Airborne City in the Sky

This is the story of a city.

A city with over a million residents -

but you won't find it on any map.

A city that few could have even imagined a generation ago.

It's a city...in the sky.

There are a million people airborne

somewhere in the world at any one time.

A city's worth of passengers,

straddling not just countries...

..but continents.

It's built out of the 100,000 flights

that crisscross the globe every day.

'I'm Dallas Campbell, a science broadcaster.

'Aviation's a big part of my family's story.'

I actually think I might be in love.

This is engineering at the limit.

I'm Dr Hannah Fry, a lecturer in the mathematics of cities.

So these are all of the planes across America, right now.

-Right now.

-Wow.

We'll be travelling the world,

uncovering the hidden global networks and complex logistics

that keep us safely in flight.

-COMPUTER VOICE:

-Pull up. Pull up.

'We'll head to the very busiest

'and biggest nerve centres of global aviation...

I absolutely love this place, it's complete mayhem!

'..to discover how flight is connecting the world

'like never before.'

We'll be meeting the people who make it all possible.

From the army of specialists who take care of us in flight...

He is now having trouble breathing,

and the repeat pulse is 240, is that correct? Over.

..to the experts that keep aircraft safe.

This city in the sky

is predicted to double in size in the next two decades,

and keeping it airborne

is testing our ingenuity to its absolute limits.

Whenever we're in flight,

most of us take it for granted that we'll stay airborne.

But that depends on a handful of fundamental laws of physics,

and it's these laws that keep all aircraft in the sky -

from the largest jets

to the smallest.

These two men had to register as aircraft in the United States...

even though their wingspan is only two metres across.

Their bodies act like an aircraft's fuselage.

And just like a large passenger plane,

they're powered by four jet engines.

Although they had to apply for a special exemption

for flying without a seatbelt.

The jet men are former fighter pilot Yves Rossy

and three-times world champion skydiver Vince Reffet.

I mean, this is the closest thing to a human being flying, solo.

I think, yeah. Really it is just beautiful, you can play with clouds.

We are getting closer to

this dream, to one of the oldest dream of human, you know,

like the flying, you know -

flying like a bird, you know, when you see a bird flying around.

And it's really powerful -

we can go up to about 160 miles per hour. It's fast.

Every kid in the world wants to be you two.

-And actually most adults, I think!

-I wish them,

they will take something like that in 20 years

-to go to the office.

-Yeah.

So you have to shake...

Flying like a bird may SOUND appealing...

..but the thought of hurtling through the sky

at 160 miles an hour strapped to this thing

is frankly terrifying.

Erm... I mean, this is... I could pretend that this was easy,

but actually that is... I don't even think I can take a single step.

Oh, my God. How do you DO this?!

It takes years of training to fly like Yves and Vince.

But fortunately,

there's a much easier way of getting up alongside them

to see just how they control their flight.

In order to fly,

they have to completely master those fundamental principles of aviation.

Though their launch is unlike any normal takeoff.

To begin with, these guys

are plummeting towards the ground with their jet packs on,

propelling them at hundreds of kilometres per hour.

Even the tiniest mistake could cause them to lose control.

They're diving towards the ground to pick up speed,

and it's only when they reach around 100 miles per hour

that they can level out.

The wing shape creates lower pressure above it than below it,

and that causes lift.

But the key to controlling the flight of any jet craft

is the angle of the wing.

When Vince arches his back, his wing tilts upwards -

just enough that the lift counteracts the pull of gravity.

This is what makes controlled, level flight possible.

The shape of the wing is the same as you get in an aeroplane.

The shape creates a pressure difference

above and below the wing

which literally sucks it up into the air.

Where airliners use a rudder and ailerons to steer,

the jet men use their hands and bodies.

If they want to pitch upwards, they arch their backs -

if they want to roll from side to side

they do it all with their shoulders.

Oh, my God...

Oh, wow.

That's ridiculous!

The forces keeping the jet men in flight

are the very same that allow every passenger plane to stay airborne.

But for most of us mere mortals,

the in-flight experience is rather less extreme.

We've become so used to jetting around the globe,

we just take it for granted.

Flying seems so ordinary these days,

with every flight more or less the same.

You know the drill...

Welcome on board.

You board the plane...

..find your seat.

make yourself comfy...

and prepare for takeoff.

Then, you're in the air.

The hours roll on by,

punctuated by welcome distractions.

Try to get some sleep,

and hope that when you wake up, you'll be there.

But while you're enjoying your nap,

there's a whole host of hidden processes at work,

making sure you get to your destination.

Not least, navigation.

Somehow, in the vast open spaces of the sky,

the pilot has to figure out how to get from A to B.

