Original subtitles

At the heart of every modern aircraft

is a computer that's vital for safe flight.

is a computer that's vital for safe flight.

Simply put, it'd

be nearly impossible to fly this airplane safely

be nearly impossible to fly this airplane safely

without flight computers.

But those computers rely on a steady stream

But those computers rely on a steady stream

of accurate data.

Starting to pass through the layers.

When they don't get it...

Can't keep this damn thing level.

Can't keep this damn thing level.

Oh, ah.

The results are sometimes catastrophic.

The results are sometimes catastrophic.

What are they doing so low?

My airspeed indicator is not working.

Something's wrong here.

Something's wrong here.

God, god.

What was that?

We got to get out.

We got to get out.

If they can't figure out what went wrong,

If they can't figure out what went wrong,

this could be the end of the B-2 bomber program.

How can computers designed to aid pilots

How can computers designed to aid pilots

hinder them instead?

Investigators search for the cause of three accidents

Investigators search for the cause of three accidents

triggered by bad data.

You don't just fly with a stick and a rudder

You don't just fly with a stick and a rudder

and look out the window anymore.

Ladies and gentlemen,

we are starting our approach.

We lost both engines.

We lost both engines.

Mask over your nose. Emergency descent.

Mayday, Mayday!

Brace for impact!

It's gonna crash!

You're good to go, sir.

Thank you.

Major Ryan Link and Captain Justin Grieve

Major Ryan Link and Captain Justin Grieve

are ending a four-month deployment at Andersen Air Force

base in Guam.

base in Guam.

OK, let's head home then.

Copy that.

They were beginning a 16-hour continuous

They were beginning a 16-hour continuous

flight back to Whiteman Air Force base,

which was our home base.

which was our home base.

They're returning home in a unique warplane,

a B-2 bomber called the Spirit of Kansas.

a B-2 bomber called the Spirit of Kansas.

Tower of Death 5, start up is complete.

You can activate our flight plan.

You can activate our flight plan.

It's a 7,000-mile journey

home from Guam to Whiteman Air Force base in Missouri.

home from Guam to Whiteman Air Force base in Missouri.

Major Link is a qualified instructor on the B-2.

Captain Grieve is the mission commander,

Captain Grieve is the mission commander,

with more than 2,500 hours of military flying experience.

with more than 2,500 hours of military flying experience.

First MCT.

The very first time I flew the B-2,

I felt like I was a bird.

I felt like I was a bird.

It was so smooth.

145, rotate.

Next thing they know, they're going straight up.

Full power.

Full power.

The B-2 is only 80 feet off the ground

and losing speed.

and losing speed.

The plane shakes violently.

It's on the verge of stalling.

It's on the verge of stalling.

From my 15 years of flying the B-2,

the only time I felt the B-2 shake is in the simulator.

the only time I felt the B-2 shake is in the simulator.

Grieve realizes they're heading for the ground.

We got to get out.

I'm stunned.

The B-2 has gone through 19 years and three wars

The B-2 has gone through 19 years and three wars

without a crash.

This is unheard of.

With the B-2's price tag of $2 billion,

With the B-2's price tag of $2 billion,

this is the most expensive aviation accident of all time.

this is the most expensive aviation accident of all time.

We want to know what the heck just happened.

Operations of the entire B-2 fleet are suspended.

Operations of the entire B-2 fleet are suspended.

The US Air Force appoints Brigadier General

Floyd Carpenter to lead the investigation.

Floyd Carpenter to lead the investigation.

You're never going to believe this.

Video of the takeoff shows that as the plane lifted off,

Video of the takeoff shows that as the plane lifted off,

it pitched nose high.

it pitched nose high.

Your first reaction

when you see that airplane pitch up is like, what are they doing?

when you see that airplane pitch up is like, what are they doing?

Investigators study the mechanical and computer

systems that control the jet.

systems that control the jet.

Perfect.

What about the actuator?

OK.

They quickly determined

that all the flight control surfaces

that all the flight control surfaces

were functioning on takeoff.

The engines were not a problem.

The engines were not a problem.

The hydraulics weren't a problem.

The flight controls were not a problem.

It's a beautiful, sunny morning.

It's a beautiful, sunny morning.

Why does a bomber pitch its nose up and crash in a fireball

on the runway at Guam?

Something happened to caused

Something happened to caused

this airplane to pitch up.

The heart of the B-2 bomber

is its computerized flight control system.

is its computerized flight control system.

On a B-2, pilots tell the computer what they want

the plane to do and the computer determines how to achieve that.

the plane to do and the computer determines how to achieve that.

Simply put, it'd be

Simply put, it'd be

nearly impossible to fly this airplane safely

without flight computers.

without flight computers.

So did something go wrong with that system?

