Departure City in the Sky

There are now around a million people airborne at any one time.

It's a city in the sky.

A city straddling not just countries,

but continents.

It's built out of the 100,000 flights

that crisscross the planet every day.

I'm Dallas Campbell, a science broadcaster.

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

This is a seat that you just don't get to sit in any more.

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

So these are all of the planes across America

right now?

We're going to be travelling the world,

uncovering the global networks

and complex logistics that make this city possible.

Do we know where this flight is right now?

-ROBOTIC VOICE:

-'Pull up, pull up.'

We'll be heading to some of the most extreme...

..and remote corners of the planet...

Looking at the incredible technology

and engineering that is constantly reshaping the way we fly.

Oh, my God! Look at this.

From today's biggest super jumbos...

Absolutely insane.

..to the very latest in personal flight.

-Oh, my God!

-That is awesome.

Those little jets strapped to those guys

have allowed them to become human aircraft

and it's the same technology that has let us construct

one of the wonders of the modern world.

An airport city.

And building it and running it has tested us to our absolute limits.

It's a city the likes of which you will have never seen before

and we're going to give you the ultimate tour.

If you want to visit the city in the sky,

the first step involves getting off the ground.

And that's not always easy.

This is Yakutsk, Siberia.

It is the coldest city on Earth,

a remote place that's snowbound for half the year.

Aviation is its lifeline

and keeping the airport open

in these extreme conditions is critical.

HE SPEAKS RUSSIAN

It's down to Alexei Filyushin and his airport maintenance team

to keep the planes flying.

It's 9am and the morning flight from Moscow's just landed.

So you've got the plane coming in now, then.

How long do you have before it goes out again?

It's going to stand here for a whole hour?

To be honest, though, I can barely stand about ten minutes out here.

It's so cold.

The plane may not be alive, but without rapid engineering first aid,

it won't be leaving here in a hurry.

Having this plane sitting out here on its own is the equivalent of me

being out here without any of my protective clothing.

Now, at the moment, I'm wearing six layers,

I've got four pairs of gloves on and it's still really, really cold.

The thing is, in this environment,

your body is literally at the limit of survival.

And the same is true for the plane.

Out here, I could get frostbite in just a few minutes

and the plane is every bit as vulnerable.

The first things that need care are its wheels.

Without urgent attention,

these rubber tyres would become so cold and brittle,

they'd be unusable.

So, the maintenance crew must act like an ER crash team for jets.

What are these, Alexei? Blankets?

Yes.

You can smell it!

Oh, really?

Oh, I see.

So you're trying to keep the heat that is already in there?

And then, when this takes off in an hour, will these still be warm?

Yes, yes.

The plane's brakes are still hot after landing and wrapping them

in heavy-duty insulating blankets traps this warmth.

-OK?

-It's OK, yeah.

It's like wrapping a human in a survival blanket,

using the body's own heat to prevent hypothermia.

But protecting the tyres is just the first step.

This jet also needs the aviation equivalent of hot cocoa.

These huge turbine engines are going to freeze up very quickly

after landing.

All of the grease that lubricates them

and other parts of the plane has a freezing temperature of -40.

So below that, everything jams up.

And today, it's -47.

It's hot air that you're putting in, is it?

Oh, really? It freezes?

Like a syrup?

At 65 degrees centigrade,

the hot air will keep the oil flowing

and stop the engine seizing up.

-Like this?

-Yes, yes.

-I don't want to break your plane, Alexei!

-It's no problem.

-And that keeps everything nice and warm?

-Yes.

-OK.

It's now been 45 minutes since the plane landed.

And while Alexei's team have been hard at work,

a new load of passengers have boarded.

The Moscow flight is nearly ready for departure.

HE SPEAKS RUSSIAN

At the very last moment, Alexei strips away

the heaters and blankets.

The plane's got just ten minutes to get off the ground

before it starts to freeze up again.

At 10am, it pulls back from the gates.

And sure enough, bang on time, it barrels down the runaway.

