Original subtitles

Alpha Lima Whiskey, 301 Santo Domingo, come in.

A Boeing 757 disappears from radar

with 189 people on board.

The plane's wreckage is soon found at sea.

There are no survivors to say what happened.

This accident was the first major loss of a Boeing 757 aircraft.

Investigators find no clues in the wreckage.

Only the plane's black box can tell them what happened.

The tape raises a perplexing question.

310, Santo Domingo, come in, please.

My airspeed indicator is not working.

What's happening?

How had the failure of one single instrument...

Sir, pull up!

...caused the crash of one of the world's most sophisticated jetliners?

Mayday! Mayday!

Gregorio Luperon International Airport in Puerto Plata, the Dominican Republic.

February the 6th, 1996.

The small Caribbean island is a popular winter getaway.

A group of German tourists has been delayed.

There are mechanical problems with the jet that was supposed to take them back to Frankfurt.

The airline has arranged to lease another plane for the flight.

The replacement jet is owned by Turkish Charter Company Birgenair.

They have a 757 that's been sitting on the tarmac for almost three weeks.

But it takes several hours to get the plane ready to go...

and to get the Turkish crew aboard.

By 10:15 p.m., the plane and most of its crew are at the gate.

More than four hours after they were supposed to take off,

the first of the passengers begin boarding the plane.

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

Puerto Plata Alpha Lima Whiskey 301... requesting push back.

Shortly after 11:30, Birgenair Flight 301 is given permission to leave the gate.

Push back granted.

Moments later, it taxis to the threshold of the runway.

Cabin crew, take your seats, ready for takeoff.

Cabin announcement is completed.

First Officer Aykut Gergin is new to the 757,

with fewer than 75 hours in the plane

in the last three months.

Thank you. Ready for takeoff.

In contrast, Captain Ahmet Erdem is one of Birgenair most senior pilots.

He's logged thousands of hours in this type of plane.

Alpha Lima Whiskey 301, ready for takeoff.

301 cleared for takeoff, runway 08.

Cleared for takeoff. Runway 08, 301. Thank you.

A good flight.

Good flight.

Good flight.

Muhlis Evrenesoglu is on this flight as a Relief Pilot.

Like First Officer Gergin, he's been flying the 757 for less than three months.

As the plane accelerates to takeoff speed, a light rain begins to fall.

- Power's set. - Okay, check.

First Officer Aykut Gergin watches his air speed indicator

for a routine instrument check.

As the airplane's accelerating to takeoff speed,

the First Officer calls 80 knots.

- Eighty knots. - Check.

The captain, in theory, should verify that

his airspeed indicator also reads 80 knots.

My airspeed indicator's not working.

The captain's airspeed should read the same as his First Officer's.

120.

But the readings do not match.

- Is yours working? - Yes, sir.

You tell me.

Erdem wants his First Officer to tell him

when the plane hits takeoff speed.

V-one.

At 150 knots, the plane hits V-one, the point of no return.

Rotate.

The captain must pull back on his column and get the plane in the air.

Positive climb, gear up.

Positive climb, gear is up.

At 11:42, the plane takes off.

Seconds later, Captain Erdem's airspeed indicator comes to life.

Is it possible to turn off the wipers?

Okay, wipers off.

- Climb thrust. - Climb thrust.

First Officer Gergin reduces power

to the engines for a gradual climb to cruising altitude.

301 airborne 45.

Switch over Santa Domingo 1243.

1243. Bye bye, sir.

Climbing through 2500 feet,

First Officer Gergin establishes contact

with the island's main tower in Santo Domingo.

Alpha Lima Whiskey 301, climb and maintain 280.

Center autopilot on, please.

- Center autopilot has command. - Thank you.

One minute and thirty seconds into the flight, the autopilot takes over.

Onboard computers now make all the calculations

and adjustments necessary to keep the plane flying safely.

Almost immediately, the computer reports a problem.

Rudder ratio. Mach airspeed trim.

