Original subtitles

- Just another hazy day. - Watch it!

(narrator): A high-speed collision over the California desert tears two planes apart.

- What the hell were those guys doing up there?

- Tower, we're going down.

(narrator): Seven years later, a 727 and a Cessna crash into a San Diego suburb.

- How did this happen again? (sirens wailing)

(shouting)

(narrator): When two passenger jets collide in India,

it's the world's deadliest mid-air collision.

- Two fires on the ground. Confirm?

(narrator): With thousands of flights in the air every day,

investigators need to find out where the system failed before another disaster occurs.

- Forget the red tape.

This is in the interest of aviation safety and saving people.

- Mayday, mayday.

- It's going up!

(indistinct radio chatter)

(narrator): Los Angeles International Airport.

Hughes Airwest Flight 706 prepares for takeoff.

There are 44 passengers on board.

The flight is travelling from Los Angeles to Seattle,

with several intermediate stops.

(Captain): Welcome aboard, folks.

We'll be getting underway... any minute now.

(narrator): Former Air Force pilot Captain Theodore Nicolay is in command today.

He has amassed more than 15,000 flight hours.

(ATC): Airwest 706 red cleared for takeoff, runway 2-4 left.

Climb via heading 2-5-0.

- Roger, 2-4 left, climb heading 2-5-0.

(narrator): First Officer Price Bruner

has even more hours in the air than Captain Nicolay.

- Weather's looking clear all the way to Seattle.

- Throttles are all yours.

- Eighty knots.

(narrator): At 6:02 p.m., the DC-9 lifts off from LAX.

(beeping) (ATC): Turn right, heading 0-6-0.

- Airwest 706 red, right 0-6-0.

(narrator): The heading takes the plane west over the Pacific Ocean

before turning northeast towards its first stop, Salt Lake City.

Four minutes after takeoff,

First Officer Bruner contacts a different control centre north of L.A.

- Los Angeles Center, good evening.

- Airwest 706 red, turn left,

heading 0-4-0 until receiving Daggett.

(narrator): The controllers guide the DC-9 out of Los Angeles.

- In addition to Airwest, the radar controller may have been talking

to five or six other jets climbing up towards the northeast,

in addition to a small number of criss-crossers back and forth through the airspace.

(alarm sounding) (narrator): Suddenly,

an emergency alarm warns the controllers

that a plane in their airspace may be in trouble.

- At this point, we looked back where Airwest 706 is; the target's missing.

The radar controller said something like:

- Hughes Airwest 706, reset your transponder. Radar contact lost.

- There's no answer.

(people screaming) Airwest 706...

- Radio check. How do you hear me? - ...no answer.

This is getting bad now. We've lost the target,

and we've got no communications with the aircraft.

(narrator): Moments later, the crew of a nearby military plane calls in devastating news.

- Center, we've just seen an explosion on the side of a mountain.

(narrator): The DC-9 with 49 people on board

has slammed into the California hills.

- Did Airwest just explode?

It had crashed for some reason and we had no idea whatsoever.

(narrator): The National Transportation Safety Board

assigns one of its top investigators to the case...

- Yeah, got it. Great. Thank you. Bye.

(narrator): ...Second World War navy pilot Dick Baker.

(sighing) - San Gabriel Mountains.

(narrator): The crash site is in a remote area of the San Gabriel mountains,

a few miles from the town of Duarte, California.

In the hours after the crash, witnesses come forward,

insisting they saw a mid-air collision

between the DC-9 and a fighter jet.

Investigators are stunned.

How did a fighter jet and a passenger plane end up on a collision course?

- Okay. Thank you. Bye-bye.

(narrator): A call from a nearby Marine Corps base provides a key detail.

- El Toro's missing a jet.

(narrator): An F-4 Phantom hasn't made it back

to nearby El Toro Marine Corps Airbase.

It's the military's most advanced fighter,

capable of outmanoeuvring almost everything else in the sky.

- In the '70s, there was lots of military training going on in Southern California,

because there were clear skies and lots of desert out there that they could train over.

(narrator): Investigators learn the identities of the F-4's two crewmen:

Marine pilot James Richard Phillips,

and Radar Intercept Officer Christopher Schiess.

- Watch it! (narrator): Remarkably, after the impact,

Lieutenant Schiess was able to eject from the doomed fighter.

- Dick Baker.