One plane, safely airborne.

Only another 34 flights for Alexei and his team to tackle today.

Same as every day of the coldest winter months.

Rather them than me.

As the global aviation network

reaches out to every remote corner of the planet,

takeoffs in extreme conditions are becoming ever more common.

The city in the sky has transformed our way of life.

Once inaccessible outposts are now just a flight away.

We can travel anywhere we want in a matter of hours.

For airports at the heart of this global aviation network,

there's a very different challenge.

Coping with the sheer volume of people now taking to the skies.

Welcome to Dubai.

Home of scorching temperatures...

..gleaming skyscrapers...

..and an airport that handles more international passengers

than anywhere else in the world.

Nearly 1,000 flights leave Dubai every day.

On average, that's about one every 80 seconds, 24 hours a day,

seven days a week, 365 days a year.

It's the aircraft themselves

which are the backbone of the entire aviation industry

which has moved towards growth and volume and efficiency.

And there's one aircraft in particular

that really symbolises that philosophy.

The Airbus A380.

The largest passenger jet of them all.

This is a plane that is revolutionising air travel.

Capable of carrying up to 853 passengers,

nearly 30% more than its biggest predecessor.

When you look at these things

through the glass of the terminal building,

you never really get a sense of quite how magnificent they are.

Now, my dad flew the 747, the famous jumbo jet,

that really revolutionised long-haul travel in the 1970s, but, suddenly,

next to these things, they don't quite seem so jumbo any more.

Our insatiable hunger for air travel

means that passenger numbers could double over the next 20 years.

Bigger planes like the A380

are one way of preparing for the ever-increasing demand.

But producing a passenger plane this size

required a major breakthrough in aviation design.

This is the village of Gimont in south-west France.

Nothing much happens here most of the time.

But once every two weeks, in the dead of night, all that changes.

Here it comes.

Just coming through the mist.

Such a weird sight,

seeing this enormous thing emerging out of the mist.

This huge section of wing coming past

and dwarfing the little French houses next to it.

Absolutely insane.

HORN TOOTS

These are the gargantuan building blocks of just one A380.

Seeing them drive these massive sections of plane

through this tiny medieval French village

does really beg the question,

why would you go to this much effort?

Why would you drive these things down such a narrow country lane?

The answer lies with its multibillion-pound price tag.

The A380 cost over £16 billion to design and build,

so no one country could carry that risk.

Instead, four nations invested - France, Germany, Britain and Spain.

In return for their money,

they each got the right to manufacture

part of the enormous plane.

This nocturnal procession is the result.

The wings travel over 900 miles from north Wales.

The fuselage, made in Hamburg, covers a similar distance.

And the giant tail section over 1,200 miles from southern Spain.

This is effectively a kit of parts

that all come together here in France.

And this convoy is the last leg of an epic European relay.

Western France lies roughly an equal distance between the main factories

and so the giant building blocks converge here...

..the Airbus final assembly plant in Toulouse.

It's one of the biggest factories in Europe, and it has to be.

So this whole hangar was designed especially so it could accommodate

these shrink-wrapped sections of the plane,

and they have to move them through here pretty fast.

They churn out one plane every two weeks from this factory.

The A380 was so big that during the design stage,

it was simply too expensive

to construct multiple physical prototypes.

Instead they created a virtual prototype

for key parts of the plane during its development...

..something never attempted before on this scale.

But when it came to building and testing the actual sections,

engineers ran into problems.

On the computerised model,

they'd underestimated the length of electrical wiring

needed to run through the vast fuselage.

In reality, it came up short.

Computerised stress tests on the wings also proved problematic.

When they ran tests on the real thing, the wings cracked.

Thanks in part to these design issues,

it took Airbus over ten years

to produce their first serviceable aircraft.

But while the design and development of the A380

relied upon cutting-edge techniques,

its assembly is a rather different story.

The process starts with moving each piece

of this giant kit of parts into the massive assembly rig.