Tonight, Lufthansa senior pilot Captain Jo Schwarzenberg

is flying the biggest passenger jet in the world,

an A380 with 480 passengers on board,

from Frankfurt to Delhi.

The problem is, for most of the 4,000 mile journey

he can't see a thing out the window.

It's the middle of the night,

and Joe's invited me to join him up in the cockpit.

We're somewhere over Afghanistan now,

we're about an hour and a half until landing.

It's absolutely pitch-black outside, we can't see any city lights,

anything like that,

which begs the question of course - how do pilots navigate,

how do they know where to point the plane,

how do they know where other planes are?

The answer lies with one of the city in the sky's

most important hidden global networks -

a web of markers dotted across the planet, known as waypoints.

To fly from A to B,

we have to have an idea how we would like to fly

so we file a flight plan,

which goes from landmark to landmark in earlier times -

nowadays we are flying from waypoint to waypoint.

So most of these waypoints aren't physical beacons,

they are virtual points?

They used to be physical objects in earlier days,

but nowadays with the use of GPS it's all coordinates.

We define points in the air

somewhere over the Earth, give them a name -

that's a five-letter name -

and then we fly from waypoint to waypoint.

Waypoints are virtual landmarks.

They allow the plane's navigation system

to know exactly where it is and which way it's heading.

To a pilot,

they're almost like imaginary signposts,

reaching up into the sky,

giving them a trail to follow through the night.

And on a familiar route,

their strange names get burnt into a pilot's memory.

Our next waypoint is NEVIV,

and we are flying further on to PATAX, MESRA and PAVLO.

PAVLO is the entry point to India,

and is also the exit point of Afghanistan.

It's like a trail of breadcrumbs.

-More or less, yes, like Hansel and Gretel.

-DALLAS LAUGHS

How many waypoints from Frankfurt to Delhi?

How many breadcrumbs?

Er... I think it's a big loaf of bread, actually...!

We have about 5,000, 6,000 miles,

and sometimes the spacing of these waypoints

is just 20, 40 miles so it's quite a lot.

Erm, that is a call from behind. ..Yeah, hello?

Erm... We have to interrupt for a short while

because our coffee's arrived.

-Oh, that's very kind.

-Yeah...

Well, hang on, there's only two cups...

Robin...?

Each one of these lines

represents the path of a real plane based on radar and transponder data.

Over 24 hours,

air traffic reaches into every corner of the globe...

..adding up to over 100,000 flights

crisscrossing our planet every day.

And with the population of the city in the sky

set to double in the next 20 years,

it's not enough for every pilot

to know just where their OWN plane's going -

they also need to avoid all the others.

By 2034,

it's predicted there will be over 44,000 passenger jets

crowding out our skies.

And the more planes,

the more opportunities for near misses or collisions.

Bringing order to the potential chaos of the skies

is down to a secret global army of air traffic controllers.

One of their most crucial nerve centres

is just outside Atlanta, Georgia.

And today, they are busier than normal,

because it's the build-up to Thanksgiving,

America's biggest holiday.

Now, you might not think it to look at it,

but this is an incredibly important room -

probably the most important in North American aviation.

Just beyond me,

the air traffic controllers are managing

the busiest airspace in the world.

80% of the American population

lives within three hours' flying time of Atlanta,

and transatlantic flights

continually cross the area.

So it's critical

that these 130,000 square miles of airspace

run smoothly.

It's the job of the controllers here

to keep track of the vast number of planes

and make sure they never collide, by fine-tuning their routes.

Shaun Sanders has ultimate responsibility

for making sure this vital system works without a hitch.

So Shaun, tell me what we're looking at here.

So what you're looking at right now

is every single aircraft

that we're tracking via radar over the United States,

and up here is Canada.

So these are all of the planes across America, right now.

Right now. As we speak.

What you're looking at is over 5,500 planes right now.

Wow. This looks like a swarm of bees -

how do you even go about organising this chaos?

Looking at it like this,

it looks like a lot and it IS a lot, but it's extremely organised.

We have invisible highways in the skies,

and these planes fly those highways

to get from point A to point B.

And each segment along the way,

they make a left turn or right turn or go straight

until they get to their destination.

But is it almost as though

you're looking at all of the cars in a city

moving around, but you just can't see the roads?

Correct.

Ordinarily it's busy enough, but over Thanksgiving

the controllers handle up to 9,000 flights in a day.

That's on average one every ten seconds.

Preventing aviation gridlock

takes total focus and concentration.

Next Wednesday is the busiest travel day of the year,

the day before Thanksgiving here in the United States.

Are you really on edge on that day?

-No...(!)

-SHE LAUGHS

Do you have anxiety dreams about this map?

