Where is Flight MH370? Horizon

This is the inside story of a disaster

that seems unimaginable in our time.

How can an airliner full of people vanish without a trace?

26 nations joined the hunt for Malaysia Airlines Flight 370.

It was almost a relief to narrow it down to a hemisphere.

It's a daunting task.

Family members should prepare themselves for the worst.

When MH370 disappeared,

the families of those on board were plunged into a nightmare...

..and the world needed answers.

SHE WAILS

This film is a forensic examination of events.

It follows the scientists and engineers

who unearthed a trail of clues where there were none.

I was delighted that the calculation had worked

but, of course, you feel the...

the depth of this, the severity of it.

It reveals the location where their data suggests the plane went down -

a location yet to be searched...

..and pieces together what might have happened on board.

..and that flammability hazard exists...

Finding MH370 is fast becoming

the most challenging search in human history.

Kuala Lumpur International Airport -

the gateway to 43 countries across Asia and beyond

for tourists, business travellers, people going home.

On Friday 7th March, 2014,

the pilots of Malaysia Airlines Flight 370 to Beijing

were filmed crossing from landside to airside.

Whatever these men did in the hours that followed,

or whatever happened to them,

lies at the heart of this mystery.

The relationship between pilots and air traffic controllers

is crucial to flying safely.

It's a very important relationship.

Any time you try and get an aircraft from A to B,

it's a matter of teamwork.

And air traffic control are a vital member of that team.

There's a real bond between controllers and pilots.

They understand the job that each other is doing

and it's a really, really important part

of the safety culture of aviation.

So how did MH370 slip the surveillance technologies

the air traffic controllers rely on?

These are the actual recordings of what happened this night.

Just as the flight had so many times before, at 12.41am,

the Malaysia Airlines Boeing 777 lifted off into the night,

bound for Beijing.

On board were 227 passengers and 12 crew.

It was a very normal flight.

Everything was calm, ordered.

It's exactly what you would have been expecting on the day.

There was no drama.

There was no reason to think anything unusual is happening.

Stephen Landells is an experienced 777 pilot

with a comprehensive knowledge

of the state-of-the-art systems on board.

'This is a Boeing 737-800 series.

'This cockpit is very similar to the 777 cockpit.'

Positive climb. Gear up.

Like all modern passenger planes,

the Boeing 777 is a technological marvel.

In service for 19 years, its safety record is excellent.

Its systems are so advanced, it can virtually fly itself.

A lot of the systems are automated.

But it is just a computer.

You use the automatics a lot,

but have you to control them

and make sure they're doing the right thing.

And that's what the pilots do.

The pilots can communicate from anywhere on the globe

using very high frequency and high frequency radio,

a text messaging service called ACARS

and a satellite link for voice calls and sending data.

I've been sitting over Greenland, listening to the HF radio,

and I've heard someone having a conversation with Mumbai.

When it comes to navigating,

the aircraft follows a route that's already been programmed in.

You'll load your route into the navigational computer.

And you can actually load that

all the way from your start point to the end point.

Less than a minute after take-off,

the crew of MH370 were told to modify their route to Beijing.

The crew were told to turn right on a more direct route to Beijing,

via a waypoint called Igari.

Waypoints are code names for coordinates on the map

that air traffic controllers and pilots use to navigate.

I'm going to add Igari.

I-G-A-R-I.

'The airways, the motorways in the sky, are...

'They're set routes.

'And they are defined by waypoints.'

Near Igari, responsibility for MH370

will pass from air traffic controllers in Malaysia

to their counterparts in Vietnam.

26 minutes into the flight,

the last ACARS message sent automatically from the aircraft

showed normal routing all the way to Beijing.

As MH370 headed out over the South China Sea,

air traffic controllers were tracking it

using a technology developed in the 1930s -

radar.

It was developed mainly by the British for the Second World War

as a device for protecting the UK shores.

The technology has changed a lot,

but the concept has remained very much the same.

Well, this is a primary surveillance radar,

very similar to the one that's in Malaysia.