You might imagine that building a modern aircraft like the A380

would require all sorts of new technologies

like lasers or state-of-the-art robots,

but, actually, it all comes down to an age-old idea.

Rivets.

It takes two people to put in each rivet.

One hammering it in from the outside...

..and another who secures it from the inside.

In charge is head engineer Jean-Francois Paul.

You sort of expect with a modern aircraft like this

something a little bit more sophisticated

than nuts and bolts, in a way.

So why do you use rivets?

Because it's the best technology we have.

It's quite simple technology, though, isn't it?

It's a very simple method.

Yeah, but sometimes simple is the best, so...

Riveting is actually a highly skilled job.

Get any one of these rows wrong

and an aircraft could tear apart in midair.

OK, Hannah. I think it's your turn.

-You're really going to let me have a go?

-Yeah.

Do I just put it straight on?

So, basically, we put the washer around the bolt.

Then we use the gun in order to tighten the rivet.

So, I just noticed you have to check every single one.

I mean, there is something quite astonishing

about a plane of this size, of this magnitude,

and it all coming down to things this tiny.

The difference in scale is just really astonishing.

-Is that OK?

-It's OK.

Are you going to just take these out as soon as I have left?

No, no. It stays. If it's good, it stays.

What's the number of this aircraft,

just so I know never to fly on it?

It's a secret.

Keep it secret!

It takes over 23,000 rivets to bolt each A380 together,

every last one put in by hand.

But it's still only a shell.

The next step involves moving the empty body

into a second vast hangar.

Here the plane is given its vital systems...

..including around 300 miles of wires and cabling.

And the crowning glory,

the four huge engines that will power it through the sky.

This is now a finished, flyable aircraft.

It's taken around two million construction hours

to build the world's biggest passenger plane.

It's longer than six double-decker buses.

At a massive 80 metres,

its wingspan is wider than a Premiership football pitch.

And its giant tail section stands taller than Buckingham Palace.

There are now over 186 of these planes in service around the world.

But with another 133 on the order books,

it's straight on to the next one.

The super-sized A380 is a plane on such a scale,

it's forced the world of aviation to change around it.

Runways have been reinforced to cope with its weight.

And any airport wanting to accommodate it

has had to modify its terminals and jet ways.

The A380 might be the biggest passenger aircraft,

but just like any other plane, before you can board,

you've got to check in.

We all know the drill.

Arrive at the desk,

tag your bag,

print your boarding pass and head through security.

Finally you make it through.

Get the obligatory super-sized chocolate bar in duty-free,

then time to find the gate.

Board the plane...

and get ready for takeoff.

That's all there is to it.

It's all very familiar.

But behind the scenes, there's a hidden world of complexity.

Take your suitcase.

Once you've checked in...

..your baggage sets out on its own long and secret journey...

..before eventually joining you on board.

Here in Dubai, they handle enormous volumes of luggage.

In just three hours during the morning rush,

they process around 50,000 bags.

Stacked like this, they'd reach as high as Dubai's Burj Khalifa,

the tallest building in the world.

Annually, the airport handles a staggering 57 million items.

That's equivalent to 1,100 Burj Khalifas.

And it's all got to be whisked through the airport.

Every bag must get to the right plane at exactly the right time.

To make sure that happens, each individual bag needs one of these.

The humble bag tag.

So on your baggage tag, which we've all seen, obviously,

you've got things like your name, and here we've got the DXB,

which is the three-digit code for the airport you're heading to.

But the really important thing

is this mysterious ten-digit number along the bottom.

This is like your bag's passport number, if you like.

So the digits identify the airline,

your particular bag's ID number,

and then there's a special message digit

which identifies the priority of the bag

or any other information they need to know.

High priority, low priority, that kind of thing.

This code is part of the universal language of aviation,

an international system that knows no borders.

And it determines exactly what will happen to your suitcase

after check-in.

25 metres beneath the airport lies a bizarre subterranean world...

..a sprawling 85 mile high-speed railway network.

Costing around £500 million to build,

this is the world's biggest luggage system.

