Cockpit Confidential (4 page)

Most turboprops are started electrically rather than pneumatically. If there's no APU and ship's batteries aren't sufficient, something called a GPU (ground power unit) provides the juice. Towed behind a small tractor, the GPU looks like one of those generators used at roadside construction sites.

You don't. Planes almost never run their engines at the gate. What you see is the wind spinning the first stage fan. Even a moderate breeze can rotate that fan quite rapidly. If this seems impossible because a plane is cornered against a building or facing the wrong direction, that's because the wind is coming
from behind
. On newer engines, the majority of intake air is blown
around
the core of compressors and turbines, providing a clear shot at the fan blades from the rear.

Would you believe $200 million for a single new Airbus A330 or Boeing 777? Or $70 million for a new 737? Even the little regional planes most of you can't stand are multimillion-dollar machines. A $20 million sticker price isn't out of the question for a high-end regional jet or turboprop (and you can remember that the next time you're walking up the stairs and cracking a joke about rubber bands). The price for secondhand aircraft differs markedly with age, upgrades, and upkeep. A lot depends on the engines, which alone can sell for millions apiece, and maintenance: how long before an overhaul is due, and what kind of overhaul? A used 737 can be had for $2 million or $20 million, depending.

Airlines do not own all, or sometimes even any, of their planes outright. They lease them from banks and leasing companies, making regular payments not unlike the way you'd finance a car. There would be no other way to afford them.

I hate this question, and it comes up all the time in slippery forms. Descriptions like “made more cheaply” belittle the complexity of an airliner, no matter the maker. No plane is cheaply made. Boeings and Airbuses are certainly different in many ways. They abide by different philosophies of construction and operation, and both have their own pleasant or annoying quirks. And occasional controversies: Airbus has been criticized for relying on control automation that, in certain circumstances, cannot be overridden by the pilot. Boeing, for its part, was dogged by rudder malfunctions that caused at least two fatal 737 crashes in the 1990s. Still, there is no statistical safety difference that merits citing, and opinions on which is the “better” plane get into the nuts and bolts of the systems—the kinds of details that'll have you (and me) yawning fast and that do
not
reveal themselves as bangs, moans, rattles, or anything else detectable by a passenger. For pilots, it comes down to personal preference and, in a way, style, more than quality or lack thereof. It's not unlike comparing Apple to PC; each has its fans and detractors.

Speed at higher altitudes is indicated by something called Mach number. Mach is the speed of sound (Ernst Mach is your man), and Mach
number
is a percentage of that speed. Long-haul planes fly slightly faster than short-haul planes. A 747, A380, or 777 will fly between .84 and .88 Mach (84 to 88 percent of the speed of sound). For smaller jets like the 737 or A320, the range is between .74 and .80 Mach. On the 767 I fly, cruising speed is anywhere from .77 to .82 Mach. Optimum speed is different for every flight. If the plane is on time, or if fuel burn is a factor, we'll be planned at whatever Mach is most fuel-efficient. If we're running late, and so long as fuel isn't an issue, we'll probably go a little faster. The recommended Mach is given to us as part of the flight plan.

On a thirteen-hour journey between New York and Tokyo, these differences matter. A slight Mach advantage saves several minutes of flying time. But on shorter hauls it's negligible, and there's no point in choosing one plane over another for the sake of punctuality. In any case, ATC (air traffic control) constraints are the primary factor in determining speed, not aircraft capabilities. On short flights especially, controllers routinely ask pilots to speed up or slow down.

The border between subsonic and supersonic, near which most planes cruise, is not an aerodynamic triviality. In a poor man's version of Einstein's speed of light conundrum, required energy increases dramatically as you cross the sound barrier. Though not an outright obstacle of physics, it's a gigantic pain in the wallet. For supersonic flight, a completely different wing is required, and fuel use soars. Remember the Concorde? It wasn't the tragic crash near Paris in 2000 that hastened the plane's obsolescence so much as its ghastly operating costs. For these reasons, despite all the other technological advances we've seen, the cruising speeds of commercial jets have not really changed since their inception. If anything, the twenty-first century airliner travels slightly
slower
than its counterpart of thirty years ago.

