Original subtitles

Outside one of India's busiest airports,

the early evening sky ignites into a fireball.

the early evening sky ignites into a fireball.

This cloud just lit up.

It felt like you could feel the heat.

Flaming wreckage falls from the sky.

Flaming wreckage falls from the sky.

It's a horrifying crash.

When I saw other blips are coming.

When I saw other blips are coming.

So I watched the sweep again, but they were not there at all.

When investigators arrive they,

When investigators arrive they,

find the twisted remains of two passenger jets.

find the twisted remains of two passenger jets.

349 people are dead.

Vital clues are buried deep underground.

Vital clues are buried deep underground.

Investigators must piece together the day's events.

Saudi 763 three will maintain 140.

Saudi 763 three will maintain 140.

Kazakh 1907 now reach 150.

Kazakh 1907 now reach 150.

How had two crews that should have known

each other's positions ended up in the world's

each other's positions ended up in the world's

deadliest mid-air collision?

Ladies and gentlemen, we are starting our approach.

Ladies and gentlemen, we are starting our approach.

We lost both engines.

Emergency descent.

Mayday, mayday.

Brace for impact!

Brace for impact!

Indira Gandhi International Airport,

Indira Gandhi International Airport,

New Delhi, a gateway to India.

New Delhi, a gateway to India.

November 12, 1996.

November 12, 1996.

Busy?

Air traffic controller VK Dutta arrives

Air traffic controller VK Dutta arrives

for the afternoon shift.

There was one supervisory officer.

There was one supervisory officer.

There was one person who was sitting beside me,

and he was assisting me, and the things were all normal.

and he was assisting me, and the things were all normal.

But normal at Indira Gandhi doesn't mean calm.

But normal at Indira Gandhi doesn't mean calm.

This is becoming one of the most congested

airports in the world.

airports in the world.

In 1990, the government of India signed open skies agreements

with several different countries.

with several different countries.

Those pacts have made it easier for foreign airlines

to land at Indian airports.

to land at Indian airports.

Many airlines are taking advantage of the new policy.

Air traffic controllers are now handling

more traffic than ever.

more traffic than ever.

The open sky policy acted as a catalyst

in the air traffic growth.

in the air traffic growth.

The volume of traffic grew from, I believe, 175 movement a day

The volume of traffic grew from, I believe, 175 movement a day

to around 225 movement a day.

to around 225 movement a day.

We have to perform.

We have to perform during that time.

So whether 10 aircraft come in that time or 20 comes,

So whether 10 aircraft come in that time or 20 comes,

so you have to handle them.

Just past 6:00, Saudi Arabian Airlines Flight

Just past 6:00, Saudi Arabian Airlines Flight

763 takes off into the sunset.

Get up.

Get up.

Clear on left.

Captain Khalid Al-Shubaily powers the Boeing

Captain Khalid Al-Shubaily powers the Boeing

747 away from the runway.

His co-pilot Nasir Khan handles all radio communication.

His co-pilot Nasir Khan handles all radio communication.

There are 289 passengers on board.

There are 289 passengers on board.

Many are Indian workers returning to their jobs

Many are Indian workers returning to their jobs

in the Middle East.

Saudi 763 airborne, zero three.

Saudi 763 airborne, zero three.

Contact radar 127 decimal 9.

Contact radar 127 decimal 9.

While Flight 763 was on the runway,

its movements were tracked and directed

by an air traffic controller in the airport's tower.

by an air traffic controller in the airport's tower.

279, good day.

279, good day.

But shortly after the plane takes off,

the tower passes the pilots over to approach

the tower passes the pilots over to approach

controller VK Dutta, who's in another room at the airport.

Approach controllers at Indira Gandhi guide planes

through the airspace beyond the runways.

through the airspace beyond the runways.

They're in charge of all arriving

and departing flights within 70 miles.

and departing flights within 70 miles.

The approach controller normally

is responsible for arrival and departures of the aircraft

is responsible for arrival and departures of the aircraft

which are coming in.

They are safely and expeditiously...

They are safely and expeditiously...

they are brought to the final approach.

Tonight, Dutta is controlling five flights.

Tonight, Dutta is controlling five flights.

Some of these are leaving the airport

while others are coming in.

while others are coming in.

His task is to keep those planes spaced

safely apart but not so far apart as to cause any delays.

safely apart but not so far apart as to cause any delays.

There's a continuous coordination with the tower

who handles the ground traffic.

who handles the ground traffic.

So he would tell approach controller

that this fellow is ready, and he is to be accommodated

that this fellow is ready, and he is to be accommodated

between these two flights.

So that kind of dynamics we do, we were doing at that time.

So that kind of dynamics we do, we were doing at that time.

Saudi 763 approaching flight level 100.

Saudi 763 approaching flight level 100.

Roger, climb flight level 140.

Roger, climb flight level 140.

Clear to climb 140, Saudi 763.

Clear to climb 140, Saudi 763.

This evening, a United States Air force cargo plane

is coming in for a landing.

Even though it's an Air Force jet,

this flight is Dutta's responsibility.

this flight is Dutta's responsibility.