The investigators turn to data from the bomber's flight

The investigators turn to data from the bomber's flight

recorder to discover what happened.

The nose is lifting off the ground,

The nose is lifting off the ground,

but the plane registers a pitch down of minus 8 degrees.

Now, obviously, this plane is not pitching down,

Now, obviously, this plane is not pitching down,

but the computer thinks it is.

but the computer thinks it is.

That is why I tried to lift the nose

higher and higher and higher.

Until it stalled.

Until it stalled.

So airspeed, climb angle, and altitude are all off.

So airspeed, climb angle, and altitude are all off.

How does that happen on this plane?

How does that happen on this plane?

General Carpenter wants to know

why the flight computers were getting faulty data.

why the flight computers were getting faulty data.

Let's see what the pilots can tell us.

Let's see what the pilots can tell us.

We started up at 9:15.

We started up at 9:15.

A few minutes later, Major Link saw the calibration message

during start up.

during start up.

Mission Commander Grieve

tells investigators that the pilots received

an unusual computer message.

an unusual computer message.

Hey, Chief, we're seeing an AIRDATA CAL message

AIRDATA CAL stands for air data calibration.

AIRDATA CAL stands for air data calibration.

In the simplest terms,

the air data calibration gives the aircraft its orientation

the air data calibration gives the aircraft its orientation

to the universe.

There are 24 sensors near the nose

of the B-2 that constantly measure air pressure.

of the B-2 that constantly measure air pressure.

The plane's computers use those readings to calculate altitude,

The plane's computers use those readings to calculate altitude,

airspeed, and angle of attack.

If they get out of balance, it calls

for an air data calibration, and the pilots call out maintenance.

for an air data calibration, and the pilots call out maintenance.

Can you put it in maintenance mode for me?

Can you put it in maintenance mode for me?

If any of those 24 sensors

If any of those 24 sensors

provides an air pressure reading that differs significantly

from the others,

a recalibration is needed to bring

a recalibration is needed to bring

them all back into agreement.

You're good to go, sir.

Pitot heat is on.

Less than an hour after the recalibration...

Less than an hour after the recalibration...

Clear right.

Good to line up.

The pilots maneuver the massive bomber

to the start of the runway.

to the start of the runway.

OK, go on.

OK, go on.

Everything was 100% routine until we hit 100 knots.

That's when we got the FCS Master Caution.

That's when we got the FCS Master Caution.

Before I could even push the button, it rescinded itself.

Stop or go?

Go.

Warning rescinded.

Warning rescinded.

In that scenario, if I was the pilot in command,

I would continue.

Why?

It's not safety of flight.

It's not safety of flight.

When we hit 145, I called for Major Link to rotate.

When we hit 145, I called for Major Link to rotate.

Then it all very quickly went to hell.

Investigators delve deeper into the calibration

performed that day.

You're good to go, sir.

Thank you.

These three weren't just off by a little.

These three weren't just off by a little.

They are way off.

They discover that three

sensors on the B-2 were providing incorrect

sensors on the B-2 were providing incorrect

air pressure readings...

100 knots.

...and that a Master Caution

...and that a Master Caution

alarm flickered on for a few seconds just before takeoff.

At that point, we really didn't know

how they were related, but we figured they might be.

What was that?

What was that?

FCS Caution.

The recalibrated sensors started providing

The recalibrated sensors started providing

faulty air data again.

But six seconds later...

Stop or go?

Stop or go?

Go.

...the flight computer resolved the sensor discrepancy

and canceled the warning.

and canceled the warning.

What is going on with this plane's sensors?

OK.

So, let's start at the top.

So, let's start at the top.

Why the need to recalibrate in the first place?

Huh.

So they got delayed by a day.

So they got delayed by a day.

Investigators learned that while the pilots waited

Investigators learned that while the pilots waited

to resume their mission, the Spirit of Kansas

sat on the tarmac.

OK.

So the jet was left outside for 24 hours because of the delay.

So the jet was left outside for 24 hours because of the delay.

So what?

Weather records show that the night

Weather records show that the night

before the accident, a tropical rainstorm settled over the base.

Tell me a rainstorm didn't take down a $2-billion airplane.

Tell me a rainstorm didn't take down a $2-billion airplane.

Tests confirm that the sensors exposed

Tests confirm that the sensors exposed

to the heaviest rainfall became saturated

and needed recalibrating.

and needed recalibrating.

See, something just doesn't add up.

See, something just doesn't add up.

They did the recalibration.

They did the recalibration.

You're good to go, sir.

Why did the recalibrated sensors

Why did the recalibrated sensors

then produce bad data?

But they still ended up with faulty data.

But they still ended up with faulty data.

That nearly killed them.

Full power.