This place is absolutely enormous.

Everywhere you go there are just miles and miles

of these conveyor belts

with these trays that carry the suitcases moving along.

It's really weird, it's like some kind of

post-apocalyptic fairground ride.

But the strange thing is, you don't see any human beings,

it's completely automated.

It's like the robots have taken over.

After check-in, your bag is spat onto a yellow tray.

Each tray has been chipped with a unique ID,

and a computer tracks which bag has landed in which tray.

So each tray is specific for each bag?

-It is. Instead of tracking that bag...

-You track the tray instead?

That tray has an ID, which allows us to track it 100%.

The human being tasked with keeping an eye over this vast system

is baggage manager Graeme Pollock.

What we have going round various points of the baggage system

are what you see here, some read stations.

-This thing here?

-This thing here.

This sensor will pick up the information from the tray.

So the tray knows where it's going,

it will tell this part of the baggage system, "Here I am,

"please send me to this location."

And then the baggage system will then divert it

to the necessary output point.

The computerised brain of the luggage system

plots every inch of your bag's journey to the aircraft.

If your flight is leaving within an hour,

the computer sends your baggage straight to the loading area.

But for those of us with better timekeeping, our bags end up here,

the early baggage storage system.

If you've checked in a little bit too early, what happens is,

the bags all wait here

and then as soon as it's time for them to make the journey

to the aircraft, a little red robot shuttle will whizz along here,

pick up the tray and put it on the conveyor belt system,

and then away it goes.

So there goes a robot.

The sheer volume of baggage moving through here is breathtaking.

It simply can't be allowed to fail,

so it's monitored constantly from the control room.

There are more people working here

than on the entire length of the conveyor system.

XX6 and 370,

you need to clear it fast, please.

If it is taking time, let me know, please.

Can you just explain a little bit about how this works?

Because it looks like a full-on...

something you might find in a railway network.

It looks incredibly complicated.

Basically, you can see right now red, yellow and green.

Green shows the system is normal, basically. The green colour.

So, red shows a fault.

There's also yellow as well, so what does yellow mean?

Yellow is basically a queuing, where the bags wait.

-So it's basically like a traffic light.

-Yes, yes.

-Green, good, yellow, might have a problem, red is like, "Argh!"

-Yeah.

Just an hour into his shift, at the height of the morning rush-hour,

Suresh spots a problem.

A red light under concourse D.

HE SPEAKS IN OWN LANGUAGE

Something seems to be jamming the system

and a luggage response team have just ten minutes to fix it.

If they can't solve the problem,

they'll soon have thousands of bags backing up,

and that could mean dozens of delayed planes.

So one of the trays has actually come off the rails here,

so, basically, what they've got to do is pull it off,

make sure there's nothing blocking it underneath.

Can you help us?

-Yes.

-OK, lift it.

-The roller is OK?

-Yeah.

The rail is clear as well.

-Yes.

-Behind that is also OK.

It's OK. So if we lower it back down onto the rails.

-Yes.

-We just need to get another inch forward.

There we go, that's it.

Good job.

This is the problem with a system like this,

because it's all moving parts, so it needs constant maintenance.

They've got to get this going.

It may only look like one tray that's got stuck,

but that's all it takes, one tray to clog up the whole system,

then basically Dubai Airport shuts down.

There we go, disaster averted.

They've fixed it. And above ground,

none of the passengers are any the wiser.

Since 2008, when it opened,

Dubai's luggage system has processed nearly 400 million bags.

And in all that time, it's never shut down.

Which is just as well.

As an international hub,

delays here could have a knock-on effect at other airports

across the global network.

But despite all this technology,

for the final few metres up to the aircraft itself,

it's back to good, old-fashioned muscle power.

That's an expensive suitcase.

OK, I'm going to be extra careful.

Wait, I've not scanned.

Sorry.

-SCANNER BEEPS OK.

-Done.

You can put it here.

I'll do this one.

You must be incredibly strong now.

Have you got huge muscles from doing this?

