Original subtitles

The Boeing 737 is one of the most popular

passenger jets in the world.

Around the globe, the plane has carried more

than 12 billion passengers.

It's the backbone of the aviation industry.

But in 1991, something happened on board

a 737 that sent shivers through the world of aviation.

- -Oh, my lord.

A deadly crash has investigators scrambling.

There was a time when I had doubts

that we'd be able to solve it.

It was like he was tracking a serial killer.

The hunt for answers will take 10 long,

grueling years.

The fate of the airline industry hangs in the balance,

and the mystery is unsolved until more

than 150 people are dead.

Ladies and gentlemen, we are starting our approach.

Put your mask over your nose.

Emergency decent.

Brace for impact!

9:40 AM, March 3, 1991.

After a short 17 minute trip from Denver,

United Airlines flight 585 is on final approach

into Colorado Springs.

It looks like a perfect day for flying,

but there's trouble in the air.

Nice looking day.

Hard to believe the skies are unfriendly.

There's Been heavy turbulence during the flight

and violent gusts of wind are forecast

over Colorado Springs.

Never driven to Colorado Springs and not gotten sick?

At the controls is 52-year-old Captain Harold

Green, a pilot with 20 years experience

and a sterling reputation.

Green's co-pilot is Patricia Eidson.

At 42, she is one of the first female flight

officers in United's history.

Flight attendants, prepare for landing.

At Colorado Springs Municipal Airport,

air traffic controller James Rayfield is

ready to bring flight 585 in.

United 585 report the airport insight.

Got it.

Yep.

Airport inside United 585.

Lower landing gear.

United 585 is cleared for a visual approach to runway 35,

weather conditions 23, 20 degrees at 16 gusting at 29.

As its speed decreases,

flight 585 becomes more vulnerable to the turbulence.

Eidson wants to know what other planes

have experienced on landing.

Any airports lately of any loss for gain of airspeed?

Yes, ma'am.

500 feet a 50 knot loss at 400 feet at 50 knot gain

and at 150 feet a gain of 20 knots.

Sounds adventurous, thank you.

Starting on down.

Just a mile from the airport,

retired policeman Harold Darnell is on his way

to a local flea market.

Half a mile overhead, Green and Eidson

focus on keeping their speed constant as they descend.

Wait, a 10 knot change here.

Yeah, I know.

Have a lot of power to hold that airspeed.

As United 585 approaches the runway,

Darnell feels something strange.

Oh, what the heck was that?

Out of nowhere, a powerful gust of wind

strikes his vehicle, almost blowing him off the road.

I know 10 knot gain.

Pretty flops.

From the control tower,

James Rayfield can now see flight 585's final approach.

As the aircraft closes in on the airport,

the ride gets even bumpier.

Wow.

40,000 feet.

Then, without warning, the 737

starts to spin out of control.

15, 12.

15.

Oh, no.

Oh my God.

Oh my God.

Oh my lord.

Crash, crash!

Rescue workers arrive within minutes,

but there is almost no sign of the 737.

The shattered remains of the 38-ton jet

lie buried in a fire blackened impact crater.

The plane, it didn't skate or bounce

like when a plane comes in normally and lands,

it just nosed right in and where it hits,

where it stayed.

There are no survivors.

All 20 passengers and five crew members

are killed instantly by the high speed

impact and exploding jet fuel.

In 10 violent seconds, Colorado Springs

has become the site of one of the most mysterious air

crashes in aviation history.

By nightfall, investigators from the National

Transportation Safety Board descend on Colorado Springs.

Known to insiders as tin kickers,

NTSB investigators examine over 2,000 aviation accidents

a year, at times by picking through the metal

debris of fallen aircraft.

A coroner has marked the location

of human remains in red.

NTSB investigators marks scraps of metal in yellow,

looking for clues to help them solve

the mystery of flight 585.

Like investigating a mass murder,

it's a tough job walking onto a crash site.

Among the investigators assigned to the case

is Malcolm Brenner, a specialist

in human performance.

His job will be to find out if the crash

was caused by pilot error.

The area was cordoned off by police,

and there were salvation army trucks.

I got a cup of coffee, a cup of hot chocolate, or something

and I thanked them for it, and they said, no, no, thank you.

And they had this look in their eyes

like, oh my God, you have to go into this site.

Clues to the fate of United 585

lie mangled in a deep black hole.