I think we probably had 3 or 4 back and forths

I think we probably had 3 or 4 back and forths

with the controller where he was verifying our altitude

or checking on our altitude, telling us about other traffic

or checking on our altitude, telling us about other traffic

in the vicinity.

Saudi 763 approaching 140 for higher.

Saudi 763 approaching 140 for higher.

Saudi Airlines Flight 763 reaches its last assigned

altitude of 14,000 feet.

altitude of 14,000 feet.

The pilots request permission to fly higher.

Roger.

Maintain flight level 140.

Maintain flight level 140.

Stand by for higher.

In order to coordinate incoming and outgoing traffic,

In order to coordinate incoming and outgoing traffic,

Dutta wants the Saudi flight to stop climbing.

Saudi 763 will maintain 140.

Saudi 763 will maintain 140.

Dutta is concerned with another plane

now flying east for a landing at Indira Gandhi airport.

now flying east for a landing at Indira Gandhi airport.

It's a passenger jet operated by Kazakhstan Airlines.

The Ilyushin 76 is a massive Russian plane.

The Ilyushin 76 is a massive Russian plane.

Originally built for the military,

a modified version is now widely used as a commercial airliner.

a modified version is now widely used as a commercial airliner.

Dutta wants it to pass over the top of the Saudi flight

Dutta wants it to pass over the top of the Saudi flight

before landing.

After that, he'll let the Saudis continue their climb.

After that, he'll let the Saudis continue their climb.

They were supposed to cross maintaining

1,000 feet of separation.

Kazakh 1907 now reaching 150, 46

Kazakh 1907 now reaching 150, 46

Miles from Delta Papa November.

Miles from Delta Papa November.

Roger.

Maintain flight level 150.

Maintain flight level 150.

Identify traffic 12:00 reciprocal, Saudi Boeing 747.

Identify traffic 12:00 reciprocal, Saudi Boeing 747.

Dutta doesn't want the Kazakh flight to be

surprised to see the Saudi jet.

surprised to see the Saudi jet.

Since planes don't have radar to track other aircraft,

they rely on controllers to warn them about other planes nearby.

they rely on controllers to warn them about other planes nearby.

Maintaining 150.

Kazakh 1907 will report.

Kazakh 1907 will report.

How many miles?

How many miles?

All pilots tuned to the approach control radio

frequency are able to hear one another as they

frequency are able to hear one another as they

communicate with the ground.

How many miles?

How many miles?

Eight miles now.

It was strictly visual and trying to pick up on the radios

It was strictly visual and trying to pick up on the radios

where everyone else is at and what they're up to.

Traffic is at eight miles, level 140.

Traffic is at eight miles, level 140.

Suddenly, a massive explosion

shatters the evening's calm.

All at once, out of the right side

All at once, out of the right side

of the window, right side of the cockpit,

this cloud just lit up.

this cloud just lit up.

Those missiles?

To my mind's eye, there were missiles corkscrewing,

To my mind's eye, there were missiles corkscrewing,

picking up speed was what they looked like,

and they looked like they were coming right at us.

We actually started veering the aircraft

We actually started veering the aircraft

away before it became apparent that they weren't coming at us.

away before it became apparent that they weren't coming at us.

The Saudi Airlines jet spirals toward the ground.

The Saudi Airlines jet spirals toward the ground.

Delhi, this is 1815.

Delhi, this is 1815.

1815, say again.

Got on the radio right away, called the controller.

We saw something that looks like a big explosion.

We saw something that looks like a big explosion.

Then it struck to me that something has gone wrong.

On Dutta's radar screen

On Dutta's radar screen

both the Saudi jet and the Kazakh plane

have simply vanished.

have simply vanished.

When I saw other blips are coming,

so I watched the sweep again.

But they were not there at all.

We then heard the controller call for the Saudi air

We then heard the controller call for the Saudi air

jet and the Ilyushin.

jet and the Ilyushin.

Saudi 763?

With no response, that was

obviously very bone-chilling.

obviously very bone-chilling.

Something tragic has happened in the skies

near New Delhi's airport.

VK Dutta is about to become the target of an investigation

into one of the deadliest plane crashes of all time.

into one of the deadliest plane crashes of all time.

Kazakh 1907, report your position.

Kazakh 1907, report your position.

At New Delhi's airport, a sense of dread

is growing.

Two planes have vanished from approach control's radar.

The worst nightmare an air traffic controller

The worst nightmare an air traffic controller

has is the mid-air collision.

Saudi 763?

Together, the two missing planes

Together, the two missing planes

were carrying 349 people.

US Air force pilot Captain Tim Place soon confirms the worst.

US Air force pilot Captain Tim Place soon confirms the worst.

Delhi, this is 1815.

1815, what did you see?

1815, what did you see?

Two distinct fires on the ground.

Two fires on the ground.

Confirm?

Confirm?

Confirmed.

Confirmed.

Roger.

Roger.

My senior came to me.

So I told him the accident happened.

So I told him the accident happened.

He told people who were to do search and rescue

He told people who were to do search and rescue

that the aircraft had crashed at 40

nautical miles west of Delhi.

nautical miles west of Delhi.