A state-of-the-art B-2 bomber stalled on takeoff

A state-of-the-art B-2 bomber stalled on takeoff

because of faulty data about its climb angle.

US Air Force investigators still can't explain why that happened.

US Air Force investigators still can't explain why that happened.

And the pressure is on to find answers.

If they can't figure out what went wrong,

If they can't figure out what went wrong,

this could be the end of the B-2 bomber program.

this could be the end of the B-2 bomber program.

OK.

So, they recalibrate at 09:34.

So, they recalibrate at 09:34.

Nearly an hour later, the Master Caution lights up

Nearly an hour later, the Master Caution lights up

because of an air data issue.

because of an air data issue.

So what happens in those 56 minutes?

General Carpenter reviews what the pilots

told them about the flight.

Routine taxi.

Routine taxi.

They hit the pitot heat, wait for the timer, and they're off.

They hit the pitot heat, wait for the timer, and they're off.

Pitot heat is a system of small heaters connected

to each of the plane's sensors.

to each of the plane's sensors.

Just before takeoff, the pilots activate the heaters

so the sensors don't freeze when the plane

so the sensors don't freeze when the plane

reaches colder temperatures at higher altitudes.

Pitot heat is on.

Pitot heat is on.

General Carpenter asks an engineer who built the system

if the pitot heat could have affected

if the pitot heat could have affected

the recalibrated sensors.

Clear right.

Get to line up.

Get to line up.

And then they turn on pitot heat when they get to the runway.

He was really concerned when he saw

He was really concerned when he saw

and understood, like he only could,

that moisture in the system and the data

that moisture in the system and the data

that we were putting into it to fix it

could cause such a problem.

could cause such a problem.

Recalibrating the sensors

brought the three wet ones in line with the others,

but turning on the pitot heat evaporated

but turning on the pitot heat evaporated

the moisture, putting the sensors back out of alignment.

the moisture, putting the sensors back out of alignment.

So the data that

was put in on the calibration now is invalid again.

And the flight computers are now trying to resolve

And the flight computers are now trying to resolve

the issue with these sensors.

What was that?

FCS Caution.

So then why did the faulty air

So then why did the faulty air

data warning disappear so quickly after it came on?

It's seconds from takeoff so it has to make a choice.

It's seconds from takeoff so it has to make a choice.

The B-2's flight computer

is constantly receiving four separate data

is constantly receiving four separate data

streams from all 24 sensors.

If there's a discrepancy in the data from those streams,

If there's a discrepancy in the data from those streams,

the computer is programmed to select any two of the channels

to proceed.

It just chose wrong.

The flight computer selected a channel that

contained incorrect information about the pitch angle

contained incorrect information about the pitch angle

from the recalibrated sensors.

145 rotate.

12 seconds later, the bad data caused

the B-2 to pitch up abnormally.

the B-2 to pitch up abnormally.

Once they rotated the aircraft on speed as they thought

Once they rotated the aircraft on speed as they thought

and left the ground, they were along

for the ride at that point.

for the ride at that point.

Full power.

That steep pitch up caught the Spirit of Kansas crew

completely off guard, leaving them vulnerable to the effects

completely off guard, leaving them vulnerable to the effects

of the faulty data.

There's no way a pilot or a maintainer

There's no way a pilot or a maintainer

would understand the system well enough

to realize what could have happened when

to realize what could have happened when

they did that data calibration.

Within two months, the B-2's flight computer

was reprogrammed to address the fault.

was reprogrammed to address the fault.

There have been no issues with bad data since.

There have been no issues with bad data since.

Well, in the end, safety is everything.

It doesn't matter if it's an airliner, a fighter jet,

It doesn't matter if it's an airliner, a fighter jet,

a space plane, or a stealth bomber.

As sophisticated as aircraft have become,

there are still situations where crucial information

there are still situations where crucial information

is communicated by radio.

In those scenarios, a failure to check and recheck that data

In those scenarios, a failure to check and recheck that data

can result in disaster.

Independent Air Flight 1851 cruises

above the Atlantic Ocean.

above the Atlantic Ocean.

There are 137 passengers aboard the Boeing 707.

There are 137 passengers aboard the Boeing 707.

Santa Maria, Independent Air 1851,

requesting MET report.

Flight engineer Jorge Gonzalez

checks the weather ahead.

He's a US Air Force veteran, as is captain Leon James Dougherty.

He's a US Air Force veteran, as is captain Leon James Dougherty.

Let's request to send.

Santa Maria control, Independent Air 1851

Santa Maria control, Independent Air 1851

would like to descend.

First officer Sammy Adcock started with Independent

First officer Sammy Adcock started with Independent

Air two weeks ago.

The crew was a balanced crew.