Never. This is just what we do.

We don't think about the number of people on the planes

or how many planes -

we know we have hundreds of thousands

of people's lives in our hand,

but that's not what's running through your mind

when you're controlling these planes.

Air traffic controllers across the world

share a system designed to stop planes colliding.

It's called "standard separation".

Aircraft are first herded

into predetermined nine-mile-wide highways.

Within these slices of the Earth's atmosphere,

controllers then regulate the speed and spacing of the planes

to prevent them ever getting closer than five miles horizontally.

But they also have a THIRD dimension to work with -

so they can stack the planes one on top of the other,

never closer than 1,000 vertical feet apart.

The safety of a million airborne passengers

depends on the precision of this system.

These highways in the sky

are what make the sheer scale of international air travel possible.

But flying so many people around the world

comes at a price.

The largest passenger jets can burn their way through

over 50 million litres of fuel every year.

That fuel is the single biggest cost to getting planes in the air -

and in the face of climate change,

the city in the sky's thirst for the stuff

can't be sustained indefinitely.

But a new generation of aircraft

is now promising to reduce

aviation's impact on the environment.

This is Boeing's aircraft assembly plant in Everett, Seattle.

It's the largest indoor space in the world,

with a floor area so vast,

you could fit the Houses of Parliament in it 12 times over.

And the most cutting-edge plane they build here

is the Boeing 787.

The Dreamliner.

This is a cross-section of the Dreamliner -

you get a fantastic sense of scale.

But this particular aircraft

it's not about the size, it's all about the weight.

The Dreamliner's built out of a revolutionary material -

one that's transforming the way all new planes are being made.

'It's the biggest change in aviation design

'since aluminium replaced wooden planes back in the 1920s.'

-It looks beautiful.

-It does, it does looks sensational.

The material is a composite of carbon fibre and plastic.

-Cos everything's been made of aluminium up to this point...

-Right.

-..and suddenly you're moving into a new material.

-Right.

I mean, why do that, what's the point?

-I mean, aluminium, we know it works.

-Right, right.

Well, one of the easiest things,

if you just compare the materials, aluminium versus composite,

you can feel the weight difference between the materials...

Oh. Considerably lighter.

We can design a airplane out of composites,

and have the structure be lighter

than it would if it was made out of aluminium.

So this composite material, this is a real game changer.

It is, absolutely. The airplane fundamentally

will use 20% less fuel

than an existing airplane of the previous generation

of the similar size.

It's estimated that if the entire aviation industry

shifts to using composites,

it could save over 6,000 million tonnes in CO2 emissions

over the next 30 years.

But this wonder material isn't just light.

By weaving carbon fibres together and embedding them in plastic,

engineers have created a material that doesn't stretch,

even under enormous pressures.

And that in turn

has a direct impact on the flying experience for us passengers.

And this is what the interior of a finished plane looks like.

Soon as you step on board, you notice the difference.

It does feel very, very spacious, very, very light.

You've got this lovely curved high ceiling.

Design's one thing,

but there's something else that has a bigger impact on us.

The unpleasant feeling we loosely refer to as "jet lag".

Some of the sensations we associate with it could be due

to not having quite enough oxygen when we're in flight.

On the other side of that window, at 35,000 feet, the air is so thin,

if you were exposed to it, you would be unconscious in seconds.

So to stop us dying from a lack of oxygen,

cabins are pumped full of air.

It's considerably less air than at ground level.

But there's a very good reason why more air can't just be pumped in.

It is a little bit like blowing air into a balloon.

I put air into that and the balloon is under pressure

and the skin, stretches as a result, and as soon as I...

let the air out and it's deflated the skin snaps back.

And although it's not as dramatic as that, in a metal aircraft,

exactly the same thing is happening.

You are going to get a tiny fraction of movement,

from the increase in pressure to the decrease in pressure,

and that in turn will have an effect

on the structural integrity of the fuselage.

So on every single flight,

the aluminium hull of a traditional plane stretches a tiny bit,

pulling against rivets and joints.

Those constant changes in pressure over an aircraft's lifetime

need to be continuously checked, and made sure they're OK

because what you don't want to happen, obviously, is this.

To reduce strain on the fuselage, most planes are pumped up

with the minimum amount of air needed to keep us comfortable.

But aircraft made with the new composite materials don't stretch,

so you can pump in more air without damaging them.

Higher air pressure means more oxygen for us to breathe

and Boeing's own studies suggest this helps reduce the side effects

of long-haul flights,

including some of the symptoms we associate with jet lag.

So all that means when you arrive at your destination,

you feel a little bit more yourself.

More and more of us now fly routinely.

Since 1991, the volume of passengers at British airports

has more than doubled.

