Departure

NARRATOR: YOU'RE HEADED FOR THE SKY.

MAYBE YOU'RE GOING TO GO SEE FAMILY... OR SETTING OFF ON A BUSINESS TRIP.

BUT FROM THE MOMENT YOU PULL UP TO THE AIRPORT, YOU STEP INTO A COMPLEX WORLD THAT YOU RARELY GET TO SEE... MAN ON RADIO: NORMAL AIR SPEED, AMERICAN 879.

[INDISTINCT] 5-2.

NARRATOR: BECAUSE GETTING YOU OFF THE GROUND TAKES FAR MORE THAN JUST A TICKET.

IT TAKES HUNDRED-MILLION-DOLLAR HIDDEN RAILWAYS TO GET YOUR LUGGAGE TO THE PLANE, ENGINEERS WORKING ROUND THE CLOCK TO MAKE SURE YOUR FLIGHT'S AIRWORTHY... AN ARMY OF CHEFS TO PREPARE YOUR FOOD, VAST INDUSTRIES CONSTRUCTING THE JETS THAT CARRY US AROUND THE WORLD, AND ALL OF THIS HAPPENS EVEN BEFORE THE WHEELS LEAVE THE GROUND.

BUT ONCE YOU'RE AIRBORNE, YOU'VE JOINED THE MILLION PEOPLE WHO ARE FLYING AT ANY ONE TIME AND WHO ARE UP THERE RIGHT NOW.

YOU'VE BECOME PART OF THE "CITY IN THE SKY."

THIS CITY STRADDLES NOT JUST COUNTRIES, BUT CONTINENTS.

IT'S BUILT OUT OF THE 100,000 FLIGHTS THAT CRISSCROSS THE PLANET EVERY SINGLE DAY.

IT'S AN INCREDIBLE FEAT OF ENGINEERING...

DEPENDENT UPON ADVANCED TECHNOLOGY AND GLOBAL NETWORKS, A HIDDEN WORLD RARELY GLIMPSED BY OUTSIDERS, UNTIL NOW.

NARRATOR: IF YOU WANT TO VISIT THE CITY IN THE SKY, THE FIRST STEP INVOLVES GETTING OFF THE GROUND.

[PERSON WHISTLING A TUNE] NARRATOR: YOU KNOW THE DRILL...

ARRIVE AT CHECK-IN.... [WHISTLING CONTINUES] NARRATOR: TAG YOUR BAG... PRINT YOUR BOARDING PASS... AND HEAD TO SECURITY.

MADE IT THROUGH.

MAYBE DO A LITTLE SHOPPING.

TIME TO FIND THE GATE... [BEEP] BOARD YOUR PLANE.

READY FOR TAKEOFF... AND THAT'S ALL THERE IS TO IT.

BUT IF YOU GO BACK TO THE BEGINNING AND LOOK AT EACH STEP THAT GOT YOU HERE, YOU'LL FIND THERE'S MUCH MORE TO IT THAN MEETS THE EYE.

IT ALL STARTS WITH GETTING YOU AND YOUR LUGGAGE THROUGH THE AIRPORT.

BUT MODERN MEGA AIRPORTS HAVE NOW GOTTEN SO BIG, THAT'S NOT ALWAYS AS EASY AS IT SOUNDS.

HARTSFIELD-JACKSON AIRPORT IN ATLANTA, GEORGIA, IS THE BUSIEST OF THEM ALL.

IT'S WITHIN 3 HOURS' FLIGHT TIME OF 80% OF THE U.S. POPULATION.

OVER A HUNDRED MILLION PEOPLE A YEAR MOVE THROUGH HERE.

ON THANKSGIVING, PASSENGER NUMBERS SURGE AS AROUND 300,000 PEOPLE HURRY HOME TO REUNITE WITH THEIR LOVED ONES.

TO STOP THE TERMINALS FROM CLOGGING UP, THE AIRPORT NEEDS TO MAINTAIN CONSTANT PASSENGER FLOW FROM CHECK-IN TO DEPARTURE GATE.

THE KEY TO KEEPING YOU AND EVERYBODY ELSE MOVING IS DESIGN.

AIRPORTS ARE PROBABLY THE MOST ENGINEERED PLACES WE ARE EVER LIKELY TO SET FOOT IN.

ALTHOUGH WE DON'T NOTICE MOST OF IT, EVERYTHING FROM SIGNS, WALKWAYS, SEATS, AND CHECK-IN DESKS HAVE BEEN DESIGNED TO CONTROL PASSENGER MOVEMENTS.

AIRPORT DESIGN GURU JIM HARDING HELPED PLAN THE LAYOUT OF ATLANTA'S INTERNATIONAL TERMINAL.

JIM: WE HAVE A SET OF VISUAL CUES THAT NATURALLY LEAD AND GUIDE YOU THROUGH THE BIG OPEN SPACE, AND IT'S A BIG PART OF YOUR JOURNEY SEGMENT, CHECKING IN, GETTING ON YOUR PLANE.

SO WHAT YOU HAVE HERE, YOU HAVE LIGHTING THAT GOES UP AND OVER AND DOWN.

YOU HAVE FLOORING THAT PULLS YOU IN AND THROUGH, AND THE TWO COME TOGETHER, THEN POINT YOU TO THE PLANE THAT YOU SEE THROUGH THE GLASS.

SO THIS DESIGN, IT'S VERY CAREFULLY THOUGHT OUT, MAKING THAT CUSTOMER EXPERIENCE EASY, NATURAL, FLUID, INTUITIVE.

NARRATOR: BY INCORPORATING DIRECTIONAL FLOORING AND LIGHTING INTO THE AIRPORT DESIGN, THE SPACE ITSELF TELLS THE PASSENGER WHERE TO GO, WHILE THE SIGNS MERELY ASSIST.

IT MIGHT SEEM COUNTERINTUITIVE, BUT SIGNS CAN ACTUALLY SLOW US DOWN.

YOU 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 WE MOVE.

IT'S ALSO ABOUT OUR PERCEPTION.

THERE'S NOTHING WORSE THAN PICKING THE SLOW LINE WHEN YOU'RE WAITING TO GO THROUGH SECURITY.

IT CREATES TENSION AND LINE ENVY, AGITATING PASSENGERS.

THAT'S WHY MANY AIRPORTS NOW USE "S"-SHAPED LINES, ATLANTA INCLUDED.

