Ask the pilot

Why not build airports on hilltops, so planes can save fuel by taking off or landing at an incline? The pilot gives the idea all the consideration it deserves.


Patrick Smith
August 22, 2003 11:30PM (UTC)

I was so depressed after last week's sobering distillation of airline financial misery that I've taken off to Malaysia and Indonesia (don't worry, I'm wearing Kevlar shorts and Jihad-resistant socks). Provided I'm not kidnapped or blown to smithereens, next week's column will be coming at you from an Internet cafe in Borneo.

On the way I'll be laying over in Dubai and Kuala Lumpur, home to two of the globe's most impressive airports, which got me thinking: In all the ranking of best and biggest I neglected to cover airports.

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If you're thinking acreage or hectares, you won't be indulged, because I find those distinctions a meaningless affair of easily consumed real estate and the placement of perimeter fences. Denver, the new Hong Kong, etc., take up city-size stretches of real estate, but so what? Most of it is grass, dirt and concrete. I'll pay Hong Kong a nod for having the most expansive and impressive terminal, but that's as far as we'll go.

People and planes are the appropriate yardsticks. And challenging ones at that, because the numbers are deceptive. Most of the busiest airports are hubs, meaning that large numbers of travelers -- sometimes the vast majority -- are passersby, temporary visitors in transit between flights. Atlanta's Hartsfield International sees more footsteps than any other airport on the planet, but I venture most of them are confined to the concourse.

The hub concept thus allows small population centers to be represented by large airports. At Charlotte, N.C., Douglas International is the 34th busiest in the world, yet by number of residents Charlotte is hardly a preeminent metropolis with anywhere close to that standing. It owes its out-of-scale aerocommerce to US Airways.

Cincinnati and Salt Lake City are comparable examples, courtesy of Delta. Nothing against the citizens of northern Kentucky, where the Cincinnati (CVG) airport is situated, but it wasn't civic warmth or tourist attractions that encouraged Delta to lay its spokes across your countryside; it was the ease of building a room-to-grow hub in the nation's heartland and the chance to develop an enormous regional feed from dozens of nearby Midwestern cities. On Delta you can fly to London, Paris and Zurich nonstop from Cincinnati, a place most Brits, French and Swiss probably couldn't locate on a map. Elsewhere cities such as Dubai, and to some extent Singapore, follow the same rule.

Of course, you'll always find bustling airports around bustling cities, and in many cases huge population centers coexist with sprawling hubs. For this reason, Chicago's O'Hare is perennially one of the two or three busiest airports in the world. Metro Chicago's population base provides vast quantities of local traffic, while the field's geographic position makes it ideal for hub-and-spoke connections. Paris, London and Tokyo are very similar. O'Hare is a rarity in that two major airlines, United and American, both run megahubs from the premises.

By pure passenger volume, as researched by Air Transport World and the Airports Council International, here were the 10 largest airports in the world last year. Note the position of Denver, which would have no business on the list at all if it weren't for United's in-transit feed. Connecting passengers are counted only once:

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1. ATL Atlanta, U.S. (76.9 million)
2. ORD Chicago -- O'Hare, U.S. (66.5 million)
3. LHR London -- Heathrow, U.K. (63.3 million)
4. HND Tokyo -- Haneda, Japan (61.1 million)
5. LAX Los Angeles, U.S. (56.2 million)
6. DFW Dallas/Fort Worth, U.S. (52.8 million)
7. FRA Frankfurt, Germany (48.5 million)
8. CDG Paris -- Charles de Gaulle, France (48.3 million)
9. AMS Amsterdam, Netherlands (40.7 million)
10. DEN Denver, U.S. (35.7 million)

As you know, plenty of cities are equipped with more than one major airport. New York's clustered threesome -- Kennedy, Newark and the comparatively smaller La Guardia -- are each among the world's 40 busiest. By combining passenger totals at multi-airport cities, we can invent a new category -- that of the busiest metropolitan areas:

1. London -- Heathrow, Gatwick, Stansted, London City and Luton (117.9 million)
2. Tokyo -- Haneda and Narita (90 million)
3. Chicago -- O'Hare and Midway (83.4 million)
4. New York -- JFK, Newark and La Guardia (79.2 million)
5. Paris -- Charles de Gaulle and Orly (71.5 million)

"Busiest," as you might guess, is a relative thing. As last week we swapped criteria in figuring the largest airlines, we can swap to determine the biggest airports. Measured by takeoffs and landings, or "movements," as we say, it all changes. The catch here is that smaller craft, those 19- to 50-seaters, count no different from a 747. In Boston, for example, close to half of all movements are regionals, lofting it to 25th place for movements versus 37th in number of people.

