot. If engaged, disengage.

[Cox] Not every failure is a major emergency.

And checklists are designed

to grade or evaluate the severity

of a system failure.

So pilots are trained

to methodically go through each step by step.

Auto throttle. If engaged...

-disengage. -Disengaged.

[Narrator] But the checklist isn't helping.

Okay, okay.

[Narrator] Now flying 5,000 feet above the sea,

Captain Suneja struggles to keep the plane's nose up.

Flight path vector may be unreliable.

[Controller] Lion 6-1-0, turn right heading 0-7-0

to avoid traffic ahead.

Set the pitch attitude.

Roger. Heading 0-7-0.

[Controller] Lion 6-1-0,

you're now descending.

We're having flight control problems

and are flying manually.

[Controller] 6-1-0, maintain heading 0-5-0.

[Cox] The cabin would have realized

that the airplane was not climbing as normal

and that it had leveled off.

And there was probably some up-and-down sensations.

[Beeping]

[Narrator] Captain Suneja has been fighting

to keep the plane's nose from pitching downwards.

Please take control for a moment.

[Narrator] He now assigns that task to his first officer...

I have control.

...so he can troubleshoot the problem himself.

Oh! This is very...

[Narrator] The first officer is also having difficulty

keeping the aircraft level.

[Cox] There was

a wide variety of problems

that they had to sort out,

and the first thing was, what's common

between all of these failures?

Because that's how you start to sort through the problems.

[Narrator] Flight 610 is flying erratically over the Java Sea

and becoming increasingly more difficult to control.

The lives of everyone onboard

now depend on the pilot's figuring out the problem...

I don't know where we are.

...and getting the plane to the ground safely.

Lion 6-1-0. I have no reliable altitude information,

all instruments disagree.

Roger, Lion 6-1-0. No restrictions.

[Carbaugh] When an aircraft declares an emergency,

the controller's number one job

is to provide assistance to that airplane.

[Narrator] The controller allows flight 610

to fly at any altitude the pilots choose.

Please clear 3,000 above and below of traffic.

Okay, will do.

What altitude would you like?

-Five thou... -[Harvino] It's diving!

-It's diving! -It's okay. It's okay.

[Narrator] Flight 610 is now speeding towards the sea...

and the pilots are out of options.

Fly up, up, up!

[Passengers Screaming]

[Automated Voice] Terrain. Terrain.

Pull up. Pull up.

Lion 6-1-0, Control.

Lion Air 6-1-0,

Control.

CityLink 8-8-2, please hold on current position.

Do you have a visual on Lion 6-1-0,

a Boeing 737 Max 8?

[Citylink Pilot] Negative. No other planes in sight.

[Narrator] Thirty minutes after crashing into the Java Sea,

the wreckage of Lion Air flight 610 is located.

There are no survivors.

Relatives of the passengers

are flown to Jakarta for trauma counseling.

While they wait for the recovery

of the bodies of their loved ones,

investigators from Indonesia's accident investigation branch,

KNKT, need to understand why

one of the best-selling new airplanes in the world

fell from the sky.

[Investigator] Okay,

what does the tracking data show?

[Narrator] Working with data from air traffic control,

KNKT investigators focus on the flight path of Lion Air 610.

They're off course.

And their altitude's all over the place.

[Man Speaking Indonesian]

[Translated] From this data,

we learned that this plane's altitude was fluctuating.

It kept going up and down.

We wanted to find out why the pilot couldn't keep the plane

at a constant altitude.

[Narrator] Investigators need to know

if the controller can shed any light

on the problems the crew was facing.

They reported that they were having a control issue.

Lion 6-1-0, what's the nature of your problem, please?

-[Alarm Beeping] -We are experiencing

a flight control problem.

Lion 6-1-0.

[Controller] That's all he said.

"A flight control problem."

Soon after that

they reported that their instruments were unreliable.

Lion 6-1-0, I have no reliable altitude information.

All instruments disagree.

Roger, Lion 6-1-0. No restrictions.

That was about it.