The fuselage is crushed like an accordion

in the impact crater.

The rest of the plane is in pieces spread over an area

smaller than a football field.

There was a lot of fire damage.

There had been a fire afterwards,

and it was all contained in a relatively small area,

which just initial impression it can be a sign

that the airplane was intact.

If there was a midair explosion or something came off

the airplane, you would expect that to be a much larger site.

My first sense that it was going to take some time

to investigate the accident was the damage

that we saw in the parts.

When they're burned and broken, the process

always takes longer.

The National Transportation

Safety Board begins a painstaking

investigation into the crash.

Engine turbines, hydraulic pressure gauges, the cockpit

voice recorder, and in-flight data recorder

are all carefully extracted from the site,

photographed, and sent to the lab for analysis.

An important step in the investigation

is the analysis of the cockpit voice recorder.

With pilot error a factor in 70% of air disasters,

Malcolm Brenner's job is to see what

role pilots Green and Eidson played in the crash.

This crew was-- and I felt this at the time--

was one of the more impressive crews

that I'd ever dealt with.

There was a little bit of tension release,

a little bit of humor.

The captain said--

Never driven to Colorado Springs and not gotten sick?

The first officer suggested that they add extra speed

as a safety margin.

The captain agreed with it.

It was good interaction.

- Got it. - Yep.

Airport insight, United 585.

Lower landing gear.

This is a sense of an excellent crew

caught randomly, if anything.

So, again, that was my first impression

is that this would be consistent more

with a hardware situation.

As more about flight 585 becomes known,

mechanical failure becomes a serious suspect.

Just seconds before it crashed, the plane rolled onto its back

and spun wildly out of control.

Investigators wonder if the sudden motion

was caused by the plane losing an engine or a wing.

From the state of the aircraft on site,

it's clear that it was intact at the time of the crash.

What investigators don't know is if the engines

were still working at impact.

Technicians examine the engine turbines.

They discover dirt has been drawn

deeply into every crevice.

These blades were clearly spinning and sucking

in air at the time of impact.

The engines may have been running but technicians

aren't sure how well.

The plane's hydraulic pressure dials are destroyed,

the glass covers broken.

The indicator needles have been snapped off

by the force of the impact,

but even these ravaged dials tell a tale.

-15 flops. -15.

On closer inspection, investigators

find a critical mark.

At the moment of impact, a dent was made on the face plate

by the jar indicator needle.

It proves that when flight 585 crashed,

its engines were running normal.

With engine failure ruled out,

there seems to be only one other mechanical explanation for why

flight 585 suddenly rolled over and then fell out of the sky.

It appears increasingly likely that the plane

had suffered a catastrophic problem

with its flight controls.

Investigators quickly become suspicious of the rudder

at the back of the tail.

We focused in, after eliminating other flight

control surfaces that we thought

could contribute to the role,

we start looking into the rudder.

Bring that up so I can take a look at it.

Investigators begin their examination

of the rudder on site, but the violence of the crash

makes the job extremely difficult.

Almost nothing left.

Most of the plane's parts

are too crushed or burned for testing,

but a vital component is still reasonably intact,

the Power Control Unit or PCU.

Used constantly during flight, especially during landings,

the PCU performs like a car's power steering.

When the pilot pushes on a rudder pedal,

the PCU uses hydraulic fluid to convert gentle movements

of a pilot's foot into the pressure needed to move

the 737's enormous rudder.

The heart of the PCU is something

called the duo-servo valve.

Cheap like a soda can, it has two slides

which glide past one another,

directing the flow of pressurized hydraulic fluid

that moves the rudder.

The server valve is very unique

that it is in effect two valves in one

and that, that creates a whole range

of interactions that don't occur in a more

conventional hydraulic valve.

When a technician opens the power control unit,

chips of metal are found floating

in the hydraulic fluid.

It's a disturbing find.

These particles could cause the servo

valve to jam, making it impossible to work

the plane's rudder.

It's a chilling prospect.

Could a microscopic fault bring down a 38-ton jet?

It's difficult for Phillips to tell.

While more intact than much of the wreck,

the PCU and duo-servo valve are both damaged.

To test what he does have, Phillips travels to California

to the labs of Parker Hannifin where the rudder

control unit is made.

The curious metal chips floating in the PCU's chambers

are dismissed.

Phillips is told that filters keep them out

of the delicate servo valve that directs fluid

and moves the rudder.