The Boeing 777-200LR has the longest duration of any commercial jetliner—some twenty hours' worth, allowing it to span 9,000 nautical miles and then some without refueling. Almost every major city pair on Earth is connectable with this astoundingly long-legged aircraft (
see longest flights
). Runner-up is the A340-500, first flown by Emirates and Singapore Airlines. Current variants of the A380, 777, and 747 have comparable but slightly lesser capabilities.

Understand that endurance, which is to say hours aloft, is the more accurate metric for measuring range, not miles, and this can vary with altitude, cruise speed, and other factors. Also, a plane's size isn't always a good indicator of how long (or far) it can fly. The old Airbus A300, probably the best example, was built specifically for short- to medium-haul markets even though it could accommodate 250 people. Meanwhile, there are nine-passenger executive jets that can stay aloft for eleven hours. Neither is it fair to say out of hand that one plane has greater reach than another. Does an Airbus A340 outdistance a Boeing 747? Some do, some don't. Technical options, such as engine types and auxiliary fuel tanks, help determine endurance. Watch the dashes. There's not just a single A340; there are the A340-200, -300, -500, and -600. At Boeing you'll discover -200s, -400s, -800s, -LRs (long range), -ERs (extended range), and so forth. And a larger suffix might not tell the whole story. An A340-500 is a smaller plane than the A340-600, but it has a longer range. A 777-200LR outlasts the substantially larger 777-300ER. Still with me? If you enjoy graphs and charts abounding with asterisks and fine print, go to the manufacturers' websites and knock yourself out.

There are weight limits for the different operational regimes, including limits for taxiing, taking off, and landing. The Airbus A380's maximum takeoff weight exceeds one million pounds. A Boeing 747's weight can be as high as 875,000 pounds. For a 757, it might be 250,000 pounds, and for an A320 or 737, it's around 170,000. A fifty-passenger turboprop or regional jet will top out around 60,000. Those are maximums. The actual, allowable takeoff weight varies with weather, runway length, and other factors.

Passengers are not required to divulge the quantitative specs of their waistlines, obviously, so instead, airlines use standard approximations for people and luggage. The values—190 pounds per person (including carry-ons) and 30 pounds per checked bag—are adjusted slightly higher during winter to account for heavier clothing (please don't ask me about trans-climate routes). The boarding tallies are added to something called the BOW (basic operating weight), another fixed value that accounts for the plane itself, replete with all furnishings, supplies, and crew. Once fuel and cargo are added in, the result is the total gross “ramp” or taxi weight. Fuel used for taxiing is subtracted to reveal the takeoff weight.

This will probably surprise you, but in the case of a fully loaded 747, four hundred passengers and their suitcases—about 75,000 pounds together—make up only around 10 percent of the total bulk. Fuel, rather than people or their belongings, is the greater factor, sometimes accounting for a third or more of a plane's sum heft. Because of this, pilots calculate their kerosene in terms of pounds, not gallons. Everything from initial fueling to en route burn is added or subtracted by weight, not volume.

Both weight and its distribution are important. A plane's center of gravity, which shifts as fuel is consumed, is calculated prior to flight and must remain within limits for takeoff and landing. Pilots are trained in the particulars of weight and balance, but the grunt work is taken care of by the load-planners and dispatchers.

Hot air is less dense than cold, negatively affecting both lift and engine performance. The takeoff roll will be longer and the climb shallower, and in very hot temperatures, a plane may no longer meet the safety margins for a particular runway—climb gradient parameters and the distance needed to stop if takeoff is aborted. A maximum allowable weight is determined for every takeoff based on weather and runway length. Going a short distance with limited fuel is unlikely to be a problem, but full tanks or a heavy payload can put you up against the limits, and cargo or people will sometimes need to be bumped.

In addition, some planes have maximum operating temperatures stipulated in their manuals. At a certain threshold, aerodynamic penalties become excessive and components begin to overheat. These limits tend to be quite high, around 50 degrees C (122 degrees F), but every once in a while flights will be grounded outright.

