Mountains flying

BASIC PREMISES

Without exception, you must adhere to the two basic premises of mountain flying, whether flying "with the mountains" or over the mountains.
Always remain in a position where you can turn toward lowering terrain
The novice mountain pilot should plan to fly 2,000 feet above the terrain along the route of flight. When approaching within ½ to ¼ mile from the mountain ridges, turn to approach the ridge at a 45-degree angle. This permits an easy escape with less stress on the airplane if downdrafts or turbulence are encountered. Never, fly in a canyon where there is not room to turn around.
Never fly beyond the point of no return.
Flying beyond the "point-of-no-return" will lead to an accident.

When flying upslope terrain, the "point of no return" is defined as the position where, if you reduce the throttle to idle, you can lower the nose for a normal glide and perform a 180-degree turn without impacting the ground. At or prior to this point, circle away from the mountain to gain additional altitude before proceeding.

MOUNTAIN METEOROLOGY

A complete check of the weather is necessary to develop a go/no-go decision. Stay out of marginal weather areas. Winds aloft greater than 30 knots at cruise altitude usually means the novice pilot should delay or postpone the flight until more favorable conditions prevail.

Landing at Possum Creek airstrip, 10,010-foot elevation.

GROSS WEIGHT

The takeoff distance varies with the gross weight. A 10-percent increase in the takeoff gross weight (while not exceeding the maximum allowable gross weight) will cause a:

5-percent increase in the speed necessary for takeoff;
9-percent decrease in acceleration to takeoff speed, and
21-percent increase in the takeoff distance.

CLIMB OUT

The first consideration for takeoff from a strip surrounded by mountains is terrain clearance. A considerable amount of time may be required to circle, climbing to the en route altitude prior to turning on course.

DOWNDRAFTS

Use visualization to determine possible downdraft areas. Air behaves like water. Ask yourself, "What would water do if it were flowing like the winds aloft?" You can then picture areas of downdrafts, updrafts and splashes of turbulence. If you encounter unexpected downdrafts, diving–away from the visualized downdraft–to maintain airspeed will generally lessen the total displacement effect of the downdraft (altitude loss). Although the rate of descent is greater at the higher airspeed, you will be under the influence of the sink for a shorter period of time.

COURSE REVERSAL

Everyone flying in the mountains will encounter situations when it becomes necessary to make a 180-degree turn. Forget hammerhead turns, wingovers, chandelles and the other fancy maneuvers. By the time you figure out you are in trouble and need to turn around, there is insufficient speed to perform these maneuvers. To turn around, slow down. This will decrease the radius of turn. Pull back on the control wheel to trade airspeed for altitude if you have extra speed. Then make the steepest turn you can comfortably make, up to 60 degrees.

Airstrip (creek bed) west of Mt. Blackburn, Alaska. Youdon't make the standard left-turn departure here.

ARRIVAL

The mountainous terrain surrounding many airstrips prevents a normal descent from cruise altitude to pattern altitude. It is necessary to make progressive power reductions to prevent thermal stresses from being induced in the engine. This allows the engine to cool slowly, preventing not only thermal shock, but also preventing de-tuning. Always make smooth power changes when adding or reducing power.

CAUTION: This is not the total information you need to fly safely in the mountains. It is merely an outline of the minimum information that should be studied.


'Mountology' The psychology of mountain flying

"I know you believe you understand what you think I said, but I'm not sure you realize that what you heard is not what I meant."
This gobbledygook, adopted by the FAA more than 20 years ago for flight instructor clinics was their attempt to demonstrate and reinforce the importance of communication. 'Mountology' is my fancifully contrived word used to describe the following proposal. Without careful study this plan may appear to contain the same double talk and confusion as the above FAA statement. Observant contemplation will prove it is not profuse verbiage or redundancy, but rather, it will ensure greater safety in all mountain-flying operations. Conditioned in psychology means exhibiting or trained to exhibit conditioned reflex or response. Reflex means an unlearned or instinctive response to a stimulus. Instinct means an innate aspect of behavior that is unlearned, complex and normally adaptive. It is necessary to define some terms before trying to persuade you to train yourself to react in mountain flying situations like one of Pavlov's dogs. These terms are conditioned, reflex and instinct. An instinctive response to a stimulus does not work at all times in an airplane. For example, when an airplane is in a spin, your instinct is to pull back on the control wheel to raise the nose. You have been taught that then the nose is down, you pull back. It has worked before, but not adaptive. In a spin situation you must be trained to break the stall before pulling back on the control wheel. This training is a conditioned response.
True mountain flying—that is, terrain, contour or drainage flying, as opposed to flying well above the mountains—can be done with total safety only when the pilot becomes conditioned to apply the basic premised during flight, without having to think about them.

BASIC PREMISE #1

Always remain in a position where you can turn toward lowering terrain.
This axiom also encompasses the idea that you will not enter or fly in a canyon where there is not sufficient room to turn around. Another way of stating this truth is to have an escape route in mind and be in a position to exercise this option.

BASIC PREMISE #2

Do not fly beyond the point of no return.
This is the position when flying upslope terrain where, if you reduce the throttle to idle and begin a normal glide, you will have sufficient altitude to turn around without impacting the terrain. Flying beyond this point drives home the southern sheriff's warning, "You're in a heap of trouble, boy."
Constantly evaluate where you are and decide if you can lose altitude before having to turn the airplane. If not, you are narrowing your options substantially.
What happens when the pilot flies beyond the point of no return? First, and usually the less serious consequence, involves landing the airplane straight ahead into whatever terrain exists. This normally results in destruction of the aircraft, but with proper technique the occupants will survive. Proper technique means the airspeed is maintained to allow transition to a normal landing attitude (often upslope terrain) without stalling the airplane.

The second outcome of flying beyond the point of no return involves the stall-spin accident. Because there is insufficient altitude or maneuvering space to complete the turn around, the pilot may try to hurry the turn with excessive bottom rudder, thus yawing the airplane. This induces a stall-spin.

These aphorisms or basic premises of mountain flying are not instinctive. They must be conditioned responses. As an example, consider that at some point in your basic flight training your instructor began constantly challenging you to find an emergency landing site. After pulling the power off, he would say some like, "Your engine just failed, proceed as you would during an actual emergency.
Soon you became conditioned so that when the instructor pulled the power, you already had a suitable landing area picked out and you headed for it, even though you might have been oblivious to your surroundings just before the simulated power failure.
This type training unconsciously caused you to seek an emergency area each time you were with the instructor. Eventually this training transfers to encompass all the time you are flying. Although you do not need an instructor to condition you for mountain flying, it helps when you first begin mountain flying. It is necessary for you to constantly think about the axioms of flight until you become conditioned to unconsciously remain in a position where you can turn toward lowering terrain and never fly beyond the point of no return.

Have you ever been caught in an un-forecast downpour during a picnic? Or have you flown in an area of anticipated updraft, yet all you find are downdrafts? Occasionally the wind defies all common sense reasoning and visualization. When this occurs it is usually due to one or a combination of the following:
subsidence
inversion
terrain modification
valley breeze
mountain breeze
Circulation (This discussion is limited to the northern hemisphere)
A quick review of some basic weather phenomena helps make the point. Circulation refers simply to the movement of air about the earth's surface. The sun heats the Earth's surface unevenly. The most direct rays strike near the equator, heating the equatorial regions more than the Polar Regions. The equatorial region re-radiates to space less heat than is received from the sun, while the reverse is true at the poles. Yet the equator does not continue to get hotter and hotter, nor does the polar region get colder. The only explanation is that heat is transferred from one latitude to another by the actual transport of air. Warm air forced aloft at the equator begins to move north at high elevation. Coriolis force turns it to the right (east). This turning develops a strong band of winds, "prevailing westerlies," at about 30º north latitude. Similarly, cool air from the poles begins a low-elevation journey toward the equator. It is also deflected to its right by Coriolis force creating a belt of low-level "polar easterlies." The result is to create an temporary impasse that disrupts simple, convective transfer. The atmosphere seeks stability and in an attempt to reach equilibrium, huge masses of air overturn in the middle latitudes. Cold air masses break through the barriers, plunging southward. The result is a mid-latitude bank of migratory storms with ever-changing weather.