I don't have huge muscles.

Without these automated baggage systems,

large airports couldn't hope to deal with their share

of the 3.2 billion pieces of luggage we fly with us annually.

It's an extraordinary logistical challenge...

..one of many that must be overcome

to get passengers and their suitcases

up into the air every single day.

But the luggage system is just one component of the vast network

that makes up the city in the sky.

The pressure on these networks has grown to a level

few could have predicted.

Take the 21st-century mega airport.

It has expanded to such an extent

that it's become a sprawling metropolis

in its own right.

It's just before Thanksgiving here in America,

which means there are 45 million people

trying to get home to see their family.

And nowhere is busier right now than the airports

and I'm headed to the busiest one of all.

Hartsfield-Jackson, Atlanta.

The busiest airport in the world.

It's within three hours' flight time of 80% of the US population.

And over 101 million people move through here every year.

It's always busy, but on Thanksgiving,

passenger numbers surge by around 35%.

There's a real sense of urgency in the airport today,

as thousands and thousands of people

are desperately trying to get home in time to see their loved ones.

It feels like everybody is in a rush.

To stop the terminal clogging up,

they need to maintain constant passenger flow...

..from check-in to departure gate.

As demand for air travel surges around the world,

it's an issue all major airports must grapple with.

But Atlanta's sprawling layout makes it a real challenge

to keep passengers on the move.

This 4,700 acre site is among the largest terminal spaces

in the world.

And the distance between you and your gate can be over a mile.

The key to managing human traffic in an airport this big is design.

Airports are probably the most engineered places

you are ever likely to set foot into.

Absolutely everything, from the signs, the walkways,

the seats, the check-in desks,

all of it has been designed to absolute precision.

But even though this space feels so familiar,

they are actually using a series of tricks

that you probably haven't noticed.

Airport design guru Jim Harding is joining me

to help unlock Atlanta's design secrets.

So you come in here, ready to check in to your flight,

not really thinking about anything.

But you guys have put in all sorts of tricks here

-to help people find their way.

-A few.

One, you have the tile that is coloured

that leads you through into your destination.

-Going in that direction.

-Right, right.

You have the planes, which you see as soon as you walk in.

Your destination. And then you have the lights that come up,

down and over and to, so the floor, the floor and ceiling all come down,

point to your destination.

Then the last piece that you see are the ticket counters.

Over here. They are all angled.

They reinforce the pattern of the floor.

It all just naturally, intuitively just flows and leads you there.

-Drawing you towards checking in and then the security gates.

-Right.

And what's great is what you don't see.

A bunch of signs all over the place that tell you where to go.

I mean, you do know instinctively when you're here

exactly which way you should be heading.

By incorporating directional flooring and lighting

into the airport design,

the space itself tells us where to go

while the signs merely assist.

It might seem counterintuitive, but signs can actually slow us down.

We can't resist stopping to read them.

So Atlanta has as few as possible.

But it's not just about the actual speed at which you are moving,

it is also about perception.

We've all stood in S-shaped queues,

and they've now been proven to be much faster for people processing

than multiple single-file lines.

And speed is not their only advantage.

For the passenger,

they feel a lot fairer than having several separate lines.

You're not looking at other queues

and constantly wishing that you could have chosen a different one.

And all of this together makes a really big difference.

If you're less stressed out,

you are a lot less likely to ask difficult questions

when you finally get to the counter.

Even once you're past the check-in queues,

through security and on the move to the gate...

..Atlanta has yet more subtle features,

helping regulate its tsunami of passengers.

Take the travelator.

We're not actually going much faster on this travelator

-than if we were walking over there.

-Not really.

But then what's the point

if it's not to get you to your destination quicker?

It helps the perception of the walking distance,

that it shortens the level of effort

that it gets from one point to the other.

The other point is it creates lanes which people choose to travel in,

which helps manage the large volumes of traffic.

It helps mitigate that traffic congestion.

Travelators create ordered human motorway lanes,

all going at different speeds.