The crew was a balanced crew.

They had flown together for about a week or 10 days,

and they were doing fine.

and they were doing fine.

The flight from Bergamo, Italy,

will refuel at Santa Maria, an island in the remote Azores,

will refuel at Santa Maria, an island in the remote Azores,

before continuing to Punta Cana in the Dominican Republic.

before continuing to Punta Cana in the Dominican Republic.

The airport at Santa Maria is not a busy one.

It has no radar.

There were only three scheduled

There were only three scheduled

airline flights per day.

Doesn't justify the cost of air traffic control radar.

You're cleared 3,000 feet on QNH 1027.

You're cleared 3,000 feet on QNH 1027.

Runway will be one niner.

Expect approach.

Expect approach.

Runway one niner, report reaching 3,000.

Runway one niner, report reaching 3,000.

The controller is relying solely on position

reports from the pilot.

So they have to be meticulous about documenting the altitude

So they have to be meticulous about documenting the altitude

that the aircraft is at.

The crew needs to fly over the 2,000 foot Pico Alto

The crew needs to fly over the 2,000 foot Pico Alto

Mountain to reach the airport.

On that day, the weather in Santa Maria

was fine.

was fine.

There was just some cloud cover in the vicinity of Pico Alto.

There was just some cloud cover in the vicinity of Pico Alto.

13 minutes from the airport,

the pilots ready the plane for landing.

the pilots ready the plane for landing.

OK, I'm going to go ahead and put the ILS in on my side.

OK.

ILS, or instrument landing system,

ILS, or instrument landing system,

is a navigation system that provides

vertical and horizontal guidance to the runway.

vertical and horizontal guidance to the runway.

That means that he can fly in clouds until he

gets onto final approach.

gets onto final approach.

As they close in on the island,

As they close in on the island,

an alert in the cockpit tells the pilots

that they are 500 feet above their selected altitude.

that they are 500 feet above their selected altitude.

I don't know if we're going to get visual or not here.

Starting to pass through the layers.

But as they enter the cloud bank over the island,

But as they enter the cloud bank over the island,

disaster strikes.

Can't keep this damn thing level.

Can't keep this damn thing level.

Pull up.

Pull up.

Pull up.

Pull up.

Four and and a half miles from Santa Maria Airport,

Portuguese firefighters and civilians

Portuguese firefighters and civilians

discover what remains of Independent Air Flight 1851.

The jet hit peak while to very near the top of the mountain.

The jet hit peak while to very near the top of the mountain.

The accident site was a chaotic scene.

The accident site was a chaotic scene.

The wreckage was strewn all over the mountain.

The wreckage was strewn all over the mountain.

All 144 passengers and crew on board are dead.

By daybreak, the Portuguese Civil Aviation Authority

By daybreak, the Portuguese Civil Aviation Authority

arrives at the crash site.

They are soon joined in the Azores

by investigators from the US National

by investigators from the US National

Transportation Safety Board.

So this is the flight path.

The plane impacts the east side of Pico Alto.

The plane impacts the east side of Pico Alto.

Correct.

Together, they examine the wreckage pattern.

Together, they examine the wreckage pattern.

All concentrated right here,

All concentrated right here,

sending debris over the mountain ridge.

Scars on the ridge offer the first clues.

Scars on the ridge offer the first clues.

Looks like low angle, high velocity.

Looks like low angle, high velocity.

They must have been flying level.

CFIT?

Looks like it.

Looks like it.

They quickly recognize this incident as a controlled

flight into terrain, or CFIT.

flight into terrain, or CFIT.

What was the altitude where they hit?

1,795 feet.

1,795 feet.

And Pico Alto?

What does the Jefferson chart show?

What does the Jefferson chart show?

It's listed as 1,936 feet.

They struck the mountain 140 feet below what

They struck the mountain 140 feet below what

was listed on their chart.

What were they doing so low?

The possibilities were one, the crew was off course.

The possibilities were one, the crew was off course.

Two, there was an altitude error.

It was our job to find out which of those

would explain the accident.

would explain the accident.

What's the minimum sector altitude?

3,000 feet.

3,000 feet.

The minimum sector altitude is

at least 1,000 feet above all terrain

at least 1,000 feet above all terrain

within 25 miles of the airport.

There's plenty of room.

Why did these guys descend so low when they knew by the charts

that the minimum altitude was 3,000 feet

that the minimum altitude was 3,000 feet

and there was a mountain there?

What was the minimum sector altitude you gave them?

What was the minimum sector altitude you gave them?

The team checks to see if the air traffic

The team checks to see if the air traffic

controller made an error.

3,000 feet.

You're sure?

You're sure?

Yeah, I even made a note of it on my flight strip.

He was perfectly calm.

