Skyfaring: A Journey With a Pilot

by Mark Vanhoenacker

  The designers of radio altimeters must also consider the deceptively simple question of where, exactly, zero is. That is, where the airplane itself begins. Given the radio altimeter’s use near landing, it makes sense to define a height of zero not by the bottom of the fuselage, where the radio altimeter itself is likely mounted, but by the bottoms of the wheels when the landing gear is extended. But this isn’t straightforward either. When a 747 comes in to land, the landing-gear legs—shock absorbers, essentially—are longer because they are not compressed. Additionally, the plane itself is nose-high, tilting upward. (Many airliners point upward not just in the climb, but throughout the cruise and much of the final descent, too, an upcast geometry of flight that partly explains the brake pedals on meal trolleys, the subtleties of flat beds, and why it is almost always harder to walk toward the front than the back of a plane.)

  Because in flight we want to know the height of the lowest point of the plane, the radio altimeter starts counting not from the altimeter itself, or from where the wheels end when they are on the ground, but from roughly where the wheels end when there is no weight on them, when they are flying freely through the air.

  At landing, though, the nose lowers and the weight of the plane presses down onto the landing gear, compressing it. Now the 747’s ever-truthful radio altimeter finds itself below where it understands the ground to be in flight. And this is exactly what it reports to us when we first walk onto a parked 747, adjust our seats, turn up the brightness on the screens, and start our takeoff preparations: that this airplane is 8 or 10 feet below the earth’s surface. Even the most sophisticated measure of our height above the earth’s surface is inconstant; it depends on whether we are coming or going.

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  One October a friend and I went to Iceland. We drove clockwise from Reykjavik, and late one night, several days and autumn storms later, we rounded the island’s far southeast corner. In England the weather makes perfect sense to me if I imagine, even in the center of London, that I am on deck, at sea; if just past the newsstand or coffee shop on the far corner of the street I picture a pounding, Turner-caliber seascape. Driving in Iceland I repeatedly had the sense not that we were at sea—though the sea was almost always nearby—but that we were flying. I’ve never been more aware of the wind’s effect on a car. Merely staying on the road required a near-permanent force to be applied to the steering wheel, left or right depending on the direction of the road and the rain-laced crosswinds. Each gust knocked us halfway out of our lane.

  Planes, too, must sometimes be briefly driven down a road in strong winds, on the runway at takeoff or landing. A plane on the ground can be steered with either the wheels or the flying controls—or with both. As the speed of a plane on the ground increases and more air flows over its flight controls, these grow in effectiveness, as a hand-wing extended from the window of an accelerating car might. This gives the unexpected and accumulating sensation that during takeoff you are simultaneously driving in the air and flying along the ground. In Iceland, after we stopped one night, I thought how much easier the driving would have been if Icelandic rental cars were equipped with some airplane-style controls, a rudder, perhaps—some recognition of and accommodation to their unintended life in the air.

  Wind, to the earthbound observer, suggests a local event against a default background of stillness, a breeze passing over a fixed point on earth; over us. But higher up, the air itself, the reference frame of flight, is almost always in motion. Once I leave the ground I no longer think of wind as a flow of air that passes over us; rather, it carries us whole, as a river or an ocean current.

  If you could produce a view of the earth showing only those things moving faster than 100 mph—a map of speed, a worldview made only of motion—you would see a few trains, and plenty of motorists in Germany, the lines of their velocity sketching out the network of autobahns. You would see many planes, materializing as they accelerated for takeoff and vanishing from the speed planet when they landed and slowed. Mostly, though, you would see the jet streams, the high winds that ring the earth. “Where are the jets tonight?” I might ask a colleague, or comment that: “All the way over we’ve been fighting a strong jet.” The jet in jet stream is said to derive from the streaming quality of the winds, not the aircraft we most associate with them. But these winds were only properly understood after we started to fly, and today the name is a pleasing convergence of the engine type and the wind patterns that both enable and shape our greatest journeys over the planet. The fastest jet stream I have flown in recently was 174 knots—a tailwind, thankfully. (Knots are nautical miles per hour; a nautical mile is equal to 1.15 regular, statute miles, so 174 knots is around 200 mph.)

  There are many factors that determine which path a plane will follow between two cities. Sectors of airspace may be congested or temporarily closed, often due to military exercises, and the varying navigation charges that countries impose mean that routes longer in time or miles can nevertheless be more cost-effective. En-route weather conditions are another consideration. But in the absence of such factors, the primary task that flight planners and pilots face is to navigate the high winds; to harness them by hitching a lift on a sky river that is flowing the right way or to actively avoid them, fleeing the tempests that would enormously slow an airplane’s progress over the world.

  Over the North Atlantic, which so many planes cross en route between North America and Europe, a new set of wind-optimized routes is charted each day, one set for the westbound flights and one for the eastbound. Each day the westbound planes may arc far to the north, swinging high onto the Labrador coast to avoid the west-to-east winds that blow further south. That night those same planes may return to Europe in a momentous arcing, a vast and more southerly swoop, seeking out the heart of the eastbound jet stream that only hours earlier they went so far out of their way to avoid. Often the winds lever the paths of opposite-directioned planes away from each other so effectively that the route of an airplane flying from London to Los Angeles, say, will never once cross the path taken the same day by a plane from Los Angeles to London.

