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MOUNTAIN

MOUNTAIN. OPERATIONS. REFERENCES : FM 3-04.202 (1-202) ENVIRONMENTAL FLIGHT AERONAUTICAL INFORMATION MANUAL (AIM). OVERVIEW. The mountain environment requires special flying techniques due to: Its severe and rapidly changing weather Impacts on aircraft performance capabilities

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MOUNTAIN

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  1. MOUNTAIN OPERATIONS

  2. REFERENCES: • FM 3-04.202 (1-202) ENVIRONMENTAL FLIGHT • AERONAUTICAL INFORMATION MANUAL • (AIM)

  3. OVERVIEW • The mountain environment requires special flying techniques due to: • Its severe and rapidly changing weather • Impacts on aircraft performance capabilities • Acceleration of crew fatigue

  4. WINDS • Winds associated with mountains can be broken down into three main categories. • Prevailing winds: upper-level winds flowing predominately from west to east in the continental US. • Local winds: also called valley winds, are created by convection heating & cooling. They flow parallel to larger valleys. During the day, these winds tend to flow up valley; at night, they flow down valley. • Surface wind: the layer of air which lies close to the ground. It is less turbulent than prevailing & local winds.

  5. DEMARCATION LINE • Demarcation line: the point which separates the up flow from the down flow of air. • It forms from the highest point of the mountain & extends diagonally upward. • The velocity of the wind and the steepness of the uplift slope will determine the position of the demarcation line. • Generally, the higher the wind speed, & steeper the terrain, the steeper the demarcation line.

  6. TURBULENCE & DOWNFLOW PREVAILING WINDS DEMARCATION LINE LOCAL WIND (UPFLOW) SURFACE WINDS

  7. LIGHT WINDS • Light winds: 1-10 knots • Accelerates slightly on the upslope, giving rise to a gentle updraft. • Follows the contour of the terrain feature over the crest • At some point past the crest, turns into a gentle downdraft.

  8. PREVAILING WINDS DEMARCATION LINE LIGHT WINDS

  9. MODERATE WINDS • Moderate wind: 11 to 20 knots • Will increase the strength of the up drafts and downdrafts and create moderate turbulence. • An updraft will be experienced on the lee (the side sheltered from the wind) slope near the crest of the mountain. • The demarcation line forms closer to the hill crest and is steeper

  10. PREVAILING WINDS DEMARCATION LINE MODERATE WINDS

  11. STRONG WINDS • Strong winds: above 20 knots • The demarcation line will move forward to the leading edge of the hill crest • Becomes progressively steeper and the severity of updrafts, downdrafts, and turbulence will also increase. • Under these conditions, the best landing spot is close to the forward edge of the terrain feature.

  12. PREVAILING WINDS DEMARCATION LINE STRONG WINDS

  13. MOUNTAIN WAVE • A phenomenon that occurs when the airflow over mountainous terrain meets certain criteria: • Low-level layer of unstable air • Stable layer of air above the lower levels • Wind direction fairly constant with altitude • Wind speed increasing w/ altitude • Mountain lying perpendicular to the airflow

  14. MOUNTAIN WAVE • The following conditions can exist in a Mountain Wave: • Vertical currents of 2,000fpm are common, 5,000fpm possible • Moderate to severe turbulence • Wind gusts up to 22 knots • Altimeters errors up to 1,000 feet • Icing can be expected

  15. STABLE LAYER WIND MOUNTAIN WAVE

  16. CLOUD FORMATIONS ASSSOCIATED WITH MOUNTAIN WAVE • When proper conditions exist, clouds will form that provide visible indications of the existence of a mountain wave. Three types of clouds may form as a result of a mountain wave. • Lenticular Clouds • Rotor Clouds • Cap Clouds

  17. CLOUD FORMATIONS ASSSOCIATED WITH MOUNTAIN WAVE • Lenticular Clouds: • lens shaped, high altitudes, 25,000-40,000’. Form in bands or as single clouds, located above and slightly downwind from the ridge of the mountain, turbulence may be encountered under the cloud • Rotor Clouds: • downwind from the ridge, several rows lying parallel to the ridge, bases at or below ridge level, up/down drafts in excess of 5,000fpm. Short duration & tend to disappear rapidly. • Cap Clouds: • formed primarily from vertical updrafts, up/down as they pass over the mountain. Part of the cloud extends upwind, with finger-like extensions running down the slope on downwind side of the ridge.

  18. LENTICULAR CLOUDS CAP CLOUD ROTOR CLOUDS CLOUD FORMATIONS ASSSOCIATED W/ MOUNTAIN WAVE

  19. SLACK WINDS STABLE LAYER STRONG GRADIENT WINDS WIND SHEAR 30K ROTOR CLOUD 25K 20K STRONG WINDS UNSTABLE AIR ROTOR STREAMING TURBULENCE

  20. WIND ACROSS A RIDGE • Smooth air and updrafts will be experienced on the windward side of the ridge and downdrafts on the lee side. • The steeper the updraft slope & the higher the wind velocity, the more severe the updrafts. • As the air flows over the crest, a venturi effect is created. An area of low pressure develops on the lee side of the mountain. • Where the ridge line is irregular, a funneling of air through the gaps will occur, causing a mixing of air on the lee side. This condition tends to increase the turbulence. • Wind striking the ridge at less than 90° produces fewer updrafts and downdrafts.

