Original subtitles

Grab your ankles. Head down.

Man: Get out of it!

Man: I can't. Man: no!

Man: Oh, God! That's it.

Narrator: A plane crash in Georgia leaves 23 dead,

including a NASA astronaut and a U.S. Senator.

Man: Anytime there's a high-profile case,

there's more stress and pressure on you.

Narrator: In search of the cause...

Man: We've got to see what happens in the air.

Narrator: Investigator Tom Haueter gambles

on a risky hunch.

Tom Haueter: When I first proposed doing the flight test,

it was not well-received.

Narrator: He puts his reputation

and the life of a skilled test pilot on the line.

Haueter: EMB-120, do you copy?

Man: Copy.

Man: This was, in my opinion, a very dangerous maneuver.

Haueter: What if this airplane crashes?

What if we lose the airplane?

Man: The risks, of course, is part of the game.

Flight attendant: Ladies and gentlemen,

we are starting our approach.

Pilot: We lost both engines!

Flight attendant: Put the mask over your nose.

Emergency descent.

Pilot: Mayday, mayday.

Flight attendant: Brace for impact!

Controller: I think I lost one.

Man: Investigation starting into this tragedy...

Man: He's gonna crash!

Narrator: Atlantic Southeast Airlines flight 2311

cruises at 15,000 feet.

Hank Johnston: It's the Braves' year. I feel it.

Mark Friedline: Sorry. I don't want to get my hopes up.

Last year still hurts.

Narrator: At the controls is Captain Mark Friedline.

The 34-year-old is an experienced pilot

with almost 12,000 flight hours.

Friedline: We got storm clouds ahead of us.

Johnston: Yep. What do you want to do?

Narrator: First officer Hank Johnston is 36.

He's been flying with Atlantic Southeast Airlines

for nearly three years.

Friedline: We're gonna go around 'em.

Tell center we'll go right.

Johnston: Center, ASA 2311.

We'd like to request a deviation for some weather.

John Maris: This was a normal day

in the life of the crew.

Nothing untoward had happened,

and I doubt they were expecting any difficulties

with the flight.

Controller: ASA 2311, roger that.

Weather deviation approved at your discretions.

Maintain current altitude.

Johnston: Okay. Thanks, center. 2311.

Friedline: Let's go... 20 degrees to the right.

Narrator: Today's flight is a short commuter route

from Atlanta, Georgia,

to the city of Brunswick on the Atlantic coast.

Friedline: This is Captain Friedline on the flight deck.

We've got a bit of weather ahead of us,

but we're gonna go around it and give you a pretty smooth ride.

Might hit a few bumps, but nothing to worry about.

We do ask you to return to your seats

and please make sure your safety belts are fastened.

Narrator: The Embraer 120 banks gently

as the pilots deviate around the storm.

Maris: The Embraer EMB-120

is designed for commuter-type operations.

It takes approximately 30 people on short haul flights

between city centers.

Narrator: The commuter airplane

is powered by two turboprop engines.

Maris: Turboprops differ from jet engines

because instead of using the exhaust to power the aircraft,

they use a propeller, which is more fuel-efficient

and is more suited for these smaller aircraft.

Narrator: Today, there are 20 passengers aboard,

including NASA Astronaut Sonny Carter.

Sonny Carter: Thank you so much.

You're a star.

Narrator: As part of the space shuttle Discovery's crew,

Sonny Carter orbited the Earth for 120 hours,

circling the planet 79 times.

Frederick Gregory served with Carter on that mission.

Fred Gregory: Sonny was not only an astronaut;

he was a renaissance man.

He was an engineer, he was a medical doctor,

he was a navy pilot.

At a very young age, he had accomplished things

that even one of which would have been

an outstanding achievement for just any other person.

Narrator: Also on the flight is another high-profile figure,

former Senator John Tower.

Tower served four terms in the U.S. Senate.

A leading republican, he was an advisor

to presidents Ronald Reagan and George H.W. Bush.