SERPENTINE LINES HAVE NOW BEEN PROVEN TO BE MUCH FASTER FOR PEOPLE-PROCESSING THAN MULTIPLE SINGLE-FILE LINES.

FOR THE PASSENGERS, THEY KEEP THINGS FAIR...

CREATING ONE ORDERED LINE, SO NOBODY MOVES FASTER THAN ANYBODY ELSE... AND THAT MEANS WE'RE ALL LESS STRESSED-OUT BY THE TIME WE REACH THE CHECK-IN DESK.

ONCE YOU'RE PAST CHECK-IN, THROUGH SECURITY, AND ON THE MOVE TO THE GATE, ATLANTA HAS YET MORE SUBTLE FEATURES HELPING REGULATE THE TSUNAMI OF PASSENGERS.

TAKE THE TRAVELATOR.

JIM: WELL, YOU MIGHT THINK WE'RE GOING FASTER BY BEING ON A TRAVELATOR, BUT WE'RE REALLY NOT, AT LEAST NOT WHEN WE'RE STANDING STILL.

THERE ARE TWO REASONS WHY YOU HAVE TRAVELATORS.

THE FIRST IS A MATTER OF CONVENIENCE.

YOU HAVE LONG DISTANCES TO WALK IN THE BIGGEST AIRPORT IN THE WORLD, RIGHT?

SO, YOU KNOW, THE PERCEPTION IS, BY GETTING ON A TRAVELATOR, IT'S EASIER TO GET FROM ONE POINT TO THE OTHER WHILE YOU'RE SCHLEPPING ALL YOUR LUGGAGE.

NARRATOR: TRAVELATORS CREATE AN ORDERED HUMAN HIGHWAY, WITH LANES ALL GOING AT DIFFERENT SPEEDS.

THEY KEEP US MOVING AND HELP PREVENT GRIDLOCK.

IN AN AIRPORT THIS SIZE, THAT'S ESSENTIAL.

AT 4,700 ACRES, ATLANTA HAS ONE OF THE LARGEST AIRPORT SITES IN THE WORLD... AND IT'S SO SPREAD OUT THAT THE DISTANCE TO YOUR GATE CAN BE OVER A MILE.

IF PASSENGERS HAD TO MAKE THE JOURNEY ON FOOT, EVEN WITH THE HELP OF TRAVELATORS, SOME WOULD BE GUARANTEED TO BE LATE REACHING THEIR PLANE, AND THAT WOULD CAUSE DELAYS.

THAT'S WHERE THE PLANE TRAIN COMES IN.

RUNNING UNDERGROUND ON A LINE THAT CONNECTS ALL OF ATLANTA'S MAIN TERMINAL BUILDINGS, IT'S THE SPINE THAT HOLDS THIS AIRPORT TOGETHER.

IT'S CONTROLLED FROM A HIDDEN BUNKER 30 FEET BELOW GROUND.

CHRISTOPHER SMITH IS ATLANTA'S TRANSPORTATION SYSTEMS DIRECTOR, AND IT'S HIS JOB TO KEEP THE PLANE TRAIN UP AND RUNNING.

CHRISTOPHER: WE MOVE, ON AVERAGE, ABOUT 94 TO OVER 100 MILLION PASSENGERS, SO, WITH THAT BEING SAID, YOU KNOW, THIS IS THE BUSIEST, UM, TRAIN SYSTEM IN THE UNITED STATES.

IF THIS TRAIN SYSTEM BREAKS DOWN, THEN WHAT YOU HAVE IS A RIPPLE EFFECT THROUGHOUT THIS AIRPORT AND THROUGHOUT THE NATION, AND HERE IN ATLANTA, WE HAVE TO MAKE SURE THAT, UH, ONE--THE TRAIN SYSTEM IS UP AND RUNNING AT ALL TIMES, AND THE EFFICIENCY FACTOR IS THERE.

WE DON'T HAVE MUCH WIGGLE ROOM AT ALL AS RELATES TO, YOU KNOW, THE EFFICIENCY OF THE TRAIN SYSTEM.

NARRATOR: BUT EVEN ONCE YOU'VE BEEN DEPOSITED AT THE GATE, THERE ARE STILL MORE HIDDEN FORCES DIRECTING THE FINAL STAGES OF YOUR JOURNEY TO THE PLANE.

JIM: WHEN YOU GET TO YOUR GATE, YOU WANT TO HAVE A SIGNAL, A CUE FOR PEOPLE TO SIT, RELAX, AND WAIT FOR THEIR PLANE, AND SO YOU CHANGE THE SURFACE FROM HARD SURFACE TO A SOFT, MORE COMFORTABLE SURFACE, AND THAT'S THE--THAT'S THE MECHANISM THAT YOU GO FROM HARD TO SOFT, WALK TO SIT.

NARRATOR: SUBTLE DESIGN FEATURES LIKE THESE ARE INDISPENSABLE IN A MODERN, BUSY AIRPORT.

INFLUENCING OUR BEHAVIOR UNCONSCIOUSLY, THEY'RE ESSENTIAL FOR PREVENTING TRAVEL CHAOS.

ATLANTA'S THANKSGIVING CRUSH MIGHT SEEM LIKE AN EXCEPTION, BUT IN FACT, THIS IS A VISION OF THE FUTURE.

THE U.S. FEDERAL AVIATION ADMINISTRATION PREDICTS THAT WITHIN TEN YEARS, PEAKS LIKE THIS WILL BE AN EVERYDAY OCCURRENCE ACROSS AMERICA'S BIG AIRPORTS.

THIS IS THE NEW NORMAL.

BUT THE HUMAN CRUSH IS JUST ONE CHALLENGE TO OVERCOME IN GETTING YOUR FLIGHT READY FOR TAKEOFF.

THERE'S ALSO THE SMALL MATTER OF UP TO 8 TONS OF BAGGAGE THAT FLIES WITH US ON THE BIGGEST JETS.

WE DON'T EVEN THINK ABOUT IT; WE DROP OUR BAG AT THE CHECK-IN AND JUST EXPECT IT TO MATERIALIZE AT THE OTHER END.

MOST OF US HAVE NEVER EVEN CONSIDERED THE VAST MACHINES, UNSEEN WORKERS, AND COMPLEX NETWORKS NEEDED TO MOVE OUR LUGGAGE FROM "A" TO "B."