Air Mass

The large air masses are high pressure areas. In the northern hemisphere, high pressure areas circulate in a clockwise direction. The high pressure system depicted on weather maps should be visualized as a mountain of air. The mountain is composed of isobars or lines of equal pressure. Consider the isobars as topographic in nature. If they are far apart, the high pressure area has a shallow topography. When close together, there is a very steep slope to the mountain of air.
Where isobars are close together it indicates the air is squeezed into a smaller, more confined area with a steep slope creating a rapid flow of air and strong surface winds.
Between the high pressure areas will be areas of low pressure where the air flows counter-clockwise. Visualize the low pressure area as a valley between air masses.
None of the pressure areas are stagnant. The earth's atmosphere is in a constant state of imbalance, but there is always a tendency to regain a state of balance.
Wind
Three forces act on wind. The pressure gradient force drives the wind. Pressure gradient is the decrease of pressure with distance and is in the direction of greatest decrease, thus, pressure gradient is from higher to lower pressure and perpendicular to the isobars. If pressure gradient was the only force acting on the wind, wind would always blow perpendicular to the isobars.
Rotation of the earth generates a force that deflects from a straight path any mass moving relative to the earth's surface. Coriolis force is zero at the equator and increases with latitude to a maximum at the poles. It is at a right angle to wind direction and is directly proportional to wind speed. Air in motion, due to pressure gradient, blows straight across the isobars from higher to lower pressure. When the air is in motion, Coriolis force begins to act at right angles to the wind, turning it to the right. Coriolis force continues to deflect the wind until is is blowing parallel to the isobars. Coriolis force and pressure gradient force balance, and above surface friction (about 2,000 feet), causes the wind to blow parallel to the isobars. The winds at the earth's surface do not blow parallel to the isobars. Instead, they cross the isobars at an angle from higher to lower pressure. Frictional force always acts opposite to wind direction. As friction slows the wind speed, Coriolis force decreases; however, friction has no effect on pressure gradient force. Pressure gradient and Coriolis forces are no longer in balance. Above 2,000 feet AGL the wind blows parallel to isobars. Below that altitude, friction causes the surface wind to blow 45º inward toward a low-pressure area and 45º outward from a high-pressure area.
Subsidence
Variations in temperature and humidity create a contrast in pressure and density. The pressure differences drive a complex system of air currents in a never-ending attempt to attain equilibrium.
Suppose an air mass (high pressure area) arrives over the plateau area of the upper Arkansas River Valley near Leadville, Colorado. The down flow, sinking are may be a stronger force than the prevailing winds aloft. The pilot departing Aspen and flying up the Roaring Fork River toward Independence Pass will be hard pressed to find an updraft in the face of this down flow. Yet it's always been there before. This pilot may be an accident waiting to happen. According to Aviation Space Environment Medicine, 232 airplanes crashed within 50 nautical miles of Aspen, CO, between 1964 and 1987. A total of 202 people died and 69 were seriously injured. This points out the need for better training in mountain flying.

Inversion

Often there is a layer of air within the troposphere that is characterized by an increase of temperature with altitude. It is called an inversion and is usually confined to a shallow layer.
Widespread sinking air (subsidence) is heated by compression and may become warmer than the air below it causing the inversion. The most frequent type of inversion over land is that produced immediately above the ground on a clear, still night. The ground loses heat rapidly through terrestrial radiation, cooling the layer of air next to it. Frontal inversions are also found in association with movement of colder air under warm air or the movement of warm air over cold air.

In a valley, expect the prevailing westerly winds to flow down the east-facing side of the mountain on the downwind side, pass through the valley and flow up on the west-facing upwind side of the next mountain. An inversion may place a cap over the area preventing the wind from flowing down the mountain. But when the wind strikes the terrain on the downwind side of the valley, it may tuck and move down the mountainside. With enough velocity, it may continue across the valley and up the other side.

Uneven terrain features may cause the air flow to be deflected downslope on what is considered the updraft side of the mountain. In the absence of wind, the sun's heating of the surface will produce convection currents known as anabatic lift.

During the day, the sun warms the valley walls and its adjacent air. The heated air being less dense will—lacking strong prevailing winds—rise gently upslope and is known as a valley breeze. The east facing mountain will receive the benefit of the sun's rays first and may cause a downslope wind on the west-facing slope as air rushes down to fill the evacuated air.
The valley breeze begins early in the morning and depending on the elevation of the mountain and the heat of the sun, may reach a peak speed of around 10 knots by noon. The significance of this is that when landing on an airstrip in a drainage, there will be a tailwind to contend with. The average wind speed is 6-8 knots.

Mountain Breeze

During the late afternoon and evening the valley walls cool quickly, cooling a layer of air next to the slope. This more dense air moves downslope into the valley causing the mountain breeze (gravity or drainage wind). The slopes cool at a rate faster than they heat up, so the mountain breeze may be stronger than the valley breeze, averaging 10-12 knots. Departing downslope will mean the airplane may be subject to the tailwind.
Coping
We tend to think in constants when contemplating the weather and associate whatever is happening as affecting a large area. Often a phenomena is isolated or may crop up in various isolated areas. Despite what is happening or where it is happening, it is important to visualize what is going on. Air is fluid, similar to water—although less dense. Ask "What would water do in this situation?" More often than not the picture becomes clear, you will know where there are areas of lift, sink and turbulence. So what will happen to the pilot heading up the Roaring Fork River toward Independence Pass? As long as he remains in a position where he can turn to lowering terrain and does not fly beyond the point of no return, Mother Nature will not have a chance to perform a "got-cha." The "point of no return" is defined as a point on the ground of rising terrain where the terrain out climbs the aircraft. The turn-around point is determined as the position where, if the throttle is reduced to idle, the aircraft can be turned around during a glide without impacting the terrain. Never fly beyond this point of no return. Turn around and maneuver for additional altitude prior to continuing. (By the way, it is not proper technique to reduce the throttle for the turn around; this merely denotes the point where the turn around must be initiated.)

Experienced pilots sometimes get into trouble with density altitude. It's not that they don't know what it is, it's just that they become complacent.


Federal Aviation Regulation 91.116 Pre-flight Action requires that a pilot check the density altitude.

(b) For any flight, runway lengths at airports of intended use, and the following takeoff and landing distance information ... other reliable information appropriate to the aircraft, relating to aircraft performance under expected values of airport elevation and runway slope, aircraft gross weight, and wind and temperature.

Density altitude is a term that sometimes causes confusion. A high-density altitude is NOT a good thing. Density altitude is defined as the pressure altitude corrected for non-standard temperature variations. And while this is a correct definition, my definition is perhaps more appropriate:

DENSITY ALTITUDE IS THE ALTITUDE THE AIRPLANE THINKS IT IS AT, AND PERFORMS IN ACCORDANCE WITH.

Density altitude can be computed on a density altitude chart, flight computer, electronic flight calculator or by rule of thumb. Density altitude gives us some idea about the expected performance of the airplane, but only if you apply the information to the performance charts. The DENALT performance computer gives values to be multiplied by the sea level takeoff and sea level rate-of-climb to predict the expected performance under current density altitude conditions.
This special DENALT calculator has information for both fixed-pitch propeller or constant-speed propeller airplanes. The sea level performance can be written at the bottom. The temperature is selected at the top center, then the pressure altitude is selected along the center, to the left for take-off factors and to the right for rate-of-climb percentage. Multiply the sea level performance by the factor and obtain the expected performance of the airplane.

