From the archives: Wolfgang Langewiesche on mountain flying

Editor’s note: Wolfgang Langewiesche is famous for writing the bible on flying, Stick and Rudder. He was also a friend of Air Facts founder Leighton Collins and a frequent contributor for the magazine. In this detailed article from 50 years ago, Langewiesche offers some timeless tips for flying in the mountains.

A briefing for the high country: canned experience for sale here

A man who has just got his license buys his first airplane and sets out across the high country of the West. It is his first big trip. As he loads in his wife and kiddies and the luggage we stand by, watching. “We” means the people who taught him to fly, gave him his license, sold him his ship. It also means the rest of us just fellow-pilots who happen to know some of the things he has yet to find out. Do we owe this man any advice?

I think we do. Too many new pilots come to grief on trips of this nature. And this is not from lack of flying skill. They have just passed their flight tests. Nor is it from lack of aeronautical knowledge in an academic sense. They have passed their writtens. In some respects they know more than they will ever use. It’s more from a sort of innocence. They are not prepared for the real-life situations they will meet. They fail to recognize the problems, or, if they do, they have no solutions ready-made in mind. They lack (of course) experience. What’s experience, other than that the problems are expected, the various solutions pre-thought-out? I think it should be possible to give the new man some advance knowledge of the problems and the solutions — equip him with some canned experience, so to speak. This is needed for many aspects of flying. Right here we’ll try to do it for the high country.

First of All

What one thinks of first, of course is the long fast take-off run and the shallow, slow climb. Landings, too, are faster and longer in the high country, but not by very much. That’s a cheerful fact — high country landings are no problem.

The big difference is in take-off and climb. Responsible is the thin air, which cuts engine power and also reduces wing lift. And what’s responsible for the thin air? Elevation and summer heat in about equal measure. Our new man should know this clearly. On a hot day, even a low level airport has thin air, and take-off there is noticeably poor. On a cold day, even a high field has reasonable dense air, and take-off is OK. Our new man will probably do his high country flying in summer, and he’ll have air that is high and warm. His take-offs will be poor.

The numbers can be picked off the clever Koch Chart, and they are startling. At 7000 feet, with the air at 100°F, the take-off run is tripled, compared to sea level, the climb is only a quarter of sea level climb. These, however, are extreme values, the air at the higher elevations rarely gets quite so hot. And the airport designer too, has consulted the Koch Chart, and has lengthened his runways to allow for the power performance. So if our man uses a regular airport, widely used by all sorts of airplanes, he has nothing to worry about. He need not be scared: just aware. He should be mentally prepared for the long take-off run and a very shallow climb. He needs no more skill, just a little more patience. He should not try to pull the airplane off too soon, or to climb it too steeply. Perhaps, before his trip, he might want to have his wheels balanced with more than usual care. If there is any wheel shake or shimmy, the higher speeds of those take-offs make it much worse and this then makes you hurry your take-off.

Mixture

Only one point of special technique is needed. Above 5000 feet or so, lean out the mixture right on the ground before take-off. At high elevations, on a hot day, our engines drown in fuel. The Koch Chart shows the performance of airplanes with the mixture right. The mixture too, responds to both elevation and air temperature. That performance is poor enough. With an over-rich mixture some airplanes may hardly get off. This effect of thin air, via the mixture, may have caused much trouble in the past. It’s been a semi-secret. Pilots where taught to have the mixture full-rich for take-off. Owners Manuals said: don’t lean the mixture until above 5000 feet — and then only for cruising, not for climb. Renter pilots were told: leave that thing strictly alone. On some rental airplanes the mixture control was safely wired in the full-rich position. Nobody wanted to say it — lean your mixture. The reason was, of course, that a lean mixture while using full sea level power can damage an engine, can even cause engine failure right on the climb-out. Nobody wanted to be responsible, let alone liable. Well, the fact is — the double-fact is: a) at 5000 or above, the power output of the engine is so restricted anyway that you are no so likely to damage it even by leaning excessively; b) the mixture runs so excessively rich at 5000 feet in summer on the ground that you can lean it out quite a lot — with a marked gain in power — and still be safely on the rich side. You don’t really lean it; you de-rich it. And of late, some Owners Manuals have begun to say it under “Engine Check Before Take-off.” “Above 5000 feet, adjust the mixture.”