  A great circle is the so-called straight line between two places, as a string would connect them around the surface of a sphere. (Indeed, in my airline’s office, to one side of a bank of flight-planning computers stands a globe with such a string still attached to it, a relic of the age when great circles might still be plotted by hand.)

  On flights from northern Europe to western North America, passengers are occasionally surprised to see from the moving map screen how far north we are—often over Greenland, where one of the planet’s most reliably spectacular panoramas of sea, ice, and mountains awaits those travelers lucky enough to have a window seat. The shape of these routes is often attributed to the marvel of great circles. But westbound planes often fly still further north than the great circle to escape the howling headwinds that would devour their time and fuel; the same winds for which that night’s returning pilots will be grateful, when they fly well south of the great circle, seeking the sky where the eastbound air tide is strongest. Occasionally I’ve started a flight from London to the west coast of North America on airways heading slightly northeast around a congested bit of airspace, rather than northwest. The overriding task on such a day is to escape the westerly wind. Only then do we take up our course.

  While planes may move to or from these rivers of air, the rivers themselves transform and wander over the earth. They strengthen or weaken, twisting and drifting away from their typical haunts in long, languid sweeps across the cold miles of sky. The optimal route—the shortest and most fuel efficient—between two cities changes constantly, and so the route that an airliner flies between them can vary dramatically from one day to the next. Some days when I fly to New York, the last I see of Europe is Northern Ireland; the next week, flying to the same city, the farewell takes place over Land’s End. When the jet streams drift far from their traditional homes, skies that are normally quiet will fill with jets for a few
hours or days, their pilots drawn like surfers to the most favorable sky-swells. The natural forces of the world shape even these, our most technologically advanced journeys; they guide our migrations with an all but biological simplicity.

  Planes also alter their vertical paths in response to the wind. At each point in a flight, a plane has an optimum altitude, based primarily on the aircraft’s weight. As fuel is burned the aircraft’s weight reduces and the optimum altitude rises. So in an ideal sky—one free of other airplanes and variations in the wind—a plane might climb continuously throughout its flight, until it was time to start the descent for arrival. But vertical differences in the strength of winds often overwhelm this ideal altitude, and so we may climb up early, to an otherwise inefficient altitude, because it is even more valuable to us to find the heart of a jet stream. Or we may descend to avoid one. On a recent flight from London to Miami, the Atlantic headwinds were so strong and wide that there was no way to avoid them horizontally. So, after climbing to 37,000 feet for the first few hours of flight, we descended to 29,000, surrendering nearly a quarter of our initial altitude, more than enough to make our ears pop. Later we climbed again, and then we descended; a kind of porpoising, a vertical wayfinding in the ocean of air.

  Our flight paperwork and the onboard computers help us make such calculations. But we also have paper tables in the cockpit called the wind-altitude trades. The name recalls the trade winds that swept ships to the New World, ships that would then arc northward to catch different winds and currents home, in an echo of the aeolian geometry that pilots and flight planners deploy every day above the same waters. Another pilot at a different altitude might ask us what wind we are experiencing—our spot wind, it’s sometimes called—which will help them decide whether to climb, descend, or stay right where they are.

  As with altitude, an airliner is also always calculating the most efficient speed for the moment-to-moment conditions of flight. You might think, as I did, that this most efficient speed would be the same regardless of whether the plane is experiencing a headwind, a tailwind, or no wind. But in the tangled calculus of the air, the damage wrought to an aircraft’s efficiency by a headwind is greater than the gift the same wind speed would offer, were it a tailwind. The stronger a tailwind, the less time you benefit from it, while the greater a headwind, the longer you are subjected to it. For this reason, the flight computers will suggest accelerating to what would otherwise be a less efficient speed to minimize the time we’re exposed to a headwind. While in a tailwind the computers will suggest slowing down; to linger awhile with the wind at our back.

  Wind is so critical to flight calculations that some manuals refer to a new kind of distance: air miles, or air distance. Air distance adds the effect of the wind to the distance along the ground that the plane flies over. As a unit of length, it is as fluid as the air itself; the high-country mile. If there is any headwind or tailwind at all, and there almost always is, then a flight from London to Beijing, for example, will have a different air distance than a flight that follows precisely the same route in the opposite direction, from Beijing to London—and both these air distances will differ from the distance along the ground.

  Occasionally, while still on the ground, after I load the route into the computers but before I enter the expected winds, the flight computers flash up a warning that the plane does not have enough fuel to complete the planned route without dipping into its sacrosanct final reserve of fuel. Then I tell the computers something about the winds over the world; the computers consider it and are satisfied. Though the miles on the ground are unchanged, though we have not even started to move, the air distance has been remade by the wind.