Two different alerts warn the pilots that the plane is traveling far too fast.

Yes... trim...

But the First Officer's airspeed indicator

Shows the plane climbing at a normal speed, 220 knots.

Something's wrong here.

Unaware that there are any problems,

the controller directs Birgenair Flight 301 to continue climbing.

Alpha Lima Whiskey 301, report Pokeg.

Okay, 280, I'll call you over Pokeg. 301.

Okay, there's something crazy. Do you see it?

In the cockpit, the situation gets more confusing.

The First Officer's airspeed indicator

shows that the plane is flying much too slowly.

Mine shows only 200 now, and decreasing, sir.

But the captain's gauge shows the plane flying far too fast.

Three hundred and twenty-five knots.

Both of them are wrong.

What can we do?

Let's check the circuit breakers.

Yes, sir.

As the first warning is eliminated,

- a more persistent warning replaces it. -

The over-speed warning tells the crew

that they are approaching 350 knots.

The maximum speed at which the plane was designed to fly at this altitude.

Okay, it's no matter.

Let's pull the air speed, let's see.

Resetting the circuit breakers turns off the alarm,

but it doesn't fix the problem.

Captain Erdem's air speed indicator still shows he's flying much too fast.

Now it's 350, yes?

Confused by the conflicting information,

Captain Erdem decides to do what the plane wants...

He slows down.

Let's take that like this...

...with terrifying results.

Oh, God!

The 757 is sending out warnings that are confusing the crew.

Bewildered, the crew struggle to solve the problem.

The lives of 189 people depend on them getting the answer right.

Shortly after taking off from the Dominican Republic,

Birgenair Flight 301 is in trouble.

God! God! God!

The cockpit is filled with an ominous sound...

The stick shaker alert.

Stick shaker warning is a warning of imminent stall.

It means that the airplane is about to attain a speed so low, that it cannot sustain flight.

The alert is so serious that it actually shakes the pilots' control columns.

Combined with a loud rattling, it's impossible to ignore.

To add to the crew's confusion, the plane begins to vibrate and dip wildly.

I'm sure every passenger on the airplane knew something was unusual, because the aircraft

started to, uh, started to shake in a very violent maneuver.

It's not the only problem the crew is facing.

A.D.I.

The Attitude Deviation Indicator is basically a round gauge,

that on this airplane is a screen

that is blue on the top and brown on the bottom.

And it shows not only the pitch of the airplane, but also roll.

On the gauge, blue represents sky.

The more blue, the steeper the climb.

Right now it's showing that the plane's nose is pointing dangerously high.

Then, more than 7,000 feet above the ocean,

the plane rolls hard to the right,

and begins to plummet from the sky.

From the time that the stick shaker activates,

it is now going to require proper action from the flight crew

to sort this out, or they will end up losing control of it.

The window of decisions is closing on them.

For if they let it stall completely,

maintaining control of the airplane will prove to be very difficult.

Captain Erdem struggles desperately to get his plane to climb.

Nose down!

He has just a few thousand feet

to pull a 100 ton airliner out of a deadly stall.

The less experienced pilots utter prayers and offer suggestions.

- Thrust. - A.D.I.!

301...

Squawk 377.

Standby!

Air Traffic Control is still unaware that Flight 301 is in grave danger.

Not climbing? What am I to do?

You can level off. Our altitude's okay.

The plane is falling fast.

Okay, 5,000 feet.

Captain Erdem is trying to fly a plane that's become virtually uncontrollable.

Thrust levers! Thrust!

Gergin pushes the throttles to full power...

but it doesn't help.

The plane spirals towards the sea.

Sir, pull up!

Oh! What's happening?

Alpha Lima Whiskey 301, Santo Domingo. Come in, please.

Alpha Lima Whiskey 301, Santo Domingo.

Come in, please.

Less than five minutes after takeoff, Birgenair Flight 301

- vanishes from radar. Alpha Lima Whiskey 301.

