MOUNTAIN FLYING MANUAL
Prepared for Yellowhead Helicopters Ltd. by: RJB Aviation Services Ltd. Valemount, British Columbia
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Table of Contents Page Introduction
3
Part I - Mountain Topography and Formations 1. Knoll 2. Ridge (Arete) 3. Saddle (Col) 4. Shoulder 5. Cirque 6. Pinnacle 7. Canyon 8. Glacier
4 4 4 4 4 4 4 4 4
Part II - Mountain Weather and Winds 1. Prevailing Winds 2. Convection Winds 3. Valley Wind 4. Boundary Air Movement
5 5 5 5 6
Part III - Helicopter Performance 1. Density Altitude 2. Engine Inlet Configuration 3. Operations in Falling or Blowing Snow
7 7 7 7
Part IV - Mountain Flying Techniques 1. Reconnaissance a. General Rules b. Key Features Figure 1: The Circle Recce Figure 2: The Figure Eight Recce Figure 3. The Figure Eight Recce – First Pass (Upwind) Figure 4: The Figure Eight Recce – Second Pass (Downwind) 2. Approach and Landing Figure 5: Approach and Landing 3. Departure
8 8 8 9 10 11 12 12 13 13 14
Part V - Illusions
15
Part VI - Physiological and Psychological Factors 1. Hypoxia 2. Hyperventilation 3. Fear, Tension and Stress
16 16 16 16
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Introduction Mountain flying, like other aspects of aviation, is the knowledgeable application of basic rules and principles. A thorough understanding of terrain, associated winds, weather, how density altitude affects the aircraft’s performance and limitations, and procedures for assessing and reconnoitring prospective landing sites is essential.
Smooth and precise application of the controls is a requisite in all phases of mountain flying and high altitude work. As the air becomes thinner with increasing altitude, the pilot finds that the aircraft does not return the same 'crisp' response to control inputs that it did at lower elevations.
Techniques for approach, landing, and take-off are designed so that application of power and control movement can be smooth and gradual. Hovering is minimized because, although our least power requirement below translation occurs very close to the ground, ground effect is often reduced due to sloping or uneven terrain at landing sites. In spite of this, the ability to hover smoothly and precisely is very important in order to take full advantage of what little ground effect may be available.
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Part I - Mountain Topography and Formations 1. Knoll A knoll is a roughly conically-shaped hill with a somewhat rounded top.
2. Ridge (Arete) Ridges are the crests of the mountaintops that normally run parallel to the adjacent valleys. They may run in straight lines for many miles or may be twisted to form an “S”. Ridges with narrow, jagged, sharp-sided, comb-shaped tops are referred to as aretes.
3. Saddle (Col) A saddle, or col, is a trough-shaped depression cutting through any piece of mountain terrain. Saddles are most commonly found at the headwalls of cirques, but can be found in many other locations in many shapes and sizes.
4. Shoulder Shoulders are usually found on sloping ridgelines and on the long tapering spines associated with the side slopes of mountains adjacent to intersecting valleys.
5. Cirque A cirque is a bowl-shaped hollow at the head of a valley.
6. Pinnacle A pinnacle is a sharp, steep-sided mountain spire terminating in a small ledge type top. Pinnacles are sometimes found along the headwalls of adjacent cirques. These tall thin spires usually stand alone and well above other surrounding terrain.
7. Canyon Canyons are narrow, steep-sided valleys formed by water erosion that has cut away rock and surface material.
8. Glacier Glaciers are large bodies of ice that do not melt substantially from year to year.
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Part III - Mountain Weather and Winds Wind is an important factor in all aspects of helicopter flying. Of all things that may get a pilot into trouble, disregard for wind is one of the most important. Wind can increase operational ceilings by several thousand feet or more. Wind can increase payload despite density altitude. It can increase range, rate of climb and cruise speed. Wind can also cause loss of lift, shorter range, and an inability to climb or even maintain altitude, and can decrease speed.
1. Prevailing Winds Prevailing wind is considered to be the air mass that has not been greatly affected by terrain, and is of a relatively consistent speed and direction. The prevailing winds become more reliable at higher elevations, especially above treeline. In Western Canada the prevailing winds at altitude are generally from the West.