(narrator): The Marines send their own man to help with the investigation:

Lieutenant Colonel Jack Zych.

Investigators hunt for clues as to how these two planes collided.

But recovering the wreckage from the remote crash site will take time.

(news): The first rescue workers had to hike six miles to get to the scene.

They reported only the tail section intact, no signs of life.

(narrator): A day after the crash,

investigators get a chance to talk to the accident's sole survivor.

- The DC-9 hit us.

Like this. His nose to our tail.

- Hold on. Back up a bit.

Tell me exactly what happened.

(narrator): Lieutenant Schiess claims that his aircraft was not at fault.

On the day of the crash, Schiess was flying in the rear seat of the F-4.

- Copy, Rick. Climb to 15,000.

(narrator): Twenty-seven-year-old Lieutenant Rick Phillips

is in the forward seat, flying the jet.

They're on their way back to home base: El Toro, California.

- We climbed to 15,000 feet. Here.

(narrator): Schiess uses his radar to scan the ground below.

- He would have his head down in the radar scope doing ground mapping,

and then the front-seater would be primarily visual,

because he knew that he lost that extra set of eyes

that was down in the radar instead of looking out for other aircraft.

(wind rushing) - Watch it, Rick!

That's when I first saw the DC-9.

Came out of nowhere and slammed into us.

(narrator): Five seconds later, Schiess ejects.

- I got out.

Rick didn't.

(narrator): The F-4 was not equipped with a black box

that can confirm Schiess's story.

And the high-speed impact obliterated the jet, leaving no clues.

Luckily, the team recovers some of the wreckage of the DC9,

including the black boxes.

But they're badly damaged and offer little help.

Hughes Airwest engineer Dave Knutsen is brought in

to see if the wreckage supports the young lieutenant's story.

By reconstructing the DC-9,

Knutsen might be able to explain the angle of impact.

- Climbing through 15,000 feet.

- Just another hazy day.

(narrator): Ten days after the crash,

searchers find the nose of the DC-9.

It's a critical piece for the reconstruction.

It reveals a large gash slicing through the cockpit.

- Looks like the stabilizer cut the plane in two.

- So if they hit like this...

- The F-4 had actually... penetrated...

the DC-9 on the left side,

a few feet from the nose.

So frankly, the F-4 hit the DC-9,

rather than the DC-9 hitting the F-4.

- Watch it, Rick!

- It cut off the nose of the airplane.

And that took away all the controls and the airplane.

As some of the observers on the ground said,

it was like a falling leaf till it hit the ground.

(narrator): Investigators know that Schiess was wrong about who hit whom.

But why couldn't the pilots see each other and avoid a deadly collision?

(narrator): Investigators are under pressure to explain how a DC-9 and an F-4 fighter

collided over California.

They wonder how fast the planes were travelling at the moment of impact.

- The F-4...

is coming in at 420 knots...

...from the north slightly east.

The DC-9...

is coming in at...

320 knots...

...from the southwest.

This is the rate of closure.

- I was able to calculate the closing speed of these two planes

was roughly 1,000 feet per second.

(narrator): In the seconds before the crash,

Lieutenant Schiess likely had his head down,

checking the ground below on his radar.

Pilot Phillips is likely scanning instruments.

- At 15 seconds, the F-4 is 1/10 of an inch big in the window: tiny.

Ten seconds, 3/10 of an inch.

Still tiny, but maybe now he can see it.

Five seconds... the entire window's filled.

- The probability of these two aircraft, uh,

either one detecting and avoiding the other...

was slim and none.

(narrator): Investigators suspect the design of the DC-9 cockpit,

with its wide window dividers, may have made the visibility problem even worse.

- You can't see it here... nor here.

(narrator): The F-4 would've been hidden... - Or here.

I mean, it's completely obstructed.

(narrator): ...for close to 25 seconds.

- Just another hazy day. - Watch it!

(narrator): None of the pilots had enough time to see the oncoming plane.

But air-traffic controllers are supposed to keep planes a safe distance from each other.

So why did they fail to separate the planes?

- Airwest 706 red, turn left,

heading 0-4-0, until receiving Daggett.

(narrator): The controllers reveal to investigators

they couldn't see the F-4, either.

- Why did the F-4, the Marine aircraft,

not show up on the radar?

- What the hell happened?

