Arrival City in the Sky

There are now around a million people

airborne at any one time.

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 a big part of my family story.

I'm going to try and remember how to fly a 737.

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're just passing Mount Everest now.

We're going to be travelling the world,

uncovering the global networks and complex logistics

that make this city possible.

It takes the most incredible technology there is

to make it all happen.

It's a city that few could have even imagined a generation ago.

-COMPUTER 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 engineering and technology

that's reshaping aviation.

Oh, my God, look at this!

And meeting the army of people

who bring us safely back down to earth.

It's not just about a plane or piece of metal.

It's hundreds of lives that are at stake.

The city in the sky is predicted to double in size

in the next two decades.

And running it is testing our ingenuity to its absolute limits.

What goes up, must come down.

In the world of aviation,

landing is the most challenging part of the flight.

And I'm heading for one of the most dangerous places to land,

anywhere in the world.

It's Paro airport in Bhutan.

'That's the highest point on earth, Mount Everest.'

There you go. The captain's just announced

we're just passing Mount Everest now.

I've got to say, in the ranking of window seat views,

that, probably number one.

I reckon.

The entire Himalayan region

is a huge jumble of jagged mountains and deep valleys.

The question is,

how on earth do you get a plane this size

down safely on the ground,

when your airport is essentially

in the biggest mountain range in the world?

Paro is one of the only places in the high Himalayas

you can land a medium-sized jet.

It's nestled in a narrow valley,

surrounded by towering 18,000-foot peaks.

The approach and landing is legendary.

Apparently it's utterly hair-raising.

So it's a good job I'm not a nervous flyer.

And luckily, the captain has invited me upfront for a better view.

Captain Kinga Tshering is one of only 26 pilots in the world

qualified to make this landing.

Hi, there. I'm Dallas.

Lovely to meet you. Thank you very, very much

for letting us come up front and get a bit of a better view

I mean, are you nervous doing this?

This is my 45th landing at Paro, so I'm OK.

-How many, 45?

-Yeah.

OK, you're fine. You're fine.

But Paro is, you know, it gives you that

rush of adrenaline every time.

OK, this is going to be interesting. This is going to be an adventure.

20 miles out, Captain Tshering's descended to 15,000 feet

and he's now preparing for his approach.

BEEPING

So that, that beeping is the autopilot going off? OK.

So they're flying manually, using the side stick.

This airport doesn't have radar to guide planes in.

So he's got no option other than to land manually.

Are you flying just using visual points?

-Yes, all visual this.

-OK.

The final approach is through a long, narrow valley.

And just 500 metres before the airport, there's a high ridge.

Until the plane passes it, pilots can't see the runway at all.

Once the plane makes its turn around the ridge,

it's got to be perfectly lined up with the runway,

at just the right height.

It should then be 100 feet off the ground

and seconds away from touchdown.

At least, that's the theory.

Time for the real thing...

I don't want to distract him now.

I don't want to distract the pilot at this point.

Captain Tshering is now taking us down into the valley,

flying alarmingly close to the mountainside.

-COMPUTER VOICE:

-Terrain ahead.

Terrain ahead.

This is seat-of-your-pants stuff.

-COMPUTER VOICE.

-Terrain ahead. Pull up. Avoid terrain.

God, we're so bloody close!

We're losing height fast

and there's still no sign of the airport.

Only 15 seconds from landing,

as Captain Tshering makes his tricky turn around the ridge,

the runway finally comes into view.

We're at 500 feet.

Now I can see the runway.

That is crazy.

-COMPUTER VOICE:

-50.

40.

30. 20.

Retard. Retard.

Got to put the brakes on, as well. It's a really, really short runway.

And...

that is...

That is pretty spectacular.

That runway is short.

I had no idea how short that is.

You don't want to make any mistakes, do you?

The minimum required runway to land is 45 metres.

But here, we have only 30 metres.

-I mean, you can only see the runway at the very, very last minute.

-Yes.

So if you make any mistakes, in terms of corrections,

there's no real room for error, is there?

There's very little room for error. No room for error at all.

Welcome to Bhutan.

This has got to be up there

as one of the most spectacular airports on the planet.

It really is flying by the seat of your pants coming in.

You can see how the whole place

is just surrounded by these high mountains.

And that short runway really is...pretty spectacular.

Aviation is opening up more and more remote corners of the planet...

..connecting us all in a way never before imagined.