He had a normal behavior.

He thought he had done a good job.

He thought he had done a good job.

Were they advised to use the ILS?

Yes.

Expect ILS approach.

Runway one niner, report reaching 3,000.

Runway one niner, report reaching 3,000.

I couldn't find anything that explains

what happened from his part.

what happened from his part.

Maybe the altitude alert survived.

Let's take a look.

The altitude alert sounds a warning when the plane

approaches a preset altitude.

approaches a preset altitude.

Investigators discover that the altitude was set to 2,000 feet,

Investigators discover that the altitude was set to 2,000 feet,

a thousand feet below the required altitude of 3,000 feet.

a thousand feet below the required altitude of 3,000 feet.

This shocked all of us.

We just couldn't believe it, how that could happen.

We just couldn't believe it, how that could happen.

They hope the cockpit voice recorder will reveal

They hope the cockpit voice recorder will reveal

why the first officer input the wrong data

into the altitude alert.

Independent 1851, roger.

You're cleared to 3,000 on QNH 1027.

You're cleared to 3,000 on QNH 1027.

Clear to 2,000.

Clear to 2,000.

Did the first officer just say 2,000?

Maybe he heard "to 3,000" and mistook it for 2,000.

Maybe he heard "to 3,000" and mistook it for 2,000.

The controller should have corrected him too, but doesn't.

The controller should have corrected him too, but doesn't.

Why?

Hang on a second.

The first officer's read back of 2,000 feet

The first officer's read back of 2,000 feet

isn't in the controller's transcript.

So he never heard it?

How is that possible?

Investigators compare the transcripts from the plane

Investigators compare the transcripts from the plane

to those from the tower.

Hang on.

They were talking at the same time.

They were talking at the same time.

Yeah.

They canceled each other out.

You're clear to 3,000 feet on QNH 1027, runway one niner.

You're clear to 3,000 feet on QNH 1027, runway one niner.

You're clear to 3,000 feet on QNH 1027, runway one niner.

We're clear to 2,000 feet and...

We're clear to 2,000 feet and...

Runway one niner.

1027.

...to 3,000.

It was stunning.

It was stunning.

We were stunned to finally understand

how the two transmissions overlapped perfectly

how the two transmissions overlapped perfectly

to cancel each other out.

I was an investigator for over 30 years with the NTSB.

I was an investigator for over 30 years with the NTSB.

I've never encountered anything like this before,

and I never encountered anything like this afterwards.

and I never encountered anything like this afterwards.

But this discovery alone

isn't enough to explain why the plane was so low when

isn't enough to explain why the plane was so low when

it crashed into the mountain.

So the controller doesn't hear it.

Investigators have discovered

that critical communications about flight 1851's

that critical communications about flight 1851's

required altitude were missed because of overlapping radio

calls with.

One niner.

One niner.

1027.

...to 3,000.

But there's still another question

that worries them.

Something doesn't line up.

Something doesn't line up.

The plane's altimeter alert was incorrectly set to 2,000 feet.

The plane's altimeter alert was incorrectly set to 2,000 feet.

Even at that altitude, they would have cleared

Even at that altitude, they would have cleared

the ridge by some 200 feet.

What else affects altitude?

What else affects altitude?

QNH.

QNH is an air pressure value pilots

QNH is an air pressure value pilots

input so their altimeter can accurately

measure the plane's height.

That value can change with weather conditions.

That value can change with weather conditions.

If the altimeter is set to a higher QNH than is actual,

If the altimeter is set to a higher QNH than is actual,

the aircraft will actually be lower than what the altimeter is

telling the pilots.

telling the pilots.

Says here they were given a QNH of 1019 at 1:44 PM.

Says here they were given a QNH of 1019 at 1:44 PM.

Then they were given a reading of 1027 at 1:56 PM.

Then they were given a reading of 1027 at 1:56 PM.

Investigators calculate the change

Investigators calculate the change

in altitude between the two different settings.

That QNH brought them at least 200 feet below 2,000.

That QNH brought them at least 200 feet below 2,000.

Right into the mountain.

They asked the controller

They asked the controller

about the two different settings he gave to the pilots.

1019 was on the MET report.

But 12 minutes later, when you gave them the 3,000 foot

But 12 minutes later, when you gave them the 3,000 foot

clearance, you said "QNH 1027."

clearance, you said "QNH 1027."

Sorry.

I don't know where I got that second number.

I don't know where I got that second number.

Investigators turn to the CVR

Investigators turn to the CVR

to see if the pilots caught the controller's mistake.

After the first officer gets the minimum descent altitude wrong,

After the first officer gets the minimum descent altitude wrong,

he questions the QNH.

Is that what they said?

Is that what they said?

1027 on the millibars?

Yep.