As it works for temperature, it works for altitude. The higher you climb, the thinner the atmosphere, degrading aerodynamic efficiency and output of the engines. High-altitude airports often entail payload penalties for takeoff. Mexico City sits at 7,400 feet and is a great candidate, as are Denver, Bogota, Cuzco, and many others. For years, before the advent of higher performance planes, South African Airways' New York–Johannesburg flight could go nonstop only in one direction, and this was part of the reason. The eastbound leg from JFK took advantage of a long runway at sea level. On the return, Johannesburg's 5,500-foot elevation entailed a sanction. Topping off the tanks meant having to leave people or freight behind, so the flight would call for fuel in the Cape Verde Islands or Dakar.

Once aloft, a flight may initially be too heavy to reach the most fuel-efficient altitude and will “step climb” its way as fuel is burned off. How high you can fly at any given time is predicated not only on the physical ability to reach an altitude, but also on maintaining applicable stall margins once it gets there.

Contrails are formed when humid jet exhaust condenses into ice crystals in the cold, dry, upper-level air—it's not unlike the fog that results when you exhale on a cold day. Contrails are clouds, you could say. Water vapor, strange as it might sound, is a byproduct of the combustion within jet engines, which is where the humidity comes from. Whether a contrail forms is contingent on altitude and the ambient atmospheric makeup—mainly temperature and something known as vapor pressure.

I refuse to devote valuable page space to the so-called “chemtrail” conspiracy theory. If you know what I'm talking about and wish to argue the matter, feel free to email. If you don't know what I'm talking about, don't worry about it.

This is a tough one for me. I'm probably greener than most people, abiding best I can by the three Rs of good stewardship: reduce, reuse, recycle. I don't own a car, and much of the furniture in my apartment was scavenged from curbsides and refurbished by hand. I've replaced my incandescent light bulbs with compact fluorescents. Then I go to work and expel hundreds of tons of carbon into the atmosphere. Am I a hypocrite or what?

Commercial aviation is under increasingly virulent attack for its perceived eco-unfriendliness. In Europe especially, powerful voices have been lobbying for the curtailment of air travel, proposing heavy taxes and other disincentives to restrict airline growth and discourage people from flying. (“Binge flyers” is the derogatory nickname for Europeans who take advantage of ultra-cheap airfares to indulge in short-stay leisure junkets.) How much of this outcry is fair and how much is gratuitous airline-bashing is debatable. Airlines are easy targets these days, but in the hierarchy of environmental threats, they are perhaps disproportionately villainized.

I'm the first to agree that airlines ought to be held accountable for their fair share of ecological impact, but that's the thing: globally, commercial aviation accounts for only about
2 percent
of all fossil fuel emissions. Commercial buildings, for one, emit a far higher percentage of climate-changing pollutants than commercial planes, yet there is little protest and few organized movements to green them up. It's similar with cars. Americans have staggeringly gluttonous driving habits, yet rarely are we made to feel guilty about them. U.S. airlines have increased fuel efficiency 70 percent over the past thirty years, 35 percent since 2001 alone, mostly through the retirement of fuel-thirsty aircraft. Average fuel efficiency of the American automobile, on the other hand, has stayed stagnant for at least three decades.

The sticking point, though, is that the true measure of aviation's environmental impact goes beyond simple percentages. For one thing, aircraft exhaust—containing not only carbon dioxide, but also nitrogen oxides, soot, and sulfate particles—is injected directly into the upper troposphere, where its effects aren't fully understood. Separately, experts contend that the presence of those aforementioned contrails propagates the development of cirrus clouds. Clouds breed clouds, you could say, and cirrus cover has increased by 20 percent in certain traffic corridors, which in turn influences temperature and precipitation. As a rule of thumb, experts recommend multiplying that previously cited 2 percent fossil fuel figure by another 2½ to get a more accurate total of the industry's greenhouse contributions. Using this formula, airlines now account for about 5 percent of the problem.