Friedline: We're still running 20 minutes late.

Johnston: Yep. Well...

Friedline: Couldn't be helped.

Narrator: Before takeoff, flight 2311 was delayed

due to a mechanical problem.

The crew was forced to switch planes.

Maris: There was a last-minute change in the aircraft,

which, while uncommon, is not extraordinary,

and it would not have thrown the crew.

Carter: These small planes do keep you on your toes.

Narrator: The new plane is running smoothly

as it leaves the storm clouds behind

and nears its destination.

Glynco Airport is a former air base with just one runway.

It's used by private planes and small commuter airlines

flying to the Georgia coast.

The flight attendant prepares the cabin for landing.

Friedline: The runway's in sight.

Narrator: The crew is just five minutes from touching down.

Controller: ASA 2311, cleared direct to Jeff-1 Glynco.

Report the airport in sight. Expect a visual.

Johnston: We do have it in sight, 2311.

Friedline: Slowing for approach speed.

Maris: The aircraft was normal.

There was nothing unexpected.

Friedline: Gear down.

Johnston: Gear down.

Three green.

Narrator: Then, the captain notices an unusual sound.

Friedline: That's weird.

Number one seems to be spinning faster.

The left is... the left is pulling a bit more.

Bringing power down to the left.

Narrator: Captain Friedline tries to compensate

for the plane's unexplained pull to the left.

Flight 2311 is less than 1,000 feet from the ground,

and the plane is getting more and more difficult to control.

Friedline: What's going on?

You see anything?

Johnston: There's nothing.

Maris: The crew were apparently caught completely by surprise

by something.

Friedline: What's going on with this thing?

I can't hold it.

Johnston: Get out of it!

Friedline: I can't. Come on!

Narrator: The plane is rolling to the left,

and the crew doesn't know why.

Maris: The crew would have instinctively applied

opposite aileron, moving the stick to the right,

to try and prevent the aircraft from rolling as it was.

Carter: Come on, guys.

Get us out of this.

Johnston: Come on! God. I can't.

Computer: pull up.

Maris: I think they would have been preoccupied

with trying to stop the roll,

maybe to the extent of not knowing

just how much peril they were in.

Carter: Do what I do.

Grab your ankles, head down. Okay?

Narrator: Captain Friedline fights desperately

to save his plane.

Computer: Pull up.

Friedline: Come on! Johnston: No! No!

Friedline: That's it. Oh, God!

Narrator: It's no use.

Maris: The aircraft crashed in the middle of woods,

which would have made the job of the first responders

and firefighting teams quite difficult.

Narrator: Rescuers make their way through the dense brush,

but when they reach the crash site,

they find no one alive to rescue.

All 20 passengers and three crewmembers are dead,

killed at the moment of impact.

Jim Ritter: It was a catastrophic crash.

There was no chance for survival.

Narrator: With two high-profile passengers on board,

the crash of flight 2311 makes headlines around the world.

Maris: In this particular accident,

Senator Tower on board, was a four-term senator, was killed,

which raised the profile of the accident a great deal,

both from the investigation point of view

and the public and the media.

Woman: And we are, at this moment,

beginning the on-scene phases of the investigation.

Gregory: I was in Spain when the accident occurred.

When I got on the plane to head back,

the pilot told me that one of the astronauts had been killed,

and that his name was Carter.

I was in shock, because Sonny and I had

had an amazing relationship for years.

We were like brothers.

Narrator: Wreckage is still smoldering

when Jim Ritter arrives at the crash site.

Though an experienced investigator

with the national transportation safety board,

Ritter is struck by what he sees.

Ritter: My God.

There was a lot of fire damage in the wreckage,

and the airplane was basically totally destroyed.

Narrator: Ritter realizes he's facing

one of the biggest challenges of his career.

Ritter: Anytime there's a high-profile case,

you're a little more nervous.

There's more stress and pressure on you

to come up with a cause for the accident.