[Man Speaking Indonesian]

[Translated] From the information we received

from the air traffic controller, we didn't get the impression

that the pilot was under pressure.

The pilot's tone was normal.

It didn't seem that he was stressed.

[Narrator] Since the pilots of flight 610

reported flight control problems

and unreliable instruments,

investigators wonder if recent maintenance records

could explain what brought down the Max 8

only 11 minutes after takeoff.

[Translated] This flight had some problems of control.

At that point, we needed to learn more

about the plane's maintenance history.

The angle of attack sensor was replaced the day before?

[Narrator] There are two angle of attack sensors

on the 737 Max 8.

The sensors calculate the angle between the plane's wing

and the oncoming air.

Their data helps determine if the plane's wings

are providing sufficient lift.

[Carbaugh] It's a very important piece of information.

The pilots need to have some kind of warning

that they are approaching stall,

and so the angle of attack sensor is what gives that.

[Narrator] For several days, the left side sensor

had been giving faulty readings.

It was finally replaced

before the plane flew from Bali to Jakarta

one day before the accident.

Investigators interviewed the crew who flew the same plane

just hours before the crash to determine if there were

any problems with the replacement sensor.

Did we have problems? You bet we did.

[Translated] We conducted an interview

with the crew of flight 043.

We learned from them that after takeoff,

the crew was also having problems.

[Narrator] What investigators hear next is chilling.

The captain explains that when he lifted off from Bali,

there were simultaneous warnings

that his airspeed and altitude indicators had failed.

Airspeed disagree, altitude disagree.

[Narrator] A few seconds later,

the Max 8 stick shaker activated,

indicating that a stall was imminent.

Keep climbing. Gear up.

[Cox] All the modern airliners

have three sets of independently powered

essential flight instruments... airspeed and altitude,

and also the attitude of the airplane.

If there is a discrepancy,

you can determine which is providing inaccurate data.

Your instruments are correct. You have control.

The failure was on my side, so I handed off.

Flaps up.

[Narrator] The captain adjusts his faulty instruments

so they display data from the first officer's side.

We're diving. Pitch up. Keep trimming.

That's when

the plane started diving. Over and over.

[Narrator] The captain reports that the plane

began a series of uncommanded dives.

Use your trim.

That's it.

[Narrator] In order to keep the plane climbing

at a constant angle, the pilot set the position

of the horizontal stabilizer at takeoff

and made minor adjustments during the flight.

That's called "trim."

Trim can either be adjusted by the autopilot

or manually by the crew.

But every time the first officer

tries to trim the nose up,

the automated system pushes it back down.

The first officer is finding it almost impossible

to keep the plane climbing.

The trim system on a modern jet

has to be very powerful.

The trim in many cases is actually more powerful

than the control column.

[Narrator] For some reason,

the Max 8 stabilizer continues to move independently,

pushing the plane's nose down,

despite the first officer's commands.

Let's see what's in the book.

[Narrator] When the automated system moves the stabilizer,

it also spins a large wheel

that's located between the two pilots.

This tells them that the system is adjusting the trim

on its own.

[Translated] When the captain bent down

to look at the checklist manual to solve the problem

during this flight, the third crew

was the one notifying the pilot

that the trim was moving abnormally.

Runaway stabilizer. Moving switches to cutout.

[Narrator] The crew realizes

the stabilizer's automatic trim system is malfunctioning.

It's continually pushing the nose down.

Disengaging the system resolves the issue.

[Carbaugh] When they cut out the trim switches,

the system stopped doing nose-down trim.

Moving the switch to cutout pretty much solved it.

[Narrator] The investigators learned that the previous crew

then did something astonishing.

So we kept going.

You... kept going?

[Man Speaking Indonesian]

[Translated] If they had decided to return and land in Denpasar,

it would have taken only five to ten minutes

and they could have landed safely.

But they decided to continue flying to Jakarta.

Lion Air 43.

We'll continue on to Jakarta.

[Narrator] Following a near catastrophe

with unreliable instruments and the stick shaker blaring,

the crew elected to continue

the 90-minute flight to Jakarta.

It surprised all of us that they continued the flight.