AT DUBAI AIRPORT, BAGGAGE PROCESSING LOOKS, ON THE SURFACE, EXACTLY THE SAME AS ANYWHERE ELSE.

BUT THIS AIRPORT HANDLES MORE INTERNATIONAL PASSENGERS THAN ANY OTHER.

IN JUST 3 HOURS OF THE MORNING PEAK, 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, EQUIVALENT TO 1,100 BURJ KHALIFAS... AND IT'S ALL GOT TO BE WHISKED THROUGH THE AIRPORT.

EVERY LAST ONE OF THEM HAS TO GET TO THE RIGHT PLANE AT EXACTLY THE RIGHT TIME.

BUT NO MATTER WHERE YOU ARE IN THE WORLD, EVERY SUITCASE HAS TO HAVE ONE OF THESE-- THE HUMBLE BAGGAGE TAG.

IT MIGHT NOT SEEM LIKE MUCH, BUT THIS TAG IS YOUR BAG'S PASSPORT.

SOME OF IT IS EASY TO DECIPHER-- PASSENGER NAME AND 3-DIGIT DESTINATION AIRPORT CODE-- BUT THE REALLY IMPORTANT THING IS THE 10-DIGIT NUMBER PRINTED ON EVERY BAG TAG.

THE FIRST DIGIT IDENTIFIES THE BAG TYPE AND PRIORITY LEVEL; THE NEXT 3, THE AIRLINE IT'S FLYING WITH; AND THE FINAL 6 ARE YOUR BAG'S UNIQUE I.D.

CODE.

THIS SIMPLE BARCODE DETERMINES EXACTLY WHAT HAPPENS TO YOUR SUITCASE AFTER CHECK-IN.

IT'S ABOUT TO EMBARK ON A JOURNEY OF UP TO 85 MILES TO REACH YOUR PLANE.

80 FEET BENEATH THE AIRPORT LIES A BIZARRE SUBTERRANEAN WORLD, A HIDDEN, HIGH-SPEED RAILWAY NETWORK.

WITH A CONSTRUCTION COST OF AROUND $700 MILLION, THIS IS THE WORLD'S BIGGEST LUGGAGE SYSTEM, AND NOT A BAGGAGE HANDLER IN SIGHT.

AFTER CHECK-IN, YOUR BAG SLIDES INTO A YELLOW TRAY.

EACH ONE HAS A UNIQUE RADIO FREQUENCY CHIP I.D., AND THE COMPUTER TRACKS WHICH BAG HAS LANDED IN WHICH TRAY.

DUBAI BAGGAGE MANAGER GRAEME POLLOCK IS TASKED WITH KEEPING AN EYE OVER THIS VAST SYSTEM.

GRAEME: THE DUBAI BAGGAGE SYSTEM HERE AT TERMINAL 3 IS VERY EFFICIENT IN TERMS OF TRACKING.

SO WHEN THE TRAY IS ON THE TRACK SYSTEM, WE HAVE RFID READERS.

THOSE READERS WILL TAKE THE INFORMATION FROM THE TRAY, AND IT WILL SEND A MESSAGE TO OUR BAGGAGE CONTROL ROOM, SAYING, "HERE I AM, THIS IS THE LOCATION OF THE TRAY."

IT'LL ALSO TELL THE BAGGAGE SYSTEM IN WHICH DIRECTION THAT TRAY SHOULD GO TO.

WE CAN TRACK 100% OF YOUR BAGS, WE TRACK THE TRAYS AS THEY GO AROUND THE SYSTEM, SO WE'LL BE ABLE TO IDENTIFY EXACTLY WHERE THAT TRAY IS AND MAKE SURE IT ENDS UP AT THE CORRECT LOCATION AT THE CORRECT TIME.

NARRATOR: THE COMPUTERIZED BRAIN OF THE LUGGAGE SYSTEM KNOWS EXACTLY WHERE EVERY BAG IS GOING WITHIN THIS HUGE NETWORK, AND IT'LL PLOT EVERY INCH OF ITS JOURNEY TO YOUR PLANE.

IF YOUR FLIGHT'S LEAVING WITHIN AN HOUR, THE COMPUTER SENDS YOUR BAG STRAIGHT TO THE LOADING AREA.

BUT FOR THOSE OF US WHO LIKE TO ARRIVE EARLY, OUR BAGS END UP HERE-- THE EARLY BAGGAGE STORAGE SYSTEM.

GRAEME: IF YOU WERE TO CHECK IN 3 TO 6 HOURS BEFORE YOUR FLIGHT DEPARTURE, THAT BAG WOULD ACTUALLY BE TAKEN TO AN EARLY BAG STORE, WHICH AT THIS MOMENT IN TIME CAN TAKE ABOUT 16,000 BAGS.

THE BAG'LL BE STORED ON THE TRAY WITHIN THE RACKING SYSTEM.

WHEN THE SYSTEM IDENTIFIES THAT THAT FLIGHT IS READY TO LEAVE, IT WILL TAKE THAT BAG FROM THE SYSTEM USING A MECHANICAL ARM AND INJECT IT INTO THE MAIN SYSTEM.

NARRATOR: THE SHEER VOLUME OF BAGGAGE MOVING THROUGH DUBAI AIRPORT MEANS THIS UNDERGROUND RAILWAY CANNOT BE ALLOWED TO FAIL, AND MONITORING IT ALL FROM THE CONTROL ROOM-- FAR MORE PEOPLE THAN ON THE ENTIRE 85 MILES OF DESERTED BAGGAGE CONVEYORS.

MAN: OPEN THE DOUBLE X6, AND 374, YOU NEED TO CLEAR IT FAST, PLEASE.

NARRATOR: SYSTEM OPERATOR SURESH BABU IS IN CHARGE OF KEEPING THE BAGS MOVING.

NARRATOR: THE INDICATOR BOARD FOLLOWS A BASIC TRAFFIC LIGHT WARNING SYSTEM.

SURESH IS ON CONSTANT ALERT FOR A RED LIGHT...

COPY THAT, 6.

NARRATOR: AND JUST AN HOUR INTO HIS SHIFT, AT THE HEIGHT OF THE MORNING RUSH HOUR, HE SPOTS A PROBLEM-- A WARNING INDICATOR ON CONCOURSE "D." [INDISTINCT] NARRATOR: SOMETHING SEEMS TO BE JAMMING THE SYSTEM, AND THE 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.