An accurate rule of thumb (usually any error will be less than 300 feet) for determining the density altitude is easy to remember. For each 10-degrees Fahrenheit above standard temperature at any particular elevation, add 600 feet to the field elevation. (And, conversely for each 10-degrees F below standard temperature, subtract 600 feet.)
Standard temperature at sea level is 59-degree Fahrenheit. For elevations above sea level, subtract 3.5 degrees per thousand feet of elevation from the sea level temperature of 59 degrees. For example, at Jackson, Wyoming the elevation is 6,444. Multiply 6.444 times 3.5 for 22.55. Subtract this from 59 (59-22.55) for 36.45. The standard temperature at Jackson is 36.5 degrees. If the existing temperature is 80 degrees, subtract (80-36.5 = 43.5). Divide this difference by 10 degrees (for each 10-degrees F above standard), and multiply 4.35 times 600 (600 feet per 10 degrees) equals 2,610. Add 2,610 to the field elevation (6,444) for a density altitude of 9,054. Under the existing conditions (of our example), the airplane will perform as it would on a standard day at 9,054 feet elevation.

Density altitude not only affects the takeoff distance and rate of climb, but also applies to the service ceiling of the airplane while en route.

A simple rule of thumb for determining takeoff distance exists that helps you deal with density altitude during takeoff. The only problem is that it does not guarantee rate of climb after takeoff, but it insures that you will be able to takeoff in the distance available for the runway involved.

Do's and Don'ts
DO'S AND DON'TS OF MOUNTAIN FLYING

DON’T fly into unimproved mountain strips without a minimum of 150-hours total flight experience. Even then, be proficient at slow flight maneuvering and the spot method for landing.

DON’T plan a cross-country flight into the mountains when the wind at mountaintop level exceeds 30 knots unless you are experienced in this type operation (strong updrafts, strong downdrafts and moderate or greater turbulence). This does not preclude taking a “look-see.” Often with a stable air mass the air will contain very little turbulence during these high-wind conditions. Expect the wind velocity to double or more in mountain passes and over the ridges due to a venturi effect.

· DON’T choose a route that would prevent a suitable forced-landing area.
· DON’T leave the airplane without a compelling reason if you have executed an emergency or precautionary landing. Temporary evacuation may be necessary if a fire hazard exists.

DON’T go if the weather is doubtful or “bad.”
· DON’T become quiescent with weather reports of ceilings of 1,000-2,000 feet. The ceiling is reported above ground level. Often, in the mountains, the weather reporting facility will be surrounded by mountains that extend thousands of feet higher than the facility. Clouds may obscure the mountains and passes in the vicinity.
DON’T fly VFR or IFR in the mountains in an unfamiliar airplane make and model. It is required that you learn the flight characteristics, slow flight and stalls in various configurations, beforehand.
· DON’T make the landing approach too slow. Some pilots feel they have to make a low approach on the backside of the power curve to get into a mountain strip. This “hanging on the prop” is a dangerous operation. Use a stabilized approach for all landings.
· DON’T operate low-performance aircraft into marginal mountain strips. If in doubt about your takeoff, use the “sufficient runway length” rule of thumb.

DON’T rely on cloud shadows for wind direction (unless you are flying at or near the cloud bases). Expect the wind to be constantly changing in direction and velocity because of modification by mountain ridges and canyons.
· DON’T fly close to rough terrain or cliffs when the wind approaches 20 knots or more. Dangerous turbulence may be encountered.
· DON’T fail to realize that air, although invisible, acts like water and it will “flow” along the contour of the mountains and valleys. Visualize where the wind is from and ask yourself, “What would water do in this same situation?”
DON’T slow down in a downdraft. By maintaining your speed, you will be under the influence of the downdraft for a lesser period of time and lose less altitude overall.

· DON’T forget or fail to realize the adverse effect of frost. Less than 1/8 inch of frost may increase the takeoff distance by 50 percent and reduce the cruise speed by 10 percent. Often, if the airplane becomes airborne, the smooth flow of air over the wings is broken up by the frost and the extra drag prevents the airplane from climbing out of ground effect.
· DON’T give insufficient attention to the importance of fuel and survival equipment. It is important to keep the airplane light, but don’t skimp on these items.

o DON’T fly the middle of a canyon. This places you in a poor position to make a turnaround and it subjects you to shear turbulence.
· DON’T fail to use the same indicated airspeed at high-altitude airports that you use at low-altitude or sea level airports for the takeoff or for the approach to landing.
· DON’T be too proud or too vain to check with experienced mountain pilots concerning operations to and from unfamiliar fields.
DON’T attempt VFR flight in mountainous terrain unless you have the minimum visibility you have established as a personal safety standard.

· DON’T become complacent about the horizon when flying with outside visual reference. A gentle upslope terrain may cause an unknown constant climb with the possibility of an inadvertent stall. The horizon is the base of the mountains some six to eight miles away.
· DO file a flight plan for each leg of your flight. Also, make regular position reports to allow search and rescue personnel to narrow down the search area if you are overdue on the flight plan.

DO check all aspects of the weather including weather reports and forecasts.
· DO familiarize yourself with the high-altitude characteristics and performance of your airplane. This includes the takeoff and landing distance and rate of climb under various density altitude conditions.
· DO spend some time studying the charts to determine the lowest terrain along the proposed route of flight. If possible, route the flight along airways.
· DO have confidence in the magnetic compass. The compass (unless it has leaked fluid or someone has placed interfering metal near its magnets) is the most reliable instrument. Charts will show the areas of local magnetic disturbance that may affect the accuracy of the compass reading.
· DO plan the fuel load to allow flight from the departure to the destination airport with a reserve to counter unexpected winds.
· DO fly a downdraft, that is, maintain speed by lowering the nose of the airplane. Unless the airplane is over a tall stand of trees or near a shear cliff, the downdraft will not extend to the ground (exception: microburst).
DO use Sectional Aeronautical Charts instead of World Aeronautical Charts (WAC) because of the greater detail (8 miles per inch).

· DO approach ridges at an angle. The recommendation is to use a 45-degree angle approach when in a position of one-half to one-quarter mile away. This allows an escape, with less stress on the pilot and airplane, if unexpected downdrafts or turbulence are encountered. Flying perpendicular to the ridge, rather than at a 45-degree angle, does not mean you cannot escape the downdraft or turbulence by making a 180-degree turn. But, it does mean the airplane will be subjected to the effects of the downdraft and turbulence for a greater period of time. Usually, a steeper bank will be required to make the 180-degree turn. This will increase the g-loading stress on the airplane.

DO use horse sense (common sense) when performing takeoffs or landings at mountain strips. If you have any doubt about the operation, confirm the aircraft performance using the Pilot’s Operating Handbook or Owner’s Manual. If the physical conditions are adverse and compromise the operation, delay the operation until conditions are better.

DO count on the valley breeze (wind blowing upstream during the morning hours) and the mountain breeze (wind blowing downstream during the evening hours). In an otherwise calm wind condition the valley breeze will create an approximate 4-knot tailwind for landing upstream. The mountain breeze will cause an approximate 8-knot to 12-knot tailwind for takeoff downstream.

· DO make a stabilized approach for landings. Since the late ‘60s the power-off approach has been discouraged because of thermal shock to the engine.
· DO remember your study of aerodynamics. It is possible to stall the airplane at any airspeed and any attitude (providing you are strong enough and the airplane doesn’t break first). If a stall is entered in the same manner, for example, with a slow deterioration of the airspeed, it will stall at the same indicated airspeed at all altitudes.