[Narrator] The crew managed

to make a safe landing at Jakarta,

and reported the problem to maintenance personnel.

I reported the issue

and filled out the flight maintenance log.

[Cox] If the airplane experiences

an abnormal or an unusual system failure,

it goes into the maintenance log.

Airspeed and altitude disagreement.

Not a word about the stabilizer problem?

[Narrator] Investigators are surprised to learn

that the captain of the previous flight

said nothing about the out-of-control stabilizer

or the action he took to correct it.

Runaway stabilizer. Moving switches to cutout.

[Carbaugh] The lives of the passengers

and the crew that follows you

is basically dependent

on you filling out the paperwork correctly.

Good morning!

Good morning.

They're done loading, so we should be able

to get out of here on time today.

[Narrator] A few hours later, the passengers and crew

of flight 610 boarded the aircraft

with no knowledge or warning of the potential problems

faced by the previous crew hours earlier.

Fuel pumps.

Fuel pumps are on.

[Narrator] Did a repeat of the problem on this aircraft

result in the deaths of the 181 passengers and eight crew?

[Narrator] It takes three days for search and rescue teams

to lock onto the signal

coming from the Max 8's flight data recorder.

Divers recover it from a depth of 115 feet.

The recorder has preserved data from the accident flight

and 18 previous flights

covering almost 1800 different parameters.

Master Caution goes off

as soon as they leave the ground,

probably because airspeed and altitude don't agree.

Stick shaker activates here.

[Narrator] The data shows a repeat of the problem

on the previous flight.

Faulty readings caused by a discrepancy

between the left and right angle of attack sensors.

[Translated] From the FDR data we received

we learned that this plane had faulty angle of attack readings

that affected both flights similarly.

Left and right angle of attack values

are off by 21 degrees for the entire flight.

[Translated] We suspected the new angle of attack sensor

installed in Bali was either faulty

or the installation process was done incorrectly.

[Narrator] The mechanic who replaced the sensor

before the flight from Bali to Jakarta

failed to ensure it was calibrated,

which resulted in faulty readings.

There's a procedure that would have shown it was erroneous

and that it was bad.

They signed off that they did it.

They could not have done it.

[Narrator] On the Max 8, the angle of attack sensor

doesn't just measure the airplane's angle...

Altitude disagree.

...it helps calculate precise airspeed and altitude.

That explains why airspeed and altitude disagreed

throughout the whole flight.

[Narrator] The malfunctioning sensor on the captain's side

resulted in a difference

between the left- and the right-side speed

and altitude displays.

Then there's this.

[Narrator] The data clearly shows

that for every nose-up trim input,

there was a corresponding automatic nose-down trim input.

Sounds like what the crew of flight 43 described.

[Narrator] The data shows investigators

that for some reason, the plane's automated trim system

was repeatedly dropping the plane's nose

while the pilots fought to lift it.

Twenty-six separate nose-down commands.

This doesn't look like a runaway stabilizer to me.

[Narrator] Runaway stabilizer

is a common malfunction of the trim system

usually resulting in one continuous uncommanded movement

of the stabilizer.

[Translated] The NTSB brought a representative from Boeing

to help us in our investigation.

We asked him to explain why in both flight 610 and 0-4-3

the same plane continued to pitch down.

We're trying to understand these automatic inputs.

Looks like the MCAS kicked in.

What's that?

[Narrator] Boeing points to an obscure automated system

known as MCAS...

the Maneuvering Characteristics Augmentation System.

That's when we first learned about the MCAS.

[Narrator] To understand what could have caused

the crash of flight 610,

investigators need to go back seven years to 2011

when Boeing first announced the development of the Max 8.

[Carbaugh] The 737 Max

was basically born out of a need to improve

the performance and sales of the 737.

[Narrator] In 2010,

Boeing's main competitor, Airbus,

unveiled the A320neo,

a fuel-efficient short-haul airplane.

It was an immediate hit with airlines

at a time of rising fuel costs.

[Cox] Boeing was caught by surprise.

The A3200neo was significantly more fuel-efficient.