But there are still a huge number of potential passengers,

who have never flown, for one very good reason...

..fear.

Around 15% of the UK population is afraid of flying,

many of them so anxious that it stops them

from ever boarding a plane.

Humans are only really built to be a land-based animal,

and so a fear of flying is just a natural reaction

to being at such extreme heights, and in some ways

the more extraordinary thing is that any of us have managed

to train our minds to be comfortable up there at 35,000 feet,

but as we become much more of an airborne species,

not getting over it really is no longer an option.

Globally, fear of flying, or aviophobia,

deprives the airlines of millions of potential passengers.

So no surprise they're interested in helping us get over it.

'I've come to the two-day Fearless Flyer course which,

'if all goes to plan, will culminate with these phobics taking a flight.

'And to help me understand aviophobia a little better,

'I'll be following one of them,

'Gordon Smith, over the next two days.'

When was the last time you got on a plane?

Probably about ten years ago.

So what is it in particular that worries you when you're in the air?

I think it's the lack of control.

You know, if something happens,

there's nothing I can do about that.

Just a feeling of impending doom. You know, just absolute trepidation.

All my family went on holiday together last year.

I had to miss out on that, so I thought I'd better

do something about it. I haven't even told my wife that I'm here.

-Oh, really, she doesn't know?

-Not a clue that I'm here,

so that if I don't go through with it,

you know, she won't be booking a holiday tomorrow night or anything.

So for the session this afternoon, and for the flight tomorrow,

both Gordon and I, we're going to be wearing these heart-rate monitors.

Now how quickly your heart beats

can be used as a measure of your anxiety levels.

And the idea is that we're going to try to get to the bottom

of what is causing Gordon's fear of flying.

Please welcome to the stage, Captain Pete West!

If you're a bit anxious,

even the sound of a soft chime... SINGLE CHIME

..may be alarming,

or even several... ANOTHER CHIME

..in rapid succession.

To help the phobics overcome their fear,

a pilot first explains those mysterious in-flight noises.

I think this next sound sounds rather like

a dog barking underneath the floor. ROUGH SCRAPING

Has anybody heard that and thought,

"Carrying a dog in the cargo hold?"

or even, "A man with a saw?"

Who wants to ask their first question?

Who's got the first question here?

What safety do you have in place if the wheels fail to drop?

What other bad weather can affect flying like wind and rain?

What if anything happened to the pilots?

In my mind, a Canada goose has just flown into the left engine,

it's all burst into flames...

HEARTBEATS PULSE

Just hearing people talk about flying

has almost doubled Gordon's normal heart rate.

Next the phobics are taught psychological coping techniques

to try to control their fight or flight response...

Breathe in...

and push out.

..which should help them handle tomorrow's exposure therapy -

the flight itself.

The next tapping point, and from here we work down the body,

it's the top of the head...

..underneath the eyes,

wrist on wrist.

OK, we've got to be tapping whilst tuned into the fear.

But for coach Lawrence Leyton, addressing the cause

of each individual's aviophobia is far from straightforward.

Well, fear of flying is not just a fear of crashing.

It's actually made up of multiple different aspects

so, for some, the fear of flying is actually the fear of heights.

For some people, it's the fear of enclosed spaces or claustrophobia.

And for some, and a lot of them, it's a fear of being out of control.

The triggers, and there are multiple triggers,

could be different in every single person.

Tomorrow morning they'll be flying for real,

and Gordon will find out whether he's learned to control his fear.

10.30am.

45 minutes until departure

and Gordon still hasn't told his wife he's here.

How are you feeling this morning?

I'm pretty scared. I'm not looking forward to it.

Just want to get it over and done with.

Yesterday I felt great afterwards, right up to about ten o'clock

last night and then, you know, the apprehension kicked back in again.

For one phobic in the group, it's all proving too much.

You imagine those feelings, cos you've got the fear

of having the panic attack, it's the fear of the fear.

Right now, Daniel, what you're doing is you're trying to suppress

that panic attack. You're trying to push it down.

So we're just about to board the flight.

We checked in a few moments ago.

The tension here among these people is really...

Well, it's quite intense,

to be honest, I think, looking round their faces, it's very obvious

just how much these people have had to make themselves come here.

Just hope it goes well on the flight.

It's their last chance to back out.

Good morning. How are you?

Er, very nervous.

That's fine. Well, you can sit anywhere after row five, all right?

This will be the first time Gordon has flown in ten years

and his heart rate monitor will be running throughout.

At the moment he's too stressed

to even talk to me.

Captain West explains what the plane is doing

at every stage of the flight.

CLICK

That click is the change over from the ground power unit to the APU,

the auxiliary power unit - remember the little jet engine in the tail?