How to Lean

This leaning out is not hard to do — brakes held, wide open throttles or nearly so, move the mixture gradually until you get roughness or a drop in RPM. Then rich it up again “some” to be safely on the rich side of Best Power. With an injector engine you also lean out steadily, but from time to time give it a quick small forward (enriching) shove on the control. When this surge of enrichment causes a surge of RPM you know we’ve past Best Power on the lean side: you richen it up some and there you are. With an Exhaust Temperature Gauge, of course, it’s easy.

The biggest problem at some fields may be to find a place where you can rev wide open without sucking a lot of gravel into your propeller. One therefore learns to do a fair enough job just by putting the mixture control where one thinks it ought to be. With a little practice, you can also adjust the mixture during the take-off run. It is not necessary, after all, to have theabsolutely best power — just so the poor thing isn’t suffocating. The thing to remember is that an airplane climbs on the power it has to spare, over and above the power it needs to maintain airspeed. Therefore a 10% increase in power may well mean a 20% or even a 30% improvement in climb. The more under powered and/or heavily loaded the airplane, the bigger the improvement.

Flap Use

Flaps on take-off? At high elevations, this is a problem. Flaps get the wheels off the runway sooner, thus reducing friction, and that is a gain. But flaps reduce the rate of climb, and that is a loss you sometimes can hardly afford. Probably the best way is to take off with some flap, the immediately, as soon as airborne, retract them — slowly. This takes a little practice, and familiarity with your airplane. In a low powered, heavily loaded airplane, with the flaps partly down you may get into an unpleasant situation. The airplane climbs quite nicely to the top of the ground cushion, say 20 feet or so. At that altitude you now pass the airport boundary. But now the airplane pauses in its climb. This is very unpleasant. The airspeed is low. The drag of the flaps keeps it from building up. The ground is too close, and maybe too rough, to do much nosing down. If you just retract the flaps you might get a sink right to the ground. If you keep them on, you’ll be a long time picking up a healthy airspeed.

Loads

All our small airplanes are being operated all over the West with no restrictions as to gross weight. But our man will operate under the least favorable conditions. The local man flies, as he drives, with his machine half empty much of the time. Our man will probably be heavily loaded. The local man flies the year around, and has the benefit of much cool air. Our man will probably come through the high country at the hottest time of the year. And he will be a stranger.

Our new man should understand that a 10% reduction in an airplane’s gross weight (not: “Load”) improves the climb by more than 10%. (This is because there is less weight to be lifted, and at the same time slightly less forward speed to be maintained; so that there is slightly more power available for lifting less weight.)

For the stranger, in summer the finest special equipment to put into an airplane is an empty seat.

Airspeed for Best Climb

Our man should accurately know his airplane’s speed for best rate of climb. Not all do. In ordinary flying we do not use this speed much. We usually climb at higher airspeeds for good cooling: sometimes, briefly, at lower airspeeds, for best angle of climb. But in the high country, speed for best rate of climb becomes important. Near its ceiling, an airplane climbs only at that one speed. The speed is shown in the Owners Manual — a slightly different value for each altitude, air temperature and gross weight. For practical purposes one figure is enough ― perhaps the one for 10,000 feet in standard air. Better to have one figure in mind, than a whole set of figures in the glove compartment. Still better to make a chalk mark on instrument panel, opposite the right place on the rim of the airspeed indicator. Such a mark has persuasive powers at anxious moments.

The Turn Toward Lower Terrain

This is the emergency exit from bad situations. If you can’t climb any more, or get a sudden sink, you turn toward lower terrain. It’s really obvious. The trick is at that moment to be in a position to do it! The Western pilot avoids sticking his nose into any place where such a turn cannot be made. He flies across a ridge slope-wise; in flying up a canyon or narrow V-shaped valley, he holds to one side; he always keeps that turn open. He is not afraid to fly quiet close to terrific mountain walls and cliffs ― provided he can keep them at his side, not in front.