MAN: OK?

IT'S IN?

SO EVERYTHING IS OK?

YES.

NARRATOR: ONE OF THE TRAYS HAS DERAILED.

[INDISTINCT] NARRATOR: IT MAY APPEAR TO BE ONLY A MINOR INCIDENT, BUT IT'S GOT THE POTENTIAL TO SHUT DOWN THE ENTIRE AIRPORT.

NARRATOR: THEY FIXED IT, AND ABOVE GROUND, NONE OF THE PASSENGERS ARE ANY THE WISER.

SINCE 2008, WHEN IT OPENED, DUBAI'S BAGGAGE SYSTEM HAS DELIVERED NEARLY 400 MILLION BAGS.

AND IN ALL THAT TIME, IT'S NEVER BROKEN DOWN.

BUT DESPITE ALL THIS TECHNOLOGY, FOR THE FINAL FEW FEET UP TO THE PLANE, IT'S BACK TO GOOD, OLD-FASHIONED MUSCLE POWER.

NARRATOR: WITHOUT THESE AUTOMATED BAGGAGE SYSTEMS, LARGE AIRPORTS COULDN'T HOPE TO DEAL WITH THEIR SHARE OF THE 3 1/2 BILLION PIECES OF LUGGAGE WE FLY WITH ANNUALLY.

YOU MAY NOW BE ABOUT TO BOARD YOUR PLANE, WHILE YOUR SUITCASE IS BEING LOADED INTO THE HOLD, BUT WHAT ABOUT THE AIRCRAFT ITSELF?

HAVE YOU EVER REALLY CONSIDERED WHAT IT TAKES TO MAKE THAT GIANT METAL MACHINE THAT'S SITTING WAITING FOR YOU AT THE GATE?

WITH NEARLY 4 MILLION PARTS, PUTTING ONE TOGETHER ISN'T EASY.

THE BIGGEST, AND ARGUABLY THE MOST CHALLENGING PASSENGER JET TO BUILD IS THIS-- THE AIRBUS A380.

FROM A SEAT IN THE CABIN, THIS PLANE FEELS MUCH LIKE ANY OTHER.

IT'S ONLY UP CLOSE THAT ITS SHEER SCALE BECOMES APPARENT.

BUT GETTING THIS MODERN MIRACLE OF ENGINEERING READY TO FLY IS A MAMMOTH TASK; ONE THAT, IRONICALLY, HAPPENS OUTSIDE A SMALL RURAL VILLAGE.

THIS IS GIMONT IN SOUTHWESTERN FRANCE.

NOTHING MUCH HAPPENS HERE MOST OF THE TIME, BUT ONCE EVERY TWO WEEKS, UNDER COVER OF DARKNESS, THE PEACE AND QUIET IS SHATTERED.

AROUND MIDNIGHT, THE ROADS ARE CLOSED TO NORMAL TRAFFIC, AND ESCORTED BY LOCAL POLICE, A GIANT PROCESSION GETS UNDERWAY.

IT'S LIKE SOME KIND OF HUSHED INDUSTRIAL CARNIVAL.

THESE ARE THE GARGANTUAN BUILDING BLOCKS OF JUST ONE A380.

THE PROCESSION OF AIRCRAFT PARTS THROUGH THE NARROW STREETS OF THIS TINY VILLAGE IS THE FINAL LEG OF AN EPIC EUROPEAN JOURNEY.

IN CHARGE OF KEEPING THIS HUGE NIGHT-TIME CONVOY ON THE MOVE IS AIRBUS TRANSPORTATION MANAGER FABIEN DARTHOUT.

NARRATOR: IT'S A SIGHT THAT'S SO STRANGE, IT MAKES YOU WONDER WHY ANY AIRLINE MANUFACTURER WOULD GO TO SUCH LENGTHS.

THE ANSWER LIES WITH THE PLANE'S $21 BILLION PRICE TAG.

IT COSTS SO MUCH TO DESIGN AND BUILD THAT NO ONE COUNTRY COULD HAVE CARRIED THE RISK.

INSTEAD, 4 NATIONS INVESTED: FRANCE, GERMANY, BRITAIN, AND SPAIN.

IN RETURN FOR THEIR MONEY, EACH GOT THE RIGHT TO MANUFACTURE PART OF THIS MONSTER PLANE.

SO THE WINGS HAVE TRAVELED OVER 900 MILES FROM THEIR FACTORY IN NORTH WALES, WHILE THE FUSELAGE HAS BEEN SHIPPED THE SAME DISTANCE FROM HAMBURG, GERMANY... AND ITS GIANT TAIL SECTION HAS COME 1,200 MILES FROM ITS CONSTRUCTION PLANT IN SOUTHERN SPAIN.

ALL OF THESE A380 PARTS ARE HEADING TO A DESTINATION JUST A FEW MILES FROM HERE, THE AIRBUS FINAL ASSEMBLY PLANT OUTSIDE TOULOUSE.

THIS CUSTOM-BUILT FACTORY IS ONE OF THE BIGGEST IN EUROPE... AND IT'S HERE THAT THE A380's COMPONENTS ARE TURNED INTO A COMPLETE PLANE.

THE PROCESS BEGINS WITH MOVING EACH PIECE OF THIS GIANT KIT OF PARTS INTO THE MASSIVE ASSEMBLY RIG.

ONCE THE PIECES ARE ALL IN PLACE, ENGINEERS HAVE TO START BOLTING THEM ALL TOGETHER, RELYING ON A SURPRISINGLY LOW-TECH METHOD- RIVETING.

HEAD OF ASSEMBLY JEAN-FRANCOIS PAUL IS IN CHARGE OF THIS STAGE OF AIRCRAFT CONSTRUCTION.

NARRATOR: IT TAKES TWO PEOPLE TO PUT IN EACH RIVET.

NARRATOR: RIVETING MAY APPEAR SIMPLE, BUT IT'S ACTUALLY A HIGHLY SKILLED JOB.

MAKE THE SLIGHTEST MISTAKE WITH ANY ROW, AND AN AIRCRAFT COULD TEAR APART IN MID-AIR.