Come in, please.

The Dominican Navy begins searching

for the missing plane and it's passengers.

Enroute, I was always thinking of what I would find.

I thought I would find people screaming, people yelling and asking for help.

They discover something very different.

The strong smell of jet fuel hangs over the water.

Pieces of wreckage float on the waves.

I thought to myself there is no one alive here.

We didn't see any survivors and we didn't see bodies.

I really thought the plane disintegrated on impact.

Within hours, more than just wreckage begins floating to the surface.

Around 5:20 in the morning, when the bodies started to come up,

I did feel a great sorrow in my heart.

I felt like I wasn't sure if I would have the strength

to continue the work at that moment.

The search continues by the light of the next morning.

American and Dominican rescue ships

scour a 1300 square kilometer area for survivors.

None are found.

Now it's up to the Dominican Republic's Aircraft Accident Investigation Bureau

to find out what caused this accident.

We established a base camp at a hotel on the Cabarete Beach,

which was directly south of the accident site.

Over the next couple of days, investigators, reporters,

and some of the victims' families arrive at the hotel.

Nearby, evidence of the disaster reaches the Dominican shores.

Wreckage and passenger's possessions are washing up on the beach.

Even the smallest piece could be a valuable clue as to what caused the crash.

The USA's National Transportation Safety Board,

Agrees to assist the Dominicans with their investigation.

They send an investigator to Puerto Plata.

We could see that this was going to take some international co-operation,

to get to the bottom of the event.

Robert MacIntosh will also provide support from the NTSB's Washington Offices.

Any signal from the recorders?

This particular accident was the first major loss

of a Boeing 757 in the water.

There was added urgency, because the aircraft was going into the livery

of many American operated airlines,

and on the market for the worldwide passenger service.

In order to understand what had happened here,

we only had one key.

That key was the black boxes.

Like all commercial airliners,

the Boeing 757 carries a Cockpit Voice Recorder

that records all the sounds in the cockpit.

And a Flight Data Recorder,

that records a wealth of information about the plane's operation during flight.

We've got underwater locator beacons on these recorders.

They work for 30 days upon immersion.

But the ocean where the plane crashed is over 7,200 feet deep.

We needed to locate them before the signals faded.

And we also needed to remove them before the data was damaged by salt water.

So we were in a race against time.

The NTSB enlists the help of the US Navy, who hire a submersible called the CURV.

CURV stands for Cabled Underwater Recovery Vehicle.

It's a tethered vehicle.

It has an umbilical and it's controlled by an umbilical. It's not autonomous.

The CURV is essentially a remote controlled submarine,

which can work at depths no manned submarine could handle.

While the CURV travels from the United States,

Major Souffront starts to examine the evidence he has.

Radar on the ground tracked the plane as it climbed into the night sky.

I have the radar. The history of the flight is recorded here.

Investigators study the radar records,

along with the conversation between the ground controllers and the crew.

I have the recording from the control tower.

Santo Domingo, good evening.

Alpha Lima Whiskey 301, climbing with you.

Alpha Lima Whiskey 301,

c limb and maintain 280.

Okay, 280.

The exchange between the controller and Flight 301 is normal.

The investigators detect no signs of trouble.

The last communication between them was only disrupted with a "stand by".

301 squawk 377.

Stand by.

As you heard, there is no reason why this plane went down.

What had caused something to go wrong,

to interrupt the flight path of the aircraft so rapidly?

Certainly it was a good... It was a good question for us.

Any debris that's found is taken to a Dominican military base to be examined.

Investigators comb through the wreckage they've recovered.

Pieces of the cabin,

life vests, even part of the landing gear have all been found.

Every piece of debris is studied for signs of an explosion, or fire.

Investigators also check if any of the life vests are inflated.

That would suggest passengers had some warning before the plane plowed into the sea.

Cords on some of the life vest are hanging loose,

But investigators conclude that could be the result of the plane's violent impact.