Although, only five flights a day

make the roller-coaster ride into Paro.

That's a tiny fraction of the 100,000 flights

that circumnavigate the earth every 24 hours,

many of them on their way to mega airports.

-HANNAH:

-This is Hartsfield-Jackson Atlanta.

To land here,

you've got to navigate some of the world's busiest airspace.

Here, just like most airports,

air traffic controllers in the tower

take charge of guiding planes in to land from five miles out.

Today, they've got their work cut out.

I'm having to speak really quietly,

because the guys behind me

have got the lives of thousands of people in their hands.

And the concentration is pretty intense.

And this time of year, in the build-up to Thanksgiving,

is the busiest time of all,

with almost everybody in America

trying to get home to their families.

If these guys make just a tiny mistake,

you can imagine the consequences.

No pressure, then(!)

1,300 planes land at Atlanta every day.

That's one aircraft to get down on the ground every 30 seconds.

During Thanksgiving week,

passenger numbers push the airport's capacity to the absolute limit.

Brian Kellman is one of the controllers guiding the planes in.

I caught up with him on his break.

We have to keep this very efficient cos, as soon as we slow down,

it could slow up the whole national air space system.

Atlanta is only able to handle the sheer volume

of Thanksgiving air traffic thanks to its unique runway layout.

The airport has five runways, all running parallel,

allowing three planes to land simultaneously.

On top of that, planes can also take off from the other two runways,

all at the same time.

-BRIAN:

-I consider this airport to be a racetrack of aircraft.

We move planes in and out very efficiently.

and I call it the speedway of air traffic right here.

At many airports, hold ups occur

as planes wait to cross an active runway

on their way to or from the terminal.

Not a problem here.

This...is Atlanta's secret weapon.

Codenamed Taxiway Victor.

And it looks like a fairly unremarkable piece of tarmac.

This plane here is taxiing down the slope and around

to avoid crossing the runway over there,

where planes are still taking off.

OK, so what?

Until you realise that there are hardly any airports in the world

which have this kind of a system.

Fortunately, Atlanta had the space

to upgrade its taxiways as it grew,

helping it retain the crown of world's busiest airport.

But for all this state-of-the-art design,

this whole place would come to a standstill

without an eagle-eyed team of runway inspectors.

Op-six would like to inspect the full length of one-zero

and I'll remain off all runways,

give way to all aircraft and all critical areas.

So right now, we're doing the runway inspection.

We're looking at any type of debris,

metal, any types of bolts, screws, even plastic.

John Ryan is responsible for foreign object debris collection.

I'm helping him scour every inch of Atlanta's tarmac.

This runway safety inspection

involves looking for any pieces of debris

that might have fallen onto the ground

from a plane or airport vehicle.

Sounds straightforward enough,

but there's just a 45-second window between landings

to check an entire runway.

And we're being chased by a 65-tonne passenger plane.

We were taking that runway, I think, at some speed...

and only just got off it in time

for another plane to come in to land.

And this is the quiet period.

This is the quiet period, yeah.

John's looking out for even the tiniest objects

that might have been left behind.

A screw.

-Oh, really?

-Actually, it's a nut.

A nut?

-So probably off a bag cart.

-Oh, OK.

-It's quite warped, isn't it?

-Yeah.

-Is that dangerous?

-Yes, definitely, it's a dangerous item.

-Yeah?

So you're driving along at 30 miles an hour

and that's enough to spot things like tiny bits of metal...?

Correct. Yeah.

-You've got skills.

-Yeah.

-THEY BOTH LAUGH

But a little bit of metal on the runway,

how much of an impact could that have?

It could have a catastrophic effect.

Even fragments as small as this

have the potential to wreak havoc.

They could puncture a tyre,

or be flicked up and turned into a projectile,

damaging an aircraft's fuselage.

Sucked into an engine,

a fragment could hit fan blades

spinning at 10,000 revolutions a minute,

causing serious damage.

As a passenger, when you're coming in to land,

it just doesn't occur to you that there's a team of people like you

-looking out for things as small as this...

-Correct.

..that could have that dramatic an impact.

-I know.

-Have a catastrophic failure for the plane.

-Yep.

It's not just that airplane or a piece of metal,

it's hundreds of lives that are at stake.

So, you know, we are at, you know, the highest level of perception

for any type of debris out there.