And you can see the bottom half of that is the main radar itself.

Air traffic controllers used two main types of radar.

Primary radar detects where aircraft are

by sending out pulses of electromagnetic radiation

and collecting their reflections

when they bounce off objects in the sky.

Its range varies, but modern systems can reach around 100 miles.

The range is limited by the power that this radar can put out.

The electromagnetic pulse has got to travel all the way out there,

bounce off the aircraft and travel all the way back.

So therefore the power, when it gets back,

is going to be very low indeed.

The other main problem is that the radar is not terribly accurate.

And it certainly can't identify the target either.

So all it can say is, "There's an aircraft there,

"at this range, in that position."

To extend their surveillance of the skies,

air traffic controllers rely on a more sophisticated type of radar

called secondary radar.

The top rectangular part is the secondary radar.

What that will do is it's an interrogator.

Secondary radar has a far longer range than primary radar

because it doesn't rely on detecting reflections.

Instead, it sends a signal out to the aircraft,

which interrogates a piece of equipment on board

called a transponder.

And it's the transponder that sends a new signal back,

identifying the aircraft, its height and course.

Controllers controlling the flights on long range,

they will nearly always rely totally on the secondary radar system

because the primary radars are just not providing the information.

38 minutes into the flight, air traffic controllers in Malaysia

could clearly see MH370 on their secondary radar.

As the aircraft neared the limit of Malaysian airspace,

the crew were told to contact air traffic controllers in Vietnam.

These are the last words from the cockpit:

At 21 minutes and four seconds past one,

Malaysian air traffic controllers saw the plane passing over

waypoint Igari on their secondary radar.

Nine seconds later...

..the radar screens went black.

The aircraft's transponder,

crucial to its visibility on secondary radar,

had stopped working.

The plane had vanished.

And the mystery that's touched millions of lives began.

What happened next is one of the key unanswered questions.

The crew made no radio contact with air traffic controllers

in Vietnam and the plane never re-appeared on secondary radar.

17 minutes elapsed before the Vietnamese controllers

contacted Malaysia.

What does seem very odd is that,

after the aeroplane was told to contact Ho Chi Minh

air traffic control, it was a full 17 minutes between then and

Ho Chi Minh phoning back to Malaysia to say, "Where is Malaysia 370?

"He's not speaking to me."

17 minutes is an incredible length of time.

Within a couple of minutes you would normally be looking to see

what's happened here.

Now the Vietnamese and Malaysian air traffic controllers began

looking for the aircraft.

Professor Stupples can reveal why they were struggling to find it.

At this point, here, that's the point

where it disappeared from the secondary radars.

What I've done here is put an overlay of the secondary surveillance radars

and can you see here, there's almost a complete coverage

and so therefore, so long as the transponder is working correctly,

the whole of this route is covered by the secondary radar.

But once MH370 was lost from secondary radar,

the air traffic controllers had no other surveillance to fall back on.

After removing the overlay for the secondary surveillance radar,

we're now left with the coverage of the primary surveillance radar.

Only about 50% to 60% of the journey so far is covered

by the primary surveillance radar.

The point at issue also is, at this point, where the transponder

stopped working, you can see from this diagram,

it is completely outside the range of any of

the primary surveillance radars.

Essentially, this aircraft has now become invisible.

MH370 was lost in a primary radar blind spot.

Such blind spots are common,

because it's estimated only 10% of the globe is covered by radar.

Aircraft often fly across oceans and remote regions beyond its reach.

In one of the busiest radar blind spots, Hudson Bay in Canada,

air traffic controllers are solving the problem with a revolutionary,

new kind of surveillance.

Between 100 and 300 aircraft are flying over Hudson Bay every day.

Most of them are aircraft coming from Europe,

going to the western coast of the United States.

The rest of them are coming from North America,

going to Asia over the North Pole.

That's quite a busy airspace.

There is no radar coverage of Hudson Bay.

When air traffic controllers had no other means to track planes,

they had to rely on pilots to stay in touch.

The orange one is a flight that is not at the moment captured by radar.

