Air Emergency (2003–…): Season 5, Episode 8 - The Plane That Wouldn't Talk: Birgenair Flight 301 - full transcript
There are many factors affecting an aircraft in flight. Any one of them can bring the plane down. But as the investigation reveals yet again, the most common one is the human factor.
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 black box can tell them what happened.
The tape raises a perplexing question.
301 Santo Domingo, come in please.
My airspeed indicator is not working
What is happening?
How had the failure of one single instrument...
...caused the crash
of one of the most sophisticated jetliners?
This is a true story.
It is based on official reports,
air traffic control
and cockpit recorder transcripts.
The Plane That Wouldn't Talk
Greogorio Luperón International Airport
in Puerto Plata at the Dominican Republic
February 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 Birgen Air.
They have a 757 that is been sitting on the tarmac
for almost 3 weeks.
but it takes several hours to get the plane
ready to go
and to get the Turkish crew aboard.
By 10:15 PM,
the plane and most of its crew are at the gate.
More than 4 hours
after they were supposed to take off
the first of the passengers
begin boarding the plane.
They have a 9 hour flight to Frankfurt
ahead of them.
Shortly after 11:30 PM, BirgenAir Flight 301
is given permission to leave the gate.
Moments later,
it taxied to the threshold of the runway.
Cabin crew, take your seats
ready for take off.
First Officer Aykut Gergin is new to the 757
with fewer than 75 hours in the plane,
all in the last three months.
Thank you, ready for take off
In contrast, Captain Ahmet Erdem
is one of BirgenAir's most senior pilots.
He has logged thousands of hours
in this type of plane.
ALW-301, ready for take off?
301 is ready for take off Runway 08
Cleared for take off runway 08, 301
A good flight
Muhlis Evrenesoğlu is on this flight
as a relief pilot.
Like First Officer Gergin,
he has been flying the 757 for less than 3 months.
As the plane accelerates to take off speed,
a light rain begins to fall.
Power set
First Officer Aykut Gergin watches his airspeed
for a routine instrument check.
As the airplane is accelerating to take off speed
and the First Officer calls: 80 knots...
...the captain in theory should verify
that his airspeed indicator also reads 80 knots.
My airspeed indicator is not working.
The Captain's airspeed should read
the same as his First Officer's...
...but the readings do not match.
Is your's working?
Yes, sir.
Erdem wants his First Officer
to tell him when the plane hits take off speed.
V1
At 150 knots, the plane hits V1,
the point of no return.
Rotate
The Captain must pull back on his column
and get the plane in the air.
Positive climb and 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
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 ft...
...First Officer Gergin establishes contact
with the island's main tower in Santa Domingo.
ALW-301,
climb and maintain 28,000 ft
Central AUTOPILOT ON, please
Central AUTOPILOT
1'30'' into the flight, the AUTOPILOT takes over.
On board computers now make
all the calculations and adjustments,
necessary to keep the plane climbing safely.
Almost immediately,
the computer reports a problem.
RUDDER RATIO,
MACH AIRSPEED TRIM
Two different alerts warn the pilots
that the plane is travelling far to fast.
but the First Officer's airspeed indicator
shows the plane is climbing at a normal speed,
220 knots
Something is wrong, here.
Unaware that there are any problems,
the controller directs Birgenair Flight 301
to continue climbing.
ALW-301, report POKEG
OKAY 280, I will call you over POKEG
In the cockpit, the situation gets more confusing
The FO'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 is flying far too fast:
325 knots
Both of them are wrong
What can we do?
Let's check the circuit breakers
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 is no matter,
let's prove the airspeed
Resetting the circuit breakers
turns off the alarm
but it doesn't fix the problem.
Captain Erdem's airspeed indicator
still shows he is flying much too fast.
Now, it is 350, yes?
Confused by the conflicting information,
Captain Erdem decides to do what the plane wants:
he slows down...
...with terrifying results.
The 757 is sending out warnings
that are confusing the crew.
Bewildered,
the crew struggles 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
The cockpit is filled with an ominous sound:
the stick-shaker alert.