So all of a sudden they were faced with a dilemma:

do you design a new airplane, a four- or five-year project,

or do you modify the existing 737?

[Narrator] But there were problems with taking a plane

that was designed in the 1960s

and turning it into a fast and fuel-efficient aircraft.

[Carbaugh] To improve the performance of the Max

they decided to install

more fuel-efficient, larger engines.

[Narrator] The only way to make those larger engines fit

was to slide them forward in the wings.

[Cox] The design engineers had a problem with

the ground clearance from the engines.

And on the 737, you can't increase

the size of the main landing gear

because of the size of the wheel wells.

It has to fit there.

So the only thing they could do

was to move the engines further forward and up.

[Narrator] That solved one problem, but created another.

It caused the 737 to pitch up at low speeds,

particularly when it was already in a nose-up position,

like during takeoffs.

So they created software

that would recognize the airplane approaching stall

and artificially force the nose down.

And, logically, they turned to the trim system to do that.

And that's the problem you solved with MCAS?

Yes. It made the Max handle like any other 737.

MCAS was designed for a very low-probability event.

[Harvino] It's diving!

-It's diving! -It's okay.

How were they trained to respond?

Well, they weren't. Not specifically.

Fly up. Up! Up!

[Narrator] Could Boeing's high-tech solution

to a design problem

have inadvertently put thousands of passengers

around the world at risk?

In order to eliminate the need for costly pilot training,

Boeing had to convince authorities that the Max 8

handled the same way as all previous 737s.

Different handling characteristics

will automatically require

time in the simulator and extra training.

[Narrator] Boeing argued that since MCAS

operated in the background,

without the need for any pilot input,

it didn't affect the airplane's handling.

Not a word about MCAS here.

[Narrator] Boeing never included mention of MCAS

in the flight control manuals.

They argued that since the system

was not under control of the crew,

it should not be included.

It's like the system doesn't even exist.

[Translated] Boeing thinks that it's an automatic system

for safety purposes

and has nothing to do with pilot operation.

[Narrator] According to Boeing, the MCAS software

would automatically move the plane's stabilizer

to push the plane's nose down if it started to pitch up

under very specific circumstances.

It only kicks in when these three conditions are met.

[Narrator] Boeing explains that MCAS only activates

when it senses that the angle of attack is excessive...

when the autopilot is off...

and when the flaps are retracted,

an extremely rare combination.

[Cox] Professional pilots don't

typically stall airplanes,

so the likelihood of an MCAS activation

was thought to be extremely low.

[Investigator] This is the data from both flights.

[Narrator] Tragically, the data shows

that because of the faulty maintenance

on the angle of attack sensor,

flight 610 ended up meeting all three conditions.

[Speaking Indonesian]

[Translated] The series of problems occurred

when the left angle of attack sensor was replaced in Bali.

[Narrator] Investigators dig deeper in to the data

and discover the MCAS system had no fail-safe.

[Translated] The MCAS installed in the plane

relied on only one sensor.

[Narrator] MCAS only took data

from one angle of attack sensor, not both.

[Beeping]

Most protection systems are designed with redundancies...

Your instruments are correct. You have control.

...so a single failure doesn't result in catastrophe.

Flaps up.

[Cox] What Boeing did not adequately do

was assess all of the other failures

that that single component would have.

The faulty angle of attack sensor

wrongly showed the plane pitching up steeply.

The autopilot was disengaged for the entire fight.

And then right here, they retract the flaps.

Exactly the same...

as the previous flight.

That's when MCAS kicks in...

and starts pushing the nose down.

[Narrator] Up to this point,

the crew only had a minor instrument problem.

-By raising the flaps... -Okay, okay.

the pilots unknowingly triggered

a much more serious problem.

We assumed that pilots would know how to respond.

[Narrator] Boeing made the assumption that pilots

would respond to the uncommanded MCAS inputs

by disengaging the automatic trim.

[Cox] The Boeing assumptions were

that the pilots would instantly recognize

the inadvertent MCAS activation

and treat it within three seconds.