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In thousands of takeoffs and landings, regardless of how many folks are aboard, here's your score:

1. ORD Chicago -- O'Hare, U.S. (924,000)
2. ATL Atlanta, U.S. (890,000)
3. DFW Dallas/Fort Worth, U.S. (765,000)
4. LAX Los Angeles, U.S. (645,000)
5. PHX Phoenix, U.S. (546,000)
6. CDG Paris -- Charles de Gaulle, France (510,000)
7. MSP Minneapolis/St. Paul, U.S. (507,000)
8. LAS Las Vegas, U.S. (497,000)
9. DEN Denver, U.S. (494,000)
10. DTW Detroit, U.S. (491,000)

These figures -- and last week's too -- allow a beautiful and comforting segue into safety. From the above we realize that in 2002 at the top two airports alone, Chicago O'Hare and Atlanta, almost 2 million airplanes arrived or departed, transporting 143 million people in the process. Not a single plane crashed and not a single life was lost.

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An article in a left-leaning magazine ran a piece about a radical idea for airports. Building a new airport at the top of an incline, the article said, could save huge amounts of fuel because planes would be going downhill for takeoff, and uphill for landing.

Having once authored some music reviews for Utne -- oops, now you know -- I'm loath to bash their reportage. Plus the reviews were shitty (god, what I did to the Jazz Butcher's "Illuminate"!), so I owe them.

This is a tantalizing concept, but easier said than done. For one, planes normally take off and land in the same direction (into the wind, if possible), not head-on. You can't be upsloping and downsloping at the same time on the same strip without a conflict, so you'd have to have at least a pair of runways.

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Further, planes need enough runway not just to reach takeoff speed, but to stop if a takeoff is aborted at high speed. Stopping along a downsloping surface commands more energy and distance than along a flat one. As you might recall from a few columns ago, existing runways with gently graded surfaces mandate slight penalties. With an overtly steep grade, a runway would need to be longer, probably much longer, to avoid incurring prohibitive weight sanctions. And no, one of those mountain-style turnoffs like those used for out-of-control trucks would not be helpful.

You're talking all sorts of revisions and asterisks to standard techniques that would, in the end, offset the benefits. Asking around, I was told the U.S. Air Force experimented with this concept back in the 1950s at Wright-Patterson Air Force Base near Dayton, Ohio. Seeing that the experimental runway has been used for the annual soapbox derby since then leads us to believe the idea was deemed impractical. Fuel savings, at any rate, would be minimal. A medium-size plane might use about 150 gallons more for your average non-slanted departure.

I used to know a guy -- he fixed furnaces for a living and thought he knew about "mechanics and stuff." It was his belief that the reason dragsters and hot-rod cars had big tires in the back was for better mileage, that the car's rear was higher and it would always "think" it was going downhill. He was a nice guy, so I never told him what an idiot he was. Now, if we could just put bigger tires on the main landing gear and small tires on the nose gear, the airplane would think it was taking off downhill all the time and save thousands of gallons of jet fuel.

Why do planes take off and land into the wind?

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To understand this, recall how a plane stays in the air and imagine there's a 20-knot headwind pointing down a particular runway. Well, if a plane's intended takeoff or landing speed is 120 knots, then 20 of those knots are already taken care of.

For the sake of argument, imagine there's a hurricane blowing at 200 knots and you tow a 757 from the hangar and turn it toward the storm. Theoretically, the plane would lift off and "fly" just as would on the way to Denver. What would the cockpit airspeed gauges read? Two hundred knots. The plane does not care how fast, or in what direction, it is moving across the ground, only how fast it is moving through the air. That is the difference between airspeed and groundspeed, and by extension, yes, a plane can fly "backwards." Up in a two-seat Cessna you can point your nose into a strong wind, slow the machine to as little an airspeed as possible, and sure enough you might find yourself drifting backwards like a kite, relative to the ground.

What happens if the wind suddenly stops or changes direction? That's windshear. Winds are always gusty and whipping around, but in extreme cases a shear can be dangerous.

Some airports are laid out with local climates in mind, and flights will try to take advantage of prevailing winds. For reasons of traffic management or to avoid noisy overflights of neighborhoods, this isn't always possible, and then you're stuck with a crosswind or tailwind. Tailwinds are beneficial when cruising along at high altitudes, but they're not much fun when taking off or landing. Tailwinds are irrelevant to airspeed, but will increase groundspeed. Racing down a runway, a plane will be pushed along, using up valuable runway while its actual "speed" is unaffected. Maximum allowable tailwinds for takeoff or landing are very low for most planes, around 10 knots or so.

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Do you have questions for Salon's aviation expert? Send them to AskThePilot and look for answers in a future column.


Patrick Smith

Patrick Smith is an airline pilot.

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