Narrator: The pressure is on to figure out what happened

aboard flight 2311.

Narrator: In Glynn county, Georgia,

investigators search for answers

at the crash site of flight 2311.

Several people at a nearby trailer park

saw the plane go down.

Man: It had come right over top of the house,

and it got real loud.

It was coming right over these trees here,

and then it got extra loud.

Ritter: The eyewitnesses saw an extreme left roll angle

from the airplane,

and so we knew that it was some kind of catastrophic failure,

a very abrupt failure that would have been difficult

for the flight crew to overcome.

Okay.

Let's start here and work backwards to first impact.

I want a record of everything.

You need to look at the crash site

to collect the physical evidence.

That's the most important aspect

of any aircraft investigation.

Maris: Investigators look at the wreckage

to try and evaluate the sequence of events leading to the crash.

They look for the two wing tips, the tip of the tail,

the tip of the nose.

Narrator: A survey of the crash site soon confirms

those key pieces are among the wreckage.

Ritter: That tells us that there was no in-flight breakup

and that the airplane stayed intact

until it collided with the ground.

Can you get a shot of this wing for me, please?

Narrator: For expert investigators,

the size and shape of the impact zone is also a clue.

Maris: If an aircraft, particularly through trees,

has a long swathe cut through the trees,

the investigators get an idea that the aircraft hit the ground

approximately flat in a shallow descent.

In this case, the wreckage was very concentrated,

which indicated the aircraft hit the ground

at a very steep angle.

Ritter: We need to get some

measurements on these trees.

Narrator: Investigators hope the broken trees will shed light

on witness statements about the way the plane was flying.

Man: I seen it fly overhead and, you know,

it looked like it was making a wide right turn,

but it was unusual because when it turned out,

it... the nose started heading toward the ground,

and I was right up toward the entrance of touchstone,

and I heard the explosion and seen the fire and the smoke.

Ritter: When the plane crashed,

it sheared the tops off of many of the trees in the woods there,

and so one of the things that we did

was we measured the heights of the trees

where the tops were sheared off,

and that was able to give us a fairly good idea

of the roll angle, which was a large left roll.

In the plane you would have felt light in your seat.

You would have turned obviously to the left

at almost 90 degrees.

Johnston: Get out of it!

Friedline: I can't. Come on!

Ritter: It would have been a traumatic experience.

Carter: Come on, guys.

Get us out of this.

Ritter: What could make it roll so far over?

When the airplane rolled to the left,

it could really only be due to two things.

Perhaps the pilot wanted to roll to the left,

or there was a malfunction that the pilots couldn't counteract.

What have you got for me?

Narrator: Ritter examines

airport flight records.

He's looking for anything that might have triggered

the deadly roll.

Ritter: Clear skies on approach.

Almost zero traffic.

There were no other airplanes in the area to avoid.

It was a nice, clear day,

so we didn't really have an explanation

for why the airplane rolled so violently to the left.

Narrator: Ritter won't be getting an explanation

from any onboard flight recorders.

At the time of the crash,

commuter planes weren't required to carry them.

Investigators will have to solve the mystery of flight 2311

without one of their most useful tools.

Ritter: Not having those made the physical evidence

all the more important.

What have you got for me?

This is the third one.

Narrator: The engines have been badly damaged in the crash.

The propeller blades have been torn off.

Did flight 2311 suffer some kind of engine failure?

It's too soon to say.

One thing Ritter does know

is that the pressure he's feeling from the media

is not about to let up.

The deaths of Senator Tower and Astronaut Sonny Carter

are sure to keep the investigation in the spotlight.

Ritter is determined not to let the pressure get to him.

Ritter: Sometimes we feel pressure

to do an investigation quickly,

but for the most part, it's more important to get it right,

and so I would rather take the time

and have a good analysis of the evidence

before they come out with a probable cause.

We won't find our answers here.

Let's get what we can back to the hangar--

wings, tail, engines, instruments.