SO THE NEXT TIME YOU FIND YOURSELF SITTING ON-BOARD ONE OF THESE HUGE PLANES, BEAR IN MIND THAT IT'S ALL BEING HELD TOGETHER BY OVER 20,000 RIVETS, EVERY LAST ONE OF THEM DRIVEN IN AND TIGHTENED BY HAND.

BUT EVEN WITH ALL THE RIVETS IN PLACE, THE AIRCRAFT'S STILL ONLY A SHELL.

THE NEXT STEP INVOLVES MOVING THE EMPTY BODY TO A SECOND VAST HANGAR.

HERE, THE PLANE IS GIVEN ITS VITAL SYSTEMS, INCLUDING OVER 300 MILES OF WIRES AND CABLING.

THE FINAL TOUCHES, INCLUDING LIGHTING, PANELING, AND SEATS ARE ALL INSTALLED AFTER THE PLANES LEAVE THIS FACTORY.

INDIVIDUAL AIRLINES EACH CHOOSE THEIR OWN CONFIGURATIONS.

THE LAST PIECE OF HEAVY ENGINEERING AT THE TOULOUSE PLANT IS THE INSTALLATION OF THE 4 HUGE ENGINES THAT POWER THE A380.

WITH THESE IN PLACE, THIS IS NOW A FINISHED, FLYABLE AIRCRAFT.

IN TOTAL, IT TAKES AROUND TWO MILLION CONSTRUCTION HOURS TO BUILD EACH AIRBUS A380.

AT 238 FEET, THIS AIRCRAFT IS LONGER THAN 6 CITY BUSES... AND IT HAS A MASSIVE WINGSPAN, MEASURING OVER 260 FEET.

ITS GIANT TAIL STANDS NEARLY 80 FEET HIGH.

THE A380 DWARFS ANY OTHER PASSENGER PLANE FLYING TODAY.

THERE ARE NOW OVER 190 OF THESE MONSTERS IN SERVICE AROUND THE WORLD.

BUT WITH ANOTHER 129 ON ORDER, FOR THE TEAM IN TOULOUSE, IT'S RIGHT ON TO THE NEXT ONE.

THE SUPERSIZED 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 HOST IT HAS HAD TO MODIFY ITS TERMINALS AND JETWAYS.

THIS IS THE CITY IN THE SKY'S BIGGEST, MOST COMPLEX PLANE, A VAST MACHINE THAT HUMS AWAY WHILE YOU RELAX IN YOUR SEAT.

AS YOU FLY ALONG, BENEATH YOUR FEET, UNDER THE FLOORS, AND WITHIN THE WALLS, ITS THOUSANDS OF SYSTEMS ARE QUIETLY AND EFFICIENTLY KEEPING IT IN THE AIR AND KEEPING YOU SAFE.

AND IT WILL CONTINUE TO DO SO FOR THE 60 MILLION MILES IT IS EXPECTED TO FLY OVER ITS LIFETIME.

BUT THIS PLANE, LIKE ANY OTHER, WOULDN'T BE GOING ANYWHERE WITHOUT ONE MAGIC INGREDIENT.

WITHOUT IT, THE ENTIRE AIRBORNE METROPOLIS WOULD STALL AND COME CRASHING DOWN.

IT'S CALLED JET A1... FUEL, THE LIFEBLOOD OF THE ENTIRE INDUSTRY.

AND KEEPING MILLIONS OF GALLONS OF THIS STUFF FLOWING CALLS FOR A SUPPLY SYSTEM ON A VAST SCALE.

GHENT, A SMALL TOWN IN THE BELGIAN COUNTRYSIDE.

IT'S HOME TO ONE OF THE LARGEST JET FUEL STORAGE FACILITIES IN EUROPE.

THIS IS WHERE MUCH OF THE CONTINENT'S JET FUEL STARTS ITS LONG JOURNEY TO THE AIRPORT.

THESE HUGE STORAGE TANKS ARE ABOUT TO BE FILLED WITH AVIATION FUEL.

EACH ONE HOLDS JUST UNDER 12 MILLION GALLONS, ENOUGH TO FILL ABOUT 370 OF THE WORLD'S LARGEST PLANES.

IT MIGHT SOUND LIKE A LOT, BUT IN FACT, IT'S JUST A TINY DROP IN THE OCEAN.

THERE ARE OVER 25 VAST FUEL TANKS PACKED INTO THIS SITE ALONE.

SPECIAL OPERATIONS MANAGER FRANK ROELS OVERSEES THIS MASSIVE FACILITY.

IN A COUPLE OF DAYS' TIME, HE NEEDS TO START FILLING THESE TANKS WITH FUEL FRESH FROM THE REFINERY.

BEFORE IT'S FIT FOR USE ON PLANES, JET FUEL NEEDS TO BE 100% PURE.

ANY IMPURITIES COULD EVENTUALLY BLOCK FUEL PIPES.

BUT WHEN THE FUEL ARRIVES HERE, IT'S NOT YET AS CLEAN AS IT SHOULD BE; THERE'S ONE UNLIKELY IMPURITY LEFT BEHIND FROM THE REFINING PROCESS... WATER, SO FRANK AND HIS TEAM NEED TO DO SOME SPRING CLEANING.

NARRATOR: YEASTS AND MOLDS IN THE WATER CAN FEED ON THE HYDROCARBONS AND OTHER NUTRIENTS IN THE JET FUEL.

AS THEY GROW, THEY COULD FORM PARTICLES THAT COULD CLOG UP FUEL FILTERS, WITH POTENTIALLY CATASTROPHIC RESULTS.

NARRATOR: SO, TO ENSURE MOLD-FREE JET FUEL, THE WATER'S GOT TO GO.

LUCKILY, THAT'S EASIER THAN IT SOUNDS.

WATER'S HEAVIER THAN FUEL, SO IT SIMPLY SEPARATES OUT, SINKS TO THE BOTTOM OF THE HOLDING TANK, AND FLOWS AWAY THROUGH THESE GIANT DRAINS.

TO ALLOW IT TO DRAIN AWAY COMPLETELY, THE BOTTOM OF THE TANK HAS TO BE SPOTLESS.

ANY OIL LEFT BEHIND FROM A PREVIOUS STORAGE HAS GOT TO GO.

ONCE THE TANK'S BEEN SCRUBBED DOWN AND THOROUGHLY CLEANED, IT'S READY TO BE FILLED WITH FUEL, BUT THERE'S ONE SMALL PROBLEM.