(narrator): Investigators examine the radar equipment used at the control centre.

What they discover is alarming.

- It was nothing more than World War II technology,

and, uh, temperatures generated by this equipment

would cause the equipment to drift drastically.

(narrator): To better understand what the controllers could and could not see,

investigators test the technology by flying an F-4 along the flight path

on that fateful day.

Did the outdated radar pick up the F-4?

- Uh, was that something there?

The F-4's travelling almost 500 miles an hour.

(narrator): The F-4 does six runs.

But the controller can barely track the fast, stealthy fighter.

- It might've been a plane, or...

maybe not.

It could just be interference that was shown frequently on the radar.

A single blip means absolutely nothing.

We have to have a history of blips to see that it's actually traffic.

(narrator): Investigators conclude it would've been almost impossible

to detect the fighter jet as it streaked across the sky.

- He's all alone... and no one knows he's there.

(narrator): To make matters worse, in 1971,

military pilots were not routinely briefed on civilian air-traffic routes.

(Schiess): We should stay clear of traffic if we cut east of Los Angeles.

(narrator): Schiess tells investigators that they hoped

to avoid commercial air traffic by skirting the city.

Unintentionally, they flew into one of the airport's busiest lanes.

- Why did the F-4 crew not get a hold of an Air Traffic Control guy

to let them know where they were and what they were doing?

- The terminal area charts would show those departures,

but the military doesn't have those,

because they don't operate out of Los Angeles International Airport.

(narrator): Investigators uncover a dangerous flaw in the American aviation system:

The military and civilian control centres

don't communicate with each other.

- Bang.

(narrator): The pilots had no idea they were flying towards each other at the same altitude.

- Could've done anything different? No, absolutely not.

It was just something that happened.

We could not have changed it. Not us.

(narrator): The exhaustive investigation produces two separate reports,

one civilian and one military.

They cover every detail of the deadly accident:

How military and civilian authorities failed to communicate

they had planes flying in the same airspace.

- Was that something there?

(narrator): How controllers couldn't track the supersonic fighter jet.

And why the crew of a DC-9 with 44 passengers on board never saw them coming.

The reports lead to important changes in the rules governing aviation.

- Military pilots, as a result of this accident,

everybody had to be on radar control,

and that means being controlled by radar operators on the ground.

(narrator): Military pilots are now advised

of all restricted air-traffic zones near commercial airports.

And the restricted airspace at busy airports is expanded

to include more of the surrounding area.

Hughes Airwest was sold in 1980 and eventually folded into Northwest Airlines.

But the legacy of the company's deadliest accident endures.

- One of the things that came out of the Hughes Airwest F-4 mid-air collision

was a need to have better communication

between the aircraft that are flying and with Air Traffic Control.

Tragically, it wasn't one that was implemented perfectly in the future.

(narrator): Seven years later,

California residents face another disaster as two planes collide over San Diego.

(narrator): Pacific Southwest Airlines Flight 182

is on an early-morning run down the coast of California,

from Sacramento to San Diego.

- Approach, PSA 182, coming out of 9-5,

descending to 7,000.

Airport is in sight.

(narrator): First Officer Bob Fox is at the controls of the Boeing 727.

Captain Jim McFeron has been with the airline for 17 years.

(ATC): PSA 182, cleared visual approach, runway 2-7.

- Thank you. Cleared visual approach, 2-7.

(narrator): There are 128 passengers on board,

including 30 Pacific Southwest employees.

An approach controller at a facility north of the airport

monitors Flight 182's approach. (indistinct chatter)

- The Approach Control Facility is quite busy, and that's stressful,

because you're handling so many different airplanes in the same airspace.

(narrator): When the controller spots a Cessna flying ahead of the 727,

he makes sure they can see it.

- PSA 182, traffic's at 12:00, three miles out, 1,700.

- Ah. Got it.

- Traffic in sight.

- Okay, sir.

Maintain visual separation. Contact Lindbergh Tower,

133.3. Have a nice day. - Okay.

- Visual separation means the pilot has another aircraft in sight and acknowledges it.

- Got it. - Once the visual approach is accepted by the pilot,

uh, he's then responsible for maintaining separation from that traffic.

(narrator): With the plane now less than five miles from the runway,

a controller in the airport's tower takes over to guide the flight in for landing.

- PSA 182, cleared to land.

- 182 is cleared to land.