Narrator: The question now--

can he find enough evidence

to solve the mystery of flight 2311?

Narrator: Investigators begin the painstaking task

of sorting through the wreckage of flight 2311.

They're searching for any evidence that might hint

at why the Embraer 120 rolled sharply to the left and crashed,

killing everyone on board.

Ritter: Alright, guys.

Let's start with the ailerons.

Narrator: They wonder if one of the plane's

flight control surfaces was malfunctioning.

Maris: Control surfaces are the moveable flaps

typically at the back of the wings, the tail, and the fin,

which allow the pilot to roll the aircraft,

to pitch the aircraft, and to yaw the aircraft--

the three motions an aircraft can do.

Narrator: They need to examine

every component of the flight control system.

Ritter: What you're looking for is continuity of the controls.

Are the hinges all intact?

All the actuators are in their proper position?

Were the control surfaces themselves

in a reasonable position at the time of impact?

Ailerons look good.

When we examined the control surfaces,

we didn't find anything unusual at all.

Everything checked out normally.

So if the control systems were all working,

why would a plane do this?

Left bank almost 90 degrees,

then almost straight down.

Maybe the engine?

Without the black boxes,

it's basically a process of elimination.

We analyze all of the physical evidence

and come up with the most compelling scenario

that matches that evidence.

Alright. Let's see what we can find in here.

Narrator: If one of the plane's two turboprop engines failed,

it might explain why the plane went into such a steep roll.

Ritter: We wanted to look for any indications

of an engine problem,

so we retrieved both the left and the right engine

and their propeller systems

and took those back to the laboratory

for further examination.

Narrator: Investigators soon find some telltale evidence--

leaves and branches inside the engines.

Ritter: When we find vegetation in the engines,

that tells us that the engine is operating

because it's sucking in air

and it's pulling in the leaves and the vegetation,

and that's an indication that it's making power.

This one was spinning to the very end,

no doubt about it.

We confirmed that both engines were operating

right up until the moment of impact.

Computer: Terrain.

Friedline: That's it.

No!

Narrator: With engine failure ruled out,

Ritter turns his attention

to the other main part of the plane's propulsion system.

Ritter: Let's take a look at these propellers.

Thank you.

Narrator: Tom Haueter is an NTSB investigator.

Haueter: When we started doing testing of the propeller system,

we didn't know where it was gonna lead us,

but it was something we had to eliminate, if nothing else.

Narrator: Deep inside the propeller unit,

investigators uncover an important clue.

Ritter: Ah-ha!

There you are.

We have a witness mark.

Take a look.

Narrator: There's a small mark

where two parts of the propeller mechanism

slammed together on impact.

The witness mark might be enough to tell investigators

how the propellers were operating.

Ritter: You can literally match up the scratch marks

between both pieces,

and you'll know what the angle of the propeller blade was

from that measurement.

Mark this one...

22 degrees.

Narrator: The Embraer 120 has what's called

a constant speed propeller.

The blades spin at a steady rate in flight.

When the pilots need more power, the blades twist,

changing their angle to take a bigger bite out of the air

and provide more thrust.

Friedline: Slowing for approach speed.

Maris: And in flight,

it acts like the automatic transmission in a car.

It's as if it's changing gears to match the engine load,

the speed, whether the plane is climbing or descending,

and it does so constantly and automatically

without intervention by the crew.

Narrator: There are witness marks inside both propellers.

Ritter: Now, this one...

Looks like three degrees?

Narrator: The marks tell Ritter the exact angle of the blades

when the plane slammed into the ground.

Ritter: We immediately noticed the difference

between some of the blade angle measurements

for the left engine versus the right engine.

These guys had a big problem with their left propeller.

The blades were almost flat.

Narrator: The left side propeller blades

are at a dangerously low angle--

one that is never used during flight.

At three degrees, the blades are so flat,

they would act like a wall,

blocking the flow of air the plane needs to maintain lift.