The Aeronautical Information Manual, paragraph 574 states, “Your first experience of flying over mountainous terrain, particularly if most of your flight time has been over the flatlands of the Midwest, could be a never-to-be-forgotten nightmare if you are not aware of the potential hazards awaiting … Many pilots go all their lives without understanding what a mountain wave is. Quite a few have lost their lives because of this lack of understanding. One need not be a licensed meteorologist to understand the mountain wave phenomenon.”
Perhaps other than IFR weather, nothing affects the pilot flying in the mountains more than the mountain wave.
To develop an understanding of the mountain wave, we need to ask and answer some questions:
What is a mountain wave?
What forms it?
Why is it of concern to pilots?
What are its distinguishing characteristics?
How do we deal with it?

The most distinctive characteristic of the mountain wave is the lenticular cloud. This is a "signpost of the sky" indicating that mountain wave activity is present.
Someone has come up with all kinds of names for the mountain wave. There is the:
· Mountain wave
· Standing wave
· Lee wave
· Gravity wave
· Standing lenticular
· ACSL (altocumulus standing lenticularis)
· Or just plane "wave"
· Pilots have developed a few names of their own, but we can't mention them here.
The wave that forms over the mountain is more properly called the "mountain wave." The waves downwind from the mountain are the "standing wave" or "lee wave." Pilots have come to accept all of these names for wave activity, regardless of position of the lenticular clouds.
How does the atmosphere go about setting up a mountain wave condition? It needs three elements:
· Wind flow perpendicular to the mountain range, or nearly so, being within about 30 degrees of perpendicular.
· An increasing wind velocity with altitude with the wind velocity 20 knots or more near mountaintop level.
· Either a stable air mass layer aloft or an inversion below about 15,000 feet.
Because of these elements, the weather service is able to predict the mountain wave condition with over 90-percent accuracy.

we have likened an atmosphere with low stability to a flimsy spring that offers little resistance to vertical motion. So while the lower coils move easily up and over the mountain, the jolt received at ground level is not transmitted very far upward.
represents a stable atmosphere that is similar to a tough, heavy spring. This air, when it strikes the mountains, tends to suppress internal vertical motion. It is essentially too tough for oscillations to be set up.
we have an arrangement of a strong coil sandwiched between two weaker springs to simulate an atmosphere with a stable layer sandwiched between areas of lesser stability. With this arrangement it is conceivable that the strong spring will continue to bounce up and down for some time after the parcel of air has crossed the mountain ridge. With a stable layer (or inversion aloft) the air stream is both flexible enough to be set in vertical motion and elastic enough to maintain that motion as a series of vertical oscillations.
As the air ascends, it cools and condenses out moisture, forming the distinctive lenticular clouds. As it descends, it compresses and the heat of compression reabsorbs the moisture. It goes through this up and down action many times forming a distinctive lenticular cloud at the apex of each crest, providing there is sufficient moisture present for the cloud formation.

The up-and-down action forms a trough at the bottom of its flow and a crest at the top of the flow. The distance from trough to trough (or crest to crest) is called the wave length. The wave length is directly proportional to wind wind and inversely proportional to stability.
The wave length is used for visualization. In the area from the trough to the crest is an area of updrafts. The area from the crest to the trough is predominately downdrafts.
In the intermountain west the wave length can vary from about 2 nautical miles to over 25 nautical miles. It averages 8 miles and extends downrange about 150-300 nautical miles. Satellite photos have shown the wave capable of extending over 700-nautical miles downwind from the mountain range.

Cap cloud of the Teton mountain rangeThis cloud is mostly on the windward side of the mountain.
FoehngapThe foehngap exists because moisture isreabsorbed during the down rush of air.
With sufficient moisture three typical wave clouds will form, although there are four types of clouds associated with the wave.
Cap cloud (foehnwall)
Lenticular
Roll (rotor, arcus)
Mother-of-Pearl
The presence of clouds merely point out wave activity and not wave intensity at any particular level. Because moist air takes less vertical distance to reach its condensation level than does dryer air, the presence of a lenticular cloud is not necessarily an indication of the strength of the updrafts or downdrafts in a mountain wave.
For example, high altitude lenticulars may indicate there is sufficient moisture at that altitude to form them, when in fact the strongest wave lift and sink occurs at a lower altitude where there isn't enough moisture to form the lenticular clouds. This is one reason visualization is so important.
The mother-of-pearl or nacreous cloud is a pancake-shaped cloud that is extremely thin and visible for only a short time after sunset or before sunrise when the sky is dark. It is normally seen in latitudes higher than 50-degree north, or over Antarctica. It is best seen in the polar regions at 80,000 to 100,000 feet when the sun is below the horizon.
Lenticulars over Montana
Rotor cloud in Alaska

The lenticular cloud appears to be stationary although the wind may be blowing through the wave at 50 knots or more. The wave lift can extend into the stratosphere, more than 10 miles above sea level, so you can't escape wave effects by flying over them. What are the flight conditions in lenticular clouds? Generally the lenticular area will be quite smooth. The only danger is the magnitude of the sustained updrafts and downdrafts. Usually individual lenticulars are composed of ice crystals, but when they are composed of super-cooled water droplets watch out for severe icing conditions.
Line of rotors - Calgary

Normally the rotor clouds are centered beneath the lenticular cloud. Most often it extends anywhere from ground level to mountaintop level, but is frequently observed up to 35,000 feet. Destructive turbulence from the rotor rarely exists more than 2,000-3,000 feet above mountaintop level. The rotor is described as a "dark, ominous-looking cloud with a rotating appearance." If it forms near the ground where it can pick up dust and debris, it is dark and ominous looking, but more often it looks similar to a fair-weather cumulus. Turbulence is most frequent and most severe in the standing rotors just beneath the wave crests at or below mountaintop level (visualization is helpful where there is insufficient moisture to form the rotor or the lenticular).
The rotor area forms beneath the lee wave where a large swirling eddy forms. Sometimes with an inversion (normally stable air), turbulence succeeds in overturning the air in the stable layer. Once warm air is suddenly forced beneath colder and denser air a vigorous convection is set up in an attempt to restore normal equilibrium. This makes the roll cloud a particularly turbulent hazard. If the top of the cloud is rotating faster than the bottom, avoid the area like the plague.
The most dangerous characteristic of the standing wave is the rotor. The rotor can be assumed to exist whenever a mountain wave forms, but a cloud will not always form to alert you to its presence. Avoid the area where the rotor will form with visualization.
Often the three conditions that must exist to form a mountain wave will exist (perpendicular wind flow, increasing wind velocity with altitude, and a stable air mass layer or inversion) ... but there is insufficient moisture for the wave clouds to form. This is called a dry wave. All of the updrafts, downdrafts and rotor turbulence exists, you just can't see the clouds. You must use visualization.
Just because a mountain wave exists, it is not a sure sign that your flight must be delayed or cancelled. The degree of stability can be determined from pilot reports or by a test flight.

Mountain wave safety practices

Altitude 50 percent above the terrain - Turbulence caused by extreme mountain waves can extend into all altitudes that you might use, but dangerous turbulence can usually be avoided by clearing the mountains at least half again as high as the height of the mountain. In Colorado there are 54 peaks over 14,000-foot elevation. Does this mean we have to fly at 14,000 plus one-half (7,000) or 21,000 feet? No, use the base of the terrain to begin measuring. For example, if the surrounding terrain is 10,000 feet and the mountaintop is 14,000 feet, use one-half of the 4,000-foot value and fly 2,000 feet above the mountaintops.
Approach at a 45-degree angle - The rule-of-thumb of flying half again as high as the mountain is designed to reduce the risk of entering the turbulent rotor zone, but it does not necessarily give you a sufficient margin to allow for height loss due to downdrafts. You must have an escape route.
Avoid ragged or irregular-shaped lenticulars - Ragged and irregular-shaped lenticulars can contain the same turbulence as the rotor area.
Climb in lift - Dive in sink - By diving in sink, rather than trying to maintain altitude, the airplane is exposed to the effects of the downdraft for a lesser amount of time. Even though the rate of descent will likely be double or more the rate of climbing at the best rate-of-climb airspeed, the airplane will loose less altitude overall.
Avoid the rotor - If rotor clouds are not present, visualize the area of the rotor and avoid it.
Visualize the wavelength - When flying parallel to the wave, fly in the updraft area.