-RECORDED MESSAGE:

-'Please be aware that your nearest exit

'may be behind you.

'If we land on water, take the life jacket from under your seat.

'Put it over your head.'

So here comes the power coming on now. Speed increasing now.

It's the moment of truth. Takeoff.

Wings effortlessly lifting us into the air.

Give yourselves all a massive great cheer.

Here we are. We're flying. Very well done, everybody. Fantastic!

'We're up. But, for Gordon, it's not over yet.

'His heart rate is already higher than normal...

'..but it's when the plane levels out,

'that it seems to suddenly spike.

'This moment appears to be the specific trigger point

'for Gordon's fear.

'But, using the relaxation techniques

'he was taught yesterday,

'he gets over it in moments.'

Remember to breathe.

It looked like you completely stopped breathing there!

'Gordon then does something he never thought possible.

'10,000 feet above the ground, he stands up.'

Ah, dude, I'm so pleased for you.

'For Gordon, it's as effective a cure

'as he could ever have hoped for.'

Now I'm feeling fantastic. I feel absolutely fine.

Already I've stood up and haven't walked far,

but I've been up, seatbelt's off and more relaxed.

When was the last time that you stood up on a plane?

25 years ago.

It's just... It is really extraordinary.

It's really extraordinary and I'm so, so pleased for you.

-CAPTAIN:

-'Give yourselves one massive round of applause,

'for becoming fearless flyers.

'Well done to everybody.'

-That's us down.

-You've literally just done a flight.

You've literally just done a flight.

'Give yourselves another round of applause.

'You've done it. Well done.'

-Well done. Congratulations!

-Thank you very much.

-Brilliant. Well done.

-Thank you very much. I really appreciate it.

Thank you. Bye.

This is genuinely a life-changing thing for you.

Absolutely. Absolutely.

And I'm 48 years old this year, you know,

I've been terrified of flying for the past 20, 25,

haven't flown for ten and just... I'm missing out,

so I need to stop missing out and get back out there.

PHONE DIALS

'Gordon can't wait to give his wife the news.'

Connecting. Hi there.

'Hi. What are you doing?'

With my camera crew up in Glasgow Airport.

'Gordon.'

-Say hi.

-'I don't want to say hi.'

-I've just been in an aeroplane.

You get to go on holiday now.

'I don't know what to say.'

Now Gordon can join the other million citizens of the sky

whenever he wants.

It is perhaps surprising that so many of us

are still afraid of flying, at a time when international air travel

has become safer than ever before.

In fact, only one in every five million flights involves

a fatal accident.

But what happens if a passenger,

rather than the plane, has an emergency at 35,000 feet?

SIREN WAILS

Banner University Medical Centre deals with a steady stream

of emergency patients from the city of Phoenix.

But many of the medical dramas they deal with here

actually take place thousands of miles away.

If you're flying on a major airline and you do get sick,

the chances are the cabin crew will talk to the medics

in this very room to find out what to do

wherever you are in the world.

Thank you for calling Medlink.

Please go ahead with the passenger age, gender...

OK, so you'll go ahead and make the medical arrangements for the child?

And how much longer do you have remaining in flight? Over.

Dr Bhow at Medlink - how do you copy? Over.

ER doctor Moneesh Bhow has been on duty since 7am

and he's just responding to his first in-flight emergency...

..a call from an aircraft travelling from the Middle East to Bangkok,

it's 8,000 miles away, somewhere over the Indian ocean.

I understand an 82-year-old male with a possible stroke.

What was the condition that brought him to your attention? Over.

For Dr Bhow, the pressure's now on to make a quick diagnosis.

OK, copy that, so the passenger was standing, he passed out,

is currently on the floor. Is he able to answer any questions? Over.

OK, is he... is he breathing on his own?

Dr Bhow's depending on the captain

and cabin crew to accurately relay the patient's symptoms.

OK, copy that, so what we need to find out

if he's still not responding, but he is breathing, I need to know what

his vital signs are and is there any spontaneous movement to his arms

or legs or is there a part of his body that he's not moving? Over.

I'm sorry, that last transmission cut out.

Could you please repeat? Over.

Captain, are you still on the line? Over.

They've lost communication.

Do we know where this flight is right now?

Yeah, they're just coming up on the coast of western India.

Western India. They're coming up on the coast, OK.

The situation is not looking good.

-What is it, stroke?

-Stroke.

From Dubai to Lagos.

I'll check Karachi to see if they have a neuro...

-Yeah, neuro and a CAT scanner.

-OK. I'll see.

If it does turn out to be a stroke,

they'll need to get the patient on the ground as soon as possible.

So we've got options, our probably last good option is Calcutta.