Two planes have gone down over Charkhi Dadri.

Two planes have gone down over Charkhi Dadri.

Charkhi Dadri is a town

40 miles west of New Delhi.

It's mustard and grain fields are

now burning with the twisted wreckage of two ruined planes.

now burning with the twisted wreckage of two ruined planes.

All of a sudden, the sky

All of a sudden, the sky

turned a bright red color, and I saw fire and smoke.

One plane started to come towards us.

There was fire, and parts of the plane were flying everywhere.

There was fire, and parts of the plane were flying everywhere.

People were running.

The plane's engine broke off, and

the plane started to spin out of control

and fell into the field.

None of the passengers aboard either plane

None of the passengers aboard either plane

has survived.

349 people are dead.

349 people are dead.

It's the worst mid-air collision of all time.

It's the worst mid-air collision of all time.

News of the crash spreads around the world.

What remains clear is that there

What remains clear is that there

was more than one set of factors that might

have resulted in the collision.

We have two very separate wreckage fields.

Captain KPS Nair is one of the first investigators

Captain KPS Nair is one of the first investigators

on the scene.

I was aghast, horrified.

I was aghast, horrified.

I can't explain it because I had never seen anything like that

I can't explain it because I had never seen anything like that

before.

It is something which I can't explain.

It is something which I can't explain.

The Kazakh flight and the Saudi Airlines jet

The Kazakh flight and the Saudi Airlines jet

have fallen four miles from each other.

Investigators have two separate crash sites to examine,

Investigators have two separate crash sites to examine,

but they know one cause will explain both accidents.

but they know one cause will explain both accidents.

It's unlike a single aircraft falling somewhere.

Two large-bodied aircraft colliding each other

Two large-bodied aircraft colliding each other

in the sky, there are different causes.

How had two planes that were supposed to be

1,000 feet apart collided?

1,000 feet apart collided?

Investigators consider three possibilities...

Investigators consider three possibilities...

an error on the part of the air traffic controller,

an error by one of the crews, or the failure of an instrument

an error by one of the crews, or the failure of an instrument

on one of the planes.

They hope the mangled wreckage will hold the clues they need.

Their first priority is to find the black boxes

from both planes.

They record cockpit conversations

They record cockpit conversations

along with critical data about the flight, like its altitude,

speed, and heading.

speed, and heading.

Although fire has ravaged the wreck sites,

the black boxes from both planes are found on the first day

the black boxes from both planes are found on the first day

of the investigation.

But for the moment, they hold their secrets.

But for the moment, they hold their secrets.

It will take several months for experts

to extract data from the recorders.

In the meantime, investigators focus

on conversations between the two planes

on conversations between the two planes

and the air traffic controller.

In this particular case, we had the evidence

In this particular case, we had the evidence

of the ATC transcript.

Without on-board radar,

Without on-board radar,

the planes around Delhi's airport

rely on air traffic controllers to guide them.

VK Dutta comes under enormous pressure.

VK Dutta comes under enormous pressure.

Did he make mistakes that caused the worst

mid-air collision ever?

mid-air collision ever?

Hi.

I'm VK Dutta.

I'm sorry to keep you waiting.

I'm sorry to keep you waiting.

Have a seat.

Investigators want to know everything that Dutta

did on the night of the crash.

did on the night of the crash.

Was traffic heavy?

Evenings are always busy.

Dutta's radar doesn't track a plane's altitude.

Dutta's radar doesn't track a plane's altitude.

Instead, controllers in New Delhi

write a plane's last reported position on a strip of paper.

write a plane's last reported position on a strip of paper.

The strips are continually updated.

It's the only way for controllers

It's the only way for controllers

to keep track of the altitude of the planes under their control.

to keep track of the altitude of the planes under their control.

Level information is not there,

so level has to be confirmed by the pilot.

so level has to be confirmed by the pilot.

Kazakh 1907 now reaching 150.

Air traffic controllers

Air traffic controllers

can only know a plane's altitude when the pilots report it.

can only know a plane's altitude when the pilots report it.

Are these your notes?

Yes, sir.

This is the Kazakh one, and this is the Saudi one.

This is the Kazakh one, and this is the Saudi one.

Investigators learn that Dutta was in charge

of five flights at the time of the accident

of five flights at the time of the accident

and that the Saudi and Kazakh flights

were flying in opposite directions

of the same aerial pathway.

of the same aerial pathway.

The area that Dutta manages is divided into a network

of air corridors.

of air corridors.

Controllers use them to channel flights in and out

of the airport, but many of the corridors

of the airport, but many of the corridors

are used for military flights.

In fact, even at such a busy airport

there's only one main corridor for commercial planes.

In cases like this, there are strict rules

In cases like this, there are strict rules

Dutta has to follow.

Between two aircraft, the requirements

Between two aircraft, the requirements

specify a vertical minimum separation of 1,000 feet.

When aircraft fly through the sky,

When aircraft fly through the sky,

they leave turbulence in their wake, like boats on the water.

It can affect the planes around them.

It can affect the planes around them.

Air traffic controllers deal with this by keeping

planes at different altitudes.

planes at different altitudes.