A 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 control columns.
combined with a loud rattling,
it is impossible to ignore.
To add to the crew's confusion,
the plane begins to vibrate and dip wildly.
I am sure every passenger on the airplane
knew something was unusual
because the aircraft started to shake
in a very violent manoeuvre.
It is not the only problem the crew is facing,
The Attitude Deviation Indicator is a round gauge
that on this airplane is a screen,
blue on top and brown on the bottom
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 is showing that
the plane's nose is pointing dangerously high.
Then, more than 7,000 ft 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 flightcrew to sort this out
or they will end up
loosing control of it:
the window of decisions is closing on
for if they let it stall completely,
maintaining control will be very difficult.
Captain Erdem struggles desperately
to get his plane to climb
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, ADI
Air Traffic Control is still unaware
that Flight 301 is in grave danger.
The plane is falling fast.
5000 ft
Captain Erdem is trying to fly a plane
that has become virtually uncontrollable.
Gergin pushes the throttles to full power.
but it doesn't help:
the plane spirals towards the sea.
ALW-301 Santa Domingo,
come in, please.
ALW-301,
here Santa Domingo
come in, please.
Less than 5 minutes after take off,
BirgenAir Flight 301 vanishes from radar.
The Dominican NAVY begins searching
for the missing plane and its passengers.
En route,
I was always thinking of what I would find.
I thought I would find people screaming
people yelling, 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 had disintegrated on impact.
Within hours, more than just wreckage
begins floating to the surface.
Around 5:20 AM when the bodies started to come up
I did feel a great sorrow in my heart.
I felt like I was unsure if I had 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 1,300 km² area for survivors,
none are found.
Now, it is 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 is directly South of the accident site.
Over the next couple of days,
investigators, reporters and
some of the victim's families arrive at the hotel.
Nearby, evidence of the disaster
reaches the Dominican shores.
Wreckage and passengers' 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 NTSB agrees to assist the Dominicans
with their investigation.
They send an investigator to Puerto Plata.
We could see that this would take some internat'l
corporation to get to the bottom of the event.
Robert Macintosh will also provide support
from the NTSB's Washington offices.
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 delivery
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 operations
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 ft 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 hired a submersible called the CURV
CURV stands for Cable Underwater Recovery Vehicle
it is a tethered vehicle
it has an imbecilic and it is controlled
by an imbecilic, it is 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.
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...
ALW-301,
come in please
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 standby.
As you heard,
there is no reason why this plane went down.
What had caused something to go wrong to interrupt
the flightpath of the aircraft so rapidly
certainly was a good question for us.
Any debris that is found is taken
to a Dominican Military Base to be examined.
Investigators comb through the wreckage
they have 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 plought into the sea.
Cords on some of the life vests 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.
The wreckage tells investigators that
the crash of 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 of he last minute
may not have been ready for the flight.
Emmanuel Souffront
I let you see some records of the BirgenAir plane.
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 the maintenance records,
the plane appears to be 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 3 weeks.
The plane's maintenance records
turn out to be one more in a series of empty leads
The CURV arrives in Puerto Plata harbour.
On February, 28th,
more than 3 weeks after the crash,
it slips below the waves,
looking for the remains of the BirgenAir jet.
It takes the robotic submarine 2 hours
just to descend to 7,200 ft to the ocean floor.
From there,
it sends back images of the wreck of Flight 301.
The cockpit was sitting upright
and it was the nose of the plane
And you could see the front-part of it,
it was 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 black boxes are the top priority.
The CURV quickly picks up the signal
from a pinger on one of the units.
Operators must now manoeuvre the sub
towards the sound.
They have to be able to see the black 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.
It was where they could see it
and they picked the first box up.
They grabbed the hold of it
and they took the arm in place
in a way that they wouldn't loose it.
The 2nd black box is also heard,
but after almost 2 hours
the CURV's cameras still can't see it.
They knew it was right there
and they were searching around a debris pile
and they could not physically see it
with the cameras of the vehicle.
So, as they wander around a couple of times
they started lifting metal up
and moving pieces out of the way
and they did find the 2nd box under some debris.