-After that...

-If we're going to go down, we're going to land...

We're going to say over here, yes.

First, the team needs to quickly work out from their database

which airports have the right medical facilities close by.

How long is this flight?

They identify several airports within range,

but only two have the necessary medical facilities

to treat a stroke.

Neither are en route.

Option one is Delhi, 600 miles out of their way.

Option two is behind them, but closer - Muscat.

And they're 400 miles away from there.

400 miles, we're looking at an hour.

They just check to make sure they have things like imaging,

so something like a CAT scan, and they're just trying to make

that decision now, so it's quite a fine balance between the needs,

the medical needs, and also the captain needs to make sure...

We're just getting them back now.

Is the passenger awake now?

Can he speak at all? Is he able to speak normally to his son? Over.

OK, so he started choking and that's what caused him to faint,

is that what I'm understanding?

It seems the passenger collapsed not because of a stroke,

but because he'd choked on food, unnoticed by the cabin crew.

OK, but we would still like an update in 30 minutes

as to his condition. Over.

MedAire handles 38,000 emergency calls a year,

and because they deal with flights across the globe,

those calls can come in at any time of day or night.

An hour later, Dr Bhow checks in with his patient,

and there's been an unexpected development.

He is now having trouble breathing

and the repeat pulse is 240, is that correct? Over.

The passenger had seemed to be recovering.

Let's continue the oxygen,

and let's plan to land at the closes possible option.

Let's plan to divert into Mumbai.

We will have medical personnel meet you on arrival.

They are turning already, yeah.

Dr Bhow suspects these symptoms

may be due to an underlying heart condition,

so he's advising the captain to divert to Mumbai.

A diversion like this can cost an airline

hundreds of thousands of dollars.

It's a huge decision.

How common is having to make that call to divert an aircraft?

I would say probably in a 24-hour period,

we're probably diverting once or twice.

Our ultimate priority is to take care of the passenger,

so if we feel that the passenger is in critical need of getting

on the ground, then, you know, cost is a secondary consideration.

But it is probably the most stressful call that we take

when we make a decision for a diversion.

As soon as the flight lands, the patient will be rushed

to hospital where local doctors will take over.

As with most of MedAire's cases, Dr Bhow may never find out

whether his patient lives or dies.

It may be possible to look after sick passengers in the air,

but with 100,000 flights crossing our skies every day,

ensuring the physical wellbeing of the aircraft themselves

is a huge challenge as well...

..especially when flying takes us

into some of the most extreme conditions on the planet.

Right now, it's about minus 40 degrees and it's staggeringly cold.

It's actually really difficult to breathe because the bits of moisture

freeze inside your nose and it feels like you're inhaling dust almost.

Any exposed skin too is really prone to frostbite within a few minutes

and if I didn't have my jacket on, I'd get hypothermia pretty quickly.

But the extraordinary thing is that these conditions are what

the average plane is flying through once it gets to cruising altitude.

So, when you're sitting there with your G&T and you're watching

your in-flight movie just a few centimetres from the outside,

remember that the plane and all of its equipment

has to function perfectly at these temperatures

for hours and hours on end.

Every day planes enter the most hostile environment imaginable.

Flying higher than Mount Everest,

battered by winds of hundreds of miles an hour,

we just expect them to function perfectly, flight after flight.

But as planes clock up the air miles, there's an extreme hazard

they'll eventually run into...

..lightning...

..by far the most dangerous powerful force of nature

your plane is ever likely to encounter.

Down on the ground, getting struck by lightning is a rare event -

not so up in the air.

Every plane gets struck by lightning on average once a year.

That means across a typical jet's lifetime,

it will get zapped an astonishing 25 times.

So why aren't passengers regularly electrocuted in flight?

To find out, I've come to Germany.

Lightning is dramatic, it's unpredictable,

it's extremely dangerous, a bolt of lightning is hotter than

the surface of the sun. You really, really don't want to get hit by it.

Kann losgehen?

OK.

Here at Darmstadt University's high voltage lab,

they study lightning protection.

A car gives you much the same protection as a plane.

They're both metal boxes with people inside.

So what happens if whichever metal box you're in

is struck by lightning?

I'm about to find out.

I can feel something. Can I feel static?

Oh, God, I can feel something in the air.

No, it's just fear, I think.

CLICK

I heard something go click and suddenly I feel really nervous.

Oh, God, I feel... OK.

Funf, vier, drei, zwei, eins...

I know it's safe, it's safe. It's safe.

As long as I don't open the door, cos he told me

not to open the door or touch anything.

HUGE BANG!

BLEEP! BLEEP!

Oh, my God.

Oh, my God.

Schuss.