[Narrator] Investigators examined the flight data

of the previous Lion Air flight

to see how that crew reacted to the MCAS activation.

The first MCAS input on flight 43 is here.

The captain pulls back on his control column

and applies manual trim,

then fights against the MCAS for three minutes and 40 seconds

before hitting the cutout switch.

I think the assumption that they were going to recognize

and act within three seconds

was very optimistic, if not unrealistic.

Lion 6-1-0. I have no reliable altitude information.

All instruments disagree.

[Narrator] Unlike the previous crew,

the pilots of flight 610 struggled with the problem

for more than ten minutes...

Fly up. Up! Up!

...and never made the connection to a runaway stabilizer.

Investigators need to understand why two crews

facing an identical problem reacted so differently.

[Narrator] Investigators struggle to understand

why the pilots of Lion Air flight 610

lost control of the aircraft.

After nearly three months of searching the ocean floor,

the cockpit voice recorder is finally recovered

and taken for analysis.

[Man Speaking Indonesian]

[Translated] The CVR was the key to our investigation.

Together with the FDR data,

the CVR could reveal all the mystery

in our investigation.

[Controller] Lion 6-1-0 cleared for takeoff.

[Narrator] Investigators hope the recording

will help to explain why the crew of flight 610

couldn't identify the problem

and take corrective action to fix it.

[Harvino, Recording] Rotate.

[Beeping]

Takeoff config.

[Suneja] Okay, but what?

[Narrator] The faulty angle of attack sensor

triggers a series of warnings as soon as the plane lifts off.

[Harvino] Airspeed disagree. What's going on?

Should we request a return to Jakarta?

Landing gear up.

[Instruments Beeping]

After takeoff, the MCAS system was activated.

and their plane started to pitch down.

[Narrator] The captain has noticed

that the plane's stabilizer

is now automatically trimming the nose down,

and does what Boeing assumed he would.

He pulls back on the control column

and uses manual trim to counteract

the computerized inputs.

Okay. Boeing was right about that.

[Narrator] But the captain never mentions the trim problem.

[Beeping]

[Narrator] He and his first officer are focused entirely

on their faulty airspeed and altitude readings.

Where's the...?

Airspeed, airspeed...

There's no airspeed unreliable.

It's there.

[Harvino] Got it.

[Translated] This is where we found significant differences

between flight 0-4-3 and 610.

[Narrator] It takes first officer Harvino

nearly two minutes to locate the appropriate checklist

for mismatched airspeed.

[Cox] I think the first officer was pretty well task-saturated.

And one of the things that task saturation does in humans,

it limits our ability to communicate.

We don't hear well and we don't verbalize things very well.

[Suneja] Props up four degrees and 75 percent at one.

[Harvino] Here it is.

[Narrator] When the automated trim system pushes the nose down

a large wheel makes a characteristic sound.

When the trim wheel moves,

it makes a sound like a freight train.

[Loud Whirring]

It's meant to be noticeable.

Following are reliable.

Attitude.

N-1.

[Harvino] Ground speed, check.

They still don't notice it.

Wrong about that.

He didn't put it together that every time he trimmed up,

The MCAS system was trimming it back down.

Thirty-four times.

He applies nose-up trim 34 times

and doesn't think to wonder why.

They did not recognize the problem

and take the corrective action Boeing predicted they would.

[Cox] In this particular case, Boeing made assumptions

about design and pilot experience and training

that didn't add up.

[Suneja] Please take control for a moment.

[Harvino] I have control.

[Narrator] Investigators now hear another crucial difference

between flight 610 and the previous flight.

That's it? "Please take control"?

Not a word about the fact that he's had to make more than...

thirty trim inputs.

[Cox] I think the captain was very frustrated

with the first officer.

Oh. It's very...

And I'm sure he didn't really want to hand it over

to the first officer,

but he felt that he needed to

in order to figure out what was going wrong with the checklist.

[Narrator] But because there's no mention of MCAS

in the manual,

there isn't a checklist for the crew to follow.

-It's diving. It's diving! -Okay.

[Narrator] With no warning from the captain

about the need for repeated nose-up trim,

the first officer quickly becomes overwhelmed.