THIS FACILITY SITS HUNDREDS OF MILES FROM THE AIRPORTS WHERE THE FUEL IS NEEDED, AND TRYING TO TRANSPORT SUCH A MASSIVE VOLUME OF FUEL BY ROAD COULD CREATE CHAOS.

IT WOULD REQUIRE A DAILY CONVOY OF TRUCKS FROM GHENT ALONE.

FACTOR IN THE CONTINENT'S OTHER STORAGE PORTS, AND THERE'D BE AROUND 300,000 MORE TRUCK LOADS A YEAR, ADDING TO THE CHAOS ON EUROPE'S ALREADY CROWDED HIGHWAYS.

THE SOLUTION IS BURIED UNDERGROUND.

IT'S A HIDDEN NETWORK KNOWN AS CEPS-- THE CENTRAL EUROPEAN PIPELINE SYSTEM-- ONE OF THE BIGGEST AVIATION FUEL PIPELINES IN THE WORLD.

WITHOUT IT, EUROPE'S SKIES WOULD BE A WHOLE LOT EMPTIER.

BUILT BY NATO BACK IN THE FIFTIES TO FUEL ITS COLD WAR BASES, THIS 3,000-MILE PIPELINE SPANS THE CONTINENT.

IN THE EVENT OF WAR, THIS HIDDEN FUEL NETWORK WOULD HAVE HELPED KEEP MILITARY JETS IN THE AIR.

MANY INTERNATIONAL AIRPORTS AND SOME IN THE U.S. ARE FED BY PIPELINES LIKE CEPS, INCLUDING THE COLONIAL PIPELINE THAT SUPPLIES SOME OF THE COUNTRY'S BUSIEST AIRPORTS, INCLUDING ATLANTA, RALEIGH-DURHAM, AND WASHINGTON DULLES.

BUT IT'S CEPS THAT CARRIES MORE JET FUEL ACROSS EUROPE THAN ANY OTHER SYSTEM, AND TODAY, IT'S DELIVERING MORE THAN EVER, AROUND 2.4 BILLION GALLONS A YEAR, ALL FLOWING INTO SOME OF EUROPE'S BIGGEST AIRPORTS.

GERMANY'S FRANKFURT AIRPORT IS ONE OF ITS MOST IMPORTANT CUSTOMERS.

AROUND 60 MILLION PASSENGERS TRAVEL FROM THIS MASSIVE INTERNATIONAL HUB EVERY YEAR.

AND MOST PASSENGERS WALKING THROUGH THE ARRIVALS HALL HAVE NO IDEA OF THE RIVERS OF FUEL FLOWING RIGHT BENEATH THEIR FEET.

THE MAN RESPONSIBLE FOR GETTING THE FUEL FROM THE PIPELINE INTO WAITING AIRCRAFT IS FUEL STATION MANAGER GUNTHER HANSEL.

GUNTHER AND HIS TEAM REFUEL AROUND 230 AIRCRAFT EVERY SINGLE DAY.

FIRST UP ON THE MEGA FORECOURT THIS MORNING--AN A380.

THIS ONE'S DUE TO FLY OUT TO DUBAI JUST 45 MINUTES FROM NOW.

TIME TO GET PUMPING.

NARRATOR: THE "DEAD MAN'S" HANDLE IS A VITAL SAFETY MECHANISM.

IN THE EVENT OF ANY ACCIDENT, LETTING GO OF IT INSTANTLY SHUTS OFF THE FLOW OF PRESSURIZED FUEL.

IN THIS BUSY TERMINAL AREA PACKED WITH LOADED PLANES, ANY FUEL LEAK WOULD BE A SERIOUS HAZARD.

NARRATOR: IT TAKES ABOUT A HALF-HOUR, AND 25,000 GALLONS, TO FILL THE AIRCRAFT'S GIANT TANKS... AND THE BILL-- A TASTY $28,000.

IT MIGHT SOUND LIKE A SMALL FORTUNE, BUT IT'S A TINY FRACTION OF THE $226 BILLION WORTH OF JET FUEL THAT THE CITY IN THE SKY CONSUMES EVERY YEAR.

GUNTHER'S TEAM ARE NOW FINISHED REFUELING THIS AIRCRAFT, BUT WITH ANOTHER 229 PLANES TO GO ON TODAY'S SHIFT, THEY'RE KEPT VERY BUSY.

EXACTLY THE SAME SCENE IS PLAYED OUT CONTINUOUSLY AT AIRPORTS ALL AROUND THE WORLD.

ACROSS THE U.S., AIRCRAFT CONSUME 63 MILLION GALLONS A DAY.

THE GLOBAL SUPPLY CHAINS DELIVERING ALL THIS FUEL MUST BE TOTALLY RELIABLE.

THE TAPS CAN NEVER BE ALLOWED TO RUN DRY.

WITH GAS IN THE TANK, PASSENGERS AND LUGGAGE ON-BOARD, AND THE PLANE ITSELF READY AND WAITING, YOU MIGHT THINK IT'S TIME FOR TAKEOFF.

BUT OUR FLIGHT'S STILL MISSING ONE OTHER VITAL ELEMENT, ONE THAT MANY DREAD...

AIRLINE FOOD.

FEEDING THE CITY IN THE SKY ISN'T EASY.

YOU'VE SEEN FLIGHT ATTENDANTS PREPPING AND SERVING MEALS.

THEY MAKE IT ALL LOOK SO SIMPLE, LIKE A WELL-OILED MACHINE.

BUT WHERE DO ALL THESE MEALS COME FROM?

WITH A MILLION HUNGRY RESIDENTS AIRBORNE AT ANY ONE TIME, THIS IS A METROPOLIS WITH A VERY LARGE APPETITE.

IN GLOBAL TERMS, THE POPULATION OF THE CITY IN THE SKY PACKS AWAY AROUND A BILLION HOT MEALS AND SALADS EVERY YEAR, GORGES ON OVER TWO BILLION CAKES AND PASTRIES, AND WASHES IT ALL DOWN WITH BILLIONS OF GALLONS OF WINE, WATER, AND SOFT DRINKS.

IT'S ENOUGH FOOD AND DRINK TO FEED A CITY THE SIZE OF AUSTIN, TEXAS.