When you see just how efficiently these guys

deal with the massive numbers of planes that are coming in to land,

it does make you wonder how much capacity there is to expand.

And with global aviation set to double in the next 20 years,

you do kind of wonder how airports are going to cope.

It's not just airports.

With passenger numbers increasing all the time,

we'll need a lot of new pilots in the years ahead.

According to some predictions,

over half a million by 2034.

But it can take as long as ten years to become a fully qualified captain

on the largest passenger jets.

So, no time like the present to join the ranks.

OK, now I've got to try and remember how to fly a 737, OK, Boeing.

OK, I've got, that.

Flaps, gear.

OK, I'm ready. How hard can it be?

-Here we go, if you're ready.

-Yeah.

V-one, rotate.

That's absolutely perfect there.

-Good.

-It's funny.

It's like anything when you do it for the first time,

like driving a car, it's very...

You know, it feels very complicated.

-Speed is good at the moment.

-Yeah.

All right, as you put the nose down,

remember that's going to have an effect on your speed,

so you may need to adjust the thrust slightly.

'Mercifully, I'm not responsible

'for bringing hundreds of innocent passengers

'safely down to the ground.'

This is a flight simulator.

Oh, my God, it's so realistic, it's so realistic.

Captain Nick Coates is a top training pilot

and today he's bravely offered to let me try a landing.

So you're going to ease it across to the left.

Left a bit, left a bit.

Oh, sorry, left a bit, the other left.

Just look inside occasionally, check your speed,

which is not too bad,

and your rate of descent, as well.

We're looking for about 750 feet a minute on final.

So you just need to ease that nose down a bit more.

This is where it's possible that you start to shy away from the landing

and maybe you'll reduce your rate of descent

and just pull the nose up a bit.

-So try and keep the aircraft coming down.

-Yeah.

That's good.

'Landing is one of the most testing phases of any flight.

'In here, Nick can make it even trickier

'by changing weather conditions.

'For my touchdown attempt,

'he's kindly thrown in some crosswinds.'

That's it, you're correcting nicely.

Keep the aircraft coming down.

Don't increase rate of descent too much.

All right, little bit off to the side of the runway.

-OK, I have control.

-OK.

BLEEP!

-I have control.

-BLEEP, sorry.

Yep, positive rate, gear up, thank you.

That was awful. I'm really sorry.

Why did I hit it down so hard?

Because I felt absolutely bang on

and just that very last minute...kerchunk!

Yeah, a bit of a gust right at the last minute

can cause that kind of a harder landing.

So the concentration then required, in those kind of conditions,

is quite a lot harder.

'Sitting here, you soon realise why it takes years to train.

'In fact, globally, around half of fatal accidents

'occur during approach and landing.'

But if things do go wrong

and a pilot has to make an emergency landing,

there's a reassuringly large number of places

dotted around the world to put down.

-HANNAH:

-Bangor, Maine, on the north-east coast of America.

With a population of around 33,000,

this is Smallville, USA.

Yet this place has an unusual claim to fame.

A sprawling, fully-equipped international airport.

With a two-mile long runway,

that can accommodate the biggest planes in the world.

It's capable of processing thousands of passengers.

But most of the time,

this huge airport handles just 20 flights a day.

I think this is the quietest international airport

I've ever been in.

I've been here all morning

and, believe it or not, this is their rush hour.

But actually, that's how you want things to be because,

apart from a few local planes pootling around,

a big passenger jet only lands here when they're in serious trouble.

Bangor is a designated airport for emergency landings...

..and there's a simple reason why.

It's the first bit of American soil many transatlantic flights reach

after crossing 2,500 miles of ocean.

If anything goes wrong during that time

and they can avoid ditching in the sea,

Bangor's their best bet.

In the last decade, around 2,000 planes

have made unscheduled stops here.

So the support team on the ground are kept on their toes 24-7.

They've got to be ready for any kind of emergency.

You want to try and get this piece underneath.

-This one?

-Yeah, and then close it up.

This is just a simulation, but it feels very real.

'I'm joining the airport fire crew's regular training drill.

'Planes making emergency landings at Bangor

'can be laden with up to a 100,000 litres of jet fuel.

'Highly flammable jet fuel.'

-There's your nozzle.

-Thank you.

'Today, the team are simulating a fuel fire with casualties onboard.'

Pull that back.

Now, move it back and forth.

My God!

The response time of you guys is just extraordinary.

