Original subtitles

NARRATOR: All that's left of Ethiopian Airlines

flight 409 lies at the bottom of the Mediterranean Sea.

This accident was very unusual, very unlikely.

Everybody was shocked that we had a major crash in Lebanon.

Turn right now, heading 270.

NARRATOR: The 737 fell from the sky

just minutes after leaving Beirut.

Oh God!

NARRATOR: Now rumors of a terrorist attack

are spreading to the streets.

They speculate that the airplane

could be hit by a bomb.

NARRATOR: And investigators are struggling

to understand the plane's bizarre flight path.

Often, the best approach is the Sherlock Holmes approach.

We need to check those trim tabs.

Eliminate everything you didn't happen.

What time did he check in?

What's left--

That's it.

--is probably what did happen.

What is it?

NARRATOR: The evidence leads to a finding so controversial.

This flight was in jeopardy from the outset.

NARRATOR: Some still refuse to believe it.

ANNOUNCER: Ladies and gentlemen,

we are starting our approach.

We lost both engines.

Keep the mask up your nose.

Emergency descend. - Mayday!

Mayday!

Brace for impact!

He's the last one.

Investigation started in 2004.

He's going to crash.

NARRATOR: January 25, 2010.

It's just past midnight at Beirut's

International Airport.

Fuel is good.

Load is calculated.

In a typical departure, the flight crew

reviews its load, reviews the fuel,

reviews the route then runs through the company checklists

to get the airplane underway.

NARRATOR: Captain Habtamu Negasa

has been flying with Ethiopian Airlines for over 20 years

and has more than 10,000 hours in the cockpit.

Exterior checks complete?

Check complete.

No problems.

NARRATOR: The first officer is far less experienced.

Aluna Beyene is a recent graduate

of the Ethiopian Airlines Flight Academy.

Tonight, there are 82 passengers

aboard the Boeing 737.

They are preparing for an overnight flight

to Addis Ababa, Ethiopia.

Many passengers are Lebanese.

Some are Ethiopians returning home after working abroad.

There's also an undercover security officer

on board tonight's flight.

Flight security officer's there post-9/11

to intercept anybody who attempts to interfere

with the flight crew.

NARRATOR: Beirut airport has seen its share of trouble.

It was the site of the 1983 marine barracks

bombing that killed 241 American servicemen.

In 2006, all three runways were destroyed by Israeli missiles

during the Lebanon war.

Today, the rebuilt airport serves

flights from around the world.

Beirut airport is a very busy, very well-put-together

civil airport.

Its only difficulty is presented by the mountains

directly to the East.

NARRATOR: The Lebanon mountains rise sharply from the coast,

forcing all flights to take off toward the Mediterranean Sea.

Flight 409's flight plan calls for it to head southwest then

make a U-turn towards a navigational checkpoint

called Chekka.

Ethiopian 409, wind's nearly calm.

Cleared for takeoff 2-1.

NARRATOR: The air traffic controller

gives flight 409 its final takeoff instructions.

Immediate right turn to Chekka.

Roger.

Cleared for takeoff runway 2-1.

Immediate right turn to Chekka.

Ethiopian 409.

Left side is clear.

Right side is clear.

NARRATOR: The captain sets his radar to display the weather.

Weather's on my side.

Roger.

Terrain on my side.

NARRATOR: While the first officer monitors the terrain.

The weather that night had mixed clouds with bases

from 2,000 feet overcast up to 20,000 feet,

and there were scattered thunderstorms in the area.

Take off thrust set.

NARRATOR: The 737 accelerates down the runway.

Speed increasing, check.

Do you see that?

Rotate.

NARRATOR: Ethiopian Airlines 409 lifts off just

after 2:30 in the morning.

Their takeoff procedure and the initial part

of the takeoff seemed entirely routine and ordinary,

and well-executed.

Gear up.

Heading select.

Heading select, check.

NARRATOR: The captain begins banking the plane to the right

as he climbs.

Ethiopian 409 control 19-3 Ma Salama.

NARRATOR: The tower controller bids the crew goodbye

and hands the flight off to a colleague.

Ethiopian 409, good morning.

Climb flight level 290.

NARRATOR: The area controller instructs flight

409 to climb to 29,000 feet.