The crash was so powerful it has compressed coffee cans into flat pieces of tin.

The wreckage tells investigators,

That the crash of Birgenair Flight 301 was sudden and violent.

But they find no evidence that there was an explosion on board.

Major Souffront looks into the possibility that the plane,

which was called into service at the last minute,

may not have been ready for the flight.

Enmanuel Souffront. - Ah. Hi.

I'd like to see some records of the Birgenair plane.

All right. They're right here.

This is it.

It had been on the ground for some time in Puerto Plata,

and that became interesting to us.

Why would an operating company have an aircraft sitting there?

Investigators discover that the plane wasn't on the ground for repairs.

Based on maintenance records, the plane appears to have been mechanically sound.

Birgenair simply didn't have enough passengers to justify the flight financially.

So they kept the plane and the crew in the Dominican Republic

for almost three weeks.

The plane's maintenance records turn out to be one more in a series of empty leads.

The CURV arrives in Puerto Plata harbor.

On February 28th,

more than three weeks after the crash, it slips below the waves,

looking for the remains of the Birgenair jet.

It takes the robotic submarine two hours

just to descend the 7,200 feet to the ocean floor.

From there, it sends back images of the wreck of Flight 301.

The cockpit pretty much was sitting upright,

and it was pretty much the nose of the plane, you know.

And you could see the front part of it, it was obviously banged up,

and cracked, and fragmented.

The clues investigators need to solve the mystery of this plane crash,

lies somewhere amongst the plane's twisted wreckage.

The flight's black boxes are the top priority.

The CURV quickly picks up the signal from a Pinger on one of the units.

Operators must now maneuver the sub towards the sound.

They have to be able to see the boxes to pick them up with the robotic arm.

It takes just 90 minutes to find the first black box.

The first one was sitting out in the open,

Okay. It was where they could see it.

And they picked the first box up.

They grabbed ahold of it and they just kind of tucked the arm up in place.

You know, so that they wouldn't lose it.

The second black box is also heard.

But after almost two hours, the CURV's cameras still can't see it.

You know, they knew it was right there,

and they were searching around a debris pile,

and they could not physically see it, you know,

with the cameras of the vehicle.

So as they went around a couple of times they started, you know,

lifting metal up and moving pieces out of the way.

And then they did find the second box under some debris.

Flight 301's Flight Data Recorder,

and Cockpit Voice Recorder are brought to the surface,

and loaded onto a waiting jet.

Within hours, the black boxes are at the NTSB labs in Washington DC.

Technicians prepare to extract the precious data from the boxes.

Investigators hope it will tell them what happened aboard Birgenair Flight 301.

They'll soon uncover a stunning miscommunication between a seasoned pilot and his plane.

To unravel the mystery of Birgenair Flight 301,

investigators are counting on the plane's black boxes.

That flight data recorder was our key.

So the technicians got busy and gave us plots, visual plots,

of what was going on with engines, and air speeds, and so on,

to allow us to try and understand why that aircraft slowed down,

and then simply departed controlled flight and entered the ocean.

That's great. That shows us all we need to see.

So it's all the flight data recording.

It's on a time line. Top is the pitch.

We've got the air speed and the altitude.

But check out the timeline, 44.

Investigators immediately notice something unusual about the flight.

Fifteen degrees pitch nose up. Seems high.

- He's almost the maximum. - And then it stays that way.

The plane began climbing normally.

Center autopilot on, please.

But investigators notice that shortly after the autopilot was switched on,

the plane's nose pitched upward.

They also see that the plane's airspeed seems much higher than it should be.

Three hundred and fifty knots.

It can't be right.

There's something definitely wonky about the airspeed numbers.

This brought us to the question of

perhaps we should be looking over on the other side

at the cockpit voice recorder and see

what kind of information was coming from there.

Can you cue that up and play it?

Investigators soon start filling in the missing pieces of the puzzle.

Eighty knots.

My airspeed indicator is not working.