Roger.

Maintain flight level 140.

Stand by for higher.

Dutta was supposed to ensure

Dutta was supposed to ensure

that the two planes were 1,000 feet apart

as they approached each other.

He planned to do what he had done many times before...

He planned to do what he had done many times before...

have the incoming plane pass 1,000 feet over the top

of the outbound plane.

of the outbound plane.

It was a routine procedure, but somehow the two planes had

ended up on a collision course.

ended up on a collision course.

One of the two planes was not where it should have been.

Investigators wonder if Dutta made a mistake

Investigators wonder if Dutta made a mistake

that led to the horrific crash.

Poring through the air traffic control transcripts,

investigators quickly learn that Dutta had given the two

investigators quickly learn that Dutta had given the two

planes the proper directions.

But since his radar doesn't display altitude,

But since his radar doesn't display altitude,

there was no way for him to tell if the planes

followed those instructions.

Investigators are so convinced that Dutta did nothing wrong...

Investigators are so convinced that Dutta did nothing wrong...

Thank you.

...that three days after the crash

he's back on duty.

When my family and other people heard this,

there was a little sigh of relief that our guy is safe.

there was a little sigh of relief that our guy is safe.

Investigators return to the crash site.

They are hoping to recover certain instruments

They are hoping to recover certain instruments

from the two aircraft.

Perhaps a mechanical failure had led one of the planes

Perhaps a mechanical failure had led one of the planes

off course.

Normally, the altimeter would have stopped at that point

Normally, the altimeter would have stopped at that point

where the accident took place.

And we wanted to know what altitude they were registering

And we wanted to know what altitude they were registering

at the time of the accident.

But the Saudi cockpit has

plunged deep into the ground.

plunged deep into the ground.

The accident investigation becomes an excavation.

The accident investigation becomes an excavation.

The Saudis' north portion was well below the earth.

It was about 10 to 12 meters below.

The end of the nose had gone that far below.

The end of the nose had gone that far below.

Machines had to be brought in, excavators to dig up

Machines had to be brought in, excavators to dig up

and lift the cockpit of the Saudi aircraft.

and lift the cockpit of the Saudi aircraft.

The altimeters of the Kazakh flight

are easier to find.

are easier to find.

That plane didn't crash nose first.

That plane didn't crash nose first.

There's some chance there are clues about its exact altitude

at the time of the accident.

at the time of the accident.

When they're pulled from the wreckage,

investigators discover that there is indeed something

strange about the altimeters.

strange about the altimeters.

Both the captain and the co-pilot

have an altimeter in front of them.

have an altimeter in front of them.

But in this case, they do not have the same reading.

There was a difference between the two by about 300 feet.

There was a difference between the two by about 300 feet.

Strange.

Perhaps the conflicting altimeters

had led the crew off course.

But the difference in readings may simply have been caused

But the difference in readings may simply have been caused

by the force of the crash.

At this point, investigators don't know.

At this point, investigators don't know.

Investigators need to discover which of the two planes, Saudi

Investigators need to discover which of the two planes, Saudi

Airlines Flight 763 or Kazakhstan

Airlines Flight 763 or Kazakhstan

Airlines Flight 1907, was at the wrong altitude

when they collided.

when they collided.

They explore other evidence.

The pattern of the damage on the two planes

may help answer a critical question.

may help answer a critical question.

What was the relative angle between the two aircraft

at the time of the their contact?

at the time of the their contact?

Most of the pieces from the two planes

are miles apart, but a large section of the tail

from the Saudi aircraft is found near the beginning

from the Saudi aircraft is found near the beginning

of the debris field.

This suggests it was one of the first pieces

to come off that plane.

to come off that plane.

The tail of the Kazakh plain appears

to have pierced through the left wing of the Saudi jet.

to have pierced through the left wing of the Saudi jet.

If that's the case, the Kazakh flight

hadn't been above the Saudi jet when they collided, as air

hadn't been above the Saudi jet when they collided, as air

traffic controllers thought.

It must have been below it.

It must have been below it.

It's a puzzling discovery that adds to the mystery.

It's a puzzling discovery that adds to the mystery.

Investigators still don't know which plane

was in the wrong airspace.

was in the wrong airspace.

What they do know is that once the two planes hit,

there was no hope for either crew.

there was no hope for either crew.

After hitting the other plane's wing,

the Kazakh plane's tail tore through

the Kazakh plane's tail tore through

the horizontal stabilizer at the rear of the Saudi 747.

11.5 feet of it is torn off.

Without it, the Saudi crew can't control their plane.

Without it, the Saudi crew can't control their plane.

The result is the aircraft goes

into uncontrollable spiral.

into uncontrollable spiral.

And in this particular case, I would say both aircraft

And in this particular case, I would say both aircraft

had gone into that situation.

What they've found in the wreckage of the two jets

frustrates the investigators.

frustrates the investigators.

They now understand how the planes collided,

but they still don't know why they were at the same altitude

but they still don't know why they were at the same altitude

or, in fact, what altitude they collided at.