Flight 301's FDR and CVR
are brought to the surface
and loaded on for 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 will 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 visual plots
of what was going on
with the engines and air speeds and so on
to allow us to try to understand,
why that aircraft slowed down
and then simply departed controlled flight
and entered the ocean.
Investigators immediately notice something unusual
about the flight.
15 degrees pitch nose up?
It seems high.
It is almost the maximum
and it stays that way.
The plane began climbing normally...
Central 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.
350 knots, it can't be right.
There is definitively something wrong
with 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.
Investigators soon start
filling in the missing pieces of the puzzle.
My airspeed indicator is not working
They learn that Captain Erdem noticed
that his airspeed indicator wasn't working.
Your's is working?
Yes, sir
You tell me
V1, Rotate
But Erdem didn't think the problem was
serious enough to abort his take off.
The tape reveals that once they were airborne,
the crew quickly became overwhelmed
by a series of warnings.
To investigators,
the Captain seems to become increasing bewildered
by the messages he was getting from his plane.
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.
It is a telling discovery
which leads investigators to focus their attention
on the device that feeds the gauge:
the pitot tube.
The 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 tube
causes the airspeed indicator's needle to move.
But if a pitot tube becomes blocked,
it can send faulty readings to the plane's gauges.
They suspect that the pitot tube which fed
the captain's indicator was somehow blocked.
We don't know why it was blocked,
but it presented
a very interesting situation to us.
We started carefully looking at
what could cause that kind of thing to happen.
Major Souffront has a theory
he returns to question the airplane's mechanics
Souffront suspects the mechanics may have
taped over the pitot tubes during maintenance.
It is a common procedure,
but if the tape wasn't removed,
it could have caused the deadly accident.
a piece of tape was left on, accidentally?
No, sir
it 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 didn't have any covers with it
We didn't take any off and we didn't put any on.
And that is when we discovered
that the pitots had not been covered
for the 25 days that the aircraft remain 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 take off.
Investigators find that
the BirgenAir's pitot tubes were never covered
and somehow,
the uncovered pitots have 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 ft 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 is not like a car,
we have only one speedometer
and in this kind of an aircraft,
you have a total of 3 airspeed-indicators
and there is a Flight Data Computer, which is
computing the velocity in relation to the ground.
The big question for investigators:
How could one faulty airspeed-source
result in a crash?
He realized it at a time when he
could have abort it and to turn 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.
Moments after lift off, Captain Erdem's
airspeed indicator appears to be working
but investigators suspect
the gauge is responding to changes in altitude.
As the plane climbs through thinning atmosphere
the air, trapped inside the tube expands,
causing a built up of pressure.
Inside the cockpit,
this causes the speed indicator needle to deflect.
Even though altitude is causing
the increase in pressure
the sensors mistakenly read it
as an increase in airspeed.
Captain Erdem may have had
5 separate sources of airspeed to rely on
but they notice that when the troubles started,
he wasn't flying the plane...
...the AUTOPILOT was.
And unless the crew reconfigures it,
the AUTOPILOT gets its airspeed information
from only one source.
The data shows that the trouble 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 travelling too fast
and raised the nose to slow it down
The AUTOPILOT is a pretty smart guy:
he already knows that he has got all the power
he has going to get for the climb
The only thing for the AUTOPILOT to do
is to 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 send out 2 different warnings:
RUDDER RATIO
MACH AIRSPEED TRIM
that the plane was travelling too fast
to be controlled safely
And the airplane begins picking up warnings:
RUDDER RATIO, a variety of things
that the airplane is sensing problems.
There is something crazy, there
You see it?
Yes, there is something crazy,
mine's shows only 200 now and decreasing, sir
Both of them are wrong.
Investigators realize
that Captain Erdem wrongly concluded that
both airspeed indicators were malfunctioning.
His First Officer's gauge was always correct:
The plane was travelling 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 to pull some circuit breakers
and that would be rather strange.
Resetting the circuit breakers turns of the alarm
but that needle continued to climb
around the clock-face
until it activated the over-speed warning.