So this one at the moment we are not 100% sure he is there.

This plane's position is an approximation,

derived from its flight plan and regular updates from the aircraft.

When you have no radar, in non-radar environment, when you have no way

to see planes, actually. You need to rely on estimates from the pilots.

Now, a new technology called

Automatic Dependant Surveillance Broadcast or ADS-B is taking

the guesswork out of tracking flights in radar blind spots.

Aircraft fitted with ADS-B take their position from a GPS satellite

and broadcast it automatically to a ground station.

Unlike radar stations, these ADS-B receivers are robust enough to

be sited in the remote regions where blind spots exist.

We have currently one aircraft under ADS-B coverage at the moment,

this is a United flight from Chicago going to Beijing.

The aircraft in white is using ADS-B to broadcast its exact GPS location

automatically once a second.

We see the aircraft, we know its there.

We know exactly where the aircraft is at all times.

In the future, ADS-B ground stations will be supplemented by satellites.

So planes will be tracked over remote land regions

or the middle of oceans.

Surveillance blind spots will be a thing of the past.

MH370 was broadcasting its position by ADS-B.

And this website was tracking it.

But the system isn't currently used in Malaysia and Vietnam.

And even if it was, it wouldn't have helped the air traffic controllers -

because the technology still relies on the transponder.

When that stopped working, this new tracking system was useless.

The disappearance of MH370 triggered intense speculation

about the fate of the 239 people on board.

The families of the missing needed answers.

Tony Cable is a veteran air crash investigator

who worked on the Lockerbie bombing and the Concorde disaster.

With any investigation, you have to go with the evidence you've got.

And in the case of MH370, it's pretty slim.

It's useful to think about the possible scenarios

based on the available evidence.

So, what could explain the aircraft's sudden disappearance

from secondary radar and the radio silence?

Any aircraft that suddenly disappears,

inevitably, you start talking about the possibilities.

And I guess they range from structural failure, terrorist action,

some other massive technical fault that could cause a loss of control.

A key piece of evidence for investigators

is what MH370 was carrying on board.

This is the MH370 cargo manifest here,

which lists out the various packages and particularly,

anything that is categorised as dangerous cargo.

There is quite an interesting item here of

lithium ion batteries.

"Must be handled with care."

And a "flammability hazard exists if the package is damaged."

Lithium batteries can be found in laptops and mobile phones.

All batteries are flammable, but lithium is one of the most volatile.

MH370 was carrying 200kg of lithium batteries.

There are tight regulations around how they are transported

because they are thought to have caused fires on aircraft before.

There was a Boeing 747 aircraft crash near Dubai in 2010.

The investigation concluded that there was strong evidence that

lithium ion batteries had started the fire.

A fire in the cargo hold could affect the rest of the aircraft.

You can get structural damage, damage to systems, a lot of smoke,

severe visibility problems and also toxic gases.

If there is a serious fire, case history suggests,

unless a plane can land quickly, it is likely to crash.

If there had been a fire on this aircraft

then the tendency would be to look for the aircraft, the wreckage,

at the point where you last had contact with it.

And projecting the flight path a little further forward.

Four hours after MH370 disappeared, a search was triggered

in the China Sea, close to where the aircraft

was last seen on secondary radar - to no avail.

We have not found any wreckage, no wreckage whatsoever.

Now the mystery of what happened to MH370 deepened.

6,500 miles away in London, one scientist was starting to think

the aircraft could not have crashed in the South China Sea.

'BBC news at 11 o'clock...'

I heard the news about the loss of the aircraft, I think

it was on the 11 o'clock BBC News.

'..the search for a missing airliner with almost 240 people on board...'

At that point I thought,

it's probably got Inmarsat equipment on.

'..no distress signal...'

And that maybe we had some data

that was of interest to the investigators.

Alan Schuster-Bruce is a scientist with Inmarsat who provided

satellite communications for MH370.

By looking at the log of the plane's communications,

Alan could see new information about the flight.