Nothing else is found that could

explain any sudden movement of the rudder on flight 585.

We didn't have any absolute indication or information

that we could point to that said the rudder power control unit,

the servo valve, or any part of that flight control

system caused that accident.

Philips still suspects a mechanical problem

but with no conclusive evidence that the PCU or servo

valve caused the crash.

He is forced to sign off on the tests.

It's a farce.

With Philips at a dead end,

only bad mountain weather remains a primary suspect.

An expert on weather related aviation accidents,

Greg Salotollo, is trying to determine

if heavy winds on the day of the crash were a factor.

There is a history of events where there

have been airplane accidents attributed

to mountain waves of rotors.

In 1966, a BOAC 707 near Mount Fuji

disintegrated in a mountain wave and rotor.

High winds crashing over mountain peaks leaves

so-called wind rotors in the lee side invisible,

highly turbulent downdrafts that come plunging down

with devastating power and are extremely

dangerous to aircraft.

We found a great deal of evidence

looking at the surface upper air data

and talking to witnesses in the area

that roters were a possibility.

The explosion was right over there.

Salotollo's hears several eyewitness

reports of bizarre mountain weather

on the day of the crash.

One of the most intriguing is from Harold Darnell.

Oh, what the heck was that?

Whose truck was struck

by a powerful gust of wind just moments before 585 crashed.

But as Greg Salotollo combs through his evidence,

the theory that a wind rotor knocked the plane from the sky

is getting less and less likely.

A nice looking day.

Hard to believe the skies are unfriendly.

Wind rotors are areas of extremely

low barometric pressure.

So if flight 585 did pass through one,

its altimeter reading would have spiked as the plane

was blown suddenly upwards.

There's no evidence that we saw that on the flight

data recorder of 585.

What the flight recorder

did show was a fast and deadly drop in altitude

as the plane fell to apart.

It's been 21 months

since the investigation into the crash

of United Flight 585 began, almost two years in which

the NTSB has studied the crew, the weather,

the rudder, and thousands of other pieces of evidence.

They've come up empty handed.

For only the fourth time in its history,

the NTSB releases a report which

doesn't reach a conclusion.

The cause of the crash of Flight 585 is undetermined.

We had put a lot of time and effort

in into the investigation, and we just weren't

sure what had happened.

It was like he was tracking a serial killer.

He was frustrated that they had not solved 585.

He did not want that to happen again.

But almost two years after the report on 585

is released, the killer strikes again.

At 7:00 PM on a clear windless day,

US Air flight 427 is nearing Pittsburgh.

Captain Peter Germano and first officer Chuck Emmett

are getting ready for their final approach.

Folks from the flight deck, we should be on the ground

about 10 more minutes.

Sunny skies, a little hazy.

Flight attendants, please prepare for landing.

I ask you to check the security, your seatbelt.

Thank you.

US Air at 309 descend and maintain 6,000.

As they close in on the airport,

the pilots are on the lookout for another flight

about six miles ahead of them.

Looking for the traffic,

turning 100, US Air 427.

I see the jet stream.

As they pass through the turbulence left

behind the other flight, their jet suddenly

and alarmingly rolls left.

Hold on, hold on.

Oh, my, shoot.

Nothing the pilots do seems to have any effect.

What the heck is this?

What the hell?

Shoot!

God, God.

427 emergency.

Oh, shoot.

Whoa, whoa.

Oh, God, no.

Rescue crews arrived quickly,

but the fate of flight 427 is tragically clear.

There is no hope for the 132 passengers and crew.

The human carnage is so bad.

Authorities declare the crash site a biohazard.

US Air 427 accident was the first US accident where

biohazard suits were used and it made it more difficult.

They were uncomfortable.

They were hot.

And to this day, when I put on a pair of rubber gloves,

for any reason, I'm instantly transformed back

to the site in Pittsburgh.

Captain John Cox, a 737 pilot and flight system

specialist with the Airline Peloton Association,

is asked to join the team investigating

the crash of Flight 427.

As coroners attempt to collect human remains,

NTSB lead investigator Tom Haueter

already knows his hunt for clues

will be long and painstaking.

When we first arrived at the crash site--

well, first of all, there was no aircraft there.

There were only bits and pieces of the airplane.

It wasn't really recognizable as an airplane.

With the help of eyewitnesses, information

from the flight data recorder, and the cockpit voice

recorder, investigators begin to quickly see

some striking similarities between 427

and the unsolved case of United 585.