The AUTOPILOT system send yet another warning
for the plane was travelling too fast
but the reality was just the opposite:
The plane was slowing down
Let's pull the airspeed.
That is when Captain Erdem
made the gravest error of all.
You can see that he pulls back on his throttles.
Investigators realize
that at the 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.
He has got a tactile sense
coming through his flight controls
that literally shakes the stick and says:
You got to lower this nose.
In a matter of seconds,
Captain Erdem was first warned
that his plane was travelling too fast
and then that his plane
was travelling dangerously slowly
They are 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 is up to the pilots
to get the plane out of the stall.
Once the AUTOPILOT reach its limits of authority
it says:
I've done all I can do,
I am out of here.
When the AUTOPILOT disengages
Captain Erdem suddenly found himself in control of
the plane at the moment of his greatest confusion
The Cockpit recordings leads investigators
to a stunning conclusion:
Captain Erdem may not have recognized
that his plane was about to stall
but the relief pilot behind him did
ADI!
This additional pilot intervened to say:
ADI ADI !
In other words:
look at that ADI and put yourself where you
would normally see the nose of the aircraft:
5 ..10 degrees nose high
The relief pilot wanted Captain Erdem to recognize
that the plane's nose was
pitched dangerously skyward
Investigators can hear First Officer Gergin
try to convey the same message:
Nose down
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.
You can level of, our altitude is okay.
The recording shows that Captain Erdem
ignored valuable advice
that could have saved the plane.
In the BirgenAir case,
there is a case of a relative 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 can kill some body
And in this case it looks like it did.
The FDR 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.
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
its 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 a life threatening condition.
The 757 itself makes the situation worse
Like many modern jets,
it uses a so called swept wing design.
The wings angles 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 are much harder to fly
as they approach stall.
To maintain control of a swept wing jet,
with no more altitude than they had
is very problematic
They are not successful
and the airplane goes into the water.
Investigators now know
why BirgenAir Flight 301 crashed
What they cannot understand is
why the flight ever left the ground
My airspeed indicator is not working.
At 80 knots, if
the pilot's and copilot's instruments disagree
take off should be aborted.
Investigators are troubled 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 take off at 80 knots.
Members of the investigative team in Puerto Plata
tried to find any clues that might explain
why Captain Erdem didn't abort his take off.
It was raining that night,
perhaps he was worried that he wouldn't be
able to stop his speeding plane in time.
Procedurally he is required to stop,
but high speed aborted take offs
are something that are very serious
and the flight-crew is trained
to avoid high speed aborted take offs if possible.
We certainly looked at 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 take off.
There is 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.
Birgen Air 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,
were simply too eager to get home.
This is the homesick factor, where minor problems
are ignored in order to get back home.
Investigators will never know
what was going through Captain Erdem's mind
when he opted to continue his take off
In this case,
the airplane is accelerating rapidly enough
the First Officer responds V1
which is the commit to fly-speed
and by training now the decision window has closed
They need to fly
And immediately after, they are 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 the 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
The simulators showed investigators
that an over-speed 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 is 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 simulated training for all airline pilots
must include a blocked pitot tube scenario.
The flight crew of the BirgenAir was faced
with a large number of warnings that kept coming
and each warning
added complexity to the environment.
There was a lot of warning lights going off.
This Captain is in a condition
that is deteriorating now very rapidly
So, there is a dramatically increase of 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 tell 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 chose which pitot tube
the AUTOPILOT is using for airspeed readings.
All to all 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 likely suspect.
It is not ice
and it is not dirt.
We know that the area around Puerto Plata
has a lot of bees and wasps...
...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 is called the mud dauber wasp
Bug experts tell investigators
about an extraordinary connection
between the wasps and the pitot tube
When the mud dauber is looking
for an area to build its nest
it is looking for a site,
a place that is 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 pitot tubes
that fed the Captains airspeed indicator
which caused it to malfunction
They didn't put covers on the pitot tubes
so, at some point in extended time,
there was an opportunity to get something
like a mud dauber in that pitot tube.