They learn that Captain Erdem

noticed that his airspeed indicator wasn't working.

- Is yours working? - Yes, sir.

You tell me.

V-one. Rotate.

But Erdem didn't think the problem was serious enough to abort his takeoff.

The tape reveals that once they were airborne,

the crew quickly became overwhelmed by a series of warnings.

Rudder ratio. Mach airspeed trim?

To investigators, the Captain seems to become increasingly bewildered

by the messages he was getting from his plane.

Mine shows only 200 now, and decreasing, sir.

Both of them are wrong. What can we do?

Investigators don't know why the Captain's airspeed indicator wasn't working.

They do notice that the Captain's gauge

came back to life as the plane started to climb.

Okay, it's no matter.

Let's pull the airspeed. Let's see.

It's a telling discovery,

Which leads investigators to focus their attention on the device

that feeds the gauges airspeed information.

The pitot tube.

A pitot tube is an airspeed sensor,

a pipe open at one end that responds to air pressure.

When the plane travels forward, an increase in air pressure inside the pitot tube

causes the airspeed indicator's needle to move.

My airspeed indicator is not working.

But if a pitot tube becomes blocked,

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

Blocked pitot tubes have been a factor in previous plane crashes.

In 1982, a Boeing 737 crashed in heavy snow in Washington, D.C. shortly after takeoff.

The pitot tubes were blocked with ice.

Investigators suspect that the pitot tube which fed the Captain's airspeed indicator

on the Birgenair jet was somehow blocked.

But they know ice can't have blocked the tubes of a plane

taking off from a Caribbean island.

We don't know why it was blocked,

but it presented a very, very interesting situation to us.

We started carefully looking at what could cause that kind of thing to happen.

Senor...

Major Souffront has a theory.

He returns to question the airplane's mechanics.

- Senor Souffront... - We're done with these, thank you.

I'd like to ask you some more questions about the Birgenair plane.

Souffront suspects that mechanics may have taped over

the pitot tubes during maintenance.

It's a common procedure, but if the tape wasn't removed,

it could have caused the deadly accident.

Maybe a piece of tape was left on accidentally.

No, sir.

They didn't have to be taped. We never did anything with the Pitots.

Did you put the pitot covers back on them when the maintenance was finished?

It did not have any coverage with it.

We did not take any off and we did not put any on.

And that's when we discovered

that the pitots had not been covered for the 25 days

that the aircraft remained parked at the international airport in Puerto Plata.

A pitot cover slips over the end of the tube.

Regulations state that these covers must be installed

any time a plane will be on the ground for an extended period of time.

A prominent flag is meant to remind pilots and technicians

to remove them again before takeoff.

Investigators find that the Birgenair pitot tubes were never covered.

And somehow, the uncovered pitots had become blocked.

Recovering the tube from the ocean floor,

is the only way for investigators to answer a pressing question.

What blocked the pitot tubes?

Nobody knows for sure.

The evidence is 7000 feet down in the Atlantic Ocean.

But even if the pitot tubes were blocked,

how could it have caused the crash of a modern jet,

and the death of 189 people?

It's not like a car where you have only one speedometer.

In this kind of an aircraft, you have a total of three airspeed indicators,

and there is a flight data computer,

which is computing the velocity in relation to the ground.

I'd like to welcome you all this afternoon.

As you know, I'm Bob Macintosh.

Using information from the black boxes,

the NTSB pieces together a real time animation,

from lift off to the final moments of Flight 301.

This is the indicator.

The captain actually realized that his speed indicator was not working.

- Is yours working? - Yes, sir.

The big question for investigators is,

how could one faulty airspeed source result in a crash?

He realized at a time that he could have aborted.

He could have turned back. But he chose to continue.

Investigators analyze the Captain's every move,

and find that he allowed a small error to escalate, and ultimately overwhelm him.

Rotate.

Positive climb, gear up.

Moments after liftoff,

Captain Erdem's airspeed indicator appears to be working.