Oh, my God. Oh, my God.

-Schuss.

-BANG

He is still alive.

A single bolt is too quick to see in detail,

but the lab can generate a slower electrical pulse to help show

what happens when lightning hits a metal box.

And what is happening to this car on the ground

is exactly the same as what happens to aircraft in the sky.

The car is acting as what's known as a Faraday cage,

named after the scientist Michael Faraday.

That huge charge hitting the car flows around the outside

of the metal skin of the vehicle to the ground,

rather than coming straight through it, keeping me completely safe.

It's thanks to the Faraday effect that we're safe

when a metal plane gets struck by lightning.

That's all very well for the passenger planes still made

of metal, but it poses a problem for the new breed of composite aircraft.

Composite doesn't disperse electricity in the same way

that metal does and so without protection, these planes

and their passengers would be in real danger.

I've come to Cardiff

to find out how engineers protect composite aircraft.

'Professor Manu Haddad's job is to make them lightning-proof.'

Well, obviously, if there was no lightning-protection design,

you would have a very disastrous effect due to a lightning strike.

Manu's going to show me what happens to unprotected composite

when it's zapped by an artificial lightning bolt.

OK, ear defenders on, please.

So when you're ready, press the green button. You want a countdown?

-Yeah.

-Three, two, one.

BANG!

Oh, can even hear it through the ear defenders. Quite loud.

With the ultra high-speed camera,

strips of carbon fibre can be seen being blasted off the surface.

Manu, it smells... it almost smells like burnt hair.

Oh, gosh, look at that, that's incredible.

The fibres are sticking up out of the surface.

Yes, because, in aluminium,

the current is able to spread itself in all directions.

Here the current is only flowing along the direction of the fibre.

It has generated a lot of heat and big forces.

This is really quite damaged...

the structural integrity of this board, though.

You definitely would not want this to happen to your aircraft.

Avoiding this kind of damage was a real challenge

for the new generation of composite planes.

After decades with no large jets lost to lightning strikes,

nobody wanted to see this threat re-emerge.

Fortunately, we have a very good solution

and this is using a copper mesh, a very thin copper mesh,

which will allow us to distribute the lightning current

uniformly on the surface and avoid the damage that you see here.

'That delicate layer of copper webbing should be enough

'to protect a composite plane.'

And this is the protected side, which has the mesh.

BANG!

Well, there's definitely a lot less of a smell this time, Manu.

-Oh, wow!

-Yes, because, er, you can see the result there.

You see how the protection works.

It actually conducted all the current safely away.

That is very impressive, though.

I mean, there's almost no significant damage whatsoever.

It's a very clear demonstration

that the lightning protection works very effectively.

BANG!

Despite everything the skies throw at us,

flying in complete safety has become the norm...

..and that reliability has allowed aviation

to transform another aspect of our lives.

As well as moving three billion passengers,

over six trillion dollars' worth of cargo

jets its way around the globe every year.

Just about anything that can fit on a plane

is today sent as air freight.

We send a bewildering array of stuff all around the world by air

these days and obviously the bigger the thing that you want to send,

the more expensive it becomes, the more problematic it becomes,

especially if that thing is fragile and an awkward shape, I don't know,

something like a horse, for example.

Now this is my new friend Chardonnay, who is off for an event.

Now, that event just happens to be 6,000 miles away

in Hong Kong on the other side of the world.

Chardonnay and the team are destined

for the prestigious Longines Masters show-jumping event.

And they're due in Hong Kong by 5pm tomorrow.

First job for equine vet Gordon Sidlow is to make sure

all the horses are disease-free before they board their flight.

Who's next, Dave?

'And the temperature check is particularly invasive.'

-Are we dealing with the rear end here?

-Yeah.

-The back end?

-We are.

-OK.

-Bring his tail up like that...

-Yeah.

-..pop it in...

-Yeah.

-..and press the button.

-OK.

-OK?

He seems pretty relaxed about the whole procedure.

There you go.

'Thankfully we don't have that at check-in yet.'

The loading team have just seven hours to get all 64 horses

health checked and boarded onto their own specially chartered plane.

'Easier said than done.'

-HORSE WHINNIES

-Come here!

In twos and threes, they're loaded into specially-designed

aviation horseboxes, the same size as a standard cargo container.

But the seating plan needs special attention.

There are a few rules.

-All the horses have to travel facing forwards.

-Right.

We generally try...or they generally try and put the stallions

at the front because you don't want stallions behind mares.

Is that actually a problem

with horses getting a little bit frisky on board?

They can be, certainly if the mare is thinking about coming in season.

Stallions are designed to react to that and they will react to that

and there's a few tricks for...

little bit of grease up the nose and what have you

to make the stallions less likely to sniff the mares.