LENGTH

Operating at mountain airstrips presents us with various passenger loads and different density altitude conditions for nearly each takeoff. These factors combine to provide a loss of performance, creating concerns about whether or not the runway is long enough for takeoff.
You might not be too concerned about landing at this airstrip. There are unobstructed approaches from either end. But, when it comes time to depart, you might have some doubts about the runway length. We have a rule of thumb that can determine if the runway length is adequate for the takeoff; although, it will not guarantee rate of climb after the takeoff. The POH (pilots operating handbook) should be consulted to determine the rate of climb.
Airstrip runs NW-SE on right side


The rule really is quite simple. It states: "Ten times the square root of the percentage of liftoff distance required is equal to the percentage of liftoff speed that should be attained in that distance."
Because airplanes stop better than they accelerate, we can easily accelerate to the halfway point of a runway and determine if there is sufficient performance to continue the takeoff. If there is insufficient speed, we can easily stop in the remaining half of the runway. (This really doesn't work well on downhill runways.)
So we will use the halfway point of the runway for "liftoff distance required."
Remember, this rule of thumb does not guarantee that the rate of climb will be sufficient to clear any obstacles after takeoff, but it does guarantee there is sufficient runway for the takeoff.
Mark the halfway point on the runway. This might require you to walk the length and count your steps, then walk back and determine a distinguishing characteristic or place a flag or marker at this point.
Using the rule, "10 times the square root of the percentage of liftoff distance," we use 50 percent for the liftoff distance and the square root of 50 is 7.07. Ten times 7.07 equates to 70.7 percent of the liftoff speed should be obtained at the halfway point to guarantee takeoff in the remaining half of the runway. If you have the speed, continue. If you do not have the speed abort the take off.

There is a concern about the use of flaps for takeoff from a backcountry strip among many pilots. Should flaps be used or not, and if used, how much flap should be used?
The majority of mountain pilots agree ... flaps should be used for takeoff.
How much flaps? The POH or Owner's Manual may give a recommendation, in which case you are obligated to use their wisdom. But, if there is no blessing listed, the following procedure will provide the maximum lift from any particular airfoil section.

Begin by making full control deflection, aileron control (wheel or stick) moved full left in this picture. This represents the maximum lift for the airfoil design. Remember, lift and drag are directly proportional. Increase lift and you increase drag. Here the manufacturer determined the maximum lift for the aileron deflection is obtained at the particular angle formed.


Next, match the flap deflection to the aileron deflection. This provides the maximum amount of lift for the airfoil (considering the effect of drag). This works for normally aspirated engines. With the Cessna-type airplanes, it is necessary to parallel the flap deflection to match the aileron deflection since they are not side-by-side. This will result, for example, in about 12-degrees flap extension in the Cessna 150-170 series airplanes.
If your airplane happens to be a turbo-super charged wild duck, or some such derivative, the flaps will probably be set at 50 percent because you are not as concerned with the balance of engine power and lift.

CANYON FLYING

Most pilots don't read a book about aerobatics and go out to practice on their own. Flying in canyons (even if you read the superb Mountain Flying Bible) is usually done after you have gained experience from someone knowledgeable in canyon flying.
Who is knowledgeable? Your flight instructor.


Generally speaking the best path to fly through a canyon will be on the updraft side (a narrow canyon is the exception). The canyon may be more or less level terrain, or it may be sloping terrain.
The airplane will have to be close to the mountain side to take advantage of the potential orographic lift. Maneuver the airplane to within a couple of hundred yards of the canyon side if lift is desired. Beyond this area the lift is insignificant.
Novice pilots often fly down the center of a canyon. This places them the farthest away from the sides of those scary old mountains. But, this is not the correct position for the airplane.

There are two good reasons for flying the side of a canyon.
First, you will avoid the shear area caused by the mixing of air flowing down one side and up the other side.
And, second, you will be in a better position from which a turnaround can be safely made. You have the full canyon width to perform the turnaround maneuver if the terrain becomes unsuitable, adverse weather is encountered or you don't want to be there.


Remember the basic premises?Basic permisis Always remain in a position to turn to lowering terrain; and, never fly beyond the point of no return. These two axioms encompass the idea that you will never enter a canyon if there is not room to turn around.
Only fly in a canyon when there is adequate room to allow a turnaround. Otherwise, fly the terrain. That is, gain altitude and over-fly the canyon area from the high end to the low end.

It doesn't matter which side you fly down a canyon, either the updraft or downdraft side, because flying downhill makes it easy to transition to either side. Normally we associate updrafts with the sunny side of a mountain, but in canyons it depends on the airflow down a slope more than whether or not the sun is shining on the surface.
The majority of mountain instructors will caution you when flying in canyons to gain sufficient altitude to go to the head of the canyon and then fly downslope terrain. This is sage advice. But, often it is necessary to fly up canyons (fire patrol, game and fish surveys, search and rescue, law enforcement).

FLYING UP CANYONS

There is nothing wrong with flying up canyons ... when you do it properly. In addition to never entering a canyon where there is not room to turn around, you must remain in a position that allows a turnaround if the canyons narrows or if the terrain begins to out climb the airplane. It is a good idea to fly at a speed faster than Vx (best angle-of-climb airspeed).


Have you ever flown over water beyond power-off gliding distance from the shore? Have you noticed the engine goes to "automatic rough?" You start hearing strange noises that you haven't noticed before. The oil pressure gauge begins ticking and the engine seems to run rough.
A similar thing happens when flying upslope terrain in a canyon. Your left arm become shorter and the airspeed decreases without you noticing it. When flying up a canyon, fly the UPDRAFT SIDE. If you can't gain altitude on one side, try the other side (Mother Nature may be fooling you about which side has the updraft).

FLYING UP NARROW CANYONS

One thing can be said about flying up narrow canyons ... if it's not done properly, it's not habit forming. Until you are experienced (with a knowledgeable mountain instructor), stay out of these areas.
Speaking of a mountain instructor, do you have to fly with a certified flight instructor to obtain mountain flight instruction? Absolutely not. Many excellent, knowledgeable pilots can provide a wealth of information about mountain flying, but they can't sign your logbook. Do you really care? I don't. I will take learning from whatever source I can.
Let's define a narrow canyon. This is one, where, if you have to turn around the turn radius exceeds one half the canyon width. This can be intimidating to experienced mountain pilots when conditions aren't perfect.
Flying up a narrow canyon requires a different technique from the "regular" canyon. Rather than flying the updraft side, you are better off flying the downdraft side. This way, if you get into trouble, when you turn around you won't be getting into a worse situation. You will be entering an area of updraft during the turn. BUT REMEMBER, the turnaround will be subject to a tail wind that will increase the radius of turn.


It is not uncommon when flying in unfamiliar terrain to encounter a blind canyon. Blind canyons leading to a dead end shouldn't be a problem, but they are. The reason is that the pilot violates the basic premises of mountain flying.
To avoid potential problems stay out of canyons where there is not room to turn around, remain in a position to turn to lower terrain, and never fly beyond the point-of-no-return.


BASIC PREMISES OF MOUNTAIN FLYING

Always remain in a position where you can turn toward lowering terrain.
Never fly beyond the point of no return.

THE POINT OF NO RETURN

The "point of no return" is defined as the point on the ground of rising terrain where the terrain out climbs the aircraft. The turn-around point is determined as the position where, if the throttle is reduced to idle, the aircraft can be turned around during a glide without impacting the terrain.
(It is not proper technique to reduce the throttle for the turnaround. This merely denotes the point where the turnaround must be initiated.)