- Gear down.

(narrator): Suddenly, First Officer Bob Fox spots a distant plane.

- There's one underneath. I was looking at that inbound over there.

(all screaming)

- Tower, we're going down.

This is PSA. (alarm sounding) - Okay.

- We'll call the equipment for you. (alarm sounding)

- Get over here.

(narrator): The approach controller's radar reveals

that the 727 has collided with the Cessna.

(bleep)

- Brace yourself.

(sirens wailing)

(news): Hundreds of people watched in horror

as the two planes collided and crashed into a quiet San Diego residential neighborhood.

(narrator): 144 people are dead,

including seven on the ground.

Twenty-two homes are destroyed.

It's the biggest airline disaster in American history to date.

- The PSA accident in 1978 I think was the lynchpin,

when the United States government

and the aviation world in general figured out:

We have to do something about this. (sirens wailing)

(narrator): Two hours after the crash,

NTSB investigator Wally Funk arrives from Los Angeles.

(Funk): The accident scene was horrendous.

There was... so many bits and parts and pieces...

around, not only the aircraft, but the homes.

(narrator): Funk needs to confirm that the wreckage of a small plane

found six blocks away

is in fact what collided with the 727.

- We had paint transfers,

we had pieces and parts from the two different aircraft.

Yes, this was an absolute mid-air collision. There's no doubt about it.

(narrator): But how did these two planes end up on a fatal collision course?

- We had to visualize, from a very mangled mess of metal,

where the two came together.

(narrator): Fortunately, the 727's black boxes are recovered from the crash site,

and rushed back to Washington, DC, for analysis.

Meanwhile, senior NTSB investigator Philip Hogue joins the team.

He's eager to speak with the approach controller.

- Can you show us the two flight paths?

- So the 727 was flying east to do...

a turnaround and land on runway 27.

And the Cessna was flying northeast,

but it was miles ahead of the 727.

- They should've missed each other by over a mile.

(narrator): To verify the approach controller's account,

investigators review a transcript of his conversation that day.

It confirms that both pilots knew each other's positions.

- PSA 182, traffic's at 12:00,

three miles out, 1,700.

- Ah. Got it.

(narrator): But if both planes knew of each other, why did their aircraft collide?

Investigators question why the approach controller didn't warn the pilots

when they were dangerously close,

especially since his radar would've sounded a proximity alarm.

- Didn't you get any warning?

- We did. We ignored it.

Well, when the alert sounded, I mentioned it to my supervisor. (alarm sounding)

It's the alarm again. I talked to both planes.

PSA 182 has confirmed a visual sighting of the Cessna.

We're not expected to contact the pilots if they're flying by visual rules,

not to mention we get about 13 alarms a day, so...

(narrator): The approach controllers overlook the alert,

but they contact the Cessna and remind them of the nearby 727.

- Traffic in your vicinity. PSA jet has you in sight. He's descending for Lindbergh.

(narrator): But at that exact moment, the planes collide.

(alarm sounding) - Get over here.

(narrator): Investigators now interview the tower controller

to better understand why he also failed to warn both pilots.

They discover he relied on an even less sophisticated radar.

- The tower controller did not have the collision alert system at the time.

(narrator): When the controller saw the planes within a mile of each other,

he made contact, warning the 727.

- PSA 182, traffic 12:00, one mile, a Cessna.

- I think he's passing off to our right. - Yeah.

- If the pilot says, "He's passing off to our right,"

this implies that he's still maintaining visual separation.

It was his responsibility, and you would not worry about it.

(narrator): After talking to both controllers,

investigators still have no answer to the key question in the mid-air collision:

Who crashed into whom?

- Now, let's have the next acetate, please.

(narrator): But when they calculate the two planes' actual radar tracks,

the answer becomes clear.

- For some reason, the 727 has rear-ended the Cessna.

- The Cessna never passed off to the right.

He was always in front of PSA.

- I was looking at that inbound over there.

(narrator): The 91-ton aircraft flying at 160 knots

slammed into the much slower and lighter Cessna.

- The PSA crew, when they acknowledged they had the Cessna in sight,

at that moment became responsible for keeping the airplanes separate.

- Traffic in sight.

(narrator): So how did the veteran 727 crew

lose sight of a plane directly in front of them?

(narrator): In Washington,

NTSB investigators review the recovered cockpit voice recording of PSA Flight 182.