THE PROCESS OF GETTING MILLIONS OF MEALS INTO THE AIR STARTS AT THE CRACK OF DAWN AT AIRPORTS AROUND THE WORLD.

DUBAI, 6 A.M., AND A PROCESSION OF TRUCKS IS DELIVERING EVERYTHING NEEDED FOR A JOURNEY INTO THE SKY.

IT TAKES AN AVERAGE OF 4 TRUCKLOADS TO FILL A JUMBO JET.

AND IN TOTAL, AROUND A THOUSAND PLANES WILL BE LEAVING HERE TODAY.

PREPARING THE MEALS FOR MOST OF THOSE FLIGHTS, THE WORLD'S BIGGEST FLIGHT CATERING FACILITY.

AND IN CHARGE OF IT ALL, CATERING SERVICES VICE PRESIDENT DUNCAN DAVIS.

DUNCAN: AT THE MOMENT, WE'RE SUPPLYING 150,000 MEALS A DAY.

WE HAVE JAPANESE CHEFS, WE HAVE CHINESE CHEFS, WE HAVE INDIAN CHEFS, WE HAVE ARABIC CHEFS, WE HAVE EUROPEAN CHEFS, WESTERN CHEFS, MALAYSIAN, SO, REALLY, ANY TYPE OF CUISINE WE CAN PRODUCE, AND IT'S A BIG VARIETY.

[OVERLAPPING CHATTER] DUNCAN: THIS AREA HERE NOW IS THE BUSINESS CLASS WORK CELL.

UH, THE--THE LADY HERE IS PREPARING A FLIGHT FOR AHMEDABAD, WHICH IS LEAVING THIS EVENING, SO WE HAVE DIFFERENT SPECIFICATIONS 'CAUSE THERE'S DIFFERENT MENUS FOR DIFFERENT FLIGHTS.

WE ACTUALLY ARE RUNNING 1,543 MENUS AT THE MOMENT FOR EMIRATES, AND THEY CHANGE EVERY MONTH, BUT THIS IS THE MENU TODAY TO AHMEDABAD.

THIS IS AN ARABIC MEAL CHOICE, AND THIS IS THE WESTERN.

NARRATOR: THE SHEER SCALE ON WHICH THIS KITCHEN OPERATES REVEALS THE IMMENSE RESOURCES AND EFFORTS THAT GO INTO MAKING AIRLINE MEALS.

NARRATOR: EXECUTIVE CHEF BRUNO TROESCH IS IN CHARGE OF FOOD ORDERING.

NARRATOR: 3 HOURS FROM NOW, THIS BATCH WILL BE SERVED UP TO HUNGRY PASSENGERS AT 30,000 FEET.

IT'S A MONSTER 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 AMOUNTS TO ONLY ABOUT 1% OF THE TOTAL WE WOLF DOWN IN FLIGHT.

AND YOU DON'T EVEN WANT TO THINK ABOUT WASHING THE DISHES.

LUCKILY FOR THEM, THEY'VE GOT THE BIGGEST AND BUSIEST DISHWASHER FACILITY IN THE WORLD TO HANDLE THE LOAD.

SO, WITH THE FOOD ON-BOARD, YOU'RE NOW READY.

YOU'VE CHECKED IN.

BAG DROPPED.

PLANE FUELED AND GOOD TO GO.

DEPARTURE IS IMMINENT.

THIS DAILY BALLET OF PREPARING PLANES FOR FLIGHT IS REPEATED MANY THOUSANDS OF TIMES AROUND THE WORLD.

WHATEVER THE CONDITIONS IN WHICH WE TAKE OFF-- RAIN, SUN, OR SNOW-- IT ALL HAS TO WORK PERFECTLY.

BUT IT'S HARDER IN SOME PLACES THAN IN OTHERS.

AND THIS PLACE-- YAKUTSK, SIBERIA-- IS PERHAPS THE TOUGHEST OF THEM ALL.

THIS IS THE COLDEST CITY ON EARTH, A REMOTE PLACE THAT'S SNOWBOUND FOR HALF THE YEAR.

AVIATION IS ITS LIFELINE.

KEEPING THE AIRPORT OPEN IN THESE EXTREME CONDITIONS IS CRITICAL.

TODAY, IT'S -53 DEGREES FAHRENHEIT.

NARRATOR: IT'S DOWN TO ALEXEI FILYUSHIN AND HIS AIRPORT MAINTENANCE TEAM TO KEEP THE PLANES FLYING IN THESE FREEZING CONDITIONS.

9 A.M., AND THE MORNING FLIGHT FROM MOSCOW'S JUST LANDED.

[WIND HOWLING] NARRATOR: IN THESE FREEZING TEMPERATURES, ANY PLANE LANDING AT YAKUTSK IS IN SERIOUS DANGER.

WITHOUT PROTECTIVE CLOTHING, ANYBODY OUT HERE WOULD QUICKLY GET HYPOTHERMIA, AND THIS PLANE IS EVERY BIT AS VULNERABLE.

UNLESS IT GETS IMMEDIATE ENGINEERING FIRST AID, IT WON'T BE GOING ANYWHERE.

THE FIRST THING THEY NEED TO DEAL WITH ARE ITS WHEELS.

THE PLANE'S RUBBER TIRES WOULD SOON BECOME SO COLD AND BRITTLE, THEY'D BE UNUSABLE.

SO ALEXEI AND HIS ENGINEERS MUST OPERATE LIKE AN E.R.

CRASH TEAM... FOR JETS.

NARRATOR: THE PLANE'S BRAKES ARE STILL HOT AFTER LANDING, AND WRAPPING THEM IN HEAVY-DUTY INSULATING BLANKETS TRAPS THE RESIDUAL WARMTH.

IT'S LIKE WRAPPING A HUMAN IN A SURVIVAL BLANKET, USING THE BODY'S OWN HEAT TO PREVENT HYPOTHERMIA.

BUT PROTECTING THE TIRES IS JUST THE FIRST STEP.

THIS JET ALSO NEEDS THE AVIATION EQUIVALENT OF HOT COCOA.

ITS HUGE ENGINES ARE IN DANGER.

THE OIL LUBRICATING THEM AND OTHER KEY PARTS OF THE PLANE HAS A FREEZING TEMPERATURE OF -40 DEGREES FAHRENHEIT.