TURN AROUND POINT

More important than the "point of no return" is the "turn around point." What or where exactly is this position where, if the throttle is reduced to idle, the aircraft can be turned around during a glide without impacting the terrain?
The reason it is an elusive value is because of the variables that may be encountered. If the airplane is flying upslope terrain at a high speed, the turn around point will be further up the upslope than it would be if the airplane is flying at minimum airspeed.
Usually, if a pilot gets into trouble while flying upslope terrain, he has experienced a phenomena known as "short arm" effect. The self-preservation instinct causes a pilot to unconsciously pull back on the control wheel to avoid the rising terrain. The airplane slows down and this reduction in airspeed is usually imperceptible to the pilot, who is probably directing his attention outside the airplane.
As the pilot, flying at or near the minimum controllable airspeed, realizes he needs to turn around, the density altitude may preclude a level flight turn around. It becomes necessary to trade altitude for airspeed during the turn. This is the main reason for the definition of the "turn around point."
One of the maneuvers we demonstrate at the Montana Aeronautics Search Pilot Clinic is the "turn around point."

CAUTION: Let me caution you before we begin, "don't do this at home." If you decide that you need to do this training maneuver for whatever reason (it really isn't necessary), have an experienced pilot accompany you.

DEMONSTRATION – TURN AROUND POINT

NOTE: This demonstration is not required to safely fly in the mountains. Search pilots operate close to the terrain (500 feet vertically and 500 feet laterally) on a continuous basis. It is felt this demonstration, with the required steep nose-down attitude, will help prevent complacency and cause the search pilot to continually be aware of his position and altitude.
While flying upslope terrain in a canyon, the "student" (actually, the participants are all experienced pilots) is asked to determine the turn around point. The Cessna 182 or T-41 is used for the backcountry flying in this course.
The instructor must monitor the position diligently in order not to fly beyond the turn-around point. This is definitely a place where complacency will "get you."


This picture shows flying up a canyon after completing the last pass of a contour search

The contour search began at the top of the ridge and moved back and forth with step-downs in 500-foot intervals

This is the last pass of the contour. In this case it results in the airplane flying upslope terrain at low altitude

The airspeed is 80 knots indicated, the speed used for the contour search technique. When the student determines the turn around point, the throttle is reduced to idle and the turn around is commenced. Because of the slow speed it is necessary to lower the nose to a position most students consider excessive; however, to maintain a constant airspeed, it is required.

The student continues up the canyonuntil reaching the "turn around point"

At the "turn around point" the throttle isreduced to idle and a gliding turn is begun

Because of the slow speed the nose must be lowered to maintain 80 KIAS. Operation in a confined area may also require a steep turn. Lowering the nose further is necessary to maintain the constant 80-KIAS airspeed.

It is in this area of the turn that the 'student's' heart rate increases. The nose is pointed downward and the airplane is approaching the trees.


If the student has judged the position properly, the airplane will complete the 180-degree turn just over the tree tops at 80 knots indicated airspeed.

At the completion of the turn theairplane is just above the tree tops

A climb, with power, is initiated after the studentdetermines he has cleared the tree tops
Most students find this demonstration quite exuberating ... and most of the time the instructor does too. This demonstration is made with the power at idle. If the student misjudges the turn-around point, power is used to get out of the situation, so it is not as dangerous as it may appear.
Required Altitude
What altitude is required for the Cessna 182 to complete the 80-KIAS turn around? It's going to be about 400-500 feet above ground level, probably closer to 500 feet.

BOX CANYON TURN

I can't imagine anyone needing the box canyon turn under normal circumstances. If you need this maneuver, you have violated the laws of mountain flying. By keeping the basic premises in mind, you will never be in a position where you will need this maneuver; however, it is fun to play around.
To explain the box canyon turn it is necessary to consider two scenarios. In the first, the pilot is flying along at cruise power setting and cruise airspeed. In the second case, the pilot is flying at minimum controllable airspeed. This minimum controllable airspeed is probably not an intentional flight condition.
Flying over water beyond the power-off gliding distance from the shore, sometimes causes the oil pressure gauge to begin ticking. And it hasn't done that before. Next the engine may appear to give a little shudder of roughness. This might happen several times before you again approach the safety of the shoreline.
A similar phenomenon occurs when flying upslope terrain in the mountains. Your left arm becomes shorter. This is a normal self-preservation aspect of flight. You unconsciously pull away from the rising terrain and often the deterioration of airspeed goes unnoticed.
Conditioned Response
Mountain flying, like Mother Nature, can be harsh and unforgiving for the novice who fails to adhere to the two basic premises for all mountain flying: It’s really a simple matter to flirt with the mountains if you always remain in a position to be able to turn toward lowering terrain and never fly beyond the point of no return.
The first law, being able to turn while having some extra altitude to descend, does encompass the idea that you never enter into a canyon if there is not sufficient room to turn around.
The second law, to never fly beyond the point of no return, requires the pilot to establish a turn-around point whenever flying upslope terrain. The point of no return is defined as a point on the ground of rising terrain where the terrain out climbs the aircraft. The turn-around point is determined as the position where, if the throttle is reduced to idle, the aircraft can be turned around during a glide without impacting the terrain. Obviously, the power is not reduced to idle. This merely is a gauge to judge and establish the point over the ground where an escape turn must be made.
For the unconcerned aviator bopping along through the mountains at cruise power setting, it is still necessary to maintain a conditioned reflex of maintaining a position where you can always turn to lowering terrain and never fly beyond the point of no return.
This must be a conditioned reflex rather than instinct, because instinct is often wrong in an airplane. For example, if you have ever experienced a spin, your first impression is that the airplane is pointing straight towards the ground while rotating. The Cessna 172, for example, has its nose 46 degrees below the horizon, only about halfway from the horizon to the vertical. Your instinct will be to raise the nose with back pressure. It's always worked before. But now you must use the conditioned reflex of relaxing the controls (or pushing the controls forward) to break the stall and then fly out of the resulting dive without exceeding the critical angle of attack (somewhere around 16-18 degrees).
Another example of the conditioned reflex is the forced landing procedure experienced at the beginning of the private pilot training. After several lessons, the flight instructor reaches out and pulls the power lever, stating something like, "You're engine just quit, proceed as you would in an actual emergency."
To begin, your first endeavors don't provide much satisfaction for yourself or the instructor. You try to pick out an area for a forced landing and next try to extend the glide to make it to that spot; however, without experience only luck will allow you to approach anywhere near your projected spot.
If you have an excellent flight instructor, someone who teaches the spot method of landing, it is easy to determine how far the airplane will glide. Using the spot method technique allows you to look at a windscreen mark during a glide and determine the spot on the ground where the airplane will glide. By mentally subscribing a line in an arc from this point, the area surrounding the airplane within which the airplane can be landed is defined.
The instructor continues this "conditioning," much as Pavlov conditioned his dogs, but hopefully without quite as much salivating. At some point during this process, your subconscious begins mentally picking out forced-landing areas. When the conditioning is complete, the instructor pulls the engine power and you, without really thinking or concentrating about it, head for a forced-landing spot. The spot may be ahead or behind the airplane, it doesn't really matter for your subconscious has already made the decision.

Box Canyon Turn 2

Until you have practiced the box canyon turn and understand the mechanics of and the ramifications of an unintentional stall close to the terrain, the best advice for escaping from a "tight," or rapidly rising terrain or the narrowing confines of a canyon, is to make a steep turn at a slow speed, using flaps if prudent.
What possible options are available for the course reversal maneuver to escape the precarious position?