That means it is at odds.

But investigators suspect the gauge is responding to changes in altitude.

Climb thrust.

As the plane climbs through the thinning atmosphere,

the air trapped inside the tube expands,

causing a buildup of pressure.

Inside the cockpit,

this causes the airspeed indicator needle to deflect.

Even though altitude is causing the increase in pressure,

the sensors mistakenly read it as an increase in airspeed.

So, at this point, the takeoff is standard...

Captain Erdem may have had five separate sources of airspeed to rely on,

but investigators noticed that when the trouble started, he wasn't flying the plane.

Center autopilot on, please.

- Center autopilot has command. - Thank you.

The autopilot was.

And unless the crew reconfigures it,

the autopilot gets its airspeed information from only one source.

Remember, the autopilot gets its data only from the Captain's pitot tube.

The one that was blocked.

The data shows that the trouble on Birgenair Flight 301

began when the autopilot took over.

Right after the autopilot is engaged, the plane's nose begins to rise.

Investigators suspect that the crew didn't realize

that the blocked pitot tube was feeding the autopilot faulty information.

The computer registered that the plane was traveling too fast,

and raised the nose to slow it down.

It soon rises to 15 degrees. Then it stays there.

Raising the nose works like an air brake.

It slows the plane by creating drag.

The autopilot is programmed to never bring the nose higher than about 15 degrees.

Any higher and the plane would slow down too much and stall.

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.

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

And it raised the nose of the airplane to its limits of authority.

But the autopilot was reacting to faulty information.

Moments later, it sent out two different warnings.

Rudder ratio. Mach airspeed trim?

That the plane was traveling too fast to be controlled safely.

The airplane begins picking up warnings, rudder ratio.

A variety of things that the airplane is sensing problems.

Okay, there is something crazy here. Do you see it?

Yes, there is something crazy.

Mine shows only 200 now, and decreasing, sir.

Both of them are wrong.

Investigators realized that Captain Erdem wrongly concluded

that both airspeed indicators were malfunctioning.

In fact, his First Officer's gauge was always correct.

The plane was traveling much too slowly.

What can we do?

Captain Erdem no longer knows which instruments to trust.

Let's check the circuit breakers.

As they saw these caution lights,

they decided they were going to start pulling some circuit breakers.

But that would be rather strange.

The actions of trying to reset circuit breakers

is something's that pilots of older generation's aircraft

have learned via experience of sometimes being able to get

an errant system back functional.

Resetting the circuit breakers turns off the alarm.

But that needle continued to climb around the clock face,

until it activated the overspeed warning.

The autopilot system sent yet another warning,

that the plane was traveling too fast.

But the reality was just the opposite.

The plane was slowing down.

At this point, the overspeed indicator is on. They're going too slow.

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

Let's pull the airspeed.

That's when Captain Erdem made the gravest error of all.

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

Investigators realize that at the plane's already slow speed...

...pulling back on the throttles was disastrous.

The crew got the most severe warning that a plane can send out.

And that's when he gets the stick shaker.

God! God!

He's got a tactile sense coming through his flight controls

that literally shakes the stick and says,

you've got to lower this nose.

In a matter of seconds, Captain Erdem was first warned

that his plane was traveling too fast,

and then that it was traveling dangerously slowly.

They're in direct opposition of each other.

And two warnings that you would never expect to get, one right behind the other.

The autopilot

is programmed to always disconnect when the stick shaker activates.

It's up to the pilot to get the plane out of a stall.

Once the autopilot reached its limits of authority,

it said, "I've done all I can do. I'm out of here."

When the autopilot disengaged,

Captain Erdem suddenly found himself in control of the plane,

at the moment of his greatest confusion.

You watch the plane at the top of the screen.

The cockpit recordings lead investigators to a stunning conclusion.

A.D.I.

Captain Erdem may not have recognized that his plane is about to stall,

but the Relief Pilot behind him did.

A.D.I.