Downdrafts

With your rate of climb so poor, it is often futile to fight a downdraft by trying to out climb it. The climb, by slowing you up, keeps you in the downdraft longer; and the net result is more sink. Better, usually, to put the nose down a bit, pick up some speed and get out of there in a hurry. (We avoid the word “dive” because it sounds too wild. There are mountain situations with rough air when you want to avoid high airspeeds, because you might get hit by a gust.) Our new man should understand the technique of the soaring pilot who puts his nose down in the downs, holds it up in the ups. That way, he spends less time in the downs, more time in the ups, and absorbs energy from the atmosphere. The pilot of the small airplane can do the same, or at least avoid doing the contrary.

The Landing at High Elevations is no Problem

This is a most pleasant fact and our man should know it. It will put him at ease. Many people almost naturally assume that the high elevation landing is stretched out in the same proportion as the take-off is. If this were true, we would have a problem! But it is not true. The mountain air does not stretch the landing in the same proportion as it stretches the take-off. If a high elevation airport is big enough to take-off, it is super-ample for landing.

I think we should tell the new man: forget the elevation. Land as you would at home. That’s what everybody ends up by doing. Specifically: make your approach at the same indicated airspeed as you would at home under similar conditions of turbulence, load, and field length. If the airspeed indicator feels the same, the wing feels the same, and the airplane power-off, behaves the same.

It is true that there are some fine points of difference. The glide (true airspeed) is faster, by maybe 20% than at sea level; the landing is faster, and the landing run is longer. Bumps in the runway are a little more noticeable. So are the imperfections, if any, in the pilot’s technique ― bounces, drop-ins, not taking all the drift out. The glide angle, power-off, is a little steeper, because at the higher true airspeed, the idling engine exerts more drag. The flare-out is a shade different, owing to the higher true airspeed and the slightly steeper glide angle: it is as if you were landing a slightly more heavily wing loaded airplane. But these effects are not highly noticeable. In fact, it is hard to demonstrate them. I think they fall within that band of errors and uncertainties that accompanies any approach and landing — up-and-down drafts, wind gradient effect, small errors of judgement ― the pilot is all primed in any case to take care of them: something tells him he needs to drop the nose, to apply a bit of power right now, etc.: there high elevation effects wash out in this more general uncertainty. And the practical truth is that there is no important difference between a power-off approach and landing at sea level and the same maneuver conducted at 7,500 feet.

A Wrong Idea

A lot of airplanes are bent in the high country because the stranger, fighting imaginary dangers, burns them on at high speed. You know how it is: he adds a couple of knots for the wife and kiddies, and a few for gusts, and a few more for being a stranger. Maybe his instructor built in a few extra knots at the outset, by never teaching him a slow, tail-down landing. If he now adds ten knots for thin air, it really is too much!

A psychological factor then comes into play. In the over fast approach and flare-out, the airplane is too responsive and jumpy. It reacts to turbulence too strongly, and also to the controls. The pilot wobbles and over controls as he floats and floats. This, in turn, produces a sort of synthetic turbulence; and that makes him want to use still more speed! That way you get one of these landings where the airplane is light on its main wheels, and the brakes don’t hold. Perhaps the airplane “wheelbarrows” on the nose wheel and sidles off the runway.

So I think we should advise the new man; “land as you land at home.” No tricks, of course. No attempts to pull off a real short landing. By all means allow extra speed for extra weight, allow for being a stranger, allow for turbulence. But do not allow extra for the thin air. That allowance is already built into the behavior of the airspeed indictor.

Once this is understood and really believed, we are free to tell our new man about some aspects of high country landing that are a little different.

The Mixture Again

If the pilot goes by the low level book ― mixture full-rich, carburetor heat on, flaps down — he will be in poor shape for a go-a-round. He would have to get his flaps at least partly up, his carburetor heat off, his mixture leaned out, before he could do much climbing: he might forget one of those items, and get into trouble trying to climb in an airplane that won’t do it. So we should tell him ― on the approach, keep your mixture properly “de-riched;” use carburetor heat only as really needed; and in case of a go-around, don’t forget the flaps.

The Power Approach

To maintain the same descent slope as at sea level, and the same indicated airspeed, the airplane needs noticeably more power than at sea level. (Since for the same indicated airspeed our true airspeed is about 20% faster, we need about 20% more RPM than we need at sea level.) This makes a lot more noise. It soundslike a lot more extra power than it really is. It shouldn’t really matter because, in any case, what we do in a power-on approach is to maintain the airspeed with the elevator and adjust the throttle experimentally so as to get the desired angle of descent. It ought to make no difference to us that here in the high country we wind up with the throttle a little further forward, and a little more buzz.