In fact, they seem to be mirror images of each other.

On final approach, United 585 rules right,

while US Air 427 rolls to the left.

I got slip.

Hang on. hang on.

Both crews are caught by surprise

and after just a few terrifying seconds,

both aircraft plummet straight to the ground.

As the investigation continues, the list of

similarities grows.

427's engines were also attached and functioning

at the time of impact.

But for all the similarities, there

is one important difference.

Unlike United 585, as US Air 427 approached Pittsburgh,

weather conditions were dead calm.

Folks from the flight deck, we should be on the ground

about 10 more minutes.

Sunny skies a little hazy.

As he did in the case of United 585,

Greg Phillips will once again lead

the investigation into the mechanical aspects

of the crash.

Almost immediately, he makes a promising discovery.

Miraculously, much of US Air 427 tail and rudder

appear intact.

The hydraulic devices inside the tail

have also sustained very little damage.

Philips and Haueter prepare to send the parts

to the manufacturer, Parker Hannifin,

for testing as soon as possible.

They need answers.

Pressure on the NTSB to solve the accident

is growing quickly.

Not only are the crashes of flights 585 and 427

disturbingly similar, both of them

involve the same kind of airplane, a Boeing 737.

But with serious questions being raised about the plane's

safety, billions of dollars, untold lives,

and perhaps the airline industry itself are at risk.

We couldn't live with the fact

as investigators of having two unsolved 737 accidents.

The airplane is in too much use,

too why to use around the world.

It carries too many people every day.

Unsolved was not an acceptable answer.

To find their killer, the NTSB can't

afford to rule anything out.

From the possibility that a collision with birds

brought flight 427 down to strange even bizarre theories.

They looked at electromagnetic interference.

They got calls from people saying it

might be Russian death rays.

They considered everything.

There were a couple of witnesses

who gave reports of the aircraft

suddenly descending and hovering before it blew up.

We discounted those.

But the investigation's

primary suspect is the duo-servo valve, part

of the power control unit that moves

the 737's rudder and a suspect in the crash of United 585.

Parker Hannifin made the valve.

At its lab in California, investigators

look inside the main cavity of the US Air power control unit.

Just like in the earlier crash, they

find tiny chips of metal floating

in the hydraulic fluid.

But once again, Parker and Boeing repeat their claim,

filters designed to stop any debris

from interfering with the delicate metal

slides have done their job.

Investigator Greg Phillips wants to be absolutely sure.

If the chips were blocking the slides,

they would have left tiny scratch marks behind where

they rubbed against the metal.

But Phillips can't find any.

Another pass.

OK.

Philips has technicians

put the servo valve from flight 427 through as many tests

as he can think of, trying to find a weakness.

If he can find one, it could explain why two planes

were ripped from the sky.

But he comes up empty.

What that unit passed all

its operational test, there wasn't any indication

that it had failed, and it operated within the parameters

we expected it to.

Once again, the investigators

are forced to shift their focus back to the pilots.

By studying the plane's flight data recorder,

investigators know that the jet's rudder

was deployed fully to one side, what's

called rudder hard over.

We were definitely focused on a rudder,

on hard over rudder, full rudder input for about

20 seconds.

It can be caused either by hardware,

something unknown in the hardware,

or it can be caused by pilot input.

First officer Chuck Emmett, who was flying 427

did indeed step down hard on his rudder,

and then held it there while the plane

plummeted toward the Earth.

It raised a grisly question, was he trying to fly

the plane into the ground?

And looking at this and being a pilot

myself is like this doesn't seem like rational behavior.

What the hell is this?

Human performance specialist Malcolm

Brenner listens closely for evidence

on the cockpit voice recorder.

What the hell?

In this case, they had microphones right

by their mouths, and you can hear as well as in real life

or better, you can hear breathing sounds.

Yeah, I sees the jet stream.

The cockpit recordings

indicate that flight 427's troubles began at the moment

it flew through the jet wake of a Delta Airlines 727

that had just passed in front of them.

Both pilots are startled by the wake.

I sees the jet stream. Whoa.

The first officer breaks off at the end of a sentence.

I see the jet stream, za, and there's

no more discussion of the jet stream or anything else.

They both focus. Something happened here.

Captain says, sheez.

Sheez.