Investigators have their answer
On February, 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
Narrator:
Jonathan Aris
Subtitles
Rein Croonen
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 black box can tell them what happened.
The tape raises a perplexing question.
301 Santo Domingo, come in please.
My airspeed indicator is not working
What is happening?
How had the failure of one single instrument...
...caused the crash
of one of the most sophisticated jetliners?
This is a true story.
It is based on official reports,
air traffic control
and cockpit recorder transcripts.
The Plane That Wouldn't Talk
Greogorio Luperón International Airport
in Puerto Plata at the Dominican Republic
February 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 Birgen Air.
They have a 757 that is been sitting on the tarmac
for almost 3 weeks.
but it takes several hours to get the plane
ready to go
and to get the Turkish crew aboard.
By 10:15 PM,
the plane and most of its crew are at the gate.
More than 4 hours
after they were supposed to take off
the first of the passengers
begin boarding the plane.
They have a 9 hour flight to Frankfurt
ahead of them.
Shortly after 11:30 PM, BirgenAir Flight 301
is given permission to leave the gate.
Moments later,
it taxied to the threshold of the runway.
Cabin crew, take your seats
ready for take off.
First Officer Aykut Gergin is new to the 757
with fewer than 75 hours in the plane,
all in the last three months.
Thank you, ready for take off
In contrast, Captain Ahmet Erdem
is one of BirgenAir's most senior pilots.
He has logged thousands of hours
in this type of plane.
ALW-301, ready for take off?
301 is ready for take off Runway 08
Cleared for take off runway 08, 301
A good flight
Muhlis Evrenesoğlu is on this flight
as a relief pilot.
Like First Officer Gergin,
he has been flying the 757 for less than 3 months.
As the plane accelerates to take off speed,
a light rain begins to fall.
Power set
First Officer Aykut Gergin watches his airspeed
for a routine instrument check.
As the airplane is accelerating to take off speed
and the First Officer calls: 80 knots...
...the captain in theory should verify
that his airspeed indicator also reads 80 knots.
My airspeed indicator is not working.
The Captain's airspeed should read
the same as his First Officer's...
...but the readings do not match.
Is your's working?
Yes, sir.
Erdem wants his First Officer
to tell him when the plane hits take off speed.
V1
At 150 knots, the plane hits V1,
the point of no return.
Rotate
The Captain must pull back on his column
and get the plane in the air.
Positive climb and 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
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 ft...
...First Officer Gergin establishes contact
with the island's main tower in Santa Domingo.
ALW-301,
climb and maintain 28,000 ft
Central AUTOPILOT ON, please
Central AUTOPILOT
1'30'' into the flight, the AUTOPILOT takes over.
On board computers now make
all the calculations and adjustments,
necessary to keep the plane climbing safely.
Almost immediately,
the computer reports a problem.
RUDDER RATIO,
MACH AIRSPEED TRIM
Two different alerts warn the pilots
that the plane is travelling far to fast.
but the First Officer's airspeed indicator
shows the plane is climbing at a normal speed,
220 knots
Something is wrong, here.
Unaware that there are any problems,
the controller directs Birgenair Flight 301
to continue climbing.
ALW-301, report POKEG
OKAY 280, I will call you over POKEG
In the cockpit, the situation gets more confusing
The FO'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 is flying far too fast:
325 knots
Both of them are wrong
What can we do?
Let's check the circuit breakers
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 is no matter,
let's prove the airspeed
Resetting the circuit breakers
turns off the alarm
but it doesn't fix the problem.
Captain Erdem's airspeed indicator
still shows he is flying much too fast.
Now, it is 350, yes?
Confused by the conflicting information,
Captain Erdem decides to do what the plane wants:
he slows down...
...with terrifying results.
The 757 is sending out warnings
that are confusing the crew.
Bewildered,
the crew struggles 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
The cockpit is filled with an ominous sound:
the stick-shaker alert.
A 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 control columns.
combined with a loud rattling,
it is impossible to ignore.
To add to the crew's confusion,
the plane begins to vibrate and dip wildly.