Flight level 290, Ethiopian 409.

NARRATOR: But the weather ahead is becoming fierce.

There's lightning in the air.

You see the flashes.

You're beginning to feel turbulence.

Sir, I suggest that, due to the weather,

you follow heading 270 to be in the clear.

2-1, say again.

Confirm heading 210.

NARRATOR: Just a few minutes into the flight, something

is going wrong.

An alarm warns the crew that their turn

is becoming dangerously steep.

The airplane is being banked beyond

its normal operational limits.

NARRATOR: Captain Negasa is struggling

to correct the problem.

He veers back to the left towards the thunderstorm the

controller wants him to avoid.

As you enter heavy precipitation,

the cockpit can become very noisy with a tremendous worst.

It gets your attention.

NARRATOR: The controller sees that flight 409 is starting

to veer back towards Beirut.

He warns the pilots again that they need to turn.

Ethiopian 409, follow heading 270.

Turn right, heading 270.

At this moment, the controller

was probably most concerned with the fact

that the crew had overshot its heading,

would be conflicting with inbound traffic

and had to be moved away from a possible conflict

with terrain.

Correct heading 270.

Roger.

OK, what heading did he say?

270.

Set.

NARRATOR: The cockpit fills with a disturbing sound.

What is it?

NARRATOR: The control columns vibrate,

warning them that the plane is about to stall.

Speak.

What is it?

Go around.

Go around.

Roger.

Go around.

NARRATOR: The captain pushes the throttle all the way up

to go around the problem.

Ethiopian 409, follow heading 270, sir.

Follow heading 270.

Turn right, heading 270 now.

Whenever a controller tells the pilot to do something now,

the controller is telling the flight that they're

in immediate danger.

Speed is going down.

Ethiopian 409, you are going into the mountain.

Turn right now, heading 270.

He was worried that the crew was

going to fly the airplane into the hills

behind Beirut airport.

NARRATOR: But their situation is even more dire.

The chaotic motion of the plane is torture for passengers.

It's horrible.

You're feeling a 3G load.

It's pushed you down in your seat.

You're getting squashed.

Your fellow passengers, some of them are silent some of them

were screaming.

God.

Oh, God.

Oh, God.

Ethiopian 409, Beirut?

Ethiopian 409, Beirut?

We've lost an aircraft.

Ethiopian.

We don't know what's happened, and we

don't know his position.

NARRATOR: Ethiopian 409 has plunged

into the Mediterranean Sea just five minutes after takeoff.

Within minutes of the crash, the Lebanese military

issued a distress call to all available ships in the area.

Local boats, as well as foreign warships, join the search.

My first reaction was this accident

was very unusual, very unlikely,

that really required a very good investigation to see

what we could learn from it.

NARRATOR: It's the first major commercial aircraft accident

in Lebanon in nearly 35 years.

Within hours, the Lebanese Civil

Aviation Authority dispatches Hamdi Chaouk to take charge.

As soon as I reached the airport,

I had to try to manage the environment of the accident.

All right.

The hardest part is how to deal with all the search

and rescue of major parties, from defense

to the interior ministry to all the concerned parties who

have never done this before.

NARRATOR: A former pilot, he's one

of the few experienced investigators in the country.

So we've got to make this our search area

right here on this grid, OK?

We have ships here, here, and here.

OK.

NARRATOR: Mohamed Aziz is his second in command.

First of all, we wanted, if by any miracle,

anybody had escaped, we wanted to be

able to pick any survivor, especially

that the first hours they discovered two or three

bodies, most probably they were thrown out

of the plane when it crashed.

Have you any sign of wreckage?

Negative, nothing.

NARRATOR: Chaouk is under intense pressure

to locate the wreckage fast.

So you want to answer very important

questions to the family.

Why my relative died?

It goes to your head as an investigator always.

I want to know the truth.

Nothing here?

No.

No?

NARRATOR: But the storm flight 409 was trying

to avoid is still raging.

A major deterrent to the search and rescue operation

was whether.

Bad weather was high waves and the sea and so on.

So this makes the search and rescue operation difficult.

OK, let's see what kind of weather they were flying.

NARRATOR: Could the storm have been fierce enough

to bring down a 737?