He was right to question it.

He was right to question it.

But the captain just dismisses it.

Thank you.

And the first officer just accepts it.

And the first officer just accepts it.

Because of the different experience levels,

because of the prominence and assertiveness

with which the captain said it, shut off any discussion.

Makes you wonder what else these guys missed.

Makes you wonder what else these guys missed.

Investigators return to the cockpit voice recording

Investigators return to the cockpit voice recording

to hear how the pilots briefed each other

before approaching the landing.

Altimeters, set and cross-check.

Altimeters, set and cross-check.

Set and cross-checked.

Seat belts and shoulder harness.

Secured.

Secured.

We're having fun now.

Hey, hey.

That's it?

Stop the tape.

Stop the tape.

They don't even mention the minimum descent altitude.

They don't even mention the minimum descent altitude.

Or Pico Alto, here.

The lack of detail is shocking.

Had they done the approach of briefing

and reviewed the information and articulated the information

as required, it's highly unlikely,

as required, it's highly unlikely,

in my opinion, that they would have struck the mountain.

in my opinion, that they would have struck the mountain.

Starting to pass through the layers.

Pull up.

Terrain, terrain.

Pull up.

The captain is ultimately responsible as the pilot

The captain is ultimately responsible as the pilot

in command.

But each crew member failed in that respect.

Pull up.

Pull up.

Pull up.

Investigators conclude that the pilots failed to follow

Investigators conclude that the pilots failed to follow

procedures that would have caught the bad data provided

by the air traffic controller.

by the air traffic controller.

One doesn't necessarily completely

trust any system or any data resource.

trust any system or any data resource.

The information that one receives, either from

The information that one receives, either from

one's senses, or from the instruments of the aircraft,

or from outside navigational aids,

has to be balanced with one's own experience and judgment.

has to be balanced with one's own experience and judgment.

When bad data slips into the second-by-second

When bad data slips into the second-by-second

calculations that a pilot makes, the consequences can be tragic.

calculations that a pilot makes, the consequences can be tragic.

Gregorio Luperón International Airport

in the Dominican Republic.

Passengers on board Bergen Air Flight 301

Passengers on board Bergen Air Flight 301

have a nine-hour flight to Frankfurt ahead of them.

Cabin crew, take your seats.

Ready for takeoff.

Exterior lights.

Exterior lights.

The pilots prepare their Boeing 757 for takeoff.

Checked.

First officer, Aykut Gergin,

has fewer than 75 hours in the plane.

has fewer than 75 hours in the plane.

Thank you.

Ready for takeoff.

Captain Ahmet Erdem is one of Birgenair's most

Captain Ahmet Erdem is one of Birgenair's most

senior pilots.

Alpha Lima Whisky 301, ready for takeoff.

Alpha Lima Whisky 301, ready for takeoff.

OPERATOR 2:301, cleared for takeoff.

Runway 08.

Cleared for takeoff, runway 08301.

Thank you.

Thank you.

Muhlis Evrenosoglu is the relief pilot.

A good flight.

Good flight.

Good flight.

Good flight.

Power set.

Clear, checked.

80 knots.

Check.

My airspeed indicator is not working.

My airspeed indicator is not working.

The captain's airspeed should read the same

as his first officer's.

as his first officer's.

120.

But it doesn't.

Is yours working?

Yes, sir.

You tell me.

You tell me.

Erdem instructs his first officer

to call out when the plane reaches takeoff speed.

V1.

Rotate.

Rotate.

Shortly after takeoff, the captain's airspeed indicator

Shortly after takeoff, the captain's airspeed indicator

appears to be functioning normally.

Climb thrust.

Climb thrust.

One minute, 30 seconds into the flight,

the crew engages the autopilot.

the crew engages the autopilot.

Central autopilot on, please.

Central autopilot, as command.

Central autopilot, as command.

Thank you.

Then the computer reports a problem.

Rudder ratio.

Mach airspeed trim.

Mach airspeed trim.

The alert warns that the plane is traveling too fast.

Yes, trim.

Yes, trim.

Something's wrong here.

Captain Erdem's airspeed indicator

Captain Erdem's airspeed indicator

shows the plane traveling at 325 knots.

But the first officer's indicates

But the first officer's indicates

the plane going much slower.

Mine shows only 200 now and decreasing, sir.

Mine shows only 200 now and decreasing, sir.

Both of them are wrong.

Both of them are wrong.

Now, a far more serious warning sounds.

This alarm indicates the plane is

approaching the maximum speed at which it was designed to fly.

approaching the maximum speed at which it was designed to fly.

Now it's 350, yes?

Now it's 350, yes?

Captain Erdem decides to do what the alerts

tell him to do, slow down.

tell him to do, slow down.