Haueter: At certain speeds and certain regimes of flight,

if the propeller goes flat enough,

you have a situation where you can't control the airplane.

Narrator: Investigators study the mechanism

used to control the left propeller.

Ritter: Will you look at this?

Narrator: They make a disturbing discovery.

Ritter: It's completely worn down.

Narrator: The teeth on a key piece of the gear mechanism,

known as the quill,

are almost entirely worn away.

Investigators may finally have the lead

they've been looking for.

Ritter: This is what it's supposed to look like.

Narrator: With its teeth worn away,

the quill can't lock onto the gear system

that controls the angle of the propeller blades.

The discovery might explain why the propeller blades

slipped to such a dangerously low angle.

Ritter: Once we noticed that the quill teeth were severely worn,

we started theorizing what would happen

in that type of situation,

and it was pretty clear that

control of the propeller blade angles could be lost.

And that really was a eureka moment for us,

because now we had a serious malfunction

that we could examine.

Ritter: This could

definitely be it.

Narrator: Ritter digs into manufacturing reports,

trying to find out how such a vital part could have failed.

But what he finds only adds to the mystery.

The quill teeth are made

of an extremely durable case-hardened metal.

Ritter: They were definitely made to last.

Narrator: It's hard to imagine what could have caused

such rugged teeth to wear down so badly.

Ritter: Something didn't work as planned.

Let's find out everything we can about every one of these pieces.

Narrator: Ritter is certain he's found the critical clue--

worn-down teeth on the quill that could have allowed

the propeller blades to slip to a dangerous angle.

But he soon learns there's a big problem with his theory.

The manufacturer says it's impossible.

Engineers at Hamilton Standard included a fail-safe feature

when they designed the propeller.

It should be impossible for the blades to go flat during flight.

Maris: Manufacturers have to demonstrate,

through a number of means, that their systems are fail-safe.

Haueter: All the tests and research

that had been done before this said

even if you have a disconnect,

that will not result in an accident.

Narrator: If there's ever a problem

with the mechanism controlling the angle,

the blades are designed to move on their own

to what's called the feathered position.

Haueter: The feathered propeller blade,

the leading edge of the blade is directly into the wind,

so that's the most minimal drag,

no thrust, but very little drag.

Narrator: A feathered propeller

can't endanger the safety of the flight.

Maris: If this rod disengaged because of any cause,

the propeller should go to feather,

which would result in the loss of the engine,

and the crew would be able to cope with that

and land on one engine, as they are trained to do.

Friedline: The runway's in sight.

Ritter: This has got to be it.

This has to be connected somehow.

Narrator: But Ritter isn't convinced

by the manufacturer's assurances.

His gut tells him the worn quill did allow the propeller blades

to move to a dangerous angle.

But without flight data,

his investigation has hit a wall.

He has no way to prove the quill brought down flight 2311.

Friedline: What's going on?

Can you see anything?

Johnston: There's nothing.

Ritter: Tom, welcome to the team.

Haueter: No problem, Jim. Glad to help.

Narrator: With the investigation stalled,

Tom Haueter joins Jim Ritter to hunt for answers

in the crash of Atlantic Southeast flight 2311.

Haueter: I was a little nervous about this one

in that when I first jumped into it,

I didn't really know what was going on

other than it was basically at a standstill

and they were looking for me to get it moving.

What do we have?

Ritter: I think everything we need to know

is right here on this table.

Haueter: You have a part of the propeller control assembly,

and the teeth on the gear are essentially gone.

That's very unusual.

Could that have been a part of the accident?

We didn't know.

Narrator: Haueter and Ritter study the design

of the propeller mechanism.

Ritter: Tom, look at this.

Haueter: We don't see anything obviously wrong with the crew.

We don't see anything wrong with the structure of the aircraft.

We don't see anything wrong with the engines

and the flight control system,

but we do have a severely worn Transfer Tube

and quill arrangement.

Is it possible that this could have resulted

in the loss of control?