- Alright, hit it. (narrator): They hope the pilots' conversation

will explain how they lost sight of the Cessna.

- Are we clear of that Cessna? - Supposed to be.

(Captain): Oh, yeah. Before we turned downwind,

I saw him about 1:00. Probably behind us now.

- Stop it. (narrator): Thirty-five seconds before impact,

the PSA crew think they've passed the Cessna.

- It was right in front of them the whole time.

(narrator): Investigators wonder if something was preventing the pilots

from seeing the much smaller plane.

- The 727, when it's flying in level flight, is a slightly nose-up condition,

so that the pilots, as they look out,

they're looking over the nose of the airplane.

(Funk): Was the nose of the aircraft high and they didn't see the Cessna?

They may not have realized the Cessna was as close as it was.

(narrator): The team conducts a visibility study

to determine how long the PSA crew could see the Cessna through their windscreen.

After measuring and photographing each pilot's view,

they plot the Cessna's location on the photos in 10-second intervals.

What they find is surprising.

The PSA crew could see the Cessna

for a much longer period than they expected.

- 170 seconds of clear view.

(narrator): How did the pilots lose track of the Cessna

when it was in view for almost three minutes?

Searching for answers,

investigators go back further in time on the cockpit recording.

- PSA 182, traffic's at 12:00,

three miles out, 1,700.

- Ah. Got it.

- Traffic in sight.

(narrator): Eighty-five seconds before impact,

the 727's pilots spot the Cessna flying ahead of them.

- Okay, sir.

Maintain visual separation. Contact Lindbergh Tower,

133.3.

(narrator): The crew must now keep the Cessna in view

while performing other tasks in preparation for landing.

- Lindbergh, PSA 182 downwind.

- The wings need to be configured,

the landing gear must be lowered, systems have to be adjusted,

so it's a busy place.

(narrator): But at this critical moment,

no one is keeping an eye on the Cessna.

- Is that the one we're looking at? - Yeah, but I don't see him now.

- The Cessna should be right here in front of them. - The Cessna was visible...

just at about the windshield level of PSA,

and it's really incredible that somehow they lost sight of it.

- Okay. Can you show me how you normally adjust your seat, please?

(narrator): To better understand how the PSA crew lost sight of the Cessna,

investigators take another look at the cockpit visibility.

- Pilots come in all sizes and shapes.

They learn quickly to adjust the seats to the position that's comfortable.

- Some pilots want to sit lower so they can see their instruments better.

(narrator): When they recalculate the Cessna's location

on the windshield based on the crew's seat positions,

they make a shocking discovery.

Instead of three minutes,

the crew would only have seen the Cessna for 5 to 10 seconds.

Even if the crew had leaned forward to check for the plane,

investigators believe the smaller plane may have been camouflaged by the background.

- They become harder to see, and the terrain makes it even more so.

- Is that the one we're looking at?

- Yeah, but I don't see him now.

(narrator): The fate of Flight 182 now depends

on the captain clearly communicating this to the tower.

- I think he's passed off to our right.

(narrator): The controller would've been able to see

that the Cessna had not passed the 727 on his radar.

So why didn't he take action?

(Captain): Okay, we had him there a minute ago.

(narrator): Investigators compare two separate recordings of the conversation

between the captain and the controller.

- Okay, Chris, let's hear the cockpit first.

- I think he's passed off to our right.

- Passed. I thought I heard "passing" before. Double-check that, please.

- I think he's passed off to our right. - He's still saying "passed."

Let's compare it with the tower, because I think I heard "passing."

(narrator): Investigators make a startling discovery.

- He's passing off to our right.

- "Passing." I was right.

It does sound like "passing."

(narrator): Radio static caused the radio controller to hear the word "passing,"

not "passed."

- The air-traffic controller heard it as: "He's passing off to our right."

That indicated that they still had visual contact with it.

- You would believe that the pilot was being able to maintain the separation.

It was his responsibility, and you would not worry about it.

(narrator): In the spring of 1979,

investigators finally conclude who was at fault.

- The determination of the board's report

is very clear...

that the crew obviously...

did not see the aircraft, the Cessna,

in time to divert it away from a catastrophic accident.

(narrator): Recommendations in their report

focus on improving the air-traffic control system in San Diego.

PSA 182 also helped fuel the search for new technology.