So, what? A couple of minutes?

Yeah, we have three minutes

to have the first vehicle on scene discharging agent

and then, all the rest have to be there within the four minutes.

-Within four minutes?

-Yeah.

So it's always water that you use?

No, usually it's a mix of water and foam concentrate

and it creates a film on top of the fuel that seals the vapours off.

OK, you can go ahead and shut if off, if you want.

That was good, yeah.

-Would you hire me as a firefighter?

-Certainly!

That was quite a bit of fun for me,

but this is something much more serious for these guys,

because they have to be on hand and ready

at any time of day,

24 hours a day, every day of the year.

I can't imagine how terrifying it is

when you really have to deal with an emergency.

'Over the years, this airport has seen its fair share of incidents.'

What kind of things have happened here before, then?

Well, we've had mechanical issues,

hijacks, bomb threats,

things of that nature.

So those are some of the emergency calls that we get.

What mechanical issues, then? What kind of mechanical issues?

Some of the mechanical issues that we've seen in the past,

we've had planes come in

-with fuel leaking inside of the aircraft.

-Oh, my gosh.

I understand you get quite a lot of refuelling issues here, as well.

Yeah, the weather actually plays a huge role

in aircraft coming across the ocean.

Generally, they cover enough fuel to get to their destination.

If they're facing headwinds, it could be an issue,

where they burn more fuel than they thought.

So one day, there were storms around the New York area

and I think we had 17 or 20 heavy aircraft that were lined up...

20?!

..across the ramps taking fuel that day.

-So...

-Wow.

So have all of these planes landed here, then?

All of these have come, except for that Lego plane over there.

That Lego plane! I don't know, I think it'd be quite cool

-to see that come in and land on the runway.

-It would.

The set-up here is all very impressive.

Sometimes, though, when things go drastically wrong,

pilots don't have the luxury of a landing on a runway.

In one of the most famous incidents of recent years,

one pilot had to make an emergency landing on the Hudson River,

in the middle of New York.

-NEWSREADER:

-'US Airways Airbus 320 plane has crashed into the river,

'in New York...'

His engines had failed shortly after take off.

'A bird strike affected this Airbus plane, bringing it down.'

Thanks to the skill of the pilot, all the 150 passengers

were able to clamber onto the wings and were taken to safety.

In the years since,

the Hudson River incident's had a lasting impact on pilot training.

DALLAS: Today, at the simulator training facility at Stansted,

I'm joining two pilots practising for a similar engine failure.

Captain Oliver Walker and Senior First Officer Colm Purcell,

have both been flying for eight years.

So cabin crew aware. Air traffic control aware.

But like all pilots,

they're still required to spend time in the simulator.

In this exercise, the plane's engines are about to fail,

thanks to a bird strike.

The exact same thing that caused the Hudson River crash.

Cabin crew released.

LOUD THUMP

Birds on the left-hand side.

BEEPING

Settling on engine number two.

Loss of thrust on both engines, heading back towards Dublin.

Mayday, Mayday, Mayday.

Ryanair 202,

dual engine failure,

attempting to return to runway 28 in Dublin.

So they've got a multiple engine failure.

There's absolutely no power.

So there is no way back from this situation, pretty much.

They have to get it on the runway.

It's a bit tight - 4,000 feet in ten miles.

But I think we can just about make it.

Captain Nick Coates is once again

overseeing the training exercise.

Nick, in terms of worst-case scenarios, how bad is this?

This is as bad as it gets.

That is a 737 glider

and they've got one shot to get that on the ground.

Without engines, the aircraft is now effectively a glider

and it's steadily drifting back to earth.

Make the brace call, make the brace call.

Brace, brace.

So we're coming in very steeply.

-COMPUTER VOICE:

-Pull up. Pull up.

Pull up.

20, ten...

-Brakes off.

-Brakes off.

-Maximum braking.

-Thrusters closed. Auto brake disarm.

100 knots.

I've got to say, that was pretty smooth.

They've done well, they've got it down on the ground.

It looked amazing. You know, we're in a simulator,

but just sitting there, I was, like, wired.

No matter how many times you get into the simulator,

the pulse rate is always slightly elevated

when you step through the door.

When the double engine failure happens,

your pulse rate definitely goes up.

You think fast, you talk fast, it's hard work.

I don't think you'd be as prepared for it, when it does happen,

without the help of the simulator.