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  Richard Bach, the author of Jonathan Livingston Seagull, once titled an essay “I’ve never heard the wind.” Few pilots today ever do. Though they make up one of the natural world’s most dramatic physical presences and determine both the path and length of all our journeys, the winds exist largely as numbers on the cockpit’s screens, where a diminutive symbol (only an arrow, sadly, not a cockerel) turns like a weathervane. The wind’s dimensions are a regular topic of conversation among both pilots and flight attendants on a trip, as casually central to our daily life as delays on train lines or morning traffic jams. We do not mind a headwind on the outbound journey, because it often means a faster return home the next day. But we do not hear or feel the wind directly.

  Jet streams occasionally produce turbulence, particularly at their boundaries. But often they are so smooth they suggest something like the opposite of their true dimensions. When it’s a little bumpy I remember that I am flying at 600 mph, in air that is moving at 200 mph, yet the plane is steadier than a car on a dirt road. Often the fastest winds are as smooth as glass. When the computerized wind readout shows even a routine wind for an airliner to experience, 50 knots for example, I think that anywhere but Iceland, perhaps, such a wind on the ground—58 mph—would make the news. We would struggle to stand against it, and yell to be heard.

  Maritime cultures, such as those around the Mediterranean, still deploy many archaic names for winds—the Bora, the Sirocco, the Khamsin. Today, England has one named wind, the Helm Wind, known for occasionally shrieking down the western slopes of the Pennines in Cumbria. But it’s easy to imagine that the so-called Protestant wind that blew the Spanish Armada away from England might have become a general term for the east wind (“Popish” winds blew, too, a century later, to delay the arrival of William of Orange). America retains a few named winds, such as the Santa Anas of southern California and the Chinook, and even a fictitious wind, the Maria, from the Gold Rush musical Paint Your Wagon (from which the singer Mariah Carey gets her name and its pronunciation). Hawaii once had hundreds of named winds; whether you could list a place’s winds and rains there was a test of whether you were truly a local.

  Imagine looking up one morning and seeing a Nile or an Amazon in the sky, in a slightly darker blue, a shimmering, partly reflective navy hue, twisting and curling in the north sky over your hometown, and migrating to the southern sky by the time you go out for lunch. Aside from the sun itself, such air rivers would be the most dramatic feature of the earth or the sky. We have so matter-of-factly fashioned the souls of cities, of literatures, of whole civilizations from rivers—the Danube, the Mississippi, the Yangtze. One manufacturer has even named its jet engines for British rivers—the Spey, the Trent, the Tay—to contrast their smooth flow with the unevenness of piston engines.

  We might have made something more of the jet streams, have worshipped and built a complete mythology around their image, had our prescientific eyes been able to see them. Flying, though one day it will feel as old as sailing does today, is still new to us. It’s not nearly too late to style the sky’s high winds, to scatter up the seeds of an aerial heritage.

  Though the jet streams run in sweeping, largely east–west bands around the earth, we might choose to give their different sections different personalities, as in England the names of some rivers and streets may change midstream. The high winds over the continental United States might be renamed the Wiley Posts, or the Post Winds, for Wiley Post, the one-eyed American aviator who was the first pilot to fly solo around the world, and who is partially credited with the discovery of the jet streams. Post died in Alaska in 1935, aged only thirty-six, in the crash that also killed the humorist Will Rogers. There’s an old-style aviation beacon named for Post and Rogers on top of the George Washington Bridge in New York, a memorial in light that once also served as a marker for aircraft taking up their westbound routes. “Our flight to Raleigh,” a pilot returning from the west might say, “is just under four hours tonight, thanks to the Post Winds.” Meanwhile, the winds over the North Atlantic, which blow so reliably and steadily from North America toward Europe, we could dub the Allied Winds, to help us remember they were best documented during the transatlantic resupply efforts of the Second World War.

  It is a joy of my job that I’m occasionally tasked wi
th drawing the winds. In the cockpit of the 747 many of our paper maps have been replaced by electronic versions. But there remains a set of disposable maps that cover the world, which are sometimes called progress charts. As a child I saw carbon copies of these mounted in the passenger cabin of the aircraft—the path of the plane, a charcoal-gray zigzag over blue sea and yellow land. I still have one or two that I asked the cabin crew for on those long-ago flights.

  These charts have space for the date and flight number, and for the pilots to write their names and ranks. Completing a progress chart, I feel as if in another age I would be crouched over a table, in heaving seas, an oil lamp or heavy brass navigational instrument on the table to hold the paper in place. I like to draw the steady lines between distant waypoints in thick green or blue ink, to sweep over countries, mountains, oceans as only a pen, or an airliner, can do. Although we have other, computer-generated maps that show the predominant winds along our route, some pilots still draw the winds onto the chart, along with the forecast areas of turbulence.

  A pilot who does not wish to waste paper might save the chart for the flight home, plotting the return route and winds in different colors from the outbound ones. But if we ever have visitors to the cockpit after landing, especially kids, we will gladly give them the chart to take home. Someday even these last of our paper charts will be removed from cockpits; they will become relics of the early jet age. For now they remain, these maps of transience and air in every sense—hand-drawn charts of one day’s unique and wind-sculpted journey and of the great unnamed rivers of the sky that hindered us or blessed us and carried us on our way.