It is not difficult, it is merely different. But in our flying we rely a lot on things notbeing different. We expect certain numbers, certain noises, certain control positions and pressures, to get us certain results. And when they don’t we may be a little slow in noticing it. So, in this case, our man will probably get a little low before he wakes up to the need for more power. And now, having got a little low, he will have to put an extra lot of extra power to get in.

This happens, I think, to everybody. Some let it undermine their confidence in the mountain air. “Gee,” they say, “this air is so thin ― if you didn’t use a lot of power, you’d drop right in.” Not so. A power-off glide would have come out perfectly normal. A power glide needs a little more power, that’s all.

Slope

Naturally, in mountain country many runways are uphill or downhill. Naturally, one would like to land uphill. But this may mean a tailwind. What to do?

Rule: Slope is more important than wind. The higher the country, and the heavier your load, and the less high powered your airplane, the more so. Western pilots land uphill, take off downhill, almost regardless of wind. They accept quite considerable tailwinds. If the tailwind is toostrong, they don’t use that field that day.

Of course, everything depends on the how much: how much slope, how much wind, load, elevation, power, etc. It is impossible to give a rule. Besides our man would find it difficult to judge slope and wind velocity from the air, so a rule would do him no good. But we should bias his mind: respect for slope, comparative disregard for wind.

Slope is a help, not a hindrance. It is what makes those glacier landings possible. Because of slope, runways which look too high or too short on the map may be quite comfortable. Unless you know the slope, the published runway lengths have little meaning and usually make the field look worse on the map than it is in reality.

Committed

The uphill landing has a string attached to it: you can’t go around. At least, not with a low powered, heavily loaded airplane, at high elevation, and if the slope is strong. Here again, everything depends; but if our man tries to go around where he shouldn’t we would have the makings of a bad accident. The terrain rises faster than he can climb. He can’t turn, at least not quickly, because the extra drag of the turn would stop his climb altogether. It is a good situation to stay away from. What follows? Or rather: what comes first? Our new man should be briefed. On the final approach to a markedly uphill landing there comes a Decision Point. If he goes on down beyond that, he can no longer go around, he then must get the airplane on the ground ― even if this means, perhaps, overrunning the end of the runway and bending something. Fortunately, he is quite unlikely to overshoot an uphill land, for reasons which follow.

Landing While Climbing

Uphill landings require extra airspeed.

The flare-out to an uphill landing is a super-flare-out, so to speak: you bend the flight path from downward not only to level but to upward. This takes extra airspeed, or else a blast of extra power during the flare. The usual story, the first time, is that the pilot at the last moment runs out of airspeed and/or elevator control, and makes a hard, bumped-on landing. Well, forewarned is fore-armed. A blast of power at the right moment will remedy the trouble. An extra few mph of airspeed, on the approach, will prevent it. So what seems like a difficulty is actually a pleasant fact. It makes life easier. On the approach to an uphill landing you can afford an ample air-speed and still not float a long way. If you do float, the float, too, is uphill and therefore short. The landing run, too, is uphill. This is one reason why, on an upslope landing, a tailwind is quite acceptable.

Tilt

An optical illusion makes you fly low and slow.

In the final approach to an upslope landing, the pilot is powerfully beset by an optical illusion. He thinks he is higher than he really is, relative to the intended touch-down point. He also thinks he is more nose down than he really is. He therefore flies lower and slower than he intends to fly. What brings on the illusion is that the runway slants up, but the pilot’s eye/mind interprets it as being level. Tilt!

This is illustrated here. Note that Picture A is simply a copy of Picture B, tilted exactly the way the pilot’s mind tilts the situation. Picture A is the illusion. Picture B is the reality. Note that the runway appears to the pilot in exactly the same perspective in both cases. It also appears at the same angle underneath the airplane’s nose, in both cases. All that is needed is the mental tilt, and it will make the pilot misjudge position and attitude by quite a lot. It is a powerful illusion.