And let's take that like this.

The result is terrifying.

God, god.

Shortly after takeoff, Birgenair Flight 301

is in trouble.

is in trouble.

God, god, god.

The cockpit fills with the ominous sound

The cockpit fills with the ominous sound

of the stick shaker.

It means that the airplane is about to attain a speed so low

It means that the airplane is about to attain a speed so low

that it cannot sustain flight.

that it cannot sustain flight.

The plane's attitude direction

indicator shows that its nose is pointing dangerously high.

indicator shows that its nose is pointing dangerously high.

ADI.

Suddenly, the plane rolls hard to the right

Suddenly, the plane rolls hard to the right

and begins to dive.

Thrust levers.

Thrust.

Pull up!

Oh, what's happening?

Oh, what's happening?

Birgenair Flight 301 vanishes from radar.

Birgenair Flight 301 vanishes from radar.

No survivors are found.

The Dominican Republic's Air Traffic Accident Investigation

The Dominican Republic's Air Traffic Accident Investigation

Bureau asks the US National Transportation Safety

Board to assist in their investigation

Board to assist in their investigation

of the downed Boeing 757.

of the downed Boeing 757.

Any signal from the recorders?

It takes three weeks to recover

Flight 301's black boxes.

That flight data recorder was our key.

That flight data recorder was our key.

Investigators immediately noticed something

unusual about the flight.

unusual about the flight.

15 degrees pitch, nose up.

Seems high.

Seems high.

He's almost the maximum.

Shortly after the autopilot is switched on,

Shortly after the autopilot is switched on,

the plane's nose pitches upward.

They also see that the indicated airspeed is

They also see that the indicated airspeed is

much higher than it should be.

350 knots.

It can't be right.

It can't be right.

They focus their attention

on the sensor that feeds airspeed information

on the sensor that feeds airspeed information

to the gauges, the pitot tube.

When the plane travels forward, an increase in air pressure

inside the pitot tube causes the airspeed indicators

inside the pitot tube causes the airspeed indicators

needle to move.

But if a pitot tube becomes blocked,

it can send faulty readings to the plane's gauges.

it can send faulty readings to the plane's gauges.

We started carefully looking at what could cause

We started carefully looking at what could cause

that kind of thing to happen.

Regulations state that any time a plane

Regulations state that any time a plane

will be on the ground for an extended period of time,

pitot tube covers must be placed on the tubes

pitot tube covers must be placed on the tubes

to prevent blockage, usually by dirt or ice.

to prevent blockage, usually by dirt or ice.

Records indicate that the plane sat

on the tarmac in Puerto Plata for 25 days

before taking off for Frankfurt.

before taking off for Frankfurt.

I like to ask you some question

I like to ask you some question

about the Birgenair airplane.

Investigators wonder if mechanics

neglected to cover the pitot tubes after maintenance.

neglected to cover the pitot tubes after maintenance.

Did you put the pitot covers back on them when

the maintenance was finished?

the maintenance was finished?

It didn't have any covers with it.

We didn't take any off, and we didn't put any on.

And that's when we discovered that the potatoes had

not been covered for the 25 days that the aircraft

not been covered for the 25 days that the aircraft

remained parked at the international airport in Puerto Plata.

The investigation team concludes that in that time,

The investigation team concludes that in that time,

some sort of blockage developed in the pitot tube

on the captain's side.

on the captain's side.

Nobody knows for sure.

The evidence is 7,000 down in the Atlantic Ocean.

The evidence is 7,000 down in the Atlantic Ocean.

A blocked pitot tube could have given

the pilots bad data in the form of conflicting

airspeed readings.

airspeed readings.

But how could that lead to such a disaster?

But how could that lead to such a disaster?

And what we've got for you is a computer...

Using information from the black boxes,

the NTSB pieces together, the flight's last moments.

the NTSB pieces together, the flight's last moments.

The captain actually realized that his speed

The captain actually realized that his speed

indicator was not working.

Is yours working?

Yes, sir.

The data shows that the problems

The data shows that the problems

on Birgenair Flight 301 began when the autopilot took over.

on Birgenair Flight 301 began when the autopilot took over.

Central autopilot on, please.

Autopilot.

Is it possible that the flight

computer was just as confused about the airspeed as the crew?

computer was just as confused about the airspeed as the crew?

If so, how did that contribute to the crash?

If so, how did that contribute to the crash?

Right after the autopilot is engaged,

the plane's nose begins to rise.

the plane's nose begins to rise.

Investigators have discovered that Flight 301's

autopilot, sensing that the plane was traveling too fast,

autopilot, sensing that the plane was traveling too fast,

raised its nose to reduce speed.

It soon rises to 15 degrees.

It soon rises to 15 degrees.