Well, there were thunderstorms west

of the airport.

Thunderstorms can be very dangerous.

They can interrupt the flight and the airplane structurally,

and they complicate the safe operation of the airplane.

NARRATOR: In rare cases, a lightning

strike can damage the electronics

that control the aircraft.

While a lightning strike on an airplane

is not uncommon and usually doesn't

create damage to the airplane, it

can under some circumstances.

NARRATOR: At the same time, rumors

are spreading that flight 409 was the target

of a terrorist bombing.

When you live in a country like Lebanon, every now

and then, you have fighting.

You have explosions.

And the first thing that comes to mind when you lose

an aircraft just like that is maybe there

is an explosion on board the flight.

NARRATOR: As day breaks, wreckage

begins to wash up onshore.

Navy ships recover floating debris,

and some human remains.

It's painfully obvious there are no survivors.

The Lebanese army have recovered seven bodies.

NARRATOR: 82 passengers and eight crew are dead.

Most of the plane is still missing.

Without more wreckage, investigators

may never know what happened.

At the airport, controller's eyewitness accounts

seem to support a possible terrorist attack.

I saw a bright orange flash.

It looked like the plane exploded.

The controller he saw a ball of fire at the place.

He presumed that the plane crashed.

So some people they say that it could be an explosion.

NARRATOR: Hard evidence of sabotage

requires a close examination of the wreckage.

You have to go back to the evidence

because the evidence speaks.

The part itself of the plane can tell

you how the accident happened.

NARRATOR: And so far, the inexperienced team is having

trouble locating the plane.

No luck yet.

Have you searched this sector here?

Yeah, we looked everywhere.

We looked here, here, here.

We were able to determine where probably the aircraft

would have been, yet when the Navy and the Air Force

started to search for the plane, they could not find it.

NARRATOR: A Navy ship is searching for signals

from the plane's black boxes.

These begin transmitting an alert

as soon as they come in contact with water.

That is what we call a pinger,

and that emits a signal for about 30 days after the crash.

NARRATOR: But two days in, the search hits a major hurdle.

Investigators learned the Navy sonar they've been using

can't home in on the signals.

It's not precise enough.

We'll never find them this way.

We don't have the right equipment.

We could not sleep.

We were always thinking that we need the recorders.

NARRATOR: Chaouk contacts aviation authorities

in France for help.

We're hoping you can come immediately.

Yeah, it's quite urgent.

NARRATOR: They have the equipment and the expertise

to find the recorders.

OK, great.

All right, thanks.

Great.

They're on their way.

It was a learning curve for everybody, the leaders

or divers or the Navy people.

NARRATOR: With the right gear--

Thank you for coming.

NARRATOR: --the team should be able to search more quickly.

But valuable time has already been lost,

and other people could be at risk.

These type of airplanes are flying all over the world.

And if there is a problem, we need

to take whatever corrective action that's needed.

NARRATOR: The United States also sends help.

Because the 737 is American-made,

the National Transportation Safety Board's

Dennis Jones joins the team.

Welcome to Beirut.

Thanks.

We still don't have a crash site, per se,

the flight recorder, which is always

a big concern of interest, was still yet to be found.

We got the flight track.

NARRATOR: With no wreckage to study,

Jones and Chaouk turned to a record

of the plane's flight path.

We got the radar track from the airport.

This should show us exactly what they did.

When we first got there, some of the information

we had that was helpful was the radar

data and air traffic control information in general.

So we were able to start evaluating

that pretty quickly.

NARRATOR: The radar paints a baffling picture.

It's like no one's flying.

Exactly.

NARRATOR: Almost from takeoff, the plane follows

an unusual and erratic path.

Once you see what happened to the plane,

you would wonder really what's happening.

As if there were no crew in the cockpit.

It is almost similar--

270.

--of a situation where nobody is in control of the plane.

NARRATOR: Now that they've seen the strange flight path.

OK, so here's the track.

So they could be anywhere along here.

NARRATOR: Investigators are more

anxious than ever to get at the wreckage

and search for answers.

Let's take a look at that monitor.

Now, what we're seeing is basically an external view

with the radar data and air traffic control,

but we didn't get an idea of what was actually going

on board the aircraft itself.