They keep us moving and help prevent gridlock.

With around 300,000 eager Thanksgiving passengers,

scrambling from one end of this giant airport to the other,

that's essential.

And even once you've made it to your gate,

there are still more subtle features directing your next move.

I've always wondered, why do they bother having carpeting on this side

compared to the tiling on this bit?

The hard surface is for high-durability traffic areas.

People keep on moving.

And when you arrive at your gate, you want to have a signal

that's soft, comfortable, where you can sit and rest.

So you are deliberately defining the zones depending

-on how you want people to behave?

-Yeah, "Walk, sit."

Design features like this are indispensable

in a modern, busy airport.

They influence our behaviour subconsciously...

..and are essential for preventing

sheer chaos at crowded super airports like Atlanta.

On the surface of it, the crazy passenger numbers

that we've seen in Atlanta might seem

that they are completely off the charts.

But, actually, this is a vision of the future.

The US Federal Aviation Administration

predicts that within ten years,

peaks like this will be a regular occurrence

across America's big airports. This is the new normal.

Around the world, new airports are opening all the time

to cope with an explosion in demand.

But there's one magic ingredient,

without which the entire airborne metropolis

would stall and come crashing down.

Fuel.

The lifeblood of the entire industry.

And keeping millions of litres of the stuff flowing

calls for a supply system on a vast scale.

This is Ghent,

a small town in the Belgian countryside

you might never have heard of.

But it's home to one of the largest jet fuel storage facilities

in Europe.

It's where much of the continent's supply begins an epic journey.

This huge, huge storage tank

is about to be filled with aviation fuel,

and you get a little bit of a sense of the scale of it all,

of just what a thirsty industry the aviation business is.

You can see the number there, just on the side of the tank -

that's 45 million litres of fuel.

But that is just a tiny drop in a giant ocean,

because if you look around, you can see, well,

we are absolutely surrounded by these things.

Oh, look at this, what a space.

Oh, my God.

It's like a huge planetarium.

In a couple of days' time,

this five-storey holding tank will be filled with fuel

fresh from the refinery.

But before it can be used in planes, jet fuel needs to be 100% pure.

When it arrives here, it's not as clean as it needs to be.

There's one surprising impurity left behind from the refining process.

And that's where this rather odd bit of spring cleaning comes in.

So, Frank, tell me, why do you have to keep

these storage tanks so clean?

Well, in the jet fuel, there's a certain amount of water in it.

Right.

The microbes grow in the water, feeding itself with the jet fuel,

causing yeast and moulds...

Oh, I see, you get mould brewing in here?

Yeast and moulds in the layer between the water and jet fuel.

Oh, I see.

If you don't get rid of the water.

Yeasts and moulds feed on hydrocarbons and other nutrients.

This could cause potentially catastrophic blockages

in an aircraft's fuel line.

If you have dirty fuel in your car, that's a problem, that's for sure.

If you have dirty fuel in the air...

I don't want to take off!

So to deliver mould-free jet fuel, the water has got to go.

Which is much easier than it sounds.

Water is denser than fuel.

It simply separates out, sinks to the bottom...

..and drains away through these giant plug holes.

To drain completely, the bottom of the tank has to be spotless.

Any oil left behind from a previous storage has to be scrubbed away.

An amazing amount of dirt comes off it.

I've being hosing this down for God knows how long.

Still pretty filthy.

Although not any more. You could eat your dinner off that.

The tank is pristine and ready to be filled with fuel.

But how do you get it from here to where it needs to be?

The facility sits hundreds of miles from the airports it has to supply,

and it would be a massive task to transport it all by road.

You'd need daily convoys of dozens of trucks from Ghent alone.

HORN BLARES

Factor in the continent's other storage ports

and there'd be over 300,000 additional trucks each year

adding to the chaos on Europe's already crowded roads.

The solution to all of this

is actually buried underground somewhere around here.

It's called CEPS, the Central European Pipeline System.