This additional pilot intervened to say "A.D.I., A.D.I.!"

In other words, look at the A.D.I. and put yourself

where you would normally see the nose of the aircraft.

Five degrees nose high, ten degrees.

So when the reserve pilot says "A.D.I." he is attempting to focus the captain's attention

to roll and pitch which are becoming problematic.

The relief pilot wanted Captain Erdem

to recognize that the plane's nose was pitched dangerously skyward.

Investigators can hear First Officer Gergin trying to convey the same message.

Nose down.

At this point, the first officer actually trying to lead the captain to some solutions,

but not actually take control of the airplane.

What the 757 desperately needed was airflow over the wings to generate lift.

The only way to get that was to point the nose down and dive.

What puzzles investigators is that the First Officer

had a control column identical to the Captain's.

He could have pushed it and brought the nose down himself.

He may have been able to save the plane.

But he didn't. Instead, he and the other Turkish crew member

continued offering suggestions to their more experienced, but overwhelmed Captain.

Not climbing. What am I to do?

You can level off. Our altitude's okay.

But the recording shows that Captain Erdem ignored

valuable advice that could have saved the plane.

And in the Birgenair case, there's a case of a relatively junior First Officer,

looking at one of the most senior captains on the airline.

It is not culturally appropriate

for him to say, "I am going to take the airplane away from you."

Instead, he tries to assist the captain, to lead the captain,

but leave the captain in command.

Other cultures, other training, other airlines,

may very well have required the First Officer

to physically take control of the airplane.

I think the social atmosphere in the cockpit will prevail

to revere age and experience to the point where it... it can kill somebody.

And in this case, it looks like it did.

The flight data recorder reveals that instead of pushing the nose down,

Captain Erdem tried to get more speed from his engines.

At this point, the crew goes to full power.

Thrust levers! Thrust!

At the angle the plane was falling,

the engines couldn't get enough air.

Applying full power was more than they could handle.

The left engine quit first,

With the right side at full throttle,

the airliner swings around as though it's left wing were caught on a branch.

The airplane goes into a classic full stall, where the nose drops,

it falls on a wing, which is now a very life threatening condition.

The 757 itself makes the situation worse.

Like many modern jets, it uses a so-called swept wing design.

The wings angle slightly backwards to reduce drag and increase fuel efficiency.

But the design has a downside.

One of the characteristics of swept wing jets is they get less and less stable.

They're they're much harder to fly as they approach stall.

Sir, pull up! What's happening?

What's happening?

To maintain control of a swept wing jet,

with no more altitude than they had in this condition

is very, very problematic,

and they are not successful, and the airplane goes into the water.

Investigators now know why Birgenair Flight 301 crashed.

What they can't understand is why the flight ever left the ground.

Eighty knots.

My airspeed indicator's not working.

At 80 knots,

if the pilot and co-pilot's instruments disagree, takeoff should be aborted.

V-one.

Investigators are troubled that the captain took off

knowing he had malfunctioning instruments.

If something is not functioning correctly,

it doesn't matter what it is, one should abort the takeoff at 80 knots.

This decision on the part of the captain has been criticized.

But there is a very short time window for this decision to be made.

Members of the investigative team in Puerto Plata

try to find any clues that might explain

why Captain Erdem didn't abort his takeoff.

It was raining that night.

Perhaps he was worried that he wouldn't be able to stop his speeding plane in time.

Procedurally, he's required to stop.

But high speed aborted take-offs are something that are very serious,

and that flight crews trained to avoid high speed aborted takeoffs if possible.

And we certainly looked at the parameters of the runway

to ensure that there was adequate runway in that particular situation.

Careful measurements are taken.

Investigators conclude that at 80 knots, when he first noticed the problem,

Captain Erdem had enough runway left to bring his plane to a stop.

He could have aborted his takeoff.

There's also the question of the hastily assembled crew.

Investigators now wonder if the last minute nature of the crew's call

could have influenced their decision to take off.