2. Convection Winds Convection winds are strongest from late spring to early fall. They become the dominating wind forces when large high-pressure systems centre over mountain ranges and bring clear sunny days with light prevailing winds. As the sun warms the surface of mountain slopes and valley floors, the blanket of air laying over them becomes warmed. Warm air rises therefore creating a vertical movement or gradient of upflowing wind. We can use this vertical movement of air to assist the helicopter by providing additional lift. As warm air rises, it begins to cool and becomes heavier and begins to descend. These downflowing winds become prevalent later in the day or on the shaded side of a slope when the effect of the sun's heat has slowed. Cool descending winds are strongest at the foot of glaciers. As pilots, we must be aware of, and use caution when operating in, areas of downflowing winds.
3. Valley Wind Valley winds are usually local and seldom reach more than a thousand feet above the valley floor, unless they are joined by the prevailing wind that is flowing parallel to the valley. Valley wind can and often does blow in exactly the opposite direction to the prevailing wind. During the summer an up-river wind will be generated, starting lightly early in the morning, increasing until mid-day then decreasing until evening when it reverses. In winter this process is reversed and in spring and fall the process is variable. The flow of air down a glacier is also a local condition. The ice and snow cools the air, which then descends along the glacier. The result is a very strong, gusty wind at the toe of the glacier. Where this wind mixes with the warm upflowing wind is a poor place to land.
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4. Boundary Layer “Boundary Layer” air is usually defined as the blanket of moving air with a vertical component lying close to the surface. This layer varies in depth and often has its own unique characteristics quite distinct from prevailing winds, convection winds, and valley winds. Understanding it is important because we always fly through it approaching or leaving a m ountain landing site.
Boundary layer movement is caused by the combined action of the factors present, e.g. prevailing wind, convection winds and valley winds, and is also affected by the shape and texture (i.e. ice, rock, trees, etc.) of the terrain. Boundary layer movement is up, over, down, and/or around the terrain in much the same way that water in a stream flows up, over, down, and around the boulders and stones in a stream bed.
Boundary layer movement is a great source of help if understood and used properly. All mountain work should be done 'close in' to take maximum advantage of the boundary layer of air.
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Part IV - Helicopter Performance 1. Density Altitude Helicopter performance is determined by the power produced by the engine and the aerodynamic efficiency of the rotor system. Engine power and rotor system efficiency (read “lift”) are both affected by Density Altitude. Density Altitude is the operating altitude (pressure altitude) corrected for the actual outside air temperature (OAT). As pressure altitude and/or OAT increases, density altitude increases. As density altitude increases, the density of air decreases, that is, there are fewer molecules of air per cubic foot or metre available for cooling the engine and for supporting combustion. In addition, rotor efficiency is negatively affected as the blades have less “air” to act upon, thereby reducing “lift”.
2. Engine Inlet Configuration Up to 75% of the air inducted into a turbine engine is used for cooling. Installation of such things as inlet filters and particle separators slow down or reduce the flow of air into the engine. Helicopter performance is reduced as turbine outlet temperature (TOT) or exhaust gas temperature (EGT) limits will be reached at lower gross weights and/or lower density altitudes than when the helicopter is not equipped with these devices. Reference must be made to the performance charts in the supplements to the Rotorcraft Flight Manual (RFM) to determine aircraft performance when these devices are installed.
3. Operations in Falling or Blowing Snow Operations in falling or blowing snow typically require the installation of snow deflectors or reverse scoops and the use of engine anti-ice. The installation of snow deflectors or reverse scoops will have a similar effect on the flow of air into the engine as inlet filters or particle separators do. Use of engine anti-ice also negatively impacts engine performance by effectively “robbing” cooling air from the engine and using it to increase the air temperature as it enters the engine, thus significantly increasing TOT/EGT. Again, refer to the performance charts in the supplements to the RFM to determine aircraft performance when these devices are installed.
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Part V - Mountain Flying Techniques 1. Reconnaissance The reconnaissance is simply a method for gathering information regarding the conditions at a proposed landing site. However, a reconnaissance must be completed thoroughly as it is crucial to the success of the approach and landing at any landing site. During the reconnaissance, referred to as the 'recce' (pronounced “REK-ee”), the following should be assessed:
a.
Suitability of the landing site, i.e. size, shape, level or off-level, positioning of helicopter at touch-down, etc.
b.
Objective hazards, i.e. avalanche falling from above, possibility of triggering avalanches below, cornice failures, crevasses, etc.
c.
Wind direction and strength
d.
Down-flowing air
e.
Drop-off (escape route)
f.
Aircraft performance
g.
Approach path
h.
Departure path
2. General Rules There are several general rules regarding how to conduct the mountain reconnaissance. •
Always maintain adequate drop-off (this is the escape route).
•
Fly accurately and in trim, maintaining constant airspeed and altitude.
•
Turns should be made away from the hill.