BELOW THAT, IT STARTS TO SOLIDIFY, AND EVERYTHING BEGINS TO SEIZE UP.

AND TODAY, IT'S -53, SO FOR ALEXEI, TIMING IS CRITICAL.

NARRATOR: AT 150 DEGREES, THE HOT AIR KEEPS THE OIL FLOWING AND STOPS THE ENGINES SEIZING UP.

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.

[MAN SHOUTS IN RUSSIAN] NARRATOR: FLIGHT 137 FOR MOSCOW IS NEARLY READY FOR DEPARTURE.

[SPEAKING RUSSIAN] NARRATOR: AT THE VERY LAST MOMENT, ALEXEI STRIPS AWAY THE HEATERS AND BLANKETS.

NOW THE PLANE'S GOT JUST TEN MINUTES TO GET OFF THE GROUND BEFORE IT STARTS TO FREEZE UP AGAIN.

IT'S 10 A.M.

IT PULLS BACK FROM THE GATE, AND SURE ENOUGH, RIGHT ON TIME, IT BARRELS DOWN THE RUNWAY.

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.

AS THE GLOBAL AVIATION NETWORK REACHES OUT TO EVERY REMOTE CORNER OF THE PLANET, TAKEOFFS IN EXTREME CONDITIONS ARE BECOMING EVER MORE COMMON, WHETHER IN SIBERIA OR THE ISOLATED ALASKAN WILDERNESS.

THE CITY IN THE SKY HAS NOW 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.

BUT WHEREVER WE'RE DEPARTING FROM, AND WHEREVER WE'RE HEADING TO, WE'VE STILL GOT TO GET AIRBORNE.

[MAN SPEAKS INDISTINCTLY OVER RADIO] NARRATOR: IT ALL COMES DOWN TO THIS VITAL MOMENT, THE POINT AT WHICH YOUR PLANE PULLS BACK FROM THE GATE AND PREPARES TO HURTLE DOWN THE RUNWAY.

SO, [INDISTINCT].

NARRATOR: CAPTAIN JOACHIM SCHWARZENBERG IS ONE OF THE MOST EXPERIENCED A380 PILOTS IN THE WORLD... AND HE'S JUST MINUTES AWAY FROM TAKEOFF.

CAPTAIN: WE HAVE TO START CHECKLISTS.

LUFTHANSA 760 IS CLEARED FOR TAKEOFF.

[INDISTINCT] READY.

NARRATOR: IT'S EASY TO TAKE THIS MOMENT FOR GRANTED, BUT EVERY TAKEOFF IS AN ACT OF GRAVITY-DEFYING BRILLIANCE.

READY?

YES, SIR.

TAKEOFF.

NARRATOR: IT STARTS WITH THE AIRCRAFT BUILDING UP SPEED.

STABILIZED.

100 KNOTS.

CHECK.

NARRATOR: CAPTAIN JO NEEDS TO GET HIS 500-TON PLANE TO AROUND 165 MILES PER HOUR IN THE NEXT 6 SECONDS.

HE PUSHES THE THROTTLE LEVER FORWARD, AND HIS 4 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 RESULT-- THRUST BLASTING OUT THE BACK, THE FORCE THAT PUSHES THE PLANE FORWARD.

WITHIN A FEW SECONDS, THIS FORCE POWERS THE AIRCRAFT TO ITS OPTIMAL TAKEOFF SPEED-- 165 MILES PER HOUR-- VELOCITY ONE, OR V1.

AUTOMATED VOICE: V1.

NARRATOR: AS THE PLANE ACCELERATES, THIS 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, AT JUST OVER 165 MILES PER HOUR, CAPTAIN JO REACHES TAKEOFF'S MOST CRITICAL POINT.

HE PULLS BACK ON THE SIDE STICK, ADJUSTING THE POSITION OF THE ELEVATORS 70 METERS BEHIND THE COCKPIT ON THE AIRCRAFT'S TAIL.

IT'S CALLED ROTATION.

ROTATION USES THE ELEVATORS TO FORCE THE PLANE'S NOSE UP.

BY ALTERING THE AIRCRAFT'S ANGLE, MUCH MORE OF THE AIR FLOWING AROUND THE WING IS FORCED DOWNWARDS, SO THE PLANE'S LIFT IS GREATLY ENHANCED.

WITHIN A SECOND OR TWO, THIS ALLOWS IT TO EFFORTLESSLY LEAVE THE GROUND.

AND WITH THAT, ANOTHER 500 PASSENGERS HAVE JOINED THE CITY IN THE SKY.

TAKEOFFS LIKE THIS ARE CARRIED OUT ALL OVER THE WORLD THOUSANDS OF TIMES A DAY.

WHETHER YOU'RE DEPARTING FROM L.A. OR NEW YORK, OR HURTLING DOWN THE RUNWAY IN THE FROZEN EXTREMES OF YAKUTSK... YOU'RE FINALLY UP IN THE AIR.

OVER THE NEXT FEW HOURS, YOU MIGHT HAVE A FEW DRINKS OR WATCH AN IN-FLIGHT MOVIE, BUT WHILE YOU'RE SITTING THERE RELAXING, THERE'S A LOT MORE GOING ON BEHIND THE SCENES THAN YOU MIGHT EXPECT, FOR YOU ARE ENTERING THE MOST ALIEN ENVIRONMENT ON THE PLANET, A PLACE WITH THIN AIR, SAVAGE WINDS, AND FREEZING TEMPERATURES.

FLIGHT IS A REMARKABLE ACHIEVEMENT, AND YOUR PLANE IS ONE OF AROUND 100,000 TAKING TO THE SKIES ACROSS THE WORLD EVERY SINGLE DAY.

THE JOURNEY'S ONLY JUST BEGUN.

Narrator: You're airborne.

A place with thin air and savage winds.

Pilot: We're headed back towards Dublin.

Narrator: But behind the scenes there's a hidden world keeping you up in the air.

Experts to protect your plane.

Expert: Wow.

Narrator: Air traffic controllers to clear your route, doctors to keep you safe in flight.

Doctor: He is now having trouble breathing.

Narrator: And all this is happening while you're at 30,000 feet.

♪♪ ANNOUNCER: "CITY IN THE SKY" IS AVAILABLE ON DVD.

TO ORDER, VISIT SHOPPBS.ORG OR CALL 1-800-PLAY-PBS.