Narrator: They discover that shortly before the accident,

Hamilton Standard started using a harder, more abrasive coating

on a key part known as the Transfer Tube.

Its grooves mesh-like clockwork into the teeth of the quill.

The change had an unexpected consequence.

Haueter: It turned it into a giant file.

Ritter: So the splines on the Transfer Tube

were much harder and rougher than the quill teeth,

and it was almost like sandpaper,

so the tube was actually

wearing down the teeth on the quill.

Narrator: The discovery explains the worn teeth on the quill.

The design of the propeller should ensure

it snaps to a safe position,

even with the worn part.

Ritter: The propeller manufacturer believed

that they had a fail-safe condition,

so that even if they had this problem,

the propeller blades would be slowly driven

to the feather position.

Narrator: In spite of what all their data says,

the investigators want to see for themselves.

They set up a test at the manufacturer's facility.

Ritter: We had an engine and a propeller combination

mounted in a test cell.

Maris: In order to determine that something is fail-safe,

the engineers use a combination of mathematical analysis,

very structured analysis,

testing in a laboratory, as you can imagine,

and by these methods,

Hamilton Standard convinced themselves

that this propeller would fail in a safe direction,

i.e., towards feather.

Narrator: Jim Ritter's doubts about the fail-safe design

may be confirmed in just a few seconds.

The technician flips a switch to free the Transfer Tube

from the teeth on the quill.

But as the test unfolds, instead of moving to flat,

the propeller blades move to the safe feathered position.

The fail-safe system performs exactly as it was designed to.

It suddenly seems that investigators

are on the wrong path altogether.

Ritter: So, when we tested the quill with the worn teeth

at the manufacturer's facility,

we found that the propeller blades went to feather,

so at that point, we were basically stumped.

Haueter: Can you play it again?

Narrator: The test results leave Ritter and Haueter wondering,

could there be some other factor that they've overlooked?

Haueter: Hold on.

That's it.

It's bolted to the ground.

The question I raised,

well, in flight, the aircraft is in turbulence,

it's bouncing around.

There's different vibrations.

With the aircraft on the ground

or an engine mounted solidly to the ground,

the airplane doesn't behave the same.

There's different vibration modes.

Is it possible that could change the outcome of the analysis?

Haueter: I think we need to see it in the air.

Ritter: Definitely.

Maris: One of the problems with doing testing

in a laboratory environment, which is very controlled,

is that you can't always anticipate what will happen

when you go out into the real world.

Carter: These small planes do keep you on your toes.

Maris: Imagine, for example, an orchestra that rehearses

in an acoustically perfect concert hall

and then performs outside with random noises,

without the sound controlled.

You can see how one might miss important factors

about the sound.

Haueter: We've got to see what happens in the air.

I said, "Well, the only way to really know

is let's do a flight test and find out."

Let's do something to absolutely determine this is the case,

'cause we were at a point in the investigation

we need to start eliminating things.

Narrator: The investigation into the crash of flight 2311

moves to Embraer headquarters in Brazil.

Ritter: We really wanted to look at

what would happen in flight, in an actual flight

with the same malfunction?

Narrator: Tom Haueter meets with representatives from Embraer

and propeller manufacturer Hamilton Standard.

The team immediately starts preparing for the test flight.

Haueter: Thank you for doing this.

When I first proposed doing the flight test,

it was not well-received by almost everybody.

People saw no need.

Why are we spending the time, the money?

Why are we doing this?

Would you mind if I used that table?

Is that okay?

But I pushed hard.

I thought, "Well, we need to really prove this."

Narrator: Embraer's chief test pilot, Gilberto Schittini,

has agreed to put the investigators' theory

to the test.

Gilberto Schittini: The risks, of course, is part of the game,

so you have, always have to reduce your risk

as much as possible,

but you cannot avoid it, so you just accept it.

Maris: The mindset of a test pilot is one

not perhaps of heroic bravery,

but certainly one wants to be unflappable

in the face of danger and unusual situations,

because you're not very productive

if you're terrified by the goings-on in the cockpit.