What one sees in the data just before take-off,

so when the aircraft is on the stand at Kuala Lumpur,

there's a flurry of activity, the aircraft takes off, there is

a flurry of activity and then everything stops.

The last communication from MH370, like all its satellite traffic,

was logged at a ground station in Perth, Australia.

After 60 minutes of inactivity, the station sends a signal

to the aircraft which says, are you still there?

Then the aircraft just replies yes.

These are what we call the handshakes or pings.

Now Alan made a baffling discovery.

The data log showed there were seven of these electronic handshakes

between the ground station and MH370, each about one hour apart.

They all occurred after the plane had vanished.

Our data indicated that the aircraft had flown on for many, many hours

beyond the last known contact with the aircraft, which clearly

meant the aircraft was unlikely to be in the South China Sea.

The story the data was revealing was

so bizarre it seemed it couldn't be true.

One of the concerns we had was in fact this could be just

one big hoax someone had played on Inmarsat, that the aircraft

went down and someone at the same time pretended to be that aircraft.

But the data checked out.

The aircraft had flown on for nearly seven more hours.

And it could be thousands of miles away from the South China Sea.

At that point it was quite clear something strange had happened

because the plane had flown on for all those many hours.

Where had the aircraft flown for all that time?

MH370 was connected to a communications satellite

called 3F1.

This is the footprint of its beam.

There is no direct way of identifying where MH370 was

within the beam when the seven electronic handshakes occurred,

but deep in the architecture of the system,

a feature had been added that might offer a clue.

'French investigators say they have recovered 400 pieces of debris

'from Air France Flight 447.

'They say the wreckage comes from all areas of the plane.'

In 2009, Alan helped with the investigation into the disappearance

of Air France 447.

They had a couple of brainstorming sessions at Inmarsat.

One of the things we did work out is that we could take some

additional measurements in the stations and that would let us

get a determination of the distance from the satellite to the aircraft

and therefore that would give a one-dimensional position fix.

So, after the Air France disaster, Alan decided to keep timing data

in the electronic handshakes that might help track an aircraft.

I was thinking we might need it one day.

It might be useful, might not be useful, but I had no idea

it would essentially be the only evidence in town.

To try to find MH370, Alan now began analysing the type of data

stored in electronic handshakes.

He knew the position of the 3F1 satellite above the Indian Ocean.

Using the timing data in each handshake,

he could work out how long it took for the signal

to travel between the satellite and the aircraft.

From that he could work out the distance between the satellite

and the aircraft when each handshake occurred.

Plotting those distances created

seven circles on the surface of the Earth around the satellite

which the plane must have crossed as it flew.

The last circle came at 8.19 in the morning.

The aircraft did not reply to the satellite 57 minutes later.

We obviously knew that that was most likely indicative

of the time the aircraft was lost.

Later that week,

Inmarsat sent their analysis to the Malaysia authorities.

The search carried on in the South China Sea.

Clearly, they've got all sorts of information coming in.

They were also probably sent information that the plane was

in the Pacific by other people,

so I'm sure it's very difficult for them.

Alan and the team began to think their methods might yield

the ultimate clue.

We suddenly realised, if you knew the initial position of the aircraft,

together with the likely speed of the aeroplane, there was

a good chance that maybe one could get the track of the aircraft.

A telephone call was arranged with Malaysia Airlines to get

the information they needed.

They did provide that information.

But certainly there was a lot of reluctance

because the last known position was based on radar data

and there was a lot of concern about the sensitivity of the radar data.

Using this new information,

Inmarsat could rule out areas of the final circle

the aircraft could never have reached with the fuel it had.

MH370 must have ended its flight

crossing one of these two arcs.

We had two possible scenarios.

It had either turned left and gone south or turned right and gone north.

We didn't know which one.

After several days of no traction for the new evidence,

suddenly the story broke from an unlikely source.

Based on new information, an additional search area may be opened in the Indian Ocean.

It seemed the Americans hoped to push the Malaysians to act.

It was a bit strange that it was the White House announcing it

as opposed to the Malaysian government which is what one

would have expected, that it would come from the Malaysian government.