•
Attempt to stay in the boundary layer.
•
Attempt to stay on the windward side of the hill when winds are strong (try to avoid areas of down-flow turbulence).
•
Make a note of the altitude of the landing site.
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3. Key Features The key features of any properly executed recce are: a.
Constant Drop-Off
Always maintain an 'escape route' throughout the reconnaissance should conditions suddenly change. This is accomplished by maintaining a constant drop-off that will allow the pilot to 'peel off' down and away from any hazard at any time.
b.
Constant Height
The reconnaissance should be flown at a constant altitude that is eye-level with the landing site. This eye-level recce will give the pilot the ideal perspective required to determine whether or not the landing site is suitably level. By noting the power required to maintain the constant altitude, the pilot can also accurately determine the location of up-flowing or down-flowing air relative to the landing site.
c.
Constant Airspeed
A certain minimum airspeed must be maintained as a basic safety measure. In addition, maintaining a constant indicated airspeed will allow the pilot to note differences in ground speed, which will assist in determining wind direction and strength. 40 mph/40 kts is an ideal airspeed for any type of recce.
d.
Close Proximity to Terrain
The closer a recce can be flown to a landing site, the more accurately the conditions at that landing site can be determined. The pilot must keep in mind that an adequate drop-off must be maintained.
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Higher Power Setting downwind Wind Direction
Lower Power Setting (into wind) Wind Flow
Figure 1:
The Circle Recce
The circle recce is used in light winds and where the terrain permits flying all the way around the proposed landing site with a safe drop-off, i.e. knolls and mountain tops.
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Landing Site
Wind Direction
Figure 2:
The Figure Eight Recce
The figure eight recce is the basic reconnaissance pattern most often used in mountain flying. It is also the safest as all turns are made away from the hill towards the drop-off. The figure eight is used when the shape of the terrain near the intended landing site does not permit adequate dropoff on all sides as required to safely carry out a circle recce, i.e. along the sides of long ridges, shoulders, saddles, and ledges. The direction and strength of the wind may also dictate that the figure eight recce is more suitable than the circle recce for a particular landing spot. The figure eight recce allows all passes to be made on the side of the landing site that takes full advantage of any upflowing air. The figure eight recce can be adapted to virtually any combination of terrain configuration and wind condition.
The typical mountain recce consists of at least two passes. This is the bare minimum. The first pass is made into wind with the second pass made downwind if wind conditions are acceptable. If the wind is very strong or erratic the second pass should also be made into wind.
The basic figure eight technique is detailed below.
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Landin Site
Wind Direction
Figure 3.
The Figure Eight Recce – First Pass (Upwind)
1.
Maintain 40 K IAS flyby at eye-level past the intended landing site.
2.
Pinpoint landing site and escape route with landmarks to identify them on subsequent passes.
3.
Check altitude at site.
4.
Do a power check (torque, N1, TOT/EGT).
5.
Check groundspeed to assess wind.
Landing Site
Wind Direction
Figure 4:
The Figure Eight Recce – Second Pass (Downwind)
1.
Once close in to the hill, stabilize airspeed at 40 K, eye-level with landing site.
2.
Check groundspeed to confirm wind.
3.
Do a power check.
4.
Confirm landing site and escape route.
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4. Approach and Landing At this stage, assuming that all conditions are deemed to be manageable, the reconnaissance is complete and the final approach and landing can be carried out. However, if any doubt remains as to the suitability of the landing site, wind strength or direction, aircraft performance, visibility, escape route, etc, additional passes must be made to either confirm or reject the chosen site before the final decision to land is made.
Landing Site
Figure 5:
Approach and Landing
The Approach and Landing phase is simply a continuation of the reconnaissance pattern. All control inputs should be minimal and must be made as smoothly as possible. The concept of constant apparent groundspeed is now employed to control the rate of closure with the landing
site. To help understand the concept think of how, when cruising at 1000 ft. AGL, the ground below appears to be passing relatively slowly, even with 100 K indicating. If the altitude is decreased and 100 K is maintained, the ground below appears to go by faster. If the aircraft speed is now sufficiently reduced the apparent groundspeed returns to that slow pace. The goal of a constant apparent groundspeed approach is to adjust airspeed in conjunction with a shallow descent to maintain that perception of the ground below going by at a walking pace until that is, in fact, the case. 1.
Approach is to be made along a shallow descent following the best path as determined by information gathered during the reconnaissance.
2.
Maintain constant apparent groundspeed to landing site.
3.
Ground effect should be acquired as, or before, translational lift is lost.
4.