It was such a smooth flight that it

was a momentary jolt that they just hadn't anticipated.

And with that, the pilots got on the controls

and immediately put in a rudder input.

Sheez.

The cockpit recorder even

records the thumping sound of the jet stream turbulence

as 427 flies through it.

As flying 427 encounters the turbulence,

Rener hears something unusual.

First officer Emmett begins to grunt.

Ah. Ah.

The grunting is unusual.

The controls are designed so that pilots

don't need to grunt.

They're specially designed around human capabilities.

So to have someone grunting is typically

a sign of an emergency.

By matching data from the flight recorder

with the crew's voices, Brenner is

able to confirm that Emmett's grunts begin a split second

after he pushed down on the rudder pedal and three

to four seconds after the wake turbulence affected

flight 427.

What the hell?

On their own, the cockpit voice recordings

proved very little, but it seems

clear that the crew wasn't trying to crash their plane.

Something happened, which took them by surprise,

but nothing they did seemed to help.

What the hell is this?

It's been almost two years

since the crash of Flight 427, and

the investigation has stalled.

Now, two 737s have gone down in startlingly similar ways,

and investigators still don't know why.

We were all frustrated as months wore into years.

What were we missing?

We were going up against an aircraft that had

an incredible safety history.

It was really-- everything you could see for 30 years,

this has been a great airplane.

We were trying to prove that there

was something wrong with the straight A student.

Unsure of where to look next

and with the trail of evidence getting colder,

investigators need a break in the case and fast.

East wing 517, you're clear for landing.

On June 9, 1996, Captain Brian Bishop

is on final approach to Richmond, Virginia, when

without warning, his East wind jet

rolls sharply to the right.

We didn't know to what extent,

but we knew we had a problem with the rudder.

I turn the yoke the opposite direction stood

on the opposite rudder pedal.

The pedal didn't move for me.

For over 30 seconds, the 737

flies in a precarious right bank

as Bishop fights to keep it from rolling over.

Then, suddenly, the unknown forces holding the jet let go,

snapping the wings back to horizontal.

In a matter of seconds, it released itself

and went back to normal.

We had started the checklist.

Almost before I could finish the sentence,

all of a sudden there was just a wham.

For a second time,

the 737 is pushed on its side again.

For 30 more harrowing seconds, the 737

takes on a life of its own.

Then, once again, as quickly as it began, the rollover stops.

After the second time, I looked at the first officer

and I said, declare an emergency.

Tell the controller we have flight control problems.

As they slow down to land, the risks increase.

If a third rollover occurs, they won't have

enough airspeed to recover.

I did at some point tell my first officer

to look out the window and find a dark spot.

It was nighttime, and we were looking

to avoid a neighborhood or a populated area.

And he very calmly responded that,

hey, here's a spot over here.

But there is no third rollover.

Bishop brings Flight 517 in high and fast

and lands safely.

Taxing in is when I realized my legs were shaking.

We got the aircraft to the gate,

and I did pick up the PA to make

an announcement to try to explain what had

just happened to these people.

I'm picking up the microphone, I realized there was nothing

I could say to make this any better and probably

for the first time in a long time,

I was at a loss of words, so I simply put the microphone

down and let it go at that.

But Bishop won't remain speechless for long.

By the next day, the investigation team

has arrived in Richmond.

There were a lot of FAA, lot of NTSB,

and they all wanted to talk to us very badly.

It gave the NTSB a tremendous break because suddenly they

had a 737 that had, had a rudder incident that was intact,

and they had a pilot who was alive

and who could talk about it.

NTSB investigators quickly determined

that what happened on board East wind

Flight 517 is alarmingly similar to events

in flights 427 and 585.

If they can discover why Bishop's 737 rolled over,

they may be able to crack two mysterious

and fatal accidents.

And when we said, well, what happened they said,

there was something wrong with the rudder pedal.

The pedal wouldn't go down.

I was standing on the rudder pedal,

and I couldn't get it to go down.

My God.

With Bishop's first person testimony,

investigators immediately zero in on East

winds rudder controls.

The power control unit is removed, inspected, and then

tested again and again.

To the frustration of everyone, the unit performs perfectly.

After a five-year hunt for clues,

a third mysterious event on a 737

and a live pilot as a witness, Tom Haueter

still lacks the evidence he needs to crack his case.

He decides to push his chief suspect, flight 427's rudder

controls, a little harder.