So we became even more eager to get the recorder.

That's it.

That's it.

That's exactly what we're looking for.

NARRATOR: Finally, eight days after the crash,

the French equipment detects the vital signals.

It was found 45 meters deep and 5 kilometers

southwest of Beirut airport.

NARRATOR: Cameras mounted on unmanned subs

captured the first images of what remains of flight 409.

We heard the Odyssey submarine

that had been used for taking photos

and survey for the wreckage located on the seabed.

NARRATOR: It's too expensive to bring all the wreckage

to the surface, so investigators

focus on the tail section where the two

black boxes are stored.

They retrieved the tail, the horizontal stabilizer,

with the tail comb as well.

They were still attached together.

And they found the FDR located underneath.

We were quite delighted about that,

and the Lebanese government immediately

started making plans so having that transported

to a facility to be evaluated.

NARRATOR: But they only find the Flight Data Recorder.

What of the CVR?

NARRATOR: The Cockpit Voice Recorder is still missing.

So it's got to be in this sector.

That's what we think.

NARRATOR: As divers continue to search for the CVR,

investigators study underwater video of the wreckage.

OK, let's start mapping this out.

NARRATOR: When a plane explodes in midair,

the debris falls in a circular pattern.

But if a plane hits the water intact,

the debris will fall in a linear pattern.

The underwater video allows investigators

to map the position of every piece of wreckage.

Another one here lining up nice and neat.

In this case, we found all the pieces

laying in the bed of the water in almost

300 meter straight line.

NARRATOR: They also search for any sign of fire damage.

You would look for a certain signature

to show us perhaps there might have been some heat

damage or fire damage.

Go back.

I want to see that piece again.

NARRATOR: But there's no sign that the metal was

ripped open by a blast and no burn marks

on any of the wreckage.

We looked at the footage.

We couldn't identify any black spot, black soot

or anything of the sort.

We saw none at all.

There's no sign of any explosion.

Ethiopian 409 Beirut.

NARRATOR: They conclude that the tower

controller may have been fooled by a trick of the light.

It was a stormy night, so throughout the night,

you were hearing thunderstorms, lightning,

and they do sound exactly like explosion,

and they give you a bright light even stronger

than any big explosion.

NARRATOR: Next, investigators focus

on the flight data recorder or FDR found in the wreckage.

Nothing so far.

NARRATOR: There are more than 1,000 parameters to analyze.

The flight data recorder records essentially

the instrument and other parameters from the aircraft,

basically what the aircraft is doing.

And that retains, in this case, 25 hours of information.

NARRATOR: Almost all the data is normal,

but one number stands out.

Take a look at that stabilizer setting.

It's a bit low, but still in the green.

NARRATOR: The stabilizer is part of the tail.

Pilots adjust its angle depending

on the weight of the plane.

Move it up, and the plane pitches up.

Move it down, and it forces the nose down.

OK.

Fuel is good.

Load is calculated.

Check complete.

No problems.

NARRATOR: The FDR reveals that flight

409 stabilizer was set further down the normal for takeoff.

Such a small variation probably wouldn't cause the pilots

to lose control of their plane, but investigators won't know

its effect until they can test the configuration

in a flight simulator.

At that point, obviously, everything was on the table.

We knew we had a lot more factual finding to do.

We got it.

Oh, here it is.

NARRATOR: In the Mediterranean Sea,

the arduous search for the CVR finally pays off.

Oh, yeah, that's it.

Hey, Aziz.

We got it.

Oh, you found it?

Yeah.

I have to praise the Lebanese Navy diver

because, with the equipment they had,

had to do a real hand search 45 meters underwater, which

is quite difficult, but they were

able to recover it at the end.

NARRATOR: Investigators can only

hope that the pilot said something that will reveal

why their plane went down.

PILOT (ON RECORDER): Fuel's good.

Load is calculated.

NARRATOR: Investigators sync up the conversation on the CVR.

PILOT (ON RECORDER): Exterior check's complete.

NARRATOR: With the plane's known flight path.

FIRST OFFICER (ON RECORDER): Roger.

Check complete. No problems.

NARRATOR: They listen for any sign of trouble.