[Beeping Continues]

Sadly, this first officer was pretty well overwhelmed,

and as the system trimmed the nose down,

he was not nearly aggressive enough in responding to that.

[Translated] In Flight 610, the pilot didn't deactivate

the automatic trim,

and the plane's nose kept coming down because of the MCAS,

and it didn't stop until the plane crashed.

[Narrator] One minute after taking control,

the first officer watches helplessly

as the plane plunges towards the Java Sea.

[Harvino] Pulling up. Up. Up!

[Narrator] KNKT investigators

discovered that Boeing's assumptions

of how pilots would recognize and overcome

an uncommanded nose-down trim on the Max 8

were fatally flawed.

They sure didn't act the way Boeing said they would.

Here it is.

"Without requiring exceptional skill or strength."

[Narrator] Investigators soon learn

why Boeing's assumptions about how pilots would react

were so wrong.

To certify the Max 8,

Boeing assured the FAA that an average flight crew

would be able to override the MCAS system.

So were these guys average?

Captain passed all his checks.

Looks like a competent pilot.

This guy...

is a whole different story.

[Narrator] Investigators are surprised

by the first officer's background.

[Cox] The first officer on Lion Air flight 610

had had challenges in training.

He had trouble staying up with the airplane,

understanding the complexities.

His manual flying skills were not optimum,

and he required additional training.

-It's diving. It's diving. -It's okay. It's okay.

[Narrator] Flight 610 proved that Boeing was wrong

about how pilots would react to an MCAS failure.

Pulling up. Up. Up!

[Screaming]

[Cox] They never really figured it out, and then...

the captain gave control to someone whose...

manual flying skills were not gonna save the day.

[Narrator] As a result of the accident,

Boeing issues new guidelines for Max 8 pilots

informing them about MCAS and detailing the procedures

to follow in the event it triggers

an uncommanded nose-down.

The bulletin advises pilots to apply manual trim

and to move the stabilizer trim switches to cutout.

This was a reinforcement to the pilots that says,

"There is a system on the airplane

that can move the trim.

If it does so, treat it as a runaway stabilizer.

Hey.

Turn the TV on.

[Newscaster] Our breaking news:

An Ethiopian Airlines has crashed shortly after takeoff

from Addis Ababa, killing all...

[Narrator] The belief that Boeing's advisory

would prevent another similar accident

is shattered four months later,

when another Max 8 crashes.

Flight tracking data shows that Ethiopian Airlines flight 302's

altitude fluctuated throughout the flight.

There's immediate speculation that once again,

Boeing's MCAS software is to blame.

[Cox] In both accidents the MCAS activated,

causing this nose-down trim situation

to occur repeatedly.

And in both cases, the crews let the airplane accelerate

far, far greater speed than it should have been.

Put those two together,

and the controllability of the airplane was lost.

[Narrator] This time, the pilots knew about MCAS

and what to do in case it activated,

yet they still couldn't control the airplane.

Boeing realized, "Well, if this crew can't handle it",

then other crews won't.

[Narrator] In spite of the FAA's assurance

that the Max 8 is airworthy,

regulators around the world ground the Max 8 fleet

until the problem with MCAS is fixed.

[Translated] The main thing in our mind was we worried

that all of the Boeing 737 Max 8s

that are currently flying all over the world

might have the potential to suffer the same catastrophe.

[Narrator] The FAA eventually follows suit.

Our concern isn't with the mistakes that were made...

[Narrator] A U.S. Congressional investigation determines

that Boeing made faulty technical assumptions

and errors in judgment which led to these accidents.

...that the pilots didn't know about this is unacceptable.

[Narrator] Boeing insists it's learned from these incidents

and is determined to make the Max 8 safe

and regain public trust.

Boeing has committed to making it easier

for pilots to override the MCAS system.

Once that override is activated,

the system will not continue to reengage.

And they're developing a training program

to familiarize pilots with MCAS.

[Cox] The 737 Max story

will change forever how airplanes are certified,

and the 737 Max will clearly be a watershed event

in aviation history.