Three years after the accident, a safety device called TCAS,

or Traffic Collision Avoidance System,

is developed and later installed in all passenger aircraft.

- All airliners are now equipped with fairly sophisticated Collision Avoidance Systems.

They have the ability, in the cockpit...

...to get instant feedback to avoid other airliners,

including instructions

as to what they should do to avoid that airliner.

- 279. Good day.

(narrator): Unfortunately, in some corners of the world,

aviation developments don't come soon enough.

In 1996, tragedy strikes again when two passenger jets collide over India.

(screaming)

(narrator): Indira Gandhi International Airport, New Delhi.

A gateway to India.

(horns honking)

Just past 6:00,

Saudi Arabian Airlines Flight 763 takes off into the sunset.

- Gear up.

- Gear up. - Clear on left.

(narrator): Captain Khalid Al-Shubaily powers the Boeing 747

away from the runway.

His co-pilot, Nazir Khan, handles all radio communication.

289 passengers on board are travelling to Dhahran, Saudi Arabia.

- 279. Good day.

(narrator): Shortly after takeoff,

Approach Controller VK Dutta guides the plane away from the airport.

- Saudi 763, approaching flight level 1-0-0.

- Roger. Climb flight level 1-4-0.

- Clear to climb 1-4-0, Saudi 763.

(narrator): After reaching 14,000 feet,

the crew request permission to continue their ascent.

- Roger. Maintain flight level 1-4-0. Stand by for higher.

(narrator): In order to coordinate incoming and outgoing traffic,

Dutta wants the Saudi flight to stop climbing.

- Saudi 763 will maintain 1-4-0.

(narrator): The controller is concerned about another plane,

a Kazakhstan Airlines Ilyushin-76 passenger jet,

which is coming in for landing at Indira Gandhi Airport.

He wants it to pass 1,000 feet above the Saudi flight before landing.

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

- Kazakh 1907... now reaching 150.

Forty-six miles from Delta Papa November.

- Roger. Maintain flight level 1-5-0.

Identify traffic 12:00 reciprocal, Saudi Boeing 747.

(narrator): Dutta warns the Kazakh flight of the nearby Saudi jet.

- How many miles?

- Traffic is at eight miles,

level 1-4-0.

(narrator): But seconds later...

...a massive explosion tears through the Saudi jet.

(alarm sounding) (shouting)

(narrator): Both the Saudi and Kazakh flights have vanished from the controller's radar.

- Saudi 763?

Kazakh 1907, report position.

So I watched the sweep again.

They were not there at all.

(narrator): A call from a nearby U.S. Air Force pilot confirms the worst.

- Two distinct fires on the ground.

- Two... two planes have gone down over Charkhi Dadri.

(narrator): In the hours following the horrific collision,

recovery teams find the wreckage of the Kazakh and Saudi aircrafts

4.5 miles apart.

The two planes were carrying 349 people.

There are no survivors.

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

- The death toll is terrible.

It's terrible if it's several hundred.

It's terrible if it's even one person.

But what has to be true, no matter how many people are killed in an event, is:

What are we gonna do about it?

(narrator): The next morning,

Captain KPS Nair is one of the first investigators on the scene.

- I was aghast. Horrified.

It is something...

...which I can't explain.

(narrator): Investigators have two separate crash sites to examine.

But they know one cause will explain both accidents.

Thankfully, the black boxes from both aircraft are found.

While investigators wait for the data to be recovered,

they focus on conversations between the two planes and the air-traffic controller.

- Hi. I'm VK Dutta. - Have a seat.

(narrator): They want to know everything that Dutta did on the night of the crash.

- Was traffic heavy?

- Evenings are always busy.

(narrator): Unlike most modern systems,

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

Instead, controllers write a plane's last-reported position on a strip of paper.

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

- Kazakh 1907...

now reaching 1-5-0.

(narrator): Dutta was supposed to ensure that the two planes were 1,000 feet apart

as they approached each other.

- Roger. Maintain flight level 1-4-0. Standby for higher.

(narrator): To confirm Dutta's instructions,

investigators review the Air Traffic Control transcripts.

They learn that Dutta gave the two planes the proper directions.

- Roger. Maintain flight level 1-4-0. Standby for higher.

(narrator): Since his radar system doesn't display altitude,

there was no way for him to tell if the planes followed his orders.

