TAKEOFF As we push back from our gate at Heathrow Airport we light the Boeing 747’s engines in pairs, starting with those under the starboard wing. A sudden hush falls in the cockpit as the air flow for the air-conditioning units is diverted. It’s this, air alone, that begins to spin the enormous techno-petals of the fans, faster and faster, until fuel and fire are added, and each engine wakes with a low rumble that grows to a smooth, unmistakable roar. We begin to taxi. In legal terms, a journey begins when “an aircraft moves under its own power for the purpose of flight.” In aircraft manuals, elaborate charts that recall da Vinci’s “Vitruvian Man” illustrate the angles and distances that the extremities of the plane sweep through as we maneuver on the ground. A pleasing terminology accompanies these images of the plane’s turning limbs: tail radius and steering angle and the wingtip that swings the largest arc. A quarter of an hour later we reach the runway. I push the four thrust levers forward for an experience that repetition hasn’t dulled: the unfurling carpet of guiding lights that say here, the voice of the controller that says now; the sense, in the first seconds after the engines reach their assigned takeoff power, that this is only a curious kind of driving down an equally curious road. But with speed comes a transition, the gathering sense that the wheels matter less and the flight controls on the wings and the tail matter more. In the cockpit we sense the airplane’s speed-born life to come in the air, we feel clearly that long before we leave the ground we are already flying along it, and as the lights of the runway start to alternate red and white to indicate its approaching end, as the four rivers of power that equal nearly a quarter of a million pounds of thrust unfurl over the runway behind us, I lift the nose. As if we are only pulling out of a driveway, I turn right, toward Tokyo. We are underway. When someone I’ve just met at a dinner or a party learns that I’m a pilot, he or she often asks me about my work. Three questions come up most often, in language that hardly varies. Is flying something I have always wanted to do? Have I ever seen anything “up there” that I cannot explain? And do I remember my first flight? I like these questions. They seem to have arrived, entirely intact, from a time before flying became ordinary.

WATER London, now, is on my side of the cockpit. The gaze of passengers on the right side may follow the Thames as far as the North Sea. From the flight deck we see the Suffolk coast directly ahead of us, a clean line of land’s end that moves steadily down the aquarium-thick panes of the windshield as we climb and accelerate. Land, not water, will predominate on this route to Tokyo — a journey across all of Eurasia, the world’s largest land mass, bookended by the blue of two seas. But these first minutes over the North Sea are enough to remind me that flying offers perhaps the last thing an aspiring pilot would expect: a close experience of water. About 70 percent of the world’s surface is ocean. Much of the land that long-haul pilots work above is covered in snow or ice. At any given time, roughly two thirds of the Earth is covered in cloud. For many miles and hours in the sky — sometimes for nearly an entire flight — water, in one state or another, is the only thing we see. It’s routine from the cockpit to see storms form in real time, and from them the fall of new rain on the roof of the ocean, or to overfly the endpoints of glaciers, where shards of the ancient snow-glass tumble into the police-light blue of northern seas. When, after long hours over desert or sparsely inhabited land a city appears, the water we see near it — lakes, dams, rivers locked in their rolling green frames of vegetation — looks holy as blood. Our image of the Wright Brothers on the windswept Carolina coast is the best reminder of the debt every pilot owes to the sea. Today in the air we still speak a nautical language — of forward and aft; cabins, galleys and bulkheads; manifests, rudders and trim. We count aircraft by hulls and fleets. Our port and starboard wingtips are marked by red and green navigation lights, arranged as upon a ship. Our speed in the blue between two cities is measured in knots. What remains of us is our wake.

