Mountain flying

2.25.2015 - Some aesthetic improvments
Mountains are often where the most beautiful airstrips are located, but they present a very unique and complex flying environment for light aircraft in terms of terrain, weather, turbulence, performance, and remoteness.
2.25.2015 - Some aesthetic improvments
Mountains are often where the most beautiful airstrips are located, but they present a very unique and complex flying environment for light aircraft in terms of terrain, weather, turbulence, performance, and remoteness.

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What's the big deal about mountains?

Some of the most beautiful and remote backcountry destinations lie within the mountains, and negotiation of this often generalized terrain feature in light aircraft can prove to be a challenge due primarily to the the less dense air of higher elevations, and weather.

Mountains come in all shapes and sizes, and can present the following concerns to a varying degree. But they all represent the same challenge to light aircraft: They are an obstacle that forces pilots to either 1) fly higher to avoid flying "within them," or 2) fly within them. Is flying within mountains a bad thing? No! It is amazing! That's where some of the best and most beautiful flying can be had, and where some of the world's most scenic and remote airstrips exist. However, operating within the mountains significantly changes the game in a few ways:

  • Operating in mountains goes hand in hand with higher altitudes, which can negatively affect the performance of aircraft engines, require higher groundspeed, and possibly have physiological effects on the human body from reduced oxygen.
  • Closer proximity to terrain is often required, and this is often made riskier by any significant wind and weather.
  • Mountains often act as a catalyst for precipitative weather events. They stick up into the atmosphere and cause moisture-rich air masses to lift up into the colder altitudes, condensing their water vapor into rain or snow. If ceilings are too low, there's no flyable space between the ground and the ceiling. Mountains sort of eat that available altitude up just by virture of being high elevation.
  • Mountains introduce drag to winds, causing that wind to become dirty, swirling, oscillatory, and rotor-like in nature. This is called mechanical turbulence and can easily overcome the ability of a light aircraft to maneuver or maintain a safe altitude above the ground.

Obviously this is a rich topic, and several books have been written about it. Two of the best-selling books, "Flying the Mountains" by Fletcher Anderson, and "Mountain Flying Bible" by Sparky Imeson, are very complete guides on the subject. However, mountain flying is simply one of those things that must be experienced in a dual-instruction scenario in addition to studying the more academic aspects. There are elements of the training that just can't be conveyed in a text. Please use this guide simply as a jumping-off point and seek out additional reading. And by all means, get qualified dual instruction.

Mountain flyingSqueaking through a pass in the Lick Creek Range, Idaho. Photo: Richard Holm

Effects of altitude

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Negotiating terrain

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Mountain weather

Mountains often act as a catalyst for precipitative weather events. They stick up into the atmosphere like a giant ramp and cause moisture-rich air masses to be lifted up into the colder altitudes, condensing their water vapor into rain or snow. If ceilings are too low, there's no flyable space between the ground and the ceiling. Mountains sort of eat that available altitude up just by virture of being high elevation.

Wind and mechanical turbulence

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Classic accident scenarios

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List of references

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  • Some random thoughts:

    I think anyone who has flown "within" the mountains has been delighted by a different, up close and personal, perspective. For the uninitiated, it can be pretty daunting and intimidating--or as a friend of mine (a relatively low time private pilot) said the first time I took him into a canyon, "Aren't we awfully close to that wall?" when we were easily 3 or 400 yards from it. But most pilots who haven't been there think that anything within a quarter mile is really, really close. But once you get past that feeling, it's a new world.

    Weather in the mountains is definitely different, especially when the day progresses and the wind comes up. That's why a lot of mountain flying is done early in the day, which is more likely to be calmer--and cooler. Not that afternoon in the mountains isn't doable--I've flown many times into the middle of the afternoon. But with both higher density altitudes and the likelihood of more wind, there always has to be a Plan B.

    Although there are those who will do it, I choose not to take any chances with marginal weather in the mountains. It's much better to have the discomfort of an unplanned layover, and I don't ever want the discomfort of knowing that right behind that next area of limited visibility may be a rock wall. Many miles of visibility is pretty important, to my way of thinking, for safe mountain flying.

    For those of us flying lower powered airplanes (mine is 180hp at sea level), it's a lot better to go light. Climb capability is already compromised a lot by the high density altitudes involved--flying near gross just makes it that much harder. Even relatively light, climbing out at 150-200 fpm isn't unusual. That's why many mountain pilots will purposely plan their fuel, so that they will need fuel as soon as they get out of the mountains, albeit with a safe margin.

    Last thought, but definitely not least: It's so much better to get some training, what some people call a "mountain checkout", than to teach yourself. There's nothing magic about piloting in the mountains, but a working knowledge of canyon flying, high density altitudes, etc., is easier and safer to acquire with the help of an experienced instructor.