I've got to say, you know, that was pretty smooth.

Not a spilt gin and tonic in the back, as well.

We do our best for our passengers!

That was...

Yeah, that was impressive.

Thanks, in part, to training like this,

fatal aircraft accidents have fallen today to an all-time low,

even as the number of flights we take is soaring.

-HANNAH:

-Based on fatalities per mile travelled,

flying is the safest form of transport there is.

According to some estimates,

up to 53 times safer than driving.

But the industry's not stopping there.

New technology is helping them go even further.

Developments in data monitoring and communications

are behind a present-day safety revolution.

New networks now stretch around the globe,

tracking the health of your flight.

The edge of the Derbyshire countryside

might not seem like the most obvious place for a hi-tech hub.

But it is.

Because these guys make over half

of the new big passenger jet engines in the world.

And the team in this building

can tell you exactly what's happening

with every single one of those engines, right now,

wherever they are on earth.

The engine is the beating heart of the aeroplane.

The component we hope will never, ever go wrong.

If a jet engine fails just once during its very long lifetime,

the results are potentially catastrophic.

So from this control room,

Rolls-Royce keep a very beady eye

on the health and wellbeing of their creations.

What's going on here, then, Matt?

So in front of us here, we can see the entire civil large engine fleet

as it's currently flying.

So we've got literally hundreds and hundreds of aircraft

quietly making their way to their destination.

And this is where each one of them is in the world right now?

That's right, right now, this is their actual position,

as close as we can represent it.

So each one of these aircraft is transmitting data

that's being analysed all at the time, looking for those symptoms

that might be indicative of a potential problem

that we can do something about.

Around the world,

the company has 4,500 large passenger jet engines in operation.

Every one of them is in wireless communication

with the Derby control room.

Tiny sensors inside each engine

monitor everything from operating temperatures to fuel pressure.

Anything out of the ordinary gets flagged.

The team are looking for warning signs

of any potential technical issues.

Are all of these ones behaving themselves at the moment, then?

Yeah, right now, we've got a well-behaved fleet in front of us,

as you can see, which is how we like it to be.

You guys can take the rest of the day off, then - no problems.

Well, it would be nice if that would be the case,

but things do go wrong from time to time

and that's what the team here is about.

With one of their jet engines taking off or landing

somewhere in the world every 16 seconds,

the team have to be ready for an alert at any moment.

And despite all the hi-tech monitoring,

this time, the cause is something rather low-tech.

What's going on with that one there, then?

Unfortunately, with this one, one of the baggage carts

actually drove into the side of one of our engines.

It does happen.

So 200 or 300 people, that were hoping to board a flight,

they're pretty disappointed right now that they can't do that,

because of the damage that happened to that particular engine.

I love the idea that all of the precision that's going on here,

everybody being so careful to ensure

there's no problems with aviation at all,

somebody goes and drives a baggage cart into the back of an engine.

Unfortunately, they did a pretty good job with the...

-Smashing it up.

-Yeah, so there were a couple of components

that we're going to have to replace.

Monitoring systems are now used

by all the biggest jet engine manufacturers.

As soon as a problem's spotted,

they'll dispatch engineers to fix it,

wherever in the world a stricken plane might be.

It's not just engines that need checking.

Nothing is left to chance

in trying to bring nine million passengers a day

safely back to earth.

To make sure that happens,

international regulations aim to control all aspects of air safety.

And one of the most crucial is aircraft servicing.

DALLAS: Dubai Airport.

It's a major crossroads in the global aviation system.

More international passengers come through here than any other hub.

So perhaps it's no surprise that this place is the base

for the world's biggest fleet of A380s.

This is one of the largest, most sophisticated,

complex machines ever built by humans.

In the thousands of hours that this is going to spend in the air,

if anything were to go wrong even once,

then the results could be catastrophic.

So in this place, their job is to make sure that never happens.

In the eight years since the first

of these massive planes came into service,

100 million people have flown on them.

Remarkably, in all that time,

not a single life has been lost in one due to malfunction.

It is an extraordinary achievement.

These machines have to work every day

in the most extreme environment on the planet.

They're being hammered by 100 mile an hour winds,

at temperatures below minus 50.

This is engineering at the limits.

'But nothing lasts forever.

'Some of the A380s based here

'have now been operating for around six years.

'After 13 million air miles,

'they're being called in for a major aircraft MOT.'