- Mostly there... and there. As close as you can get it.

(narrator): One of the planes must have drifted from their assigned altitude,

but which crew is responsible for the fatal collision?

(narrator): Investigators in India catch a break

when engine pieces of the Saudi aircraft are found

near the beginning of the debris field.

It reveals that they were some of the first pieces

to come off the plane after the collision.

- The significant point of contact

was between the tail end of...

...the IL-76...

and the wing portion of...

...the Boeing 747 of Saudi Air.

(narrator): The tail of the Kazakh plane appears to have pierced

through the left wing of the Saudi jet.

Surprisingly, the Kazakh flight wasn't above the Saudi jet when they collided,

as air-traffic controllers thought.

(alarm sounding)

- Between two aircraft,

the requirements specify a vertical minimum separation

of 1,000 feet.

(narrator): Investigators wonder which plane was at the wrong altitude.

Unfortunately, the recovered cockpit instruments provide little help

in verifying the aircrafts' positions at impact.

- I can't find anything. Too much damage.

- I agree. Look at this.

(narrator): Having learned all they can from the crash site,

the fate of the investigation now lies

in what details are stored in the flight-data recorders.

Three months later,

data from both the Kazakh and Saudi black boxes is successfully downloaded.

In order to avoid any suggestion of bias,

the boxes are analyzed in England by the experts

at the Air Accidents Investigation Branch.

- 279. Good day.

(narrator): They concentrate on the data from the Saudi Flight 763 first.

- Saudi 763 approaching 1-4-0 for higher.

- Roger. Maintain flight level 1-4-0. Standby for higher.

- Saudi 763 will maintain 1-4-0.

(narrator): Both the CVR and the flight-data recorder reveal that the Saudi pilots

received clear instructions from the controller and followed them meticulously.

- It had levelled at its assigned altitude of, um,

14,000 feet, uh, and continued to fly level.

(narrator): But when investigators examine the Kazakh's flight data,

they discover that it descended

to just over 1,000 feet below assigned altitude,

putting it within 10 feet of the Saudi flight.

To understand why the Kazakh plane was below its assigned altitude,

investigators turn to the cockpit voice recorder.

- Kazakh 1907, report level passing.

- Passing 2-4-0, Kazakh 1907.

(narrator): Because the Ilyushin is a modified military plane,

it has another unusual feature:

a position for a radio operator in the cockpit.

Egor Repp handles all communications for the Kazakh flight.

As they near the airport,

Repp gets in touch with Approach Controller Dutta.

- I told, uh, Kazakh to descend and maintain flight level 1-5-0.

That is 15,000 feet.

(Repp): Kazakh 1907 now reached 1-5-0.

(narrator): It's one minute before the impact,

and the Kazakh plane is in position,

1,000 feet higher than the Saudi plane.

But investigators know that instead of levelling off,

the plane continued to descend.

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

- Identified traffic 12:00 reciprocal,

Saudi Boeing 747 and... 10 miles.

Likely to cross in another five miles. Report if in sight.

(narrator): He tells them to watch out for the Saudi flight,

but the Kazakh jet just keeps flying lower.

- Ahead? - Ahead.

(narrator): Suddenly, the radio operator recognizes the plane is flying too low.

- Keep the 150! Do not descend! - Accelerate, Sanya!

(narrator): But his warning comes too late.

- Get to the 150 because at the 140... that one!

(narrator): Investigators are stunned.

Why weren't the pilots monitoring their altitude?

- Report eight miles.

(narrator): They go back to earlier in the recording.

While Repp communicates with the ground,

neither the pilot nor co-pilot confirm the altitude instructions.

- Switch on. Engine...

(narrator): The pilots are busy discussing arrival procedures.

Repp appears to be the only one focused on their altitude.

- Hold the level! - What level were we given?

(narrator): The final report points a finger squarely at the crew of the Kazakh plane.

The Kazakh pilots' failure to maintain altitude

led to the deaths of 349 people.

Investigators are also critical of the outdated radar

that was being used in New Delhi.

Today, new radar systems allow controllers across the country to see

an airplane's flight number, altitude and heading,

preventing mid-air collisions from ever happening again.

- It's not a matter of who did something wrong,

it's a matter of how can we change the way we do business

to make sure this can't happen again -

not that it is unlikely, but that it can't.

Subtitling: difuze