One fellow mentioned a test they had done in the military

of a thermal shock where if you had the actuator being very

cold and put in very hot hydraulic fluid,

it would cause it to react in strange ways.

So we put together a thermal shock test,

and this test was extreme to say the least.

On August 26, 1996 in Valencia, California,

NTSB investigators gathered to watch the torture test

of US Air 427 PCU.

After soaking it and dry ice, the PCU

is blasted with nitrogen gas to simulate the minus 40 degree

temperatures at 32,000 feet.

Then, it's quickly injected with

superheated hydraulic fluid and given

the command to start working.

As we were standing there listening

to the actuator move left and right left and right.

It stopped, and it was not commanded to stop.

Systems investigator Greg Phillips

now asks that the valve be taken apart

and scanned for scratches.

They find none.

Look at that.

Doesn't leave a trace.

It is a crucial breakthrough to solving

an almost perfect crime.

They have proven that the valve which controls the rudders

can jam but no evidence is left behind.

Tom Haueter and his team have now

found that a small hydraulic valve that controls the rudder

of the world's most popular commercial jetliner

can jam in the right circumstances.

It's an ominous discovery but incredibly,

there's another shocking surprise in store

for the investigators.

The most important breakthrough

came when a Boeing engineer examining the data

from that test discovered some numbers

that indicated the valve at that point

had actually reversed.

Whoa.

It is a stunning revelation.

Not only can the servo valve jam,

but it can then function in reverse.

It means that any time a pilot tries to correct a rollover

by pushing on the rudder,

the rudder might turn in the opposite direction,

causing a fatal accident.

And the reversal is like driving your car.

You turn it to the right, it goes left.

You're not going to figure out this failure mode

until you go off the road.

And in these cases, that's the pilots were faced with,

something so unusual that they didn't understand

what was happening.

What the hell is this?

They had evidence now

that the valve was unique, that the valve not only

could jam but would reverse.

427 emergency.

That would explain why the first officer, Chuck Emmett,

would keep his foot on the rudder

pedal because he's thinking,

why isn't the plane going right, and he's feeling

the plane go to the left.

To the very end, Chuck Emmett pushes hard,

hoping his rudder will help him pull out of his deadly spiral.

Tragically, he has no way of knowing

that he's steering his aircraft straight into the ground.

Never driven to Colorado Springs

and not gotten sick?

Flight attendants, prepare for landing.

Satisfied that they've determined the cause

of the crash of US Air Force 427,

the NTSB turns its attention to the unsolved case

of United 585.

Another turnout game.

Going back to Colorado Springs,

and you could follow a progression

of what the captain was doing.

He's close to the ground and suddenly

underwrote a reversal.

He puts in a little bit of pedal.

The pedal violently pushes his leg back.

-15 fly. -15.

But a reversal certainly fits what I know about this crew

and how it fits.

We were able to show the failure mode.

It matched the flight data recorder from each aircraft.

It felt like a glove.

So we now had a lot more information

we could apply to United 585.

And based on that, we redid the accident report.

-Oh, my God! -Oh, no!

From rudder reversal to impact

took less than 10 seconds.

585's flight crew had no chance to save

their plane or passengers.

In the aftermath of the investigation,

sweeping changes were made to improve

the safety of the 737 and the entire aviation industry.

New training protocols were designed to help pilots react

to unusual in-flight events.

In the 737 fleet, pilots are now

trained on how to react to both rudder hard overs

and reversals.

Oh!

The scenario, the US Air 427 accident,

if the crew had the information that we have today, I

believe they would have landed safely

in Pittsburgh that evening.

The FAA also directed Boeing to redesign

the rudders duo-servo valve to eliminate

the potential for reversal.

Boeing spent hundreds of millions of dollars

to replace the valves on thousands of 737s

around the world.

One thing we don't like of the safety board

is to have an undetermined accident

because then we can't make a change to improve safety.

So out of US Air 427, United 585,

we have a much safer 737 fleet.

It took NTSB 10 kickers, 10 years

to solve the mysterious crashes of flights 585 and 427,

the longest investigation in aviation history.

There are still some people in aviation who don't

think the NTSB got it right.

But I became convinced after talking

to many, many, many people, pilots engineers,

people at Boeing,

and spending a lot of time with the investigators

that they did get it right.

Since the replacement of the 737 servo valves,

there hasn't been a similar crash

of the most popular, most profitable plane in the world.