We want to try to get a better understanding if there

might have been some kind of mechanical problem

based on what they were perceiving.

European 409, wind's nearly calm.

Cleared for takeoff 2-1 immediate right turn

to Chekka.

PILOT (ON RECORDER): Roger.

Cleared for takeoff runway 2-1.

Immediate right turn to Chekka, Ethiopian 409.

Everything seemed to be going just right.

Now, once they took off, the first part of the takeoff

was normal.

Turn right, initially heading 315.

315, roger.

NARRATOR: Investigators hear the controller give the pilots

a new heading, but the plane goes

off in a different direction.

As they approached the heading

that they had been assigned, they overshot the heading.

He was supposed to turn this far, but he just kept going.

Mark?

They're way off course.

Sir, I suggest that, due to the weather,

you follow heading 270 to be in the clear.

NARRATOR: Each time the pilots tried to correct their course,

they turned too far and banked too steeply.

It's a sure indication that the airplane has lost control.

Ethiopian 409, you are going into the mountain.

Turn right now, heading 270.

The airplane was rolling into an ever steeper bank.

Its lift vector was decreasing, so the nose

was dropping toward the sea, ultimately

leading to a spiral.

Oh, God.

The plane was out of control.

NARRATOR: But there's nothing on the recording indicating

a mechanical failure.

And we just were not hearing anything

that showed a malfunction which was consistent with the flight

data recorder.

It was just something that we certainly

didn't have any answers for in the beginning.

NARRATOR: Desperate to know what

brought down the 737, investigators dig

into maintenance records.

They learn that some 737 sevens

have a small but dangerous flaw in a vital part of a tail.

Hey, Dennis, I think we need to check those trim tabs.

NARRATOR: Trim tabs are small control surfaces set

into the tail of the plane.

They counteract the powerful flow

of air pushing against the tail,

making it easier for the pilot to fly the plane.

To use an analogy with cars, it's like a power steering as

compared to manual steering.

NARRATOR: If the trim tabs were damaged,

it could explain why the captain was struggling

to control the aircraft.

Left heading 270.

Roger.

Left heading 270.

My experiences of flying an airplane out of trim it

can make it extremely difficult to fly.

It can even go beyond the forces

that the pilot could actually use or input to counter it.

You can bring that over here.

NARRATOR: Investigators are in luck.

The stabilizer and trim tabs are

among the few pieces of wreckage

recovered from the sea.

The team assembled to evaluate this aircraft

hit the water close to 400 knots,

so we're expecting a lot of things to be damaged.

So we wanted to kind of evaluate

it to see if there was anything that was pre-existing

that might have somehow contributed

to this sequence of events.

NARRATOR: But it's another dead end.

A close inspection of the trim tabs reveals no damage at all.

No sign of any malfunction.

They did not affect the pilot's ability to steer the plane.

Jones and the team have mechanical failure.

Now they'll focus on the final part of the doomed aircraft,

the cockpit.

Investigators traveled to Seattle,

Washington, to Boeing state-of-the-art

flight simulator.

OK, we're going to run the Ethiopian 409.

Going to set the trim to match theirs.

NARRATOR: The flight data has shown

that flight 409 stabilizer was set to a shallower

than normal takeoff angle.

Investigators want to know if that affected the pilot's

ability to handle the plane.

You kind of get a front-row seat of perhaps what

the flight crew were seeing at the time and how

the aircraft was handling.

OK, let's see how this thing is going to fly.

NARRATOR: The low angle of the nose

makes the plane difficult to handle at first.

It's definitely not happy.

The trim was mis-set for takeoff by a small margin

but nevertheless by enough to create an undesirable pressure

for the pilot on the controls.

So the pilot was always fighting the airplane

to one degree or another.

NARRATOR: But in the simulator, the pilot has no difficulty

correcting the problem.

OK, well.

Try it with no trim at all.

Every single time we try to recover this aircraft,

we are able to recover it.

Well, they should have been able to recover.

NARRATOR: They conclude that the low stabilizer setting

did not cause this crash.

Something else made the 737 spiral into the sea.

Officials from Ethiopian Airlines

still believe terrorism is to blame.

They insist that an onboard bomb cannot be ruled out

until more of the wreckage is recovered

from the Mediterranean.