Narrator: Schittini will fly an Embraer 120

that has been modified to recreate the failure

on flight 2311.

Haueter: So, we've modified the quill.

The teeth have been worn down just like flight 2311.

Narrator: A worn quill will be placed

inside the propeller unit.

Haueter: This was potentially very high risk,

because once we disconnected the Transfer Tube in flight,

the pilots would have no way to control the propeller.

We put a pitch lock here.

It won't go past 22 degrees.

Narrator: A mechanical lock has also been added

to stop the propeller from going flatter than 22 degrees.

Haueter: It would be too dangerous in the flight test

to have the propeller blade go all the way to flat pitch.

You'd lose control of the airplane.

That was almost guaranteed.

If the blades move to 22 degrees,

then we know that they would have gone flat.

All good?

Narrator: The propeller blades don't need to go completely flat

to prove that Haueter's on the right track.

Schittini: This was a high-risk test.

We had to take extra precautions

in order not to repeat the accident.

Narrator: Real-time data will tell the team on the ground

whether the propeller blades are going safely towards feather

or moving dangerously flat.

Haueter: Everything says that if you have a disconnect,

the normal frictional drag within the system

will cause the components to rotate

towards the feather position,

but will that really happen in flight the same way?

Narrator: They're about to find out.

Haueter: We were comfortable that this test

could be safely accomplished,

but there's a difference

between believing it can be safely accomplished

and knowing.

Narrator: As the test plane climbs,

Schittini takes it over an unpopulated area,

just in case.

Haueter: There was a potential

for a severe controllability problem

such that the pilots might have to abandon the aircraft

and parachute to the ground.

Narrator: The propellers have been set

to a normal angle for flight--

around 30 degrees.

Haueter: EMB-120, do you copy?

There was a lot on the line, in terms of the fact

that what if this airplane crashes?

What if we lose the airplane?

Certainly I'm the investigator in charge.

I'm the one, you know, who's basically running this test.

This could be all my responsibility.

Schittini: Copy.

We are ready to disengage the prop.

Haueter: Basically they would pull the lever

that would disconnect the propeller control system

from the propeller

and see what happens.

Narrator: The most dangerous part of the test flight

is now under way.

Schittini: I just thought that, well, it's happening.

Let's do what we have to do and get this airplane on the ground.

Maris: This was, in my opinion a very dangerous maneuver,

because after all, they didn't know

what the outcome was going to be,

and they already knew the aircraft wasn't controllable

under certain circumstances.

Schittini: Propeller blade angle is causing no problems.

No control issues.

We were thinking about the test to do and nothing else.

You have to focus on the job that you have to do ahead,

and once you focus you forget about everything else.

Narrator: As soon as the propeller quill is disengaged,

the blades begin doing what they were designed to do--

moving towards the feathered position.

Haueter: As it starts drifting towards feather,

we thought, "Okay.

Well, this test is gonna be a bust.

It's just gonna prove what everybody said it would do."

You could see it in their faces.

They didn't say anything,

but you could just, you know, hear the relief.

Narrator: The propeller blades keep moving

toward the fail-safe position.

For Tom Haueter, Brazil is a long way to come for failure.

It seems like the test

that he hoped would solve the mystery of flight 2311

is going to leave the investigation

back at square one.

Narrator: With the cause of the Atlantic Southeast crash

still unknown

and the entire investigation on the line,

the Brazilian test flight takes a dramatic turn.

Schittini: We saw that the RPM was increasing slowly,

but it was increasing, so we knew that the propeller

was going in the wrong direction.

Narrator: As the flight continues,

the blades begin drifting in the opposite direction,

towards the dangerous flat position.

Haueter: Ah-ha.

Here we go.

Ritter: The aerodynamics, the vibration,

the actual in-flight loads on the propeller

are something that you just can't predict in a test.

It's something that actually had to be flown.