I am sure every passenger on the airplane
knew something was unusual
because the aircraft started to shake
in a very violent manoeuvre.
It is not the only problem the crew is facing,
The Attitude Deviation Indicator is a round gauge
that on this airplane is a screen,
blue on top and brown on the bottom
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 is showing that
the plane's nose is pointing dangerously high.
Then, more than 7,000 ft 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 flightcrew to sort this out
or they will end up
loosing control of it:
the window of decisions is closing on
for if they let it stall completely,
maintaining control will be very difficult.
Captain Erdem struggles desperately
to get his plane to climb
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, ADI
Air Traffic Control is still unaware
that Flight 301 is in grave danger.
The plane is falling fast.
5000 ft
Captain Erdem is trying to fly a plane
that has become virtually uncontrollable.
Gergin pushes the throttles to full power.
but it doesn't help:
the plane spirals towards the sea.
ALW-301 Santa Domingo,
come in, please.
ALW-301,
here Santa Domingo
come in, please.
Less than 5 minutes after take off,
BirgenAir Flight 301 vanishes from radar.
The Dominican NAVY begins searching
for the missing plane and its passengers.
En route,
I was always thinking of what I would find.
I thought I would find people screaming
people yelling, 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 had disintegrated on impact.
Within hours, more than just wreckage
begins floating to the surface.
Around 5:20 AM when the bodies started to come up
I did feel a great sorrow in my heart.
I felt like I was unsure if I had 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 1,300 km² area for survivors,
none are found.
Now, it is 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 is directly South of the accident site.
Over the next couple of days,
investigators, reporters and
some of the victim's families arrive at the hotel.
Nearby, evidence of the disaster
reaches the Dominican shores.
Wreckage and passengers' 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 NTSB agrees to assist the Dominicans
with their investigation.
They send an investigator to Puerto Plata.
We could see that this would take some internat'l
corporation to get to the bottom of the event.
Robert Macintosh will also provide support
from the NTSB's Washington offices.
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 delivery
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 operations
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 ft 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 hired a submersible called the CURV
CURV stands for Cable Underwater Recovery Vehicle
it is a tethered vehicle
it has an imbecilic and it is controlled
by an imbecilic, it is 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.
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...
ALW-301,
come in please
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 standby.
As you heard,
there is no reason why this plane went down.
What had caused something to go wrong to interrupt
the flightpath of the aircraft so rapidly
certainly was a good question for us.
Any debris that is found is taken
to a Dominican Military Base to be examined.
Investigators comb through the wreckage
they have 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 plought into the sea.
Cords on some of the life vests 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.
The wreckage tells investigators that
the crash of 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 of he last minute
may not have been ready for the flight.
Emmanuel Souffront
I let you see some records of the BirgenAir plane.
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 the maintenance records,
the plane appears to be 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 3 weeks.
The plane's maintenance records
turn out to be one more in a series of empty leads
The CURV arrives in Puerto Plata harbour.
On February, 28th,
more than 3 weeks after the crash,
it slips below the waves,
looking for the remains of the BirgenAir jet.
It takes the robotic submarine 2 hours
just to descend to 7,200 ft to the ocean floor.
From there,
it sends back images of the wreck of Flight 301.
The cockpit was sitting upright
and it was the nose of the plane
And you could see the front-part of it,
it was 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 black boxes are the top priority.
The CURV quickly picks up the signal
from a pinger on one of the units.
Operators must now manoeuvre the sub
towards the sound.
They have to be able to see the black 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.
It was where they could see it
and they picked the first box up.
They grabbed the hold of it
and they took the arm in place
in a way that they wouldn't loose it.
The 2nd black box is also heard,
but after almost 2 hours
the CURV's cameras still can't see it.
They knew it was right there
and they were searching around a debris pile
and they could not physically see it
with the cameras of the vehicle.
So, as they wander around a couple of times
they started lifting metal up
and moving pieces out of the way
and they did find the 2nd box under some debris.