  21. WIND WIND ACROSS A RIDGE

  22. WIND ACROSS A SNAKE RIDGE • Down drafts and turbulent air may be encountered on the windward slope of succeeding ridges. • The severity will be determined by the distance between the ridges, the depth of the valley, and the angle the wind strikes the slope. • The closer the ridges are together and the closer the wind is to 90° to the slope, the updrafts and turbulence will be more severe. • Greater turbulence will be experienced on the downdraft slope of succeeding ridges due to turbulent air flowing over the ridge.

  23. WIND SNAKE RIDGE

  24. WIND ACROSS A CROWN • Airflow in the vicinity of a crown is normally lateral around its outer edges and over the top. • Turbulence will develop on the lee side of the hill, but will not extend too far out from the ground.

  25. WIND WIND ACROSS A CROWN

  26. SHOULDER WIND • The airflow around a shoulder is extremely turbulent regardless of the wind direction. • Extreme downdrafts may be experienced if the shoulder is located on the lee side of the mountain. • Rotary turbulence may be experienced on the uplift side of the shoulder.

  27. WIND BACKLASH SHOULDER WIND

  28. WIND ACROSS A CANYON • Usually the lower winds flow parallel to the canyon floor. The degree of turbulence in the low areas of a canyon depends on the width & depth of the canyon and the wind speed. • In a narrow canyon, the most severe turbulence is in the low area • In a wide canyon, the low area may be turbulent free.

  29. STRONG WINDS WIND ACROSS A CANYON

  30. TECHNIQUES FLYING

  31. FLYING TECHNIQUES • During Mountain Flying the aviator’s senses are sometimes unreliable. • A natural tendency is to judge airspeed as too slow and altitude too high. • Difficulty may be experienced in maintaining the proper flight altitude. • Frequent reference should be made to the flight instruments. • Update the PPC to compensate for gross weight changes and center of gravity.

  32. MOUNTAIN TAKEOFF • Hover power check should be conducted. • PPC: as a minimum: max torque available, go/no-go torques, predicted hover torque • When performing a mountain takeoff, apply torque as necessary to gain forward airspeed while maintaining sufficient altitude to clear any obstacles until climb airspeed is reached. • Where drop-offs are located along the takeoff path, the aircraft may be maneuvered downslope to gain airspeed.

  33. NORMAL TAKEOFF AIRSPEED OVER ALTITUDE MOUNTAIN TAKEOFF

  34. FLIGHT ALONG A VALLEY • Aircraft should be flown in the smoother upflowing air on the lifting side of the valley. • Requires less power and gives the aircraft a safe flight path. • The velocity of the wind will determine how close you will fly to the lifting side. • In strong winds, it is advisable to avoid flying close to the slope because of turbulence caused by irregular projections may be encountered. • In light winds, aircraft should be flown closer to the side of the valley to allow for maximum horizontal clearance for a 180° turn

  35. WIND DOWNDRAFT & TURBULENCE UPDRAFT FLIGHT ALONG A VALLEY

  36. RIDGE CROSSING • Crossing at a 45° angle facilitates turning away from the ridge should the helicopter be carried below the crest by a downdraft.

  37. RIDGE CROSSING 45° ANGLE

  38. 180° TURN OR EARLY CLIMB

  39. APPROACH & LANDING

  40. FACTORS IN THE CONSIDERATION OF AN APPROACH PATH • Wind direction and velocity • Vertical air currents • Escape routes • Terrain contour & obstacles • Position of the sun • Approach paths and areas to be avoided

  41. TYPE OF APPROACH • There is no standard type of mountain approach. • Light wind/when demarcation line is shallow: • A relatively low angle of descent or flat approach should be used- requires less power & control movement. If downdrafts are encountered insufficient altitude may be available to continue the approach. • Stronger wind/steeper demarcation line: • Steeper approach angle. Higher rate of descent & requires more power to terminate the approach. Provides more terrain clearance if downdrafts are encountered. • Running landing: • Used if insufficient torque to make a normal or shallow approach and landing area is suitable. Effective translational lift is maintained until contact with the ground.

  42. LZ FIGURE EIGHT CIRCULAR LZ LZ RACETRACK LZ RECONNAISSANCE

  43. After Reconnaissance • Avoid descents greater than 700fpm • Normally, pattern altitude will not exceed 500 feet above the touchdown point. • Mountain approach: • When 50’ above the touchdown point begin losing effective translational lift. Do not hover OGE. Prior to reaching the near edge of the landing area, the descent should be stopped & forward airspeed reduced to a brisk walk.

  44. WIND AREA TO BE AVOIDED

  45. AREA TO BE AVOIDED WIND

  46. WIND AREA TO BE AVOIDED

  47. OTHER CONSIDERATIONS

  48. SETTLING WITH POWER • Vertical / Near Vertical Descent • at least 300fpm • Low Forward Airspeed • Using some of available Engine Power • 20%-100% HOVER OGE -Large blade-tip vortexes -High velocity of induced airflow HOVER IGE -Reduced rotor tip vortex -Reduced velocity of induced airflow

  49. QUIZ Click on the link below to access the Mountain Flying Techniques Quiz http://ang.quizstarpro.com Log-in and Click “Search” Tab Class Name = Mountain Flying Techniques

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