I think there was a certain amount of relief that finally the secret

that we were holding was now out in the public domain.

For those trying to find the aircraft,

the search had been narrowed, but it was still vast.

More than two million square miles

stretching from Kazakhstan in the north to the southern Indian Ocean.

The mystery of MH370 had taken a staggering twist.

The sensitive information Inmarsat had used to help work out the arcs

turned out to be top-secret military radar data that

showed MH370 made an inexplicable turn west, off its course

to Beijing, after it disappeared.

It then flew across the Malaysian Peninsular...

..before making another turn, this time north-west.

It was last recorded near the Andaman Islands at 2.22am.

This new radar data raised a sinister possibility.

These movements are consistent

with deliberate action by someone on the plane.

From the available evidence,

hijacking is clearly one plausible possibility.

The fact that MH370 had deviated from its course after it had

become invisible to secondary radar suggested the aircraft's

transponder could have been turned off deliberately.

It's actually such an important part of your navigational equipment

on modern aircraft that you wouldn't want to turn it off.

But those with a criminal intent might.

It's fairly common that the hijackers know enough

about aircraft that they will require the transponder

either to be switched off or left on its original code.

Investigators began a trawl for suspects.

The passenger list was a crucial starting point.

Police quickly focused on two Iranians who were

travelling on forged passports, but they were ruled out.

The pilots themselves came under intense scrutiny,

but no evidence of a terrorist link has been found so far.

That, of course, does not demonstrate that there was not

a hijacking by crew or passengers - that is a possibility.

It's just that the things against hijacking in this case is

that nobody has claimed responsibility, which is

pretty unusual, I think, for a terrorist act.

More than a week after MH370 vanished, no sign

of the aircraft had been found, despite the efforts of 26 countries.

That gave many of the families of those on board

hope that they would be found alive.

At Inmarsat in London,

a new attempt was being made to help target the search.

They knew the plane had ended up crossing one of two arcs.

Chris Ashton was trying to work out

whether the aircraft had gone north or south.

Of course, the big question is which route was taken?

There was one more avenue to explore in the electronic handshakes,

a second piece of data -

the frequency at which the signal from the aircraft

arrived at the ground station.

We had a northern

and a southern route that were

so very different, so very far apart,

the frequency information at that stage

was something that was probably going to be good enough

to discriminate between those two routes.

The satellite MH370 was in contact with

doesn't stay still in the sky.

The satellite moves north and south over the equator...

..and because the plane is also moving, there is

a variation in the frequency of the signals between them.

Since that variation, known as the Doppler effect,

is predictable, it can be used to work out the direction

the plane is travelling in.

The calculations were incredibly complex

and there was no guarantee of success.

We'd attempted this calculation two or three times and abandoned it,

as we were working at it for a long time and not getting a good match

between the measured data and the predicted data.

But then came the break.

We'd been working on the Doppler analysis all day long,

the end of a week of investigating and collecting data.

Quite late on the Friday night, about eight o'clock in the evening,

suddenly the graphs matched, the data worked, the calculation was solved.

Chris had eliminated a hemisphere, but he didn't yet know which.

That was quite a nice feeling, that we'd got the calculation to work,

and then I checked to see which of the flight paths it was

and we then identified it was, in fact, the southern route.

That meant flight MH370 must have flown south.

Then, there's, of course, the realisation that this is the...

This is not good news for the people on the plane.

This isn't the aircraft is hijacked and is flying up to Kazakhstan,

landing safely and everybody's in a hangar, this was the specific one

where it flies south into the middle of the Indian Ocean.

You feel the depth of this, the severity of it.

It means very little chance for the people on the aircraft.

There was no land there. There's nothing at the end of the route

and so the elation didn't last for very long

when you realised what this meant.

Chris's evidence was sent to the Malaysian authorities.

According to this new data,

Flight MH370

ended in the southern Indian Ocean.

The fact that we'd done a calculation that indicated

a lot of people had died

and was being used by the Malaysian government to inform

the next of kin that they believed that their relatives had died

was quite, um, humbling, let's say.