The investigators don't agree.

He told them that it's quite a remote possibility

that there was something put on board that plane.

When the plane explodes with a bomb on board,

it flies its own route, and it explodes.

It doesn't go up left and right and up and down,

and then something explodes on the plane.

NARRATOR: But stamping out rumors is never easy.

Let's go over here.

NARRATOR: Investigators are under growing pressure

to explain what happened.

If it wasn't a bomb, then what did bring down flight 409?

An aircraft accident investigation,

often the best approach is the Sherlock Holmes approach.

What you do is eliminate everything you didn't happen.

What's left is probably what did happen.

The controllers did their job.

Turn right, initially heading 315.

The ground-based navigational systems were working.

The airplane was functioning properly.

So what we have left is the crew.

NARRATOR: Investigators return to the CVR.

They hope the crew's conversation can shed light

on why two qualified pilots lost control of a mechanically

sound airplane.

Looks pretty normal.

Exterior checks complete?

Check complete.

No problems.

NARRATOR: noticed something odd.

The mood, even the speed of the voice or even the tone--

Feels good.

Load calculated.

--did not reflect what is really actually

happening in the aircraft.

During the takeoff roll--

Do you see that?

--the captain saw something because he tells first

officer did you see that?

But then, there was no reaction from the first officer.

NARRATOR: The first officer is uncharacteristically quiet.

OK, engage the autopilot.

NARRATOR: Even worse, he's not following

his captain's commands.

Hold on.

Stop for a second.

That would have changed things.

The advantage of engaging the autopilot in that situation

is that the pilot can then let the autopilot worry

about the attitude of the airplane

while he sits back and takes the big picture,

maintain situational awareness.

NARRATOR: The autopilot can adjust the throttles

to maintain a safe airspeed and can keep the plane

on the right heading.

But investigators learned it was

impossible for the autopilot to engage on flight 409.

There's no way it could come on.

PILOT (ON RECORDER): OK.

Engage the autopilot.

NARRATOR: It's designed not to switch on if one of the pilots

is pulling other control column as the captain was.

And for some reason, the first officer

didn't tell the captain the autopilot wasn't on.

Had the autopilot been engaged when the captain

ordered the first pilot to engage,

it would have saved the whole flight.

The interaction between the crew members

were not what we would expect from a professional crew

at the time.

NARRATOR: The crew's behavior is baffling.

It forces investigators to consider

an unlikely explanation for what went wrong,

something called subtle incapacitation.

It's very difficult to recognize

a subtle incapacitation.

If the pilot at the control has a stroke and slumps

over the control wheel, there's no question that you've got

a person who's incapacitated.

Confirm heading 210.

Negative, sir.

To proceed, direct Chekka.

Turn left now, heading 270.

Left heading 270.

Roger.

Left heading 270.

However, if the pilot at the controls

starts to lose the picture and does so silently

and starts to misapply controls or push the wrong buttons,

it may take a while before the other crew members

pick up on that failure.

That sequence is called subtle incapacitation.

NARRATOR: It's a controversial idea

that goes beyond the usual definition of pilot error.

What is it?

Subtle incapacitation can come

from physiological reasons, psychological reasons,

or a combination of both.

It could be something minor.

Medications could cause it.

Stress could cause it.

Fatigue could it.

NARRATOR: Because commercial aviation demands

such high levels of performance,

drug and alcohol use by pilots is closely scrutinized.

Drug testing is part of any transportation employee,

from baggage handlers all the way up to cockpit.

Typically, it's done on a random basis.

It's done.

NARRATOR: But there's no formal test for fatigue.

Other accidents with the same kind of sequence

of events taking place.

NARRATOR: In 2009, Colgan air flight

3407 crashed outside Buffalo.

The two overtired pilots failed to react properly to a Warning

that the plane was about to stall.

All 49 people on board were killed.

PILOT (ON RECORDER): This room doesn't make you sleepy?

NARRATOR: Investigators continue to analyze

the cockpit recording.

What are these guys doing?

NARRATOR: They listen to what the pilots were

saying just before takeoff.

PILOT (ON RECORDER): This room doesn't make you sleepy?

If you hear someone in the recorder saying sleep,

immediately our antennas stick up.