Oh, my God, look at this!

The entire cockpit's just completely stripped away.

This isn't just an oil change and a quick once-over,

this is how deep they go, in terms of stripping it back.

God, look at that!

All the seats are completely stripped out.

And if you look, you can actually see all the floorboards

have been removed from the upper deck, there's great gaps.

And you can see the whole structure, all the wiring, all the mechanics,

all the hydraulics.

This is the strip down.

A380s are made up of around four million individual components

and over an eight-week period,

engineers will carefully remove 1,600 key parts.

Then they'll pore over every inch of the empty shell.

Inside each of these huge hollow wings

are 49 horizontal ribs

that maintain the shape and structural integrity of it.

And each one of those ribs

is supported by lots and lots of brackets.

And if I just grab this light and climb inside,

you might be able to see them.

In fact, there's one that's been removed and is being supported.

So that one's... There was obviously something wrong with it

and it's being replaced.

But they look at these brackets to make sure

that there's no cracks in them at all or any flaws in them.

The idea is to find a micro crack before it can spread

and become a serious problem.

Left unattended, even the tiniest flaw

could eventually bring down a giant plane.

Sometimes, you might get cracks

that are too small to actually see with the naked eye,

so they've got this little device here.

It's an electronic flaw detector.

And this is one of the brackets here,

which I'm just going to have a little look at.

If I just put this wand, connect it to the metal...

MACHINE BEEPS There we go.

You can hear that beep and there's big spike on the screen.

MACHINE BEEPS Right there is a tiny, tiny crack.

MACHINE BEEPS

And it's this incredible attention to detail that is so important

in terms of keeping these enormous things

in the air and everybody safe.

Once they've put it back together, this aircraft could

fly for a further six years before needing another major overhaul.

Thanks, in part, to this level of safety checking, its chances of

a fatal crash caused by mechanical failure should be close to zero.

While major accidents can still happen,

they're now vanishingly rare.

But there is still one type of mishap that occurs

with monotonous regularity.

Turning up at baggage reclaim to find your suitcase missing.

Around three and a half billion suitcases

fly around the world alongside us every year.

The technology in place to get them to their destination is

becoming ever more sophisticated, but despite all of this,

around seven bags per 1,000 passengers still go astray.

Most bags catch up with their owners within a day or two.

But not all of them.

An estimated 1.4 million cases stay permanently lost.

Some airports and airlines destroy lost luggage,

others give it to charity.

And others sell it off.

That's exactly what this auction in Buhl, Germany, is all about.

This one, has it actually got a tag on?

Because I don't even...

How do they get lost?

Why are these suitcases here? What is the story behind them?

-Each one of these has got an owner that's hugely disappointed.

-Yeah!

This is a blind auction.

You're not allowed to see inside the bag before bidding on it.

-Here's a lovely one...

-A YSL bag!

-Oh, look at this!

And you're not even allowed to touch it.

THEY LAUGH EXCITEDLY

This is like the best day ever.

Any one of the bags on sale today

could potentially contain rich pickings.

So Dallas and I are each going to bid for one.

We've set ourselves a limit of 200 euros per bag,

so we'll have to pick our targets carefully.

Already I can see what the techniques are.

It's going to be things like go for the smaller bag,

cos that's where you put your valuables.

That's where you put your watch, your laptop.

You know, if it's a big duffle bag,

-it's just going to have...

-Pants!

Auction organiser Mark Zoor's been working here for three years.

How often do you have this auction here, then, Mark?

-Twice a month.

-Every two weeks?

Do you have this many bags here?

Always about 400 pieces.

-400 bags every two weeks.

-Yes.

How much do they tend to go for?

Normally, about 100 euro.

OK, so when I'm doing the auction, give me tips,

what should I look out for?

-For expensive bags.

-Expensive bags, yeah, check.

-Something extraordinary.

-Ooh, like a pink fluffy case?

Like a pink fluffy case. Yes.

HE SINGS IN GERMAN

It's so wonderfully weird.

HE SPEAKS IN GERMAN

They've got 400 cases to flog off by the end of the day.

So they don't hang about.

HE SPEAKS QUICKLY IN GERMAN

It's quite popular.

After a couple of hours' frenzied bidding,

it's time for lot 223.

So the bag that I'm going to bid on is up next.

30, 30, 30. Put it up, put it up.

What's he saying, what number?

130. 150.

I now own a case.