Science had broken open the mystery of what had happened to MH370,

generating evidence where none existed.

From Kuala Lumpur, the plane had been tracked by secondary radar

until it disappeared here.

Then it had been tracked by military primary radar to here.

Then, in the absence of other surveillance,

Inmarsat's analysis had shown the plane must have turned south

crossing each arc as it flew on for six hours.

From now on, locating the crash site becomes a matter of prediction,

probability and possibility.

What might explain the drastic course change south

and the long flight over the ocean?

The veteran crash investigator Tony Cable believes

an earlier air disaster might help explain the final southward turn.

In 2005, the crew of a Helios Airline's Boeing 737 failed to

make radio contact with the ground, just like MH370.

The aircraft was intercepted by a couple of F-16s

and they flew alongside and saw the captain's seat empty, the co-pilot

slumped over the controls and oxygen masks hanging down in the cabin.

There was a fault with the aircraft's pressurisation system,

but the crew hadn't realised.

There is a quantity called "time of useful consciousness"

after a depressurisation, and at 35,000 feet,

the average is something like 30 to 60 seconds.

The pilots passed out from lack of oxygen,

but the aircraft kept flying on autopilot.

What might explain what happened to MH370

is what the fighter planes saw next.

They saw one of the cabin attendants enter the flight deck

and sit in the captain's seat.

Now, he presumably had a cabin attendant oxygen set

which will probably last quite a long time

and was presumably attempting to control the aircraft.

If the pilots of MH370 had become incapacitated,

might somebody else have tried to fly the aircraft?

If the plane was on autopilot, making a controlled turn

or a series of turns, is something anyone could have done.

We can command the autopilot directly ourselves

through the mode control panel up here.

So we can do that quite easily by selecting a new heading

through this knob here.

So now the aircraft is banking to the left and we're gradually... You see

outside, we are banking to the left and turn onto that heading.

So could somebody other than one of the pilots

have turned the aircraft off its course?

The kind of thing that happened on the Helios 737 might be

a possibility for this aircraft.

And if there was somebody conscious for longer than the others,

possibly could explain the track corrections

before they also were incapacitated.

Even if everybody on board was unconscious, the autopilot

could have kept the aircraft flying until it ran out of fuel.

But how and why MH370 came to be so far off course heading south

is still to be established for certain.

There are several possible scenarios for this accident.

I don't have any feeling about which is the more likely.

As an investigator, you can only go on the evidence that is there.

For those touched by this disaster, the best hope of finding answers

lies somewhere at the bottom of the Indian Ocean.

Piecing together what really happened depends on finding

one piece of equipment the aircraft was carrying.

This is what they call a black box,

but I've never seen one that's actually black.

This makes it more visible in wreckage

and indeed it's got reflective tape on it,

so that if it's at night, a torch will light it up

or if it's under the water, a diver's light will make it more visible.

The black box is a data recorder which continually stores

a record of how the aircraft is performing.

From that information, you can recreate in detail

what happened to the flight.

You are looking at an animation of the data taken from a recorder.

You've got the actual way the aircraft is moving through space,

and on the left is a representation of the cockpit instruments -

what the pilot would be seeing.

The data in the black box is crucial to finding out what happened...

..if you can find it.

If it's in water, the underwater locator beacon,

which emits a ping every second or so can be homed in on.

But the batteries that power the locator beacon

only last for about 30 days.

In the southern Indian Ocean,

in an area dubbed as close to nowhere as it's possible to be,

the race to find the black box was on.

Aircraft and ships from eight nations

were scouring 620,000 square miles of ocean.

Could anything be done to help target the search?

Back in London, Inmarsat had been scrutinising probable flight paths

MH370 could have taken.

And what they had discovered was astonishing.

By modelling a flight with a constant speed

and a constant heading consistent with

the plane being flown by autopilot,

they had found one flight path that lined up with all their data.