How had the Kazakh jet, which was

How had the Kazakh jet, which was

supposed to be above the Saudi flight, ended up below it?

Almost two weeks after the accident,

Captain Ashok Verma joins investigators at the scene.

Captain Ashok Verma joins investigators at the scene.

By that time, the operations for digging

the Saudi Air cockpit had been completed.

the Saudi Air cockpit had been completed.

Whatever equipment was recoverable had been recovered.

Whatever equipment was recoverable had been recovered.

Like the rest of the evidence uncovered so far,

Like the rest of the evidence uncovered so far,

the instruments from the Saudi plane

don't help explain what happened.

The force of the crash has completely destroyed them.

The force of the crash has completely destroyed them.

The case now depends on what they can

find out from the black boxes.

find out from the black boxes.

Investigators hope that somewhere on the cockpit

Investigators hope that somewhere on the cockpit

recordings or buried in the flight data

are the clues they need.

are the clues they need.

In order to avoid any suggestion of bias,

the boxes from the Saudi flight are being analyzed in England.

the boxes from the Saudi flight are being analyzed in England.

Technicians from the Air Accidents Investigation branch

try to extract valuable data.

try to extract valuable data.

The neutrality of the state where the recorders are handled

The neutrality of the state where the recorders are handled

was an essential thing.

Each plane was equipped with two black boxes...

Each plane was equipped with two black boxes...

a flight data recorder and a cockpit voice recorder.

The flight data recorder contains information on dozens

The flight data recorder contains information on dozens

of aspects of a plane's performance,

among them the altitude, the airspeed,

among them the altitude, the airspeed,

and the changes pilots make to the flight controls.

The cockpit voice recorder, or CVR,

picks up all the conversations in the cockpit.

picks up all the conversations in the cockpit.

279, good day.

279, good day.

As investigators try to learn more

about the collision near New Delhi,

they use the information stored on the black boxes

they use the information stored on the black boxes

to make a chronology of events.

to make a chronology of events.

Peter Sheppard is head of the recorder section of the Air

Accidents Investigation branch.

He'll work backwards from the moment of impact.

The point of collision is reasonably

The point of collision is reasonably

well defined by rapid changes in parameters on each aircraft.

If we make that time zero point, we can then

If we make that time zero point, we can then

relate that to the individual times

and build up a common time base.

and build up a common time base.

First, Sheppard and his team

concentrate on the Saudi 747.

concentrate on the Saudi 747.

Saudi 763 approaching 140 for higher.

Saudi 763 approaching 140 for higher.

Roger, maintain flight level 140.

Stand by for higher.

Saudi 763 will maintain 140.

Saudi 763 will maintain 140.

The CVR reveals that the Saudi pilots received

clear instructions about their altitude

clear instructions about their altitude

and seemed to have understood them.

After being told to hold at 14,000 feet,

After being told to hold at 14,000 feet,

there was no discussion of climbing to a higher altitude.

Which would have taken them into the path of the Kazakh flight.

Which would have taken them into the path of the Kazakh flight.

Next, Sheppard looks at the flight data recorder

to confirm that the Saudi flight actually followed

to confirm that the Saudi flight actually followed

the instructions it was given.

The recorder from the Saudi flight

showed us that the altitude had been normal during climb out.

showed us that the altitude had been normal during climb out.

The Saudi pilots leveled off at 14,108 feet,

The Saudi pilots leveled off at 14,108 feet,

well within their safe corridor.

It had leveled at its assigned altitude of 14,000 feet

It had leveled at its assigned altitude of 14,000 feet

and continued to fly level.

and continued to fly level.

Air traffic controllers

wanted the two planes separated by 1,000 feet

and wanted the Saudi plane to fly below the Kazakh jet.

and wanted the Saudi plane to fly below the Kazakh jet.

If the Saudi pilots did nothing unusual,

suspicion is growing that somehow it was the Kazakh plane

suspicion is growing that somehow it was the Kazakh plane

that was in the wrong place.

Alarmingly, when investigators examine the information

from the Kazakh jet's flight data recorder,

from the Kazakh jet's flight data recorder,

they discover that it descended far below the 15,000 feet

they discover that it descended far below the 15,000 feet

it was supposed to stay at.

Moments before the collision, the Kazakh plane

Moments before the collision, the Kazakh plane

is at 14,100 feet, almost feet lower

is at 14,100 feet, almost feet lower

than its assigned altitude and less than 10

feet below the Saudi flight.

feet below the Saudi flight.

It then powered directly into the Saudi jet.

The Kazakh crew had not stopped

descending at the altitude they were cleared to.

descending at the altitude they were cleared to.

That was 15,000 feet.

But why had the Kazakh flight

But why had the Kazakh flight

dropped so badly off course?

Kazakhstan Airlines presents one theory for their plane's

dramatic loss of altitude, a loss

that resulted in one of the deadliest crashes

that resulted in one of the deadliest crashes

in aviation history.

The Kazakhstan defense mainly relied

The Kazakhstan defense mainly relied

on presence of turbulence.

Perhaps a sudden burst of turbulence

Perhaps a sudden burst of turbulence

had forced the plane lower.

