Ask the pilot

Do airlines cut down the flow of oxygen in the cabin to save fuel? Can wind shear rip off a plane's wing?


Patrick Smith
July 18, 2002 11:30PM (UTC)

OK, readers will have to take my word that I do indeed feel sympathy toward those of you with white knuckles. The ill-at-ease flier in 34B does nothing to enhance the merriment or livelihood of the crew, and in many ways it injures our pride to know we can usually do little to ameliorate your irrational fears of crashing. After evaluating dozens of e-mails in which readers worry over bizarre calamities the likes of randomly snapping wings and spontaneous plunges to watery doom, the best I can do is throw out the usual flying-vs.-driving comparisons and other statistical encouragement: At major airports alone, across America and around the world, airplanes come and go at a rate approaching 100 per hour. This happens every day, every week, every month, every year. Of these, the number of flights that fail in their attempt to successfully defy gravity can be totaled in very short shrift.

If my explanations, which tend to be the stuff of numbers, statistics and hard facts, fail to provide comfort, then you'll need to seek it elsewhere. I am not qualified to dissect irrationality or wavering, ambiguous fears of undefined situations ("I feel the plane is going to fall from the sky"). I cannot pretend to be a psychologist, nor, to at least one reader's disappointment, am I able to recommend nerve-calming sedatives.

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Also, many travelers are getting lousy advice. I'm losing count of how many letters begin, "My friend says ..." or, "A colleague once told me ..." or, worst of all, "I saw on the Internet ..." inevitably finishing up with such boldly ludicrous assertions as "So what's the point? If we crash, we're all going to die anyway." Who are these people, spies from Amtrak looking to drum up riders? Or are some of you loath to admit your own superstitions? There are many stories making the rounds, both electronic and otherwise, that are the aviation equivalent of "urban myth," some of them tantalizingly believable. I realize the airlines are losing more and more respect among fliers every day, and I anticipate a level of cynicism. But please check with me before perpetuating nonsense.

In my original discussion of pressurization, I misleadingly wrote, "Normal cabin pressure aboard a plane is actually a little higher than sea level." What I meant is that the altitude the cabin is a little higher. At 35,000 feet, the cabin altitude (not the same as the altitude outside the airplane, in accordance with the purpose of pressurization) will read 5,000 feet or so, roughly that of Denver. This changes as the plane climbs or descends, and at the point of touchdown the cabin altitude will equal that outside.

Also, a few readers rebuffed some of my answers by throwing military planes into the mix, negating this or that first or biggest plane. I assumed it was understood we were discussing civil aviation only. If such a point was missed previously, allow me to assert it, as the flight attendants love to say, at this time. Also culled from any future discussion are piston-powered, single-pilot aircraft. Following my statement that a passenger had never taken the controls after crew incapacitation, three readers were eager to debunk me by bringing up the case of the student pilot who recently landed a Cessna 402 operated by Cape Air. I was familiar with this, but had excused this category of airplane from the discussion of things "airliner."

Would you comment on the air quality in commercial airliners? I've heard that the pilots decrease the airflow in order to save fuel. Also, is it true that the amount of oxygen is intentionally reduced to keep passengers docile?

Somebody is getting a lot of mileage (pun intended) from the "decreased fresh air to save fuel" bit. This comes up quite often. But while the airlines might be penny pinchers, never once, at any company, have I been instructed to cut down on air circulation to save fuel. Somehow I think a planeload of pissed off passengers negates the marginal benefit of a few saved gallons of kerosene. That said, yes, the air conditioning systems on certain airplanes are better than others, some of them notoriously deficient. But the crew has no control over inherent design, and no pilot would cut back the air to stretch out fuel.

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There is no truth whatsoever to the second and far more outrageous part of the question. Keep in mind that the cockpit is not a sealed chamber with its own pressurization system. Passengers and crew are breathing the same air, and there is no way to tinker with the oxygen in the cabin without affecting the cockpit as well. The crew could don oxygen masks, I suppose, but the idea of the pilots sitting there with masks on, dialing up the pressurization to partially suffocate the passengers, is a bit preposterous, don't you think?

What can you tell me about the process of takeoff? I live in San Francisco, where takeoffs are very nerve-racking. Can you explain how a plane takes off and why it bumps, jigs and turns, sometimes at a high angle?

Interestingly, takeoff is the more critical point than landing. Here the airplane is making the transition from ground to flight, and its grip on the latter is much more tentative than during landing.