Then it stays there.

The autopilot's a pretty smart guy.

The autopilot's a pretty smart guy.

He already knows he's got all the power that he's

going to get for the climb.

going to get for the climb.

The only thing for the autopilot to do is raise the nose.

But the autopilot is reacting

But the autopilot is reacting

to faulty airspeed information from the captain's pitot tube.

to faulty airspeed information from the captain's pitot tube.

The autopilot gets its data only

from the captain's pitot tube, the one that was blocked.

from the captain's pitot tube, the one that was blocked.

Moments later, it sends

out two different warnings.

Rudder ratio, mach airspeed trim.

Rudder ratio, mach airspeed trim.

And the airplane begins picking up warnings.

Rudder ratio, a variety of things that the airplane

Rudder ratio, a variety of things that the airplane

is sensing problems.

Investigators realized that Captain Erdem wrongly

Investigators realized that Captain Erdem wrongly

concluded that both airspeed indicators were malfunctioning.

concluded that both airspeed indicators were malfunctioning.

In fact, his first officer's gauge was always correct.

The plane was actually traveling much too slowly.

The plane was actually traveling much too slowly.

What can we do?

But that needle continued to climb around the clock face

But that needle continued to climb around the clock face

until it activated the overspeed warning.

until it activated the overspeed warning.

The autopilot system sends a warning that the plane

The autopilot system sends a warning that the plane

is traveling too fast.

But in reality, it's slowing down.

They're going slow.

They think they're going too fast, and confusion is set in.

They think they're going too fast, and confusion is set in.

Let's pull the airspeed.

Let's see.

That's when Captain Erdem

That's when Captain Erdem

makes the gravest error of all.

You can see that he now pulls back on his throttles.

You can see that he now pulls back on his throttles.

At the plane's already slow speed.

Pulling back on the throttles puts the plane

Pulling back on the throttles puts the plane

on the verge of stalling.

And that's when he gets the stick shaker.

God, god, god.

God, god, god.

The autopilot is programmed

to always disconnect when the stick shaker activates.

to always disconnect when the stick shaker activates.

With one warning telling him the plane is flying too fast

and another indicate it's flying too slow,

and another indicate it's flying too slow,

Captain Erdem is overwhelmed.

That airspeed warning horn combined

That airspeed warning horn combined

with a stick shaker was a tremendously

mind-boggling experience.

mind-boggling experience.

They're in direct opposition of each other, and two warnings

that you would never expect to get one right behind the other.

that you would never expect to get one right behind the other.

In response to the investigation's findings,

the FAA asks Boeing to change some of those warnings.

the FAA asks Boeing to change some of those warnings.

Those changes include the addition

of a new warning, which alerts both pilots when

of a new warning, which alerts both pilots when

their instruments disagree.

In addition, Boeing modifies its planes so that pilots can easily

In addition, Boeing modifies its planes so that pilots can easily

choose which pitot tube the autopilot

choose which pitot tube the autopilot

is using for airspeed readings.

You can't fly a modern aircraft without the proper data

You can't fly a modern aircraft without the proper data

because you don't just fly with a stick and a rudder

and look out the window anymore.

Your data is your flight.

Your data is your flight.

More than 1,400 Boeing planes worldwide are

More than 1,400 Boeing planes worldwide are

affected by the new directives.

One final question remains.

What blocked the plane's pitot tubes

What blocked the plane's pitot tubes

and caused the airspeed indicator to malfunction?

What's happening?

What's happening?

With Birgenair Flight 301's pitot

tubes lost in the ocean floor, investigators

tubes lost in the ocean floor, investigators

look at the area surrounding the airport in Puerto Plata

and think they found a likely suspect...

The mud dauber wasp.

The mud dauber wasp.

When a mud dauber is looking for an area

to build its nest, it's looking for a site, a place

to build its nest, it's looking for a site, a place

that's more or less tubular.

They didn't put covers on the pitot tubes.

They didn't put covers on the pitot tubes.

So there was an opportunity to get something like a mud

dauber in that pitot tube.

dauber in that pitot tube.

More than ever, aircraft

depend on complex flight computers for safe flight.

depend on complex flight computers for safe flight.

Even the smallest scrap of bad data can prove to be deadly.

Even the smallest scrap of bad data can prove to be deadly.

Aircraft and aircraft systems have become much more

sophisticated over the years.

But even with the most sophisticated aircraft,

But even with the most sophisticated aircraft,

it's essential and necessary for pilots

to know how to deal with those systems,

to know how to deal with those systems,

how to understand how they work, how to not use them if they're

how to understand how they work, how to not use them if they're

giving them bad data, and how to manage

whatever they have to continue to fly the airplane.

whatever they have to continue to fly the airplane.