The data recorder of the Kazakh flight

does seem to indicate that the crew had a bumpy ride.

does seem to indicate that the crew had a bumpy ride.

It shows two distinct and sudden drops of more than 400 feet.

It shows two distinct and sudden drops of more than 400 feet.

The airline claims both of these drops

were caused by turbulence.

were caused by turbulence.

But Peter Sheppard isn't so sure.

When we saw the jumps of 250, 500 feet,

When we saw the jumps of 250, 500 feet,

our initial response was that these can't be right.

our initial response was that these can't be right.

I mean, it was the rate at which they

change was beyond that that an aircraft

change was beyond that that an aircraft

could actually perform.

What else could cause the plane

to drop so quickly, or at least seem to drop so quickly?

to drop so quickly, or at least seem to drop so quickly?

Sheppard searches for an explanation.

Sheppard searches for an explanation.

We tried to resolve the inaccuracies in the Kazakh

recording by looking at the other parameters that were

recording by looking at the other parameters that were

recorded and trying to derive altitude

recorded and trying to derive altitude

using these other recordings.

It's intricate math.

By using information, including the speed and rate of descent

By using information, including the speed and rate of descent

from the flight data recorder, Sheppard

determines that the plane was on a steady downward approach.

determines that the plane was on a steady downward approach.

The reason for the apparent sharp drops is simple.

The reason for the apparent sharp drops is simple.

Sheppard learns that the sensor that

sends altitude information to the flight data recorder

sends altitude information to the flight data recorder

was faulty.

It would stick and temporarily stop sending information.

It would stick and temporarily stop sending information.

When it got unstuck, it would wrongly

appear as though the plane had lost considerable altitude.

appear as though the plane had lost considerable altitude.

Investigators can now conclusively dismiss turbulence

as a factor in the collision.

as a factor in the collision.

So there is no sudden descent.

Scanning maintenance records,

Scanning maintenance records,

investigators also discover that there

was no problem with the Kazakh plane's altimeters.

was no problem with the Kazakh plane's altimeters.

They conclude that the difference

found in the cockpit instruments was a result of the crash.

found in the cockpit instruments was a result of the crash.

It didn't cause it.

To understand why the Kazakh plane kept descending after it

To understand why the Kazakh plane kept descending after it

was told to hold, investigators turn

to the cockpit voice recorder.

to the cockpit voice recorder.

It begins long before the crash itself.

Initially, there are no hints that anything is wrong.

Initially, there are no hints that anything is wrong.

Kazakh 1907, report level passing.

Kazakh 1907, report level passing.

Passing 140.

Kazakh 1907.

Kazakh 1907.

Because the Ilyushin is a modified military plane,

it has another unusual feature...

it has another unusual feature...

a position for a radio operator in the cockpit.

Igor Repp mans that position and handles all communications

Igor Repp mans that position and handles all communications

for the Kazakh flight.

Roger.

Over to Delhi approach 127 decimal nine.

Over to Delhi approach 127 decimal nine.

127 decimal nine.

Bye-bye, Kazakh 1907.

Bye-bye, Kazakh 1907.

As the aircraft nears the airport,

Repp gets in touch with approach controller Dutta.

Repp gets in touch with approach controller Dutta.

Delhi approach, good evening.

Kazakh 1907 passing 230 to 180.

Kazakh 1907 passing 230 to 180.

I told Kazakh to descend and maintain flight level 150.

I told Kazakh to descend and maintain flight level 150.

That is 15,000 feet.

Roger, Kazakh 1907.

Roger, Kazakh 1907.

Descend flight level 150.

Report reaching.

Report reaching.

1,000 feet vertical separation is sufficient,

and that was granted to the two aircraft.

and that was granted to the two aircraft.

Kazakh 1907 now reach 150.

Kazakh 1907 now reach 150.

The Kazakhstan radio operator had at one time

The Kazakhstan radio operator had at one time

stated reaching flight level 150.

It's just one minute before the impact.

It's just one minute before the impact.

And at this point, the Kazakh plane

appears to be right where it's supposed to be,

1,000 feet higher than the Saudi plane.

1,000 feet higher than the Saudi plane.

But investigators know that instead of leveling off,

But investigators know that instead of leveling off,

the plane continued to descend.

This is where the trouble starts.

This is where the trouble starts.

As investigators compare the flight data

information to the cockpit voice recording,

information to the cockpit voice recording,

they notice something disturbing.

Kazakh 1907 now reach 150.

Kazakh 1907 now reach 150.

When Repp calls out that they've descended

to 15,000 feet, he's actually over 1,000 feet higher

to 15,000 feet, he's actually over 1,000 feet higher

than he thinks he is.

Investigators wonder how he could

make such an enormous mistake.

Why would he say he was at 15,000 feet

Why would he say he was at 15,000 feet

when in fact he was at 16,000?

when in fact he was at 16,000?

They consider the layout of the cockpit.

A radio operator does not have his independent altimeter.

A radio operator does not have his independent altimeter.

There are two metric altimeters fitted in front of one each

There are two metric altimeters fitted in front of one each

in front of the pilots.

With some effort, the radio operator could also see this.