We can identify a path that matches exactly

with all those frequency measurements

and with the timing measurements and lands on the final arc at a particular location,

which then gives us a kind of hotspot area on the final arc

where we believe the most likely area is.

But as the battery life of the black box ran down,

events in the Indian Ocean were unfolding fast.

At the forefront of the search was the Ocean Shield,

a 6,500 tonne Australian Navy support vessel,

carrying an elite team of deep-ocean salvage experts.

We left port on approximately day 23 of the pinger,

the battery life on the pinger -

this countdown clock, so to speak.

30 was the magic number.

Suddenly, a new lead emerged, and Ocean Shield responded.

A British vessel seemed to have found a clue

to the location of the black box.

HMS Echo believed they had detected a 37.5 kilohertz pulse in the water.

So we headed to that area and came up with a search plan.

Now, Ocean Shield joined the hunt for signals from the black box,

working its way south-east, away from HMS Echo.

To try to detect the elusive underwater pings,

the team used a device they call the towed pinger locator.

The towed pinger locator looks much like a bat wing

and designed that way on purpose

so when it's pulled from its tow point here,

it's flying pretty smoothly through the water.

The real meat of this is underneath it.

What you see here is the electronics

that is housed in a 6,000 metre pressure vessel.

You can get down 6,000 metres,

that's covering about 80% of the world's ocean depths.

And what you see on the back here is the omnidirectional hydrophone.

It's a microphone, a big microphone, hemispherical.

It can see 180 degrees to each side and down.

We're fishing for sound in this case. Patience is key throughout.

Even if you can detect the sound of a black box pinger,

locating its origin is a huge challenge,

especially in an ocean four and a half kilometres deep.

The pinger locator is lowered until it is a kilometre above the sea bed

where it is towed as it listens with its hydrophone.

PINGING

At that depth, it avoids plankton

and changing water temperatures above,

which can affect the way the sound travels.

And what's more, the sea bed itself can obscure the origin of any sound.

Wreckage can deflect the sound path, the topography of the bottom.

We are seeing a lot of steep hills, valleys, ridges,

the sound will find a path of least resistance.

As Ocean Shield worked its way

along one of MH370's possible flight paths, there was bad news.

During that survey leg, HMS Echo was able to deduce

that the 37.5 kilohertz pings they were hearing were not valid.

The trail had gone cold.

We're running our line this way along the projected flight path.

At that point, we regrouped

and went back to our best known last position,

being the eight minute arc.

And our intention was to work our way south.

South was determined to have a higher probability,

a more probable flightpath.

North-west side to the south-east.

The search area referred to as the eight-minute arc

is based on the final handshake

between MH370 and the Inmarsat satellite.

It came eight minutes after the previous handshake

and contained new information.

The data revealed the system on the plane was actually booting up,

just as it would have done at the start of its flight.

Why it would do this may hold a clue to the plane's final resting place.

It's theorised to have been

that the plane was going down, low on fuel.

It did a roll.

When the plane rolled, the fuel then...

The engine was able to restart and part of the start-up sequence

was initialised in this handshake with the Inmarsat.

And it was an incomplete handshake.

So we're working on the premise that perhaps this last handshake

is where the plane was in its final stages.

We were towing for 24 hours a day for days on end,

for as long as the battery is going to last.

The hunt for the black box

was not so much like trying to find a needle in a haystack.

Chris and his team hadn't even found the haystack.

But what if they didn't have to search at all?

In Ottawa in Canada there's a new technology

that is bringing the black box into the 21st century.

To see it, you need to visit a part of the plane

passengers never normally go to.

OK, so this is the E bay of the 767,

and this is really the heart of the electronics for the aircraft.

The data is fed from all the various sensors and equipment

to the flight data recorder.

What's unique about what we've done

is we've added this unit here, which is the AFIRS.

The Automated Flight Information Reporting System

examines the data generated by the aircraft

as it is being sent to the black box.

The flight data recorder is a passive device.

It takes the information and stores it,

it doesn't actually look at it.

This is actually analysing the data as it's going into the box.

So it's actually reading the files. It's looking at them

and seeing, "What's happening with this aeroplane?