Hammerhead Turn

Pilots, in all seriousness, have asked my advice about performing the hammerhead turn as an emergency procedure for getting out of a tight spot. There are several problems that immediately jump to mind, negating the possibility of performing the hammerhead turn.
First by way of definition, the hammerhead turn is an aerobatic maneuver where the airplane enters a vertical climb from maneuvering speed (or the recommended indicated airspeed for the aerobatic airplane involved). As the airplane slows, but before it encounters stall buffet, the pilot initiates the turn. For a left turn, the torque of the engine aids in making the turn. Application of left rudder is coordinated with the application of right aileron and forward movement of the control wheel (left rudder and left aileron used together causes the airplane to roll onto its back). When the airplane pivots to a nose-down position, back pressure is used to fly out of the resulting dive. Definitely it is best to avoid this maneuver in a "tight."
The airplane is usually at a dangerously low airspeed when the pilot arrives at the "tight." This precludes even thinking about performing the hammerhead maneuver. Even with plenty of airspeed, it would be stupid (as in not exhibiting common sense) to try the hammerhead.
The airplane used for mountain flying is probably not an aerobatic certified machine.

Wing Over

The wing over is more of a fun maneuver than an emergency escape maneuver. Usually the pilot pre-plans the wing over, allowing sufficient airspeed to transition from level flight to a climbing pitch attitude of about 40 degrees. During the increase in pitch, a coordinated bank is begun. The maximum pitch is reached after about a quarter turn (45 degrees of turn). At this point the back pressure is completely relaxed, but the bank continues to increase to 90 degrees. The bank is rolled out during the last quarter of the turn and back pressure is increased to arrest the descent. The airplane should arrive at the 180-degree turn point at the same altitude at which it began the maneuver.
Again, this is a maneuver that is intentionally performed for fun, rather than to escape during an emergency situation.
Steep Turn
The safest and perhaps the most commonly used method of course reversal is the steep turn. It is very similar to the box canyon turn.
The stall speed of an airplane increases as the square root of the wing load factor. In a 60-degree coordinated turn, regardless of airspeed, the airplane experiences a 2-g load factor. The square root of 2 is 1.41, so there is a 41 percent increase in stall speed.
Most pilots don't really care how to determine the radius of turn. By formula, the radius of a turn is equal to the velocity in true airspeed (knots) squared and then divided by a constant of 11.26 times the tangent of the bank angle in degrees.
The valid information this formula provides is the fact that the radius of turn can be shortened by either reducing the true airspeed, or by increasing the angle of bank. A combination of the two provides the greatest benefit.
The ratio of turn radius to an increase in airspeed at a constant bank varies as the square of the true airspeed. If the airplane doubles its speed, it will quadruple the distance traveled. So even if the airplane is going faster (twice as fast in this case), it still takes twice the amount of time to complete the turn around (four times further traveled).
What about using flaps during this steep turn? Definitely, use them as appropriate to the flight conditions. Flaps were invented to allow an airplane to increase its approach angle without an increase in airspeed. They work because lift and drag are directly proportional. If the lift is increased (by applying flaps to increase the camber of the wing), the drag is increased (and hence, no increase in airspeed).
For most airplanes the addition of flaps, up to half the total available, provides more lift than drag because the drag can be “subdued” with excess power.
At a high density altitude it may not be possible to use full flaps without intentionally losing altitude to maintain a safe airspeed. If a trade-off between altitude and airspeed cannot be made because of rapidly rising terrain, limit the use of the flaps to the extent that the airplane will maintain a constant altitude during the turn.
Remember too that flaps reduce the structural strength of the airplane. Many of the normal category airplanes are stressed for 3.8 gs (g = gravity unit). This is the limit-load factor that should not be exceeded. Okay, you say, what about the ultimate load factor, you know, that 50-percent safety factor built into the airplane? Shouldn't the airplane be capable of flying at 5.7 gs?
The correct response requires a definite and emphatically strong NO. For certification the airplane must be able to withstand the ultimate load factor for a period of fewer than 2 seconds without permanent deformation of the structure. More time than this at a load greater than the limit-load factor and the airplane may experience structural failure (that is, the wing breaks off).
Check the POH (pilots operating handbook) to determine the amount of reduction in structural strength with the application of flaps. The book may say: normal category 3.8 gs; flaps extended 2.2 gs (a 42 percent reduction).

Box Canyon Turn - Introduction

The box canyon turn varies from the steep turn in that it is either performed from level flight at such a slow airspeed that an unintentional stall is imminent, or some excess airspeed at the beginning of the maneuver allows the nose to be raised above the horizon prior to initiating the bank and the airspeed, during the turn, will be too slow to sustain level flight.
We have learned the airplane always stalls at the same critical angle of attack. When banking the airplane, the stall speed increases (remember? it increases as the square root of the wing load factor). Whenever the airplane is banked in a coordinated turn, it is balancing the centripetal force (horizontal lift component that causes the turn) and the centrifugal force (the force of the turn). The turn takes place because the centripetal force pulls the airplane towards the inside of the turn.
Without a compensating increase in the amount of total lift during a turn, the airplane will lose altitude. The total lift (lift) is divided between a vector force that sustains the weight of the airplane and its contents (weight). The portion of lift that is directed sideward (centripetal force) causes the turn. The centrifugal force acts towards the outside of the turn.
To maintain level flight while turning it is necessary to increase back pressure (more lift equals an increase in angle of attack). This increases the load factor and stall speed.
Some pilots get into trouble with the box canyon turn without realizing it because they have been "conditioned" to maintain level flight when performing steep turns.

Box Canyon Turn -Procedure from Cruise Flight

The first time a pilot has to perform a box canyon turn in a true life situation, he may feel like the lady who climbs on a stool to avoid a mouse scampering across the floor. A little scream to get the adrenaline flowing wouldn’t hurt either.
The box canyon turn could be described as a combination of the steep turn and wing over (when entered at or near cruise airspeed). The nose is raised above the horizon, but nowhere near the 40-degree attitude of the wing over. About five to 20 degrees is about right, depending on the airspeed.
This does two things for you. First it trades airspeed for altitude and second, it slows the airspeed for a smaller radius of turn.
At the same time, full power is added and full flaps (providing the airspeed is within the flap operating range) are applied while beginning the bank. The bank will be a minimum of 60 degrees and may approach 90 degrees.
To insure that the g-load factor is not exceeded during the steep bank it is necessary to relax the backpressure once the bank passes about 45 degrees. The back pressure is not increased again until the bank passes through about 45 degrees toward zero degrees during the rollout.
Initiate the turn - the procedure requires coordination to accomplish all items at the same time:
Increase pitch attitude
Increase power
Begin a bank
Apply full flaps
At approximately 45 degrees of bank increasing toward 60-90 degrees:
Relax back pressure from the control wheel
Recovery - at approximately 45 degrees of bank, decreasing from 60-90 degrees:
Increase back pressure on the control wheel to arrest any loss of altitude.
When the airplane is in a position that allows, reduce flaps to one half
Box Canyon Turn -Procedure from Climbing Flight
When operating near cruise airspeed the box canyon turn was described as a combination of the steep turn and wing over where the nose was raised above the horizon.
Hopefully, the airspeed is near the best rate-of-climb speed or best angle-of-climb speed. This is usually a critical situation because the airspeed will probably be slower than Vy or Vx due to the “short-arm” effect.
While applying full power and full flaps, a bank is established at a minimum of 60 degrees. Again the bank may approach 90 degrees.
Previously we stated that the back pressure was relaxed to insure that the g-load factor was not exceeded. This is not as much of a problem at low speed, but it still exists. At the slow speed the airplane will probably stall before it exceeds the structural limitations. The main reason for relaxing the back pressure now is so the airplane does not stall. The back pressure is not increased again until the bank passes through about 45 degrees toward zero degrees during the rollout.
Initiate the turn - the procedure requires coordination to accomplish all items at the same time:
Maintain pitch attitude initially
Increase power
Begin a bank
Apply full flaps
At approximately 30 degrees of bank, increasing toward 60-90 degrees:
Relax back pressure from the control wheel
The pitch attitude will fall below the horizon
Recovery - at approximately 30 degrees of bank, decreasing toward zero degrees:
Increase back pressure on the control wheel
Reduce flaps to one half