-No in-flight movie?

-Absolutely not.

I've just got visions of them watching Black Beauty for nine hours

-on a loop.

-On a loop, yes.

In total, they'll have around 32 tonnes' worth of horses

on the flight.

So it's vital the cargo handlers load up the boxes evenly

throughout the plane to make sure it isn't unbalanced.

There you go, here's a little pre-flight snack.

If they upgrade you,

they might give you a carrot or an apple or something.

So I'm actually going to have to say cheerio to Chardonnay for now

because to make their flight as stress-free as possible,

only the grooms and the vets and the owners are actually allowed

on the flight, so I'm going to take a different flight

and I'm going to meet them on the other side of the world

in Hong Kong tomorrow.

By the time they've finished loading,

I'm already well on my way to Hong Kong.

Five hours after mine, their flight leaves Liege,

setting off on its 6,000-mile journey through the night.

Its destination?

The city known as the gateway to China

and its 1.4 billion citizens.

Hong Kong imports and exports more cargo

than any other airport in the world.

To keep this vast flow of goods moving through the skies,

Hong Kong's built the biggest cargo hub on the planet.

It's here that the horses will be arriving from Belgium

in just a few hours' time.

Cargo super terminal one is at the epicentre.

It's a hangar the size of Wembley Stadium...

..handling up to three and a half million tonnes of cargo a year

from every corner of the world.

Most air freight that arrives here is sorted

and stored in a vast automated filing system

until it's ready to be spat out again and sent on its way.

If you just think about that tiny little movement that you make

with your index finger

when you click on the buy button on your phone or your computer,

whatever it is, far from it just having ramifications

in a virtual world,

it actually sets in motion huge cargo centres just like this.

'But not all cargo goes into storage.'

-25.

-25, OK, got it.

'Some goods have to reach their destination without delay.

'Everything arriving in the perishables area must get

'to the clients within an hour and a half of landing.'

-Can we open and have a look and see what we've got here?

-Yes.

Right, what do we have in here?

Oh, my God, look at these beautiful crab.

Wow, look at that. Whereabouts have these come from?

Korea.

OK, one, two, three.

Snails from Taipei.

Taipei.

I absolutely love this place.

It's complete mayhem cos the whole thing about it

is about speed so there's no waiting about -

things just come in and they go out straightaway again.

It's all about getting these expensive delicacies

from here to the restaurants in double quick time.

-These have come all the way from Colombia.

-Colombia.

I'm just trying to work out what they are, actually.

I can tell you that they are exotic, and that they come from Colombia.

-I like it.

-You like to eat it? Nice. What does it taste like?

-Sweet.

-Very sweet.

-Very sweet. Very sweet.

Air cargo has completely transformed our lives

in the most extraordinarily short amount of time.

We just expect exotic fruit like this

to be on our supermarket shelves,

irrespective of the season, irrespective of where we live.

And it's because of aircraft, the fact that this can travel

all the way round the world and get to you fresh before it rots.

But there's another category of cargo they deal with here.

Just landed right on schedule,

the 64 show-jumping horses from Belgium.

They've been in the air for 16 hours,

and travelled 6,000 miles.

And with only two days to go before the event,

it's crucial the horses now reach their stables as quickly as possible

for some much needed rest.

'Vet Gordon Sidlow made the journey along with them

'and has to make sure they're match fit.'

Horses do get jet-lagged, some more so than others,

but it's relatively poorly understood

because it's more difficult

to tell if a horse is jet-lagged or just simply tired.

Within two hours flat, every horse has been whisked away.

'The next morning and 6,000 miles since we last met,

'I've come to see how Chardonnay's flight went.'

Oh, hi.

Hi.

Look at you. Look at you, hey.

The annoying thing is Chardonnay looks a lot fresher

and in a lot better shape after his long-haul flight than I do.

There we go, look. Look at that.

Keeping a million passengers constantly in the air

alongside a parallel world of flying cargo is an astonishing feat

which the vast majority of us take completely for granted.

And it's only possible

because modern aviation is a truly global system,

linking the world as never before.

But what goes up must eventually come down.

Next time, we prepare for the final

and most challenging part of any flight...

..touchdown.

From landing at one of the most dangerous airports in the world...

That is crazy.

-ELECTRONIC VOICE:

-'Pull up. Avoid terrain.

..to keeping the busiest runways open...

It could have a catastrophic effect.

It's hundreds of lives that are at stake.

..to witnessing a plane's final moments.

Oh! It's like watching an animal being torn apart by another animal.

If you'd like to find out more about the design

and engineering of this most incredible City In The Sky, then

go to the website below and follow the links to the Open University.