Birgenair started with a crew that probably didn't expect to fly that night.

They didn't have adequate rest.

They got out to the aircraft and perhaps were rushed in some of their planning.

Investigators consider the possibility that the crew,

who had been away from home for more than two weeks was simply too eager to get home.

Zero eight three zero one. Thank you.

- Good flight. - Good flight.

This is the homesick factor,

where the minor problems are ignored in order to get back home.

But investigators will never know what was going through Captain Erdem's mind

when he opted to continue his takeoff.

In this case, the airplane is accelerating rapidly enough.

The First Officer responds...

V-1.

...which is the commit to fly speed.

And by training, now the decision window has closed.

They need to fly.

Rotate.

And immediately thereafter, they're airborne.

Once the plane was in the air, its blocked pitot tubes

caused Captain Erdem to make a series of critical mistakes.

But how were the tubes blocked in the first place?

Investigators will find that the death of 189 people

was caused by something the size of a paperclip.

Investigators now know that a blocked pitot tube

led to a series of conflicting warnings that confounded Flight 301's Captain.

Now they want to know how those same warnings would affect other pilots.

We went to a flight simulator and in the simulator,

we tried to recreate the conditions of what happened

On the night of February 6th, 1996.

Gentlemen, stand by.

The simulator showed investigators that an overspeed warning,

followed by a stick-shaker warning caused even the most seasoned pilots to freeze.

The contradictory warnings were potentially dangerous.

When the stick shaker activated, it was very unnerving.

It's really overwhelming.

That would tell me that Mach airspeed warning horn,

combined with the stick shaker was a tremendously mind-boggling experience to a line pilot.

As a result, the FAA issues a directive

that simulator training for all airline pilots must include a blocked pitot tube scenario.

The flight crew within Birgenair was faced with a large number of warnings,

that kept coming and each warning added complexity to the environment.

There's a lot of warning lights going off.

This captain is in a condition that is deteriorating now very rapidly.

So there is a dramatically increased demand on the captain to fly the airplane.

The FAA asks Boeing to change some of those warnings.

Those changes include the addition of a new warning,

which tells both pilots that their instruments disagree,

and the ability for pilots to more easily silence troublesome alarms.

Finally, Boeing modifies its planes,

so that pilots can easily choose which pitot tube the autopilot is using for airspeed readings.

All told, more than 1400 Boeing planes worldwide are affected

by the new directives.

One final question remains.

What had blocked the plane's pitot tubes?

Investigators conduct an extensive search for Birgenair Flight 301's pitot tubes.

They are never found.

But at Puerto Plata's airport, they don't have to look far to find the likeliest suspect.

It's not ice, and it's not dirt.

We know that the area around Puerto Plata

Has a lot of bees, and wasps, and...

and animals, and birds, and insects that like to build nests.

One of the insects is well known to pilots flying out of the Dominican Republic.

It's called the Mud Dauber wasp.

Bug experts tell investigators

about an extraordinary connection between the wasps and a pitot tube.

When a Mud Dauber is looking for an area to build its nest,

it's looking for a site,

a place that's more or less tubular.

When the Mud Daubers make their mud nest,

the mud, when it dries, hardens and condenses.

It gets hard.

Mud dauber wasps are squatters that make their nests in available places.

Like crevices in homes, or even the pitot tubes of planes.

That the plane was stopped for so long, 25 days,

was enough time for any species of the Mud Dauber to build its nest in the pitot tubes.

Investigators can only conclude

that Mud Dauber wasps blocked the uncovered pitot tubes

that fed the captain's airspeed indicator, which caused it to malfunction.

They didn't put covers on the pitot tubes.

So, at some point in time, extended time,

there was an opportunity to get something like a Mud Dauber

in that pitot tube.

Investigators have their answer.

On February the 6th, 1996,

a tiny insect led to a series of mistakes that brought down an airplane,

and changed the design of the world's most successful series of airliners.