A very expensive one, mind you.

236 euros.

Way over budget.

Now it's my turn.

And I know what I'm going for.

HE SPEAKS GERMAN

He's making some jokes that I don't understand.

You can.

Why is everyone bidding for this one?

90!

120!

Hooray!

'That's 188 euros for me.

'48 euros less than Dallas paid. Result!

'But the proof is in the pudding.'

Mine's not even long enough, Dallas.

I can't even hold on to it comfortably.

-THEY GASP

-That's so satisfying.

So nice. OK.

Oh, oh, oh, oh.

Here we have some brand-new...

-cotton

-T-shirts. T-shirts.

-Anyone?

-A stylish guy, that's for sure.

-You have got pants there, you have got pants.

-Yes! I knew it.

They've surely got a resale value.

That's a decent sort of Nike running top.

"The healthy ball as cultural gift of China."

-Oh, they're very pretty.

-Cultural balls.

These are like stress balls, aren't they?

Where you do like this thing with them.

-They're yours, you can have those.

-Thanks.

I've got quite low expectations with this.

I think I may have got a bit carried away with myself

and went for the hot tip.

Oh, OK, OK.

I think this might actually be a 14-year-old girl's suitcase.

-That, for example, would look lovely on anyone.

-It's nice.

Oh, they're Russian.

That's quite nice. I like the idea that you can...

-You can imagine what they look like.

-I think it's not your size.

It's probably just not really me, is it?

That's probably the best thing so far.

But you know what, actually, looking through it,

I feel a little bit sad for the person who lost all of this stuff.

I mean, there's a person on the other end of this bag,

who's missing, you know, their, like, favourite skirt and stuff.

It's a bit of a weird experience.

I think the overall conclusion, though, Dallas,

is that we probably shouldn't go to auctions.

Since 2011, they've auctioned off over 20,000 bags here.

If these hadn't been sold, they might have ended up as landfill.

Globally, that could mean 22,000 tonnes of extra rubbish a year.

The city in the sky is certainly not the only

metropolis to dump huge quantities of waste.

'But you don't find full-size passenger planes

'on the average scrapheap.'

Right after 9/11, a lot of people became nervous about flying,

particularly in America,

and they'd take fewer journeys or they might drive instead.

And it also meant there was a lot of half-empty aeroplanes in the sky,

and when that happens, when you get a drop in demand for whatever

reason, it can make a lot more financial sense to actually

take the planes out of the sky and keep them on the ground.

So where do you park up a few dozen spare jets?

Roads? Where we're going, we don't need roads.

I've driven 90 miles south of Phoenix, Arizona,

deep into the desert.

I absolutely love it here - it's the perfect place

to escape the British weather.

350 days a year of blue skies.

It's big, it's hot and, crucially, it's bone dry.

The average rainfall here is just seven inches a year.

Making this place very useful to the aviation industry.

It is pretty much the perfect spot to mothball your aeroplane.

It's warm, even in the middle of winter.

It can just sit here, baking away in the sunshine in a kind

of suspended animation until it's needed again.

This sprawling 400-acre site is currently home to 150 aircraft.

It's absolutely beautiful out here.

And quite eerie and alien seeing all these incredible shapes

in the desert sky, but, actually, the thing that really strikes you

being here is just the stillness and the quiet.

We're so used to thinking about aviation and being about

frenetic movement and noise and being out here is rather lovely.

For now, these planes may be resting quietly, but at any moment,

an airline might call up

and order one of their sleeping giants back into the sky.

Let's have a little look.

Is there a theoretical time limit

about how long you can keep a plane sitting here in the desert for?

You can keep them in the desert indefinitely

as long as they're on an active storage programme

because daily, weekly, every two weeks, monthly,

there's some activity going on the aircraft like, for instance,

we checked the tyre pressures on this aircraft today.

Let's have a look.

That is exactly 140.

I quite like doing that - it's reassuringly familiar.

It can be a long hibernation.

But aircraft storage manager Ed Meyer and his team of technicians

keep them primed for a sudden re-awakening.

The idea is to do as little maintenance as possible

to get it ready to fly.

In this condition, all the systems are kept active,

kept operational, so, theoretically, all you would have to do is

basically unwrap the aircraft, check out a couple of systems and fly it.

Brilliant.

Starting on a Monday,

we could have the aircraft ready to fly that Friday.