Natural Horizon

The natural horizon is used to teach flying by outside visual reference. An instructor demonstrates a climb attitude at the best rate-of-climb airspeed. The student mimics this attitude. The airspeed indicator can be covered and the student, by noticing the pitch attitude in relation to the horizon (where the horizon intersects the side of the nose cowling), is able to fly at the best rate-of-climb airspeed within plus or minus one knot. Learning the “climb attitude” can provide for a very accurate climb speed, without looking at the airspeed indicator.
The instructor also demonstrates where is the nose in relation to the horizon in level flight, where are the wings in relation to the horizon in level flight, and where is the nose in relation to the horizon in a steep turn (left and right turns).
This natural horizon is easy to use in the flatlands as a reference for basic attitude flying. In the mountains, the natural horizon may disappear. By visualizing a horizon, basic attitude flying can still be maintained. The base of the mountains, at least six to eight miles away, represents the natural horizon.
What if the airplane is closer than the six to eight miles? Visualization must be used. Perhaps the mountains at least six to eight miles in the distance are visible out the side window. Project the same horizon visually to the front of the airplane.

The box canyon turn is an emergency procedure. It is best to practice it with an experienced instructor prior to the time when it becomes necessary as a life-saving maneuver.
Without practice it is very easy to get into an accelerated stall condition that will exacerbate the original situation.
Caveat
You must exercise caution in using full flaps during the practice of the box canyon turn and for drainage searches because of the possibility of the flaps failing in the extended position. For practice you may want to restrict the use of flaps because of the real possibility of the flaps failing to retract. It is possible to demonstrate and learn the box canyon turn without full flaps where the same technique, using full flaps, is applicable to a real "tight" or emergency condition.

CROSSING RIDGES

Without experience the visual aspects of mountainous country can be very deceptive. It is difficult to be able to look out the windshield and say with any certainty whether or not you are higher than the ridge you are approaching.
In approaching and crossing ridges, the novice pilot is well advised to start out by maintaining a 2,000-foot clearance over both mountains and valleys.

When a mountain ridge is approached from the upwind side there is usually a cushion of air to help you up and over the ridge, providing the wind is blowing somewhat perpendicular to the mountain. Once the wind hits about 20 knots or more at mountaintop level there will be turbulence associated with any downdrafts on the lee side, but this depends a great extent on the stability of the air. Under stable conditions, there may only be a laminar flow with smooth down air on the downwind side of the mountain. And, too, the updraft generated on the upside of the mountain may extend beyond the mountaintop to form updrafts on the downwind side (above ridge level).


If a mountain ridge is approached from the downwind or lee side, the pilot runs the risk of encountering a downdraft and turbulence. When the airplane is flown perpendicular to the mountain there is also a possibility of encountering a downdraft that could cause the airplane to impact the mountain.
I am not implying that there will not be sufficient room to turn away from the ridge if it is approached "head on, but when you approach the mountain at an angel, it will permit a safer retreat with less stress on the aircraft should severe turbulence or downdrafts be experienced.

Remember that in addition to the load factor induced by the turbulence, the load factor also increases during a banked turn. These are not separate forces, but add together for a total force on the airplane. Also, the stall speed increases as the square root of the wing load factor. In a 60-degree bank, the load factor is 2 Gs (gravity units). The square root of 2 is 1.41 or a 41 percent increase in stall speed.
For this reason, ridges are always approached at an angle, a 45-degree angle is recommended by most instructors. Even when the stability of the air is such that the 45-degree angle approach isn't necessary, do it anyway (or at least remain in a position to turn to lowering terrain). The reason for this recommendation is because Mother Nature can provide some surprises.
As an example of such a surprise, consider the pilot who departs Aspen, Colorado with a right downwind from runway 33. He follows the Roaring Fork River to Independence Pass. Knowing he is in an area of prevailing westerly winds aloft, the pilot assumes there will be a cushion of air to help him up and over the pass. But, Mother Nature may have stalled a high pressure area over the Upper Arkansas River Valley near Leadville.
This high-pressure area is a mountain of air that is creating an instability in the atmosphere. In regaining stability, it subsides, that is, the air flows down the mountain toward areas of lesser pressure. This might occur in the vicinity of Independence Pass and the subsidence can overpower the westerly winds aloft, presenting a downdraft where an updraft is expected. So, for safety sake, remain in a position to turn to lower terrain!

EXITING DOWNDRAFTS

Whenever you are caught in a downdraft, it is wise to immediately turn toward lowering terrain. Compute the rate of climb for the density altitude that you are flying. Perhaps the POH gives a value of 400 fpm rate of climb at 8,000-feet density altitude. In a strong or sustained downdraft, if the descent rate, after transitioning to the best rate-of-climb airspeed, is greater than your computed best rate of climb, transition to cruise speed to escape the downdraft. If turbulence is a concern, accelerate to the maneuvering speed.
Perhaps you are descending at 500 feet per minute and transition to cruise airspeed. The airplane may now be descending at 1,100 feet per minute. Accept this temporary increase in descent rate. Although the airplane is descending faster, it will exit the area of the downdraft in lesser time, providing an altitude loss that will be less than fighting the downdraft at the best rate of climb speed.

Although we (mountain instructors) advocate that it is best to approach mountain ridges at a 45-degree angle, it is not necessary to do so when you are four or five miles away from the mountains. Wait until you are within about 1/2 mile to 1/4 mile from the ridge, then maneuver to approach at the 45-degree angle. If you are crossing a series of ridges, you might consider crossing one ridge to the right and the next to the left and so on, to stay somewhat on course.

If you elect to make a flight without maintaining the 2,000-foot clearance altitude above the ridges, you can determine if you have sufficient altitude to cross the ridge by picking two spots. The first spot is whatever you can see over the ridgeline. The other spot is an arbitrary point. In the example to the right, the first point is the bottom of the yellow arc and the arbitrary point is the top of the yellow arc.
As you get closer to the ridge the spacing between the two spots will increase if you are higher than the ridge (the pick arc). If the distance decreases, there is not sufficient altitude to cross the ridge.


I don't like this method of determining sufficient ridge clearance. As an instructor I found my students developing "tunnel vision," where they concentrated only on the points and became unaware of other things going on in and around the airplane.
It is easier (and better) to just be aware of the terrain. If you can see more and more of the terrain on the other side of the ridge, you are higher than the ridge and can probably continue. If the terrain on the other side of the ridge is disappearing, get out. Turn around, gain more and try again.
If this technique causes you worry or concern rather than challenging your ability, don't do it. Fly over the ridge with 2,000-foot terrain clearance.


The wind is from the west-northwest (left rear of the airplane). The airplane is being flown up the right (south) side of the canyon to be in an area of updraft. Can the pilot make a commitment to cross the ridgeline at this point? NO.

Once the pilot maneuvers to a position (maintain the 45-degree angle approach) where the throttle can be reduced to idle and the airplane has sufficient altitude to dive and hit the top of the ridgeline, the pilot can make the commitment to cross the ridge. I'm not suggesting that it is proper procedure to reduce the throttle to idle -- this is how you just the proper position for making a commitment.
If you have gotten to this position without encountering a downdraft, any downdraft experienced can be overcome by lowering the nose slightly to maintain airspeed while crossing the ridge. Once you have made the commitment it is a good idea to fly toward lowering terrain. This "safe ridge crossing" technique may be used whether approaching the ridge from

upwind or downwind.

A word of caution. If you are trying to cross an extended plateau as opposed to the ridgeline, this rule will not work. In this case you will need additional altitude and you must remain in a position to turn to lower terrain................Sky wings