The characteristics of every takeoff are basically the same. The plane reaches a predetermined speed, based on weight. The point at which it reaches this speed depends on temperature and other factors. The pilots then rotate the aircraft to a specific angle and begin the climb. All of this, from the rotation point to the thrust setting to be used, is calculated beforehand. After breaking ground, the pilots follow a "profile" of speeds and altitudes at which they retract the landing gear, flaps, slats, reduce or increase climb angle, etc., all while turning to assigned headings or fixes and climbing to assigned altitudes. It is probably the busiest portion of any flight.

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If it seems that takeoffs from certain airports are unusually hectic, it is probably because the plane is following noise-abatement procedures on behalf of residents below. These can change the departure profiles somewhat, and usually require lower-altitude turns or steeper climbs. You are more prone to feel turns and jigs because you are climbing, close to the ground, at high power settings. The sensations tend to be exaggerated.

What is wind shear? And can it rip the wings off?

Well, to keep it simple, wind shear, one of those horrific buzzwords that scare the crap out of passengers, is a sudden change in the direction and/or velocity of the wind. It can happen vertically, horizontally, or both, as in the case of a microburst preceding a thunderstorm. A microburst is an intense, localized burst of air from a storm front. Think of it like an upside down mushroom cloud. The strength of the shear can run the range of barely noticeable to potentially deadly. Fortunately it has become easier to predict, and as a rule wind shear does not simply appear out of nowhere, flipping a plane upside down without warning.

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This "rip the wings off" business is something I can't begin to address. It's like asking, "Can a wave break a ship in half?" Theoretically, yes. Practically speaking, no. In the case of wind shear, pilots are not worried about losing wings, they are worried about losing speed when a certain number of knots from a headwind suddenly "shear" to a tailwind. But again, conditions in which this will happen are generally predictable, and pilots are trained to deal with them. Wind shear got a lot of press in the 1970s and 1980s when it was still a misunderstood phenomenon. The crash of Eastern Flight 66 at Kennedy Airport in 1975 is considered the watershed accident after which experts began to study it more seriously. The last major accident attributed to wind shear was in Dallas in 1985.

Is it helpful to speak up about something that doesn't look or sound right? Is it even possible that a passenger could discover something the crew doesn't know about?

Customers pass along concerns like this all the time. Never once have I known a pilot to sneer or mock anybody's well-intentioned query. The only time crewmembers take offense is when it's done arrogantly, such as when a guy pokes his nose into the cockpit and mumbles, "Hey, your tire's flat," and then walks off. (Of course, the tire is not flat.) It's never happened to me, but I've heard of instances where a passenger discovered a minor mechanical discrepancy. Usually it's just a missing rivet or some such, but always the information is appreciated.

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Often it seems like the airlines only want to fly in good weather. Yet the weather service routinely flies low-tech planes through hurricanes. How much of avoiding weather is safety, and how much is the airlines just not waiting to scare the passengers? I would rather endure a few bumps and arrive on time, than sit at the airport for three hours.

While NASA or the weather service may occasionally fly research airplanes through hurricanes, it is not anything you want to try, trust me.

The vast majority of weather delays are caused by traffic congestion at destination airports, or en route saturation along routes, or "airways." In the first case, separation requirements change as ceilings and visibility go down, and aircraft must be funneled into instrument approach patterns. Fewer aircraft can land in a given stretch of time, backing up the arrivals. In the second case, even high-altitude routes often become blocked by storms, and so flights are diverted around them, causing backlogs. Often these two situations occur simultaneously, and the congestion can reach a point where departing flights are held on the ground so they don't exacerbate the gridlock.

If a flight is diverting around a weather cell, it is not doing so to placate squeamish passengers. If that very airplane were empty but for the pilots themselves, they would be making the same decisions.

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According to several accounts, pilots are notoriously cheap. Wanna take a swipe?

If pilots are cheap it's because it often takes them years and years of slugging it out at low-paying commuter airlines before they ever make a halfway decent blue-collar salary. The pilots on the upper parts of a major airline's seniority list indeed make a good living, but it didn't come easy. Those working for smaller regional carriers often make embarrassingly poor salaries, and it can take many years before they join the ranks at a better-paying major airline, if ever.

Flying, it has been said, is much like acting, painting (or writing for online magazines), etc. Rewards loom for the fortunate, but many pilots are suffering for their art.

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

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Patrick Smith

Patrick Smith is an airline pilot.

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