There is another version of the same thing ― even more sneaky. The airport lies on a smooth plain, many miles from any mountains. The runway does not visibly slope relative to the terrain immediately surrounding it. But the whole plain is sloping up quite strongly toward those distant mountains. Your eye does not appreciate this slope ― at least, not fully.

In Practice

The pilot has two ways to break the power of this optical illusion.

1. Pay attention to his airplane ― his airspeed indicator, his trim, his stick forces. “Attitude Flying” is no good if you judge your attitude from a phony reference!
2. He should let his eye sweep over the whole scenery, instead of getting too hypnotized by the perspective of the runway. His eye will then usually perceive the slope of runway, the slope of the plain upon which the airport lies, the whole lay of the land. The optical illusion will be gone. Will it? Perhaps not quite. It is very powerful. It works on you even when you know what’s happening. It sort of sucks you down.

What is the effect? Here again, it takes the pilot a little time to realize what’s happening. (It will take him less time if we have forewarned him.) By the time he wakes up, he is quite low and perhaps quite slow. He now will have to add a lot of power to drag himself in. I have sometimes goofed so badly that my “final” was really a stretch of level flight, across up-sloping terrain, to the touch-down point. This sequence of events ― the optical illusion that puts you down, the delayed reaction, the subsequent need for a lot of power ― may be another reason why people sometimes claim that the high country air doesn’t hold you up properly. The contrary is true. The mountain air is OK! The best way to calm down one’ approaches and avoid that last minute roar of power, is to plan a high, steep approach, using little or no power. “Land as you would at home.”

Take-Off or Landing

When in doubt about some ranch strip or other non-standard field, why not try it first alone? Park the family and try for yourself, light. Then, when you have the measure of the field, come back and ferry people and luggage, maybe in two trips. This is only common sense. But in the real-life situation it sometimes does not seem to occur to people that they have that option.

En Route

What can we tell the new man, beforehand, that will be useful to him in high country? It’s difficult. Flying is flying and air is air, and once we are up and en route it makes less difference what the country is like. On the other hand, all the factors are so variable; terrain, weather, season, airplane, load. It seems almost impossible to say anything except “Take it easy.”

Just the same, there are tendencies for things to behave in certain ways.

Routes

Clouds, showers, thunderstorms, snow showers tend to build up over the mountains first, and sometimes over the mountains only, leaving the valleys clear for easy flying. It is therefore much easier to follow the early transcontinental airways ― which, in turn, followed the early transcontinental railroads, which, in turn, favored the low and flat passages.

For the same reason, it pays to cross the big humps early in the day, and perhaps cross them where they are lower. On any particular trip this may turn out to be poor advice. On enough trips, it will average right.

The Winds

Local winds tend to blow up the slopes in the daytime, down the valleys at night ― provided, of course, the overall wind is not so strong that it overpowers those local tendencies. Turn-around time is before sunset. By sunset a strong local breeze blows down many canyons. This is the best time to land on a canyon or valley runway ― upwind, upslope. The best time for take-off downhill but not downwind is midmorning after the downhill winds have stopped, but before the air gets too hot.

The higher the country, the tougher it can get. It is not always tough. It can be calm, sunny and smooth among the big summits. But it can turn tougher, faster, in the really high country. The airplane’s performance is poor. The weather is more inclined to violent changes, cloud build-ups, snow showers, strong winds, downdrafts, turbulence.

Rotors

In the very high country, Sierra Nevada, for example, or the Rocky Mountains West of Denver, in days with strong winds aloft, you are in the region of Standing Waves or Lee Waves, and their associated “Rotors.” Here, small areas of really extremely rough air can be found; sometimes with clear air, sometimes with generally smooth air all around. It pays to be suspicious.

More airplanes have been lost in those very high sectors than seems explainable by the standard causes ― weather, engine trouble, out of gas, etc. In my personal opinion Rotor turbulence got some of them. We should caution the new man: Flying at mountain peak level on days with strong winds aloft, be cautious. How? Don’t build up high airspeeds, even though the air at the moment may be smooth. And tighten the seat belt down hard, so you don’t suddenly hit the roof.

It’s True

What else? Oh yes: all that propaganda about oxygen above 10,000 feet ― it’s real.

Lack of oxygen really does make people unobservant, stupid, and clumsy. And this sad state really is not noticeable to the pilot himself.