It's actually the biggest aviation fuel pipeline network in Europe,

and without it, Europe's skies would be a lot emptier.

It was built by NATO back in the '50s to fuel its Cold War bases.

The 3,000 mile pipeline now spans the continent.

Today it pumps over nine billion litres a year

to many of Europe's major airports.

Including the continent's busiest hub - Frankfurt.

Around 60 million people travel through Frankfurt every year

and the key to keeping all these people in the air

is the precious jet fuel,

but what all these people walking around the terminal

might not realise is that that jet fuel

is flowing beneath their feet right now.

Frankfurt has flights to more international destinations

than any other airport in the world.

And all those planes need a lot of fuel.

The man responsible for getting it

from the CEPS pipeline into the aircraft is Gunter Hansel.

What's the next thing we have to do?

If you look at here...

'First up, we have to refuel the world's biggest passenger plane.'

Blimey, this is really heavy.

'And this one is about to head off to Dubai

'in just 45 minutes from now.'

OK, that's good. All right.

Better get pumping.

So we've attached the actual pipes to the fuel tank.

How much fuel are we going to put in it today?

We think about 80 tonnes, so 95,000 litres, round about.

OK. How fast does the fuel actually flow into the aircraft itself?

Round about 3,500 litres a minute.

3,500 litres a minute?

Gosh. That's extraordinary.

Interestingly, it doesn't have how much it costs.

No euros or pounds.

Round about euros, I think.

It takes half an hour to fill the aircraft's giant tanks.

And the bill? A cool £20,000.

It might sound like a small fortune,

but it's just a tiny fraction of the £150 billion-worth of jet fuel

that the city in the sky consumes every year.

'It might be a lot of fuel...'

Don't forget the petrol cap.

'..but it's also an awful lot of greenhouse gas emissions.'

Something the airlines are all too aware of and need to keep tackling.

It is easy after a while to become quite desensitised

with all the enormous numbers that you keep hearing,

whether it's the size of the aircraft

or the amount of fuel that they use, or the number of meals served.

But the one thing I keep finding absolutely staggering

is that this is a 24-hour-a-day operation.

It never stops.

These global supply chains must be totally reliable.

The taps can never be allowed to run dry.

And that's just as true whether the fuel in question is jet fuel

or fuel for us humans.

Behind me, this almost military-style procession of trucks

is loading up everything that you need while you are in the air.

Now, it takes four of these just to fill a single A380 for a day.

There are a lot of planes leaving here, and that means a lot of stuff.

Arguably the most important cargo on board these trucks

is something we love to hate...

..but certainly wouldn't want to go without.

Delicious airline meals.

This is the world's biggest flight catering facility.

A four-storey kitchen

that turns around more aeroplane food

than anywhere else on the planet.

A plate of food like this doesn't look like very much

when it lands in front of you,

but you have to imagine the extraordinary amount

of organisation and manpower that goes into making

175,000 of these every single day,

as they do here.

We've got 6,000 meals to churn out in the next hour

for just six of tonight's flights.

No pressure.

And so the cucumber has to be at exactly that angle, right?

-Yes.

-Hang on, hang on.

I go right now, we have to speed it up a bit.

Actually...

Ah!

I thought it was going to be easier than this.

-Wait!

-Don't let the team down.

Argh!

OK, I think we have to slow the belt down a bit for Hannah,

she can't catch up with the speed.

How are you managing to do this?

I'm struggling to keep up, but in this business there are no excuses.

Three hours from now, this batch needs to be up in the air.

And by the time passengers are tucking into these salads,

the chefs here will have cranked out another 50,000-odd meals.

It's a monster 24/7 operation, running 365 days of the year,

a kitchen that never sleeps.

And even though Dubai handles more international passengers

than any other airport,

all the food they rustle up here is only around 1%

of the total amount we wolf down in flight.

In global terms,

the population of the city in the sky packs away around a billion

hot meals and salads every year.

We gorge on over two billion cakes and pastries.

And wash it all down with billions of litres of soft drinks,

wine and water.