With some effort, the radio operator could also see this.

Whatever the reason, Repp

is mistaken about his plane's height,

is mistaken about his plane's height,

and he's the only one in contact with the ground.

Despite being told to remain at 15,000 feet,

Despite being told to remain at 15,000 feet,

the plane continues to descend.

As it does, Dutta issues a warning to the Kazakh pilots.

As it does, Dutta issues a warning to the Kazakh pilots.

Identify traffic 12:00 reciprocal,

Saudi Boeing 747 and 10 miles.

Saudi Boeing 747 and 10 miles.

Likely to cross in another five miles.

Report if in sight.

Report if in sight.

He tells them to watch out for the Saudi flight,

but the Kazakh jet just keeps flying lower.

but the Kazakh jet just keeps flying lower.

Ahead?

Ahead.

Just before the crash, Igor Repp

Just before the crash, Igor Repp

seems to have recognized that the plane is

now flying dangerously low, but his warning

now flying dangerously low, but his warning

doesn't come in time.

Keep the 150.

Do not descend.

The cockpit voice recorder

proves what investigators found in the flight data.

proves what investigators found in the flight data.

At the time of the crash, the Kazakh jet

was trying desperately to get back on course.

was trying desperately to get back on course.

Get to the 150.

Descend to 140.

Descend to 140.

That one!

But investigators are still puzzled.

But investigators are still puzzled.

Why had the Kazakh plane kept descending?

After ruling out controller's error,

After ruling out controller's error,

ruling out mechanical failure, you

have to go further into details of human behavior

have to go further into details of human behavior

during the operation of a flight.

Kazakhstan is one of several now

Kazakhstan is one of several now

independent republics that used to be part of the Soviet Union.

independent republics that used to be part of the Soviet Union.

The national airline has a reputation

at Indira Gandhi Airport.

There was always a sense that these were small fly-by-night

There was always a sense that these were small fly-by-night

operators essentially doing the charter business,

and they didn't necessarily follow the conventions

and they didn't necessarily follow the conventions

of modern Western aviation.

We examined their background of knowledge

We examined their background of knowledge

of English language.

The crew in the Soviet states, they pass English examination,

The crew in the Soviet states, they pass English examination,

but they're not fluent in spoken English.

but they're not fluent in spoken English.

Verma now listens more closely to the cockpit voice

Verma now listens more closely to the cockpit voice

recorder, looking for an indication

that the crew misunderstood their instructions.

Had a language barrier caused the crash?

Had a language barrier caused the crash?

How many miles?

Traffic is at eight miles, level 140.

Traffic is at eight miles, level 140.

Did the Kazakh pilots confuse their own altitude

Did the Kazakh pilots confuse their own altitude

with that allocated to the Saudi aircraft?

with that allocated to the Saudi aircraft?

Report eight miles.

Verma finds that members of this crew

Verma finds that members of this crew

weren't communicating clearly with each other.

Igor Repp was responsible for communication with the ground,

Igor Repp was responsible for communication with the ground,

but there's no indication that the pilot and co-pilot were

listening to his instructions.

listening to his instructions.

Switch on engine inlet heating.

While the rest of the crew

was busy discussing arrival procedures,

was busy discussing arrival procedures,

Repp alone seemed to be occupied with their altitude.

Now looking, 1907.

Now looking, 1907.

It is a usual practice that the briefing for the arrival

It is a usual practice that the briefing for the arrival

is completed before start of descent

so that all crew can pay full attention to the radio.

so that all crew can pay full attention to the radio.

While the radio operator appears

to have understood that the Saudi plane was at 14,000 feet,

to have understood that the Saudi plane was at 14,000 feet,

investigators believe the co-pilot

thought he was cleared to 14,000 feet and continued his descent.

thought he was cleared to 14,000 feet and continued his descent.

Hold the level.

Hold the level.

What level were we given?

When the pilot does respond, he seems confused.

When the pilot does respond, he seems confused.

I think pilots did not pay that much attention

and relied too much on the radio operator

and relied too much on the radio operator

to navigate the aircraft during this critical phase.

to navigate the aircraft during this critical phase.

The decision to increase power and stop

descending ends in tragedy.

Keep the 150.

Keep the 150.

Do not descend.

Get to the 150.

Descend to the 140.

Descend to the 140.

That one!

The final report points a finger squarely at

the crew of the Kazakh plane.

In the wrong place at the wrong time,

In the wrong place at the wrong time,

a simple misunderstanding led to the deaths of 349 people.

a simple misunderstanding led to the deaths of 349 people.

The investigation concluded that the primary cause of this

The investigation concluded that the primary cause of this

mid-air collision was non-adherence

mid-air collision was non-adherence

to the authorized altitude allocated

to the Kazakhstan aircraft.

to the Kazakhstan aircraft.

Investigators are confident they know what caused

the worst mid-air collision in aviation history,

the worst mid-air collision in aviation history,

but there are steps they want the industry

to take to help make Indira Gandhi Airport safer.

to take to help make Indira Gandhi Airport safer.

What they find is that the technology

that could have prevented this accident

that could have prevented this accident

was already at the airport.