That sums up what I think the new pilot can usefully be told, beforehand, about flying in the high country. It assumes that he knows how to fly an airplane, knows VFR from IFR, knows about line-of-sight reception of omni ranges, and generally is a man of sense.

Can we put information of this sort into a sort of check list? I have tried that in the following bunch of questions and answers. The idea is that an instructor or more experienced pilot could ask the questions. For that matter, anybody could. If our man can recite the right answers, we can consider that we have prepared him for his high country trip ― so far as this can be done with words.

Note that there are no explanations. If our man believes our statements he will think out, argue out, or read up on the reasons. There are no trick questions. We are not trying to deepen our man’s understanding of flying, let alone test it; we merely want to make sure he has in mind, ready for use, certain ideas, facts, possible courses of action, that may be of value to him.

Note that there is little imperative in this check list. It is not our purpose to admonish anybody to be good. There’s too much of that around! There also are no skulls and cross-bones, no “Always” and no “Never.” What follows is awfully mild and bland. May it be useful.

Q. What is the main difference in airplane performances at high elevation fields?

A. A long take-off run and a shallow climb.

Q. What is the cause of this performance loss?

A. Thin air, caused in about equal parts by high elevation and high air temperature.

Q. What can a pilot do to make up for some of this performance loss?

A. Keep his load light. Take off at times when the air is cool.

Q. What special pilot technique is needed for high country flying?

A. Adjust the mixture for best power before take-off. Do not return the mixture to full-rich for the landing approach.

Q. At what air speed does an airplane have its best rate of climb?

A. The speed is different for each airplane. It is slightly different for each altitude. It is shown in the Owners Manual. For my airplane at 7500 feet, on a warm day, it is 88 mph (indicated).

Q. What is the effect of flaps on take-off?

A. They shorten the take-off run, but lessen the rate of climb.

Q. When a pilot encounters a strong downdraft what should we do?

A. Instead of trying to out climb the downdraft, he should pick up speed and fly out of the downdraft.

Q. When flying close to mountains, what is the main safety rule?

A. Stay in a position to turn toward lower terrain.

Q. In a landing approach at a high elevation field, what should the airspeed indicator read?

A. The same it would read at a low elevation airport under similar conditions of load, wind, and turbulence.

Q. Is a power-on approach to a high elevation field different from a power-on approach to a low elevation field?

A. More power is needed to maintain the same indicated airspeed at the same angle of descent.

Q. If a runway has a strong slope, what is more important ― wind direction or slope?

A. Slope is usually more important than wind. You land uphill, take off downhill almost regardless of wind. If the unfavorable wind is too strong, you don’t use that field that day.

Q. Does a sloping runway present a problem to the pilot?

A. On final approach for an upslope landing there is an optical illusion which makes the pilot think he is higher than he really is and more nose-down than he really is. This tends to make him fly too low and too slow.

Q. In landing uphill on a markedly sloping runway pilots often experience a last moment surprise. What is it?

A. They find they have insufficient airspeed to accomplish the uphill flare and they make a hard landing.

Q. In landing uphill at a strongly sloping field, what should the pilot have in mind as he “thinks ahead of the airplane?”

A. Do not attempt a go-around toward rising terrain ahead.

Q. When in doubt about take-off or landing at some high elevation field, what is a good course of action?

A. Try the field first alone, with a light load.

Q. Is anything predictable about mountain weather?

A. Clouds, showers and snow flurries and thunderstorms often build up over the mountains while the valleys are clear.

Q. How do you choose easy routes through high country?

A. The lower, flatter routes often have better weather.

Q. What is usually the best time to cross big mountain ranges?

A. Early in the day.

Q. What is the effect of altitude on the pilot?

A. Above 10,000 feet unless the pilot takes oxygen he becomes unobservant, stupid, and clumsy. Above 12,000 the loss of ability is severe. It gets worse the longer the pilot stays at altitude without oxygen.

Q. Is this loss of ability noticeable to the pilot himself?

A. No.

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Air Facts Staff

Air Facts was first published in 1938 by Leighton Collins, dedicated to “the development of private air transportation.” It’s a different world now, and it’s a different Air Facts. Relaunched in 2011 as an online journal, Air Facts still champions, educates, informs and entertains pilots worldwide with real-world flying experiences.

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