Flight 301's FDR and CVR
are brought to the surface
and loaded on for 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 will 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 visual plots
of what was going on
with the engines and air speeds and so on
to allow us to try to understand,
why that aircraft slowed down
and then simply departed controlled flight
and entered the ocean.
Investigators immediately notice something unusual
about the flight.
15 degrees pitch nose up?
It seems high.
It is almost the maximum
and it stays that way.
The plane began climbing normally...
Central 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.
350 knots, it can't be right.
There is definitively something wrong
with 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.
Investigators soon start
filling in the missing pieces of the puzzle.
My airspeed indicator is not working
They learn that Captain Erdem noticed
that his airspeed indicator wasn't working.
Your's is working?
Yes, sir
You tell me
V1, Rotate
But Erdem didn't think the problem was
serious enough to abort his take off.
The tape reveals that once they were airborne,
the crew quickly became overwhelmed
by a series of warnings.
To investigators,
the Captain seems to become increasing bewildered
by the messages he was getting from his plane.
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.
It is a telling discovery
which leads investigators to focus their attention
on the device that feeds the gauge:
the pitot tube.
The 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 tube
causes the airspeed indicator's needle to move.
But if a pitot tube becomes blocked,
it can send faulty readings to the plane's gauges.
They suspect that the pitot tube which fed
the captain's indicator was somehow blocked.
We don't know why it was blocked,
but it presented
a very interesting situation to us.
We started carefully looking at
what could cause that kind of thing to happen.
Major Souffront has a theory
he returns to question the airplane's mechanics
Souffront suspects the mechanics may have
taped over the pitot tubes during maintenance.
It is a common procedure,
but if the tape wasn't removed,
it could have caused the deadly accident.
a piece of tape was left on, accidentally?
No, sir
it 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 didn't have any covers with it
We didn't take any off and we didn't put any on.
And that is when we discovered
that the pitots had not been covered
for the 25 days that the aircraft remain 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 take off.
Investigators find that
the BirgenAir's pitot tubes were never covered
and somehow,
the uncovered pitots have 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 ft 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 is not like a car,
we have only one speedometer
and in this kind of an aircraft,
you have a total of 3 airspeed-indicators
and there is a Flight Data Computer, which is
computing the velocity in relation to the ground.
The big question for investigators:
How could one faulty airspeed-source
result in a crash?
He realized it at a time when he
could have abort it and to turn 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.
Moments after lift off, Captain Erdem's
airspeed indicator appears to be working
but investigators suspect
the gauge is responding to changes in altitude.
As the plane climbs through thinning atmosphere
the air, trapped inside the tube expands,
causing a built up of pressure.
Inside the cockpit,
this causes the speed indicator needle to deflect.
Even though altitude is causing
the increase in pressure
the sensors mistakenly read it
as an increase in airspeed.
Captain Erdem may have had
5 separate sources of airspeed to rely on
but they notice that when the troubles started,
he wasn't flying the plane...
...the AUTOPILOT was.
And unless the crew reconfigures it,
the AUTOPILOT gets its airspeed information
from only one source.
The data shows that the trouble 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 travelling too fast
and raised the nose to slow it down
The AUTOPILOT is a pretty smart guy:
he already knows that he has got all the power
he has going to get for the climb
The only thing for the AUTOPILOT to do
is to 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 send out 2 different warnings:
RUDDER RATIO
MACH AIRSPEED TRIM
that the plane was travelling too fast
to be controlled safely
And the airplane begins picking up warnings:
RUDDER RATIO, a variety of things
that the airplane is sensing problems.
There is something crazy, there
You see it?
Yes, there is something crazy,
mine's shows only 200 now and decreasing, sir
Both of them are wrong.
Investigators realize
that Captain Erdem wrongly concluded that
both airspeed indicators were malfunctioning.
His First Officer's gauge was always correct:
The plane was travelling 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 to pull some circuit breakers
and that would be rather strange.
Resetting the circuit breakers turns of the alarm
but that needle continued to climb
around the clock-face
until it activated the over-speed warning.
The AUTOPILOT system send yet another warning
for the plane was travelling too fast
but the reality was just the opposite:
The plane was slowing down
Let's pull the airspeed.