AIR Perhaps the simplest question about any flight is, How high are we? Three altimeters in the cockpit — two bright digital readouts, and one old-school device with hands that turn like those of a clock — show 31,000 feet. Yet we know that we are probably not as close to 31,000 feet as these altimeters suggest. We are somewhat lower; or perhaps we are higher. One thing is certain — it would be easy to find a dozen airliners flying over different parts of the world, all of whose altimeters displayed 31,000 feet, none of which are at the same altitude. How is this possible? Planes calculate their altitude by measuring air pressure. The air lies most heavily on places that are lowest, the places that have the most air piled above them. A barometric altimeter (baros, meaning weight) equates high air pressure — lots of air weighing down — with low altitude. As a plane climbs, there is less air above it. The altimeter senses less air weight and reports a higher altitude. There’s a problem, however. Air pressure is not constant. It varies across the Earth. It also varies in each place as time and weather pass. Consider an airplane parked at an airport. If the air pressure changes, then what’s displayed on its altimeters changes too, even though the airplane has not moved an inch up or down. It’s a regular occurrence to board a parked airplane whose altimeters claim that it’s either well underground or already climbing up in the sky. Such anomalies are dealt with by adjusting the altimeter. Before we depart we obtain a measurement of the current local air pressure. With our altimeters correctly tuned, we can ensure that at low altitudes we are safely separated not only from other airplanes but from nearby obstacles and hills. Measuring Altitude Altimeters measure air pressure to determine altitude. Pressures are higher closer to the ground, but they also vary with time and location. Pilots account for this in different ways, depending on the stage of flight: At cruising altitudes: Here the only obstacles are other planes. Pilots set their instruments to determine altitude based on a global average air pressure. Air pressures are translated into assigned altitudes called flight levels, where pilots must fly to avoid one another. As air pressure fluctuates, planes rise or descend in tandem, sticking to their assigned flight levels. 32,000 ALTIMETER READING: 32,000 32,000 FEET 31,000 31,000 31,000 30,000 High-altitude readings are usually different from the actual elevation above sea level, but no matter: the point is to maintain a consistent separation. ALTIMETER READING: 31,000 FT. ELEVATION ABOVE SEA LEVEL: 31,400 FT. Around takeoff and landing, pilots need to measure their true altitude more accurately in order to maintain their separation from nearby obstacles and the ground itself. ARRIVAL AIRPORT Precise elevations needed for land features DEPARTURE AIRPORT SEA LEVEL SEA LEVEL To ensure altimeter readings that accurately reflect safe clearance from earthbound hazards, pilots set their altimeters to local sea level air pressure. This is given by air traffic controllers and aviation weather reports. These rigorous calibrations to the local air were a surprise to me when I was first taught about them. But even more surprising is the fact that at the higher points of flight, we abandon them. At high altitudes we are far from any obstacles below. But we face a new problem: Our local altimeter setting would soon become inaccurate — both to the changing air around us, and to the settings of other aircraft that departed from other cities. So, to ensure our safe separation from other high-flying aircraft, we all set standard. We switch the reference point for our altimeters to a common pressure setting that’s derived from a universal, standard model of the Earth’s air. To ignore local air pressure, of course, is to ignore our true altitude. Indeed, planes following altitudes referenced to the standard atmosphere collectively and continuously adjust their degree of wrongness — gently climbing or descending in a collective, school-of-fish-like movement as the true air pressure below changes with time and location. Locked for hours at what our altimeters show to be 31,000 feet, our true altitude may vary constantly. Think of an ocean, of all the boats across its vast expanse rising and descending on their local swells. All the boats are on the surface, though their true elevation varies. An altitude referenced to the standard atmosphere is called a flight level and it is just like such a surface: a membrane encircling the Earth, pressed with indentations and textured with rises, shimmering invisibly on the aerial imperfections of the world.

SKY COUNTRIES “Call now London,” an air traffic controller says to us, followed by a new frequency. Since takeoff we’ve been passed from one London controller to another, sharing a few minutes of airtime before we’re handed over to the next as simply as a baton. But now we’re nearing the invisible border of London’s aerial dominion. The last of today’s London controllers says “Contact now Maastricht. Good flight.” The world’s airspace is divided. There are various sorts of divisions. To the pilots who cross them every day, their borders form what we may regard as the countries of the sky. London is such a sky country. Maastricht is another — indeed, it’s one of Europe’s busiest and most important volumes of named air. It covers much of the higher airspace over the northwest corner of Europe, a new and unified dominion above some of the Continent’s historically bloodiest borders. America’s sky countries look much as its states might, if some pitiless war or committee had hugely reduced their number. The sky called Salt Lake City covers parts of nine states, from southern Nevada, north over the Great Salt Lake itself to the Canadian border, which it meets between the air-states of Seattle and Minneapolis. There is a region called New York; yet most of New York State lies in Boston, which also encompasses all of New England. Air Traffic Control Zones SEATTLE BOSTON MINNEAPOLIS SALT LAKE NEW YORK CLEVELAND CHICAGO OAKLAND INDIANAPOLIS DENVER WASHINGTON KANSAS CITY Atlantic Ocean LOS ANGELES MEMPHIS ATLANTA ALBUQUERQUE FT. WORTH JACKSONVILLE HOUSTON MIAMI Pacific Ocean Gulf of Mexico KZSE KZBW KZMP KZLC KZNY KZOB KZAU KZOA KZDV KZID KZDC KZKC KZTL KZLA KZME KZAB KZJX KZFW KZHU KZMA The names of some sky countries are familiar to pilots before we fly anywhere. Paris, Delhi, Bangkok; world cities beneath their eponymous air countries. Other aerial names correspond to places less familiar to a pilot, like me, who grew up in western Massachusetts. The syllables then form a kind of aerial poetry, the drumbeat of distant sky-lands beyond the next fold of the chart: Turkmenabat and its sister Turkmenbashi; Vientiane, Wuhan and Kota Kinabalu; Petropavlovsk-Kamchatsky, Norilsk and Poliarny. Or the names are among the last you might imagine would rise to prominence in the brightly modern sky: Arkhangelsk, Dushanbe and Samarkand. In the borderlands, where pilots transfer from one set of controllers to another, there’s a certain majesty to the place names heard so high above the turning Earth. Several sky countries after Maastricht, the sun is setting behind us, and the first stars appear in the night we are racing toward. A Finnish controller says “Sir, call now Sankt-Peterburg. You are released.”