"Is everything working correctly?"

And if it's not, it tells people, it lets them know.

Aircraft fitted with this technology

automatically stream black-box data to the ground

if anything unusual happens.

'Flight CFFNE flight stream activated.'

Rather than having to recover the physical black box,

now its data can build a picture of what happened

before a flight even ends.

It would seem to make a lot of sense

to seriously consider real-time transmission of data.

And in a case like MH370

it may make it redundant to,

from the accident investigation point of view,

to actually go and find the wreckage,

which is clearly going to be very, very difficult,

very expensive, very time-consuming.

Finding MH370 is a huge challenge.

But advances in technology could mean

that no aeroplane is ever lost again.

In Montreal, aviation is being brought into the digital age.

So here's the Piaggio Avanti P180 flight research aircraft

we'll be flying today.

It is the world's fastest civilian turboprop.

Many of the technologies we are testing

are surveillance technologies,

because surveillance is the next wave of evolution

of flight operations.

John has been testing new ways

of using Automatic Dependant Surveillance Broadcast -

the technology that is revolutionising air-traffic control.

They're up and indicating.

John's aircraft doesn't just transmit ADS-B signals -

crucially, it receives them too.

With ADS-B in, I can see the traffic, I can see the direction they're moving in,

and we can see if they're a threat,

and we can see if they're climbing and descending as well.

These two are potentially a threat. This one is 1,900 feet above us.

With ADS-B in, we could actually, with that data,

even recreate what that aeroplane is seeing from its cockpit.

This live view of the flight John is making

could be viewed by anyone, anywhere in the world,

at any time, via ADS-B and the internet.

When you go to an autonomous node, which is what this aircraft becomes,

you open up enormous possibilities.

You know where everybody is for the first time,

no matter where they are in the world.

Perhaps what's most surprising about this technology

is that it isn't already a fact of life in the skies.

You no longer have helpless recipients

of radar energy flying around.

You have contributors to a big information picture

that everyone can use.

Losing aircraft would become a thing of the past.

Using advanced aviation technologies

like live black-box streaming,

and the total surveillance offered by ADS-B,

could mean that losing an aircraft like MH370

should never be possible again.

But the promise of the future

is a world away from the challenges of the present.

Back in the Indian Ocean,

on the day before the battery on the black-box pinger

was predicted to die,

Chris and his team thought they heard something.

The towfish is at about 3,800 metres of depth

and we're doing about two and a half knots.

It started growing louder and louder.

And we had a detection.

Big moment.

Are you sure that's what we heard?

Are you sure that's what we're... Is it not us, you know?

It was a elation and panic and self-doubt.

Wonderment, to "let's get busy and find this thing,

"let's track it down."

They tracked the ping for two hours and 20 minutes before losing it.

They detected another, 11 kilometres away.

And then two more two days later.

My thoughts were they were probably going to traverse down the final arc

to go over our hotspot area

but, of course, they found their ping detection very early on.

Ocean Shield could not ignore the detections it had heard.

The search entered a new phase.

The decision was made that

we had had enough detections

and it was time to shift over to the AUV ops.

The Autonomous Underwater Vehicle

began searching the ocean floor for wreckage.

It was a monumental task.

The unexplained disappearance of MH370

has left the families of those on board

needing the kind of certainty

that only finding the wreckage will bring.

Ocean Shield spent two months

searching 850 square kilometres of sea bed,

inspired by the pings they heard.

Ocean Shield had chased down leads as they emerged.

But they turned up nothing.

It was by no means an unrealistic location,

but it was further to the north-east

than our area of highest probability.

Perhaps the best place to look for MH370

was always further to the south.

Inmarsat's hotspot on the final arc

where their data says MH370 is most likely to have crashed

is here...

On Saturday 8th March 2014,

MH370 took off on a routine flight to Beijing.

Just under 40 minutes later it vanished.

There have been many theories as to the fate of the plane

and the global effort continues

to try to solve the mystery

and bring closure to the families of those who lost their lives.