What are they doing up there?

Was there weed in it?

Did you feel dizzy?

All right, I couldn't sleep.

Well, me too.

NARRATOR: Investigators are shocked to hear

the pilots joking about being tired

and the reference to weed.

That would have changed things.

NARRATOR: Subtle incapacitation may not be such

an unlikely cause after all.

Trying to explain the behavior of the pilots

on that particular night was really the most difficult

part of this investigation.

And this is why we considered every single issue

starting from the food they had the type of rest they had.

NARRATOR: Piecing together the pilot's movements in the hours

leading up to the crash.

What time did he check in?

NARRATOR: Is now the top priority.

In the case of this accident, the pilot's bodies

weren't recovered, so there was no way they could

do post-mortem examinations.

We immediately called the hotel

to check the garbage if there was any bottle

of alcohol or any drugs.

Did they see the crew out having drinks or something?

NARRATOR: Investigators study security footage for any signs

that the pilots were impaired.

We also looked at the footage of the crew

coming into the airport.

They were walking normally.

Everybody we spoke to, they said no.

No, they were normal.

NARRATOR: Investigators traveled

to Ethiopia to interview family members

about the crew's habits.

Thank you for taking the time to see me.

I'm very sorry for your loss.

I just wanted to ask you a few questions about your brother.

Did he ever drink?

No.

There's no evidence to suggest either pilot

abused alcohol or drugs.

The captain didn't drink at all.

So he was a sport guy concentrating on his sports.

NARRATOR: Subtle incapacitation is difficult to prove.

In the crash of Flight 409, the evidence so far is mixed.

But what investigators discover next could tip the balance.

Gear up.

NARRATOR: Employment records detailing

the pilot's flight hours.

Heading select.

Heading select.

Check.

NARRATOR: Revealed critical information about the captain

of flight 409.

He'd been working almost non-stop

for nearly two months.

The 51 days he probably flew something

like 45 days out of the 51.

Daily, daily, daily flying, just taking the minimum rest.

It's legal, but it is quite a lot of work.

Ethiopian 409 wind's nearly calm.

Prepare for takeoff 2-1.

Work, work, work.

NARRATOR: The crew's last chance to rest

was a scheduled stopover after flying into Beirut.

I could use some food that didn't come from an airplane.

What do you say?

Yeah.

A good meal will be good.

All right, let's do it.

You have any a lot of water today?

Yeah, she'll bring back something.

She'll bring something.

Oh, here we go.

Prior to the flight, they had a heavy launch,

and they were not able to rest properly,

so they were commenting on not being able to rest

properly prior to the flight.

Did you feel dizzy?

Oh, I couldn't sleep.

NARRATOR: Investigators suspect that the heavy meal

kept them awake at night.

Indigestion and fatigue they definitely

they affect the pilot behavior throughout the flight process.

Sir, I suggest that, due to the weather,

you follow heading 270 to be in the clear.

2-1, say again.

NARRATOR: The storm conditions likely

added to the pilot's stress.

The weather could be a factor in adding

pressure on the pilots.

NARRATOR: Fatigued and under increasing stress,

they lost track of where they worked

and what they were doing.

This flight was in jeopardy from the outset.

What is it?

It seems that the crew was never fully

on top of what was happening.

Go around.

Go around.

Go around.

Roger.

Go around.

NARRATOR: Investigators conclude the accident was

caused by a crew that was simply

too tired or too confused to recover

from the first wrong turn.

It's a textbook example of subtle incapacitation.

We could prove that the symptoms that we saw

are similar to the symptoms of somebody who

has a subtle incapacitation.

Oh, God.

NARRATOR: The accident exposes a risk

to aviation that no amount of engineering can overcome.

After the crash of flight 409, investigators

suggest Ethiopian Airlines introduce

much more rigorous rules regarding crew rest.

It's one thing to have the experience and the expertise

to do the work, but you have to be in good condition

in order to perform.

As long as airplanes are operated by humans, fatigue,

distraction, and other human weaknesses

can only be managed, never erased.

I'm not sure that we can prevent subtle incapacitation.

But we should at least try to eliminate

all the possibilities that are related to human factor

because human factors are still the majority

of most of the accidents.

Check complete.

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