It's an astronomical amount of food and drink.

And I don't even want to think about the washing up.

Getting ready for departure is a monumental task.

Whether it's the huge food factories feeding hundreds of thousands

of passengers every day...

..the computerised baggage systems

moving millions of cases around the world...

..the fuel lines delivering the city's energy supply...

..or the mega planes that are the workforces of this metropolis...

..together these elements make the city work.

And it all has one simple goal.

Getting us airborne.

It's finally time for the big moment.

This is what it's all about.

Takeoff. We are about to join the city in the sky.

And today, I've been offered the best seat in the house.

Doors to automatic and crosscheck.

Captain Joe Schwarzenberg

is one of the most experienced A380 pilots in the world.

And he's invited me to join him up front in the cockpit.

It is a real privilege being in here.

This is a seat that, well, you just don't get to sit in any more.

So being allowed here is amazing.

Have to start checklists.

My dad was a captain

and when I was young, he'd sometimes let me sit in the cockpit with him.

Compared to the jumbo jets he flew back in the '80s and '90s,

this is like a spaceship.

-CONTROL:

-Flight LH513, cleared for takeoff.

Lufthansa 760 is cleared for takeoff...

It's easy to take flying for granted.

But the science of takeoff

truly is an act of gravity-defying brilliance.

-Ready?

-Yes, sir.

Takeoff.

He's winding the engines up now.

Stabilised.

Up to the correct power and off we go.

It starts with building up enough speed.

You can really feel the acceleration pushing me back in the chair.

-100 knots.

-Checks.

Captain Joe needs to get his 500-tonne plane

to around 165mph in the next six seconds.

He pushes the throttle levers forward

and his four massive engines spring to life.

They're sucking huge volumes of air through their turbine blades,

compressing it before it mixes with jet fuel and ignites.

The resulting thrust blasting out the back

is the force that pushes the plane forwards.

Within a few seconds,

this force powers the aircraft to its optimal takeoff speed,

just over 165mph, velocity one, or V1.

In a moment we are going to get to V1,

which will be 145 knots, and that's the moment of no return...

-COMPUTERISED VOICE:

-'V1.'

..where it is safer to take off than to try and abort a takeoff.

As the plane accelerates,

the huge increase in speed has all the while been generating

a stream of air moving around the wing.

This airflow creates an effect called lift,

and the faster the aircraft goes, the more lift it generates.

Then the plane reaches takeoff's most critical point.

Captain Joe eases back the side stick...

..adjusting the position of the elevators

70 metres behind the cockpit on the aircraft's tail.

It's called rotation.

Rotation, that's when the nose comes up,

that's when we change the angle of attack of the wing

and that gives us more lift.

Rotation uses the elevators to force the plane's nose up.

By altering the aircraft's angle like this,

much more of the air moving around the wing

is forced downwards and so the plane's lift is greatly enhanced.

And within a second or two, it effortlessly leaves the ground.

We've now unstuck, the plane is now unstuck.

145 knots.

Up we go.

And with that, another planeload of passengers are airborne.

It really is a wonderful experience being able to sit here.

It's a completely different experience of flying

than it is when you are actually sitting in the aircraft back there.

Being up here, you are flying,

you are reminded that you are flying an aeroplane again.

Takeoffs like this are carried out all over the world,

thousands of times a day.

Whether you are departing from Frankfurt...

..or hurtling down the runway in the frozen extremes of Yakutsk.

So you're finally up in the air,

and over the next few hours, maybe you'll have a few G&Ts,

watch an in-flight movie.

But while you are sitting there relaxing,

there's a lot more going on behind the scenes

than you might expect.

You are entering one of the most alien environments on our planet.

A place with thin air, savage winds and freezing temperatures.

Your flight is a truly remarkable achievement.

Next time, we are in the air.

But keeping 100,000 flights a day up here is no mean feat.

It needs a hidden army looking after us...

Age, gender and seat-assignment, please.

Over.

..and incredible life-saving technologies.

LOUD BANG

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.