WAYPOINTS If you asked me where we are right now, seven or so hours into our flight, I would say we are in the sky country called Irkutsk. More specifically, we are approaching INTAK. INTAK is a waypoint. An airplane typically navigates through sky countries along a route composed of a few radio beacons and many waypoints. Waypoints are defined by coordinates or their bearing and distance from a beacon, and by a name, which typically takes the form of a five-letter capitalized word — EVUKI, JETSA, SABER — that’s pronounceable and distinct to controllers and pilots regardless of their first language. Waypoint names are the sky’s audible currency of place, atomized and distinct. Many waypoint names are random, but others are not. Near the border of India and Pakistan is TIGER. Another TIGER forms part of an arrival pattern for London, as if lifted from Britain’s former empire as incongruously as an animal taken from a warm place to a zoo in a cold city. From Singapore to London, I may overfly both. There are five SHARK waypoints — one east of Sydney, the others off the islands of Jersey, Maui, Taiwan and Trinidad. It’s America’s sky-mappers who have gone to the greatest lengths to localize its skies. Near Kansas City are BARBQ, SPICY, SMOKE, RIBBS, and BRSKT. Near Detroit is PISTN; also MOTWN and WONDR (Stevie, Michigan-born). Waypoints With a Message WEWIL NEVVR BUCKO HONNR COURG FORGT DRRON SEPII BRVRY PLDGE ALWYZ Final approach Reagan National Airport TRUPS OOURR USAAY SUPRT JARHD WEEDU SEALZ PJAAE RANJR Above: waypoints along two initial approaches to Reagan National Airport in Washington. These routes guide planes to their final approach. Boston has etched a particularly rich constellation onto the heavens above New England. There is PLGRM, of course; CHWDH, LBSTA and CLAWW; GLOWB and HRALD for the city’s newspapers; while SSOXS, FENWY, BAWLL and OUTTT trace the fortunes of the city’s baseball team in long arcs across the stars. There’s a NIMOY waypoint; Leonard was born in Boston. In a letter written in 1869, Mark Twain wrote that “the grand problem of aerial navigation” is “a subject that is bound to stir the pulses of any man.” Twain, the pilot of riverboats who died seven years after the first flight at Kitty Hawk, never flew. But he might be pleased by the thought of 747s, and of TWAIN, the waypoint over Hannibal, his childhood home on the Mississippi.

NIGHT It’s been dark for hours now. There are three pilots on a flight this long and now it’s time for my break. A colleague takes my place in the right-hand seat of the cockpit. Before I go to the bunk, located at the rear of the cockpit, I stay for a moment by one of the side windows, to gaze out and up. If you look into the night sky from an airplane for more than a few minutes you may well see a shooting star. My eye catches something. I look, smile and say to myself, There’s another one. I don’t even mention them to a colleague; another will be along soon enough. One winter night, before I became a pilot, I sat in a window seat on the left side of the plane for a flight from Chicago to Boston. It was bitterly cold in both cities. About halfway through the flight, I looked out the window and saw what could only be the aurora borealis, the northern lights. I had never seen them before. The slow transformations in shape and brightness took the form of milk poured into a glass of iced coffee, or of dye landing in water. A few minutes later one of the pilots came out to stretch his legs. He told me he was nearing the end of a long career in aviation, and this night’s display was the finest he had seen so far south in the planet’s skies. That night I thought it must be a wonderful thing to be a pilot, to see such a sight regularly. In winter’s long darkness the auroras are our clouds of light, from beneath which wisps of illumination drift away, like rain swept sideways by the wind. Yet as the years since I became a pilot go by I find that the northern lights have come to represent a challenge I didn’t expect. Sometimes I find it hard to remain interested — in the northern lights, in the ceaseless meteors or a hundred other phenomena of the sky and Earth — because they appear so regularly, because to pilots, they are ordinary. My original excitement returns, at least in part, when I try to share what I see with others. When I see the auroras start to form I often tell the flight attendants, so they can look from a window or come to the cockpit for a wider, clearer view. Sometimes, if a passenger is awake, one of the cabin crew may quietly point to the window, to the surf of light breaking along the sky’s northern shores. Afterward the crew member and I may talk about the sight in the galley, as if it was almost new to us again.