    Cary

    Comment last edited on about 2 years ago by Cary
  • Thanks Cary, will incorporate some of these ideas.

  • You have to be a bit on the Bold side of confidence when flying in the mountains, at least Alaska mountains. My first 500hours as a new pilot were in Alaska Range. The only instruction I got was talking to Ol' time bush pilots, reading books and cautiously venturing deeper and deeper into new valleys. It's not for everybody, but once you start understanding the hazards it's like any other type of flying. Some of the most experienced Mt flyers say you never really master it but you certainly learn how to work with it. Youtube search "Alaska Range Wood River"

  • Within the mountains is where the oregraphic lift (hydraulic lift or ridge lift) exists. For most two and four seat airplanes, oregraphic and thermal lift far exceeds excess engine thrust for climb. When flying very near ceiling and very near terrain, knowledge and application of natural lift becomes critical.

  • Under "Negotiating Terrain" could you cover the sources of energy, other than engine thrust, that we might utilize in mountain flying? Gravity thrust of altitude can be a useful backup to engine power if we take off toward lower terrain. Gravity thrust of altitude can also be used to prevent load factor in the descending turn portion of the energy management turn. Acceleration in low ground effect can greatly increase our takeoff performance anywhere, but can make a critical difference in short and/or soft field takeoffs. This extra low ground effect energy becomes even more critical at high density altitude fields. Orographic or ridge lift can provide the extra lift necessary, with low powered aircraft, to make high pass crossings in warm and windy conditions. Thermal lift, when managed, can provide climb rates much greater than that provided by our engine.

    If we always at least know which way is down hill, and especially if we take off toward lower terrain where practicable, we can use gravity thrust of altitude to make takeoff easier and safer. Much of the time this technique is not necessary, but when it becomes necessary to prevent an unscheduled landing on terrain that cannot be out climbed, it might have been more prudent to have taken off down hill. Not to worry if we have a valley or drainage to make an energy management turn in to get back to lower terrain. While utilizing ridge lift to get up valley, we have rising terrain left, right, and ahead. If we ride the ridge closely, we get greater lift and have more room to make a descending, no load factor, turn toward the deeper center of the valley or drainage rather than the taller other ridge defining the valley.

    Wind is necessary for ridge lift and heat, or at least upward temperature change is necessary for wind. Unfortunately, this means the best orographic lift will be in the warmer, higher density altitude, part of the day. This is especially true of thermal lift. Thus, a trade off calculation becomes necessary to determine the better or safer flight time. And sometimes choice is not practicable as with pipeline patrol, bush, fire fighting, etc. work.

    If we use the extra kinetic energy of pressure airspeed available in cruise to climb wings level, we can use that now available extra gravity thrust of altitude to make steep turns safe by lowering the nose in the turn. Now if we level the wings prior to pull up, we can safely return to the original altitude using the extra kinetic energy of pressure airspeed of the dive. This energy management turn is the safest turn anywhere in the mountains, but especially in the box canyon turnaround or where a high pass cannot be made safely. Dynamically, the vertical space used is neutral and the horizontal space used is the least of any turn back technique. Of course, if at high density altitude, we will simply make a descending turn to the deepest part of the valley. We are already at Vy just to maintain altitude in neutral air.

    If we use the extra kinetic energy of pressure airspeed available when level in low ground effect we accelerate much faster making short and/or soft field takeoffs safer. If we use the basic low ground effect takeoff as our normal takeoff, we will less likely find ourselves out of ground effect and mushing where our only solution is to push forward on the stick to stay even or go up.

    Because of a perceived need to maintain altitude, thermal energy is the least understood and very much the least used natural energy available in the mountains. Mountain flying in small aircraft seldom comes under any hemispheric rule and even if it does, the safety of free altitude is the greater need. If we simply fly slow in updrafts and fast through downdrafts, we will have a net gain in altitude and ground speed. This is because small aircraft cannot overcome a two thousand feet per minute downdraft but can easily take advantage of a two thousand feet per minute updraft. Attempting to maintain altitude gives the small aircraft the huge disadvantage of losing altitude badly in the downdraft and taking no advantage of the updraft for a net loss in altitude and ground speed. It is easy enough to identify either updraft or downdraft with the VSI until we learn to identify them by feel. Neutral air can be identified by the VSI needle wiggling rapidly at the end either a downdraft or updraft. It will be pegged down but will wiggle when we are no longer going down. It will be pegged up but will wiggle when we are no longer going up. Also, there is usually a big bump, bottom and top, so feel is easy here.

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Disclaimer

While this knowledge base is a compilation of information from various sources, some official in nature, it is not a recognized or acredited source of aviation training information, and thus should be considered entertainment. Please consult a FAA-certificated flight instructor or mechanic prior to putting any information found here into practice.