Arrive at landing site with little or no forward speed, no flare, and a no-hover landing.
NOTE: The pilot must always bear in mind that mountain flying conditions can and do change rapidly. The pilot should, therefore, always be prepared to abort the approach using the predetermined escape route.
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5. Departure Departure from any mountain landing site should be made as much into wind as possible, with consideration given to such things as obstacles, sharply rising terrain, distance to drop-off, and aircraft gross weight vs. performance.
a.
Check appropriate gauges, including N2 and NR for full RPM.
b.
Gently lift off to a low (six inch) hover to determine remaining available power and to ensure the aircraft is clear of ground.
c.
Plan take-off into wind and/or updraft.
d.
Departure to be as smooth as possible to make use of ground effect, wind, and/or updraft while maintaining positive rate of climb until well over the drop-off.
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Part VI - Illusions Illusion is our inability to determine a true picture of the terrain we are looking at relative to our present position. Illusion varies in degree and intensity depending on the shape of the terrain and our position and view of the area. The primary cause of illusion in mountainous terrain is the disruption of our normal visual horizon due to sloping ground.
Illusions are commonly found:
1.
Flying up a long valley. The gradient of the valley and valley floor can be very difficult to determine visually without reference to altimeter, airspeed, and rate of climb.
2.
Flying toward high peaks. From 10 - 20 miles the top of the high ground may appear higher or lower but may actually be the same height as your present viewpoint.
3.
Viewing landing areas such as small shoulders or “nubbins”, on long, gentle slopes. The actual elevation of these sites relative to the pilot’s position can often be difficult to determine. Cross-checking altitude and airspeed while passing this type of terrain is critical and a proper 'eye-level' pass combined with confirmation of the actual altitude of the landing area is a must.
4.
Turning toward high ground on final approach to log pads or platforms surrounded by sloping terrain. When the pilot’s field of view is suddenly filled with approaching terrain, a common experience is a sense that the rate of closure with the landing site is too great resulting in a premature reduction of power and airspeed on final approach.
5.
During high altitude operations in cirques. The intensity of these illusions can be increased or decreased with variations in the reconnaissance and approach. Difficulty may be experienced while trying to determine the elevation of a landing site in a cirque relative to the pilot’s elevation. The pilot’s peripheral vision tends to overemphasize the surrounding slopes which distorts 'the look' of the site as compared to that of landing sites with normal backgrounds. Correct reconnaissance procedure with a well-balanced scan and accurate eye-level passes are the keys to overcoming these illusions.
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Part VII - Physiological and Psychological Factors 1. Hypoxia Hypoxia is the lack of sufficient oxygen for the body to operate normally. Its onset is insidious and may be accompanied by a feeling of wellbeing or euphoria. Even minor hypoxia impairs night vision and, more importantly, slows reaction time. More serious hypoxia interferes with reasoning, gives rise to unusual fatigue and, finally, produces unconsciousness.
As altitude increases, atmospheric pressure decreases and, with it, the partial pressure of oxygen. At 10,000 feet the level is such that all pilots will experience mild hypoxia and some will become symptomatic. Pilots operating at this altitude or higher should be alert for unusual difficulty completing routine tasks and should take corrective action (descend to 8,000 feet or lower) if difficulties are noted.
2. Hyperventilation Hyperventilation is breathing at a faster and/or deeper rate than the body requires for good oxygenation at the existing work level. Pilots may notice a slight dizziness, a feeling of coldness, a sensation like a tight band around the head, and pins and needles in the hands and feet. They will
often
feel
they
cannot
get
enough
air.
Continued
hyperventilation
may
cause
unconsciousness.
Hyperventilation most commonly occurs in association with anxiety, fear, or during intense concentration on a difficult task. The symptoms, particularly shortness of breath, are not unlike those of hypoxia. The corrective action is also similar to that for hypoxia. In addition, consciously slow the rate of breathing to 10 – 12 breaths per minute and do not breathe deeply. Keep the respiratory rate slow until symptoms disappear and then resume a normal breathing pattern.
3. Fear, Tension and Stress For the mountain pilot, the combination of high density altitudes, difficult winds, high gross weights and reduced aircraft performance may seem a bit intimidating and even frightening. Fear can cause tension which, in turn, reduces the pilot’s ability to be smooth and precise on the controls. As mentioned earlier, this ability is of key importance to the mountain pilot. Knowledge of what to expect when flying in the mountains, and the experience that comes with using that knowledge, will greatly assist the pilot in controlling the natural stress reactions that come with flying in a different or unusual environment.
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