Narrator: Schittini remains smooth and precise

on the controls.

Schittini: Reducing speed.

Easy does it.

We started feeling a rolling moment to the left

and a yaw moment to the left.

Narrator: The blades go as flat as this test will allow,

22 degrees.

For Haueter, it's a victory.

The risky test flight has paid off.

His theory about the crash is back on solid ground.

Haueter: The Hamilton Standard and the FA people

just went white.

I mean, they were just shocked.

You could tell that everything they believed

had just been thrown out the window.

That's as flat as they're gonna get.

Schittini: Do you have what you need?

Haueter: Affirmative.

We have everything we need.

Schittini: Okay, we're going back.

Once the test part is finished, it is finished.

Don't stay around looking for trouble.

Go back home.

Haueter: Good work.

Thanks very much.

Seeing the data right then, it took a load off.

I said, "Okay, wow."

I mean, we now know what happened.

It was obvious.

Looks like you have some work to do.

Ritter: Hello.

Narrator: The team has just one more question to answer

before they can explain the crash.

What happens when blades go completely flat?

Ritter: In the flight test,

they were only able to go

to a blade angle of about 22 degrees

for safety reasons.

Start it.

But during my flight simulations,

I went down to flight angles as low as three degrees.

Anytime.

Narrator: In a flight simulator,

Jim Ritter recreates the fatal propeller malfunction

aboard Atlantic Southeast Airlines flight 2311.

Ritter: As the blade angle got to very low values,

the airplane was essentially uncontrollable.

Narrator: The simulation allows him to experience

what the test pilot couldn't.

Haueter: Flight tests proved

we could have a blade go to flat pitch.

The simulator proved you'd lose control if it did.

Ritter: Thanks.

That was... helpful.

You could say that the simulator testing

was kind of like the final piece of the puzzle.

Narrator: Investigators finally understand the full story

behind the deadly crash.

Ritter: When the flight crew began preparations for landing,

the teeth on the quill were worn down,

but still operational.

Friedline: Slowing for approach speed.

Narrator: Preparing for landing put renewed pressure

on the already worn teeth in the quill.

They could no longer hold.

Once the teeth gave way,

the propeller blades were free to drift to a different angle.

As the turbulence of flight

and mechanical vibrations from the engine

shook the propeller,

the blades moved to a dangerously flat position.

Ritter: The fail-safe failed.

The propeller's design couldn't hold the blades at a safe angle,

and the plane became less and less controllable.

Friedline: What's going on?

You see anything?

Johnston: There's nothing.

Friedline: What's going on with this thing?

I can't hold it.

Johnston: Get out of it!

Friedline: I can't. Come on. Come on!

Haueter: For a while, you can kind of fight this,

putting in control movements with the wheels, the rudder,

but, unfortunately, they were in a situation

where it didn't matter

if you were the best pilot on the planet.

You were not going to be able to control that airplane.

It's going to roll over.

It's gonna dive towards the ground.

Maris: Ironically, human error is almost always underneath

the causes of an accident,

even if it wasn't the pilot or a mechanic.

In this particular case, an engineering change was made,

which, well-intentioned, actually, did not work out.

Johnston: No!

Friedline: That's it. Oh, God!

Johnston: No.

Haueter: The worn quill teeth

was a time bomb waiting to go off.

There was nothing they could have done to save that plane.

What I really felt was, "Okay, now that we know it,

we've got to tell the rest of the world

and get operators to start changing their equipment,

like, right now."

The fail-safe system doesn't work.

Narrator: After the accident, additional safeguards were added

to prevent this type of failure--

a change that affected not only the Embraer,

but several other turboprop aircraft as well.

The FAA also ordered more frequent inspections

of propeller quills.

Haueter: The most important thing we have learned

from the accident at Brunswick

is assumptions.

You cannot rely on assumptions.

It was assumed that ground tests were as good as flight tests.

That one assumption unfortunately turned out

to be fatal for some people.