That is when Captain Erdem
made the gravest error of all.
You can see that he pulls back on his throttles.
Investigators realize
that at the 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.
He has got a tactile sense
coming through his flight controls
that literally shakes the stick and says:
You got to lower this nose.
In a matter of seconds,
Captain Erdem was first warned
that his plane was travelling too fast
and then that his plane
was travelling dangerously slowly
They are 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 is up to the pilots
to get the plane out of the stall.
Once the AUTOPILOT reach its limits of authority
it says:
I've done all I can do,
I am out of here.
When the AUTOPILOT disengages
Captain Erdem suddenly found himself in control of
the plane at the moment of his greatest confusion
The Cockpit recordings leads investigators
to a stunning conclusion:
Captain Erdem may not have recognized
that his plane was about to stall
but the relief pilot behind him did
ADI!
This additional pilot intervened to say:
ADI ADI !
In other words:
look at that ADI and put yourself where you
would normally see the nose of the aircraft:
5 ..10 degrees nose high
The relief pilot wanted Captain Erdem to recognize
that the plane's nose was
pitched dangerously skyward
Investigators can hear First Officer Gergin
try to convey the same message:
Nose down
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.
You can level of, our altitude is okay.
The recording shows that Captain Erdem
ignored valuable advice
that could have saved the plane.
In the BirgenAir case,
there is a case of a relative 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 can kill some body
And in this case it looks like it did.
The FDR 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.
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
its 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 a life threatening condition.
The 757 itself makes the situation worse
Like many modern jets,
it uses a so called swept wing design.
The wings angles 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 are much harder to fly
as they approach stall.
To maintain control of a swept wing jet,
with no more altitude than they had
is very problematic
They are not successful
and the airplane goes into the water.
Investigators now know
why BirgenAir Flight 301 crashed
What they cannot understand is
why the flight ever left the ground
My airspeed indicator is not working.
At 80 knots, if
the pilot's and copilot's instruments disagree
take off should be aborted.
Investigators are troubled 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 take off at 80 knots.
Members of the investigative team in Puerto Plata
tried to find any clues that might explain
why Captain Erdem didn't abort his take off.
It was raining that night,
perhaps he was worried that he wouldn't be
able to stop his speeding plane in time.
Procedurally he is required to stop,
but high speed aborted take offs
are something that are very serious
and the flight-crew is trained
to avoid high speed aborted take offs if possible.
We certainly looked at 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 take off.
There is 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.
Birgen Air 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,
were simply too eager to get home.
This is the homesick factor, where minor problems
are ignored in order to get back home.
Investigators will never know
what was going through Captain Erdem's mind
when he opted to continue his take off
In this case,
the airplane is accelerating rapidly enough
the First Officer responds V1
which is the commit to fly-speed
and by training now the decision window has closed
They need to fly
And immediately after, they are 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 the 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
The simulators showed investigators
that an over-speed 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 is 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 simulated training for all airline pilots
must include a blocked pitot tube scenario.
The flight crew of the BirgenAir was faced
with a large number of warnings that kept coming
and each warning
added complexity to the environment.
There was a lot of warning lights going off.
This Captain is in a condition
that is deteriorating now very rapidly
So, there is a dramatically increase of 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 tell 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 chose which pitot tube
the AUTOPILOT is using for airspeed readings.
All to all 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 likely suspect.
It is not ice
and it is not dirt.
We know that the area around Puerto Plata
has a lot of bees and wasps...
...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 is called the mud dauber wasp
Bug experts tell investigators
about an extraordinary connection
between the wasps and the pitot tube
When the mud dauber is looking
for an area to build its nest
it is looking for a site,
a place that is 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 pitot tubes
that fed the Captains airspeed indicator
which caused it to malfunction
They didn't put covers on the pitot tubes
so, at some point in extended time,
there was an opportunity to get something
like a mud dauber in that pitot tube.
Investigators have their answer
On February, 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
Narrator:
Jonathan Aris
Subtitles
Rein Croonen