Saudi 763.

Investigators have determined that poor cockpit

communication and a simple misunderstanding

communication and a simple misunderstanding

caused a devastating accident which killed almost 350 people.

caused a devastating accident which killed almost 350 people.

But technology existed that could have helped avoid

this accident, systems that would have

this accident, systems that would have

helped both the pilots in the air and the controllers

on the ground.

Investigators are especially critical of the radar that

Investigators are especially critical of the radar that

was being used in New Delhi.

Air traffic controllers did rely on fairly outdated

Air traffic controllers did rely on fairly outdated

technology at that stage.

There wasn't any secondary radar available at Delhi Airport.

There wasn't any secondary radar available at Delhi Airport.

There was only an old primary radar.

Primary radar sends out radio signals

Primary radar sends out radio signals

to locate airplanes in the sky.

The signal bounces off the plane and back to a dish

The signal bounces off the plane and back to a dish

on the ground.

It reads a plane's position but not its altitude.

It reads a plane's position but not its altitude.

The primary radar gives you a 2D picture.

Secondary radar works differently.

Secondary radar works differently.

A transponder aboard an aircraft sends a message

to the ground with key information about the flight,

to the ground with key information about the flight,

including its altitude.

Saudi 763 approaching flight level 100.

Saudi 763 approaching flight level 100.

Roger, climb flight level 140.

Roger, climb flight level 140.

On the day of the collision,

approach controller VK Dutta could only

approach controller VK Dutta could only

rely on what the crews told him about their aircraft's

altitudes.

altitudes.

Kazakh 1907 now reach 150.

The Kazakh radio operator said that they

The Kazakh radio operator said that they

were flying at 15,000 feet.

But Dutta had no way to confirm that.

But Dutta had no way to confirm that.

If he had known the Kazakh flight's actual altitude,

he could have diverted the Saudi flight from its path.

he could have diverted the Saudi flight from its path.

That is the 3D picture.

So you can... you have some time to react to it.

So you can... you have some time to react to it.

You can take the aircraft away.

At the time of the accident,

At the time of the accident,

India had ordered a $118 million air traffic control system

India had ordered a $118 million air traffic control system

with secondary radar and more sophisticated communications

and navigational equipment.

and navigational equipment.

The system had originally been scheduled to be installed

two weeks before the accident.

two weeks before the accident.

But on the day of the crash, the system

hadn't even been unpacked.

hadn't even been unpacked.

Secondary radar is an advancement

on the primary radar.

And in this particular case also, by getting the altitude

And in this particular case also, by getting the altitude

information, it could have been possible

information, it could have been possible

that the accident of this nature could have been avoided.

that the accident of this nature could have been avoided.

In the year following the accident,

there would be three near misses near Indira Gandhi Airport.

there would be three near misses near Indira Gandhi Airport.

It would take more than two years for the secondary radar

system to be installed.

system to be installed.

Today, controllers at Indira Gandhi International Airport

Today, controllers at Indira Gandhi International Airport

see an airplane's flight number, altitude, and heading.

see an airplane's flight number, altitude, and heading.

It's far more information than controller

VK Dutta had available to him on the day of the accident.

VK Dutta had available to him on the day of the accident.

Experts believe another piece of technology

could have helped prevent the collision...

could have helped prevent the collision...

TCAS.

TCAS equipment generates caution and warnings

TCAS equipment generates caution and warnings

for the crew.

It allows them time to react, draws their attention

It allows them time to react, draws their attention

to the situation around, and it looks

to the situation around, and it looks

into the vertical separation.

into the vertical separation.

TCAS is a collision avoidance system that can be

installed on board airliners.

installed on board airliners.

In many countries, the technology is mandatory.

It alerts pilots when other flights are coming too close.

It alerts pilots when other flights are coming too close.

The system also automatically tells them what evasive action

The system also automatically tells them what evasive action

they should take.

Neither plane was equipped with TCAS.

The Indian airports authority has also made the airport safer

by redesigning the air corridors coming

by redesigning the air corridors coming

and going from the runways.

At the time of the collision, there was one main air corridor

At the time of the collision, there was one main air corridor

for commercial planes landing and taking off from Indira

Gandhi International Airport.

Gandhi International Airport.

With the increase in air traffic,

that single corridor was becoming too crowded.

that single corridor was becoming too crowded.

In the wake of the accident, more air corridors were

opened for commercial flights.

opened for commercial flights.

In general, aviation safety standards have improved.

The concern for the safety has improved.

VK Dutta went on to have a long career

as an air traffic controller.

as an air traffic controller.

Today, he works at a college training young controllers.

So I'm chief instructor there.

So I'm chief instructor there.

So I'm training

I'm addicted to my job.

I love it.

I really love it.

I really love it.

Dutta, who was initially suspected of having

caused the crash, helped implement the changes to make

caused the crash, helped implement the changes to make

new Delhi's airport safer.

His efforts have paid off.

The airport now handles 20 million passengers a year.

The airport now handles 20 million passengers a year.

Since the new radar system was installed

and the new corridors opened, there

hasn't been a fatal accident at this airport.