But this isn't just a place where planes

come for a holiday in the sun.

The time comes for every workhorse of the sky

to be put out to pasture.

There's no long and leisurely retirement in store.

This is where some planes...

come to die.

This is a McDonnell-Douglas DC9.

It's 36 years old, it's done 77,854 flight hours,

and this is its very last day on earth.

You guys have got the best job ever. What do you have to do?

You're just pulling all this stuff off?

Only... You have to get cutters.

-We have to cut those.

-I've always wanted to do this.

Just like that.

I tell you what, this is very satisfying.

If you've ever been stuck in an airport

and got cross with your airline...

HE GROWLS

Where's my gin and tonic?!

At the end of a jet's working life,

many of its components can be recycled.

Its dismembered guts are packed with valuable materials.

We have to recycle all the metal,

the trash, like this plastic,

everything's plastic, insulation, fibreglass.

We have to go to the dumpster.

Only we save the seats and wire

and every little bit counts,

-and you can re-use them. It's beautiful.

-Brilliant.

What about these?

This is goes to trash.

I might take one of these as a souvenir.

No, this is going to the trash.

Finally, they're left with a picked-over empty carcass.

Globally, aircraft are being scrapped on a vast scale.

Since the dawn of the jet age back in the 1950s,

over 8,500 passenger planes

have winged their way to the knacker's yard.

Stacked nine-deep,

they'd fill a scrapyard the size of Regent's Park.

But for the scavengers feeding off their corpses, it's not over yet.

Meet the crusher.

That is extraordinary!

It's such a dramatic and violent end of an aircraft's life.

But all of that material, all that metal, all the aluminium,

will be used again.

It'll all be recycled.

The plane can be reborn.

Just the noise is extraordinary.

In my imagination, it'd be a much slower kind of process.

I thought they'd just gently take it apart, but it's so violent.

Oh!

It is quite tragic,

it's like watching an animal being torn apart by another animal.

The pile almost seems too small, doesn't it?

It's hard to believe that this was a huge, great big aircraft

and now it's...

Well, it's just completely vanished.

For this plane, it's all over.

But as a result of the relentless growth of the city in the sky,

new planes are being built far faster

than old ones are being scrapped.

In the decades ahead,

there's one major issue that may yet threaten the city's survival -

power.

Oil won't last forever.

Finding an environmentally friendly power source is

the Holy Grail for the aviation industry.

Millions of pounds are being pumped into research to find

an alternative means of keeping the city airborne.

Just outside Bedford, one radical solution is taking shape.

I am very, very excited today

because I have come to see the world's biggest aircraft.

What is inside these wonderful, wonderful hangars is next level.

It's unbelievable, isn't it?

It's like something from a sci-fi movie.

Oh, my God, that is massive! Look at the size of it. Look at it.

I actually think I might be in love.

The biggest aircraft in the world isn't a fixed wing aeroplane at all.

It is this, an airship.

It's called the Airlander 10.

This is the ultimate hybrid aircraft.

It's based on traditional airship design,

but it gets its lift from both the helium gas it's filled with

and the unusual shape of its hull.

Its engines allow it to hover in one place like a helicopter

for days or even weeks.

It's expected to carry 48 passengers when it launches later this year

and it won't need an airport.

It can take off and land on any open space the size of a football pitch.

It's not exactly zippy.

Its top speed is only 90mph,

but it's got one huge advantage over conventional planes.

Its designers claim it could use less than a third of the fuel

a jet plane burns on a comparable journey.

Can you imagine in a few years' time, perhaps,

flying around the world in something like this?

Other designers have even more radical visions

of the shape of planes to come.

Airbus are developing electric passenger planes

and, already, their prototype,

the E-Fan, has become the first electric plane to cross the Channel.

And two pioneering Swiss scientists recently made

a record-breaking flight in their solar-powered plane.

The Solar Impulse flew around 5,000 miles nonstop

from Japan to Hawaii.

These, or other new technologies, could totally reshape aviation

in the decades ahead

and make the city in the sky unrecognisable.

100 years ago, nobody could have imagined an airborne metropolis

that would become a global network,

reaching into the most far-flung places.

Or that it would carry around nine million passengers a day.

All with a single language and its own universal systems.

On current trends, the city is predicted to

double in size in the next 20 years.

Environmental issues could yet threaten its survival,

but if we can find new ways to power the city,

the sky is quite literally the limit.

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.