Mountain Flying Techniques

							            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

  – Acceleration of crew fatigue
                      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.
      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.
PREVAILING WINDS              TURBULENCE
                                   &
                               DOWNFLOW
LOCAL WIND
 (UPFLOW)




              SURFACE WINDS
             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.
PREVAILING WINDS




              LIGHT WINDS
        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
PREVAILING WINDS




              MODERATE WINDS
          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.
PREVAILING WINDS




              STRONG WINDS
         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
         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
       STABLE LAYER
WIND




       MOUNTAIN WAVE
       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
          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.
       LENTICULAR
         CLOUDS




CAP CLOUD
                          ROTOR
                          CLOUDS


            CLOUD FORMATIONS
              ASSSOCIATED W/
              MOUNTAIN WAVE
 SLACK WINDS               STABLE LAYER

30K                                 WIND
                   ROTOR            SHEAR
25K                CLOUD

20K
                                 STRONG
                                 WINDS


               ROTOR STREAMING
                 TURBULENCE
         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.
       WIND




WIND ACROSS A RIDGE
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.
WIND




       SNAKE RIDGE
   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.
WIND




       WIND ACROSS A CROWN
         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.
WIND BACKLASH




      SHOULDER WIND
  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.
STRONG WINDS




     WIND ACROSS A CANYON
FLYING   TECHNIQUES
      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.
       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.
            NORMAL TAKEOFF




        AIRSPEED OVER ALTITUDE




MOUNTAIN TAKEOFF
   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
        WIND
                   DOWNDRAFT
                  & TURBULENCE




               UPDRAFT
FLIGHT ALONG A VALLEY
        RIDGE CROSSING
• Crossing at a 45° angle facilitates turning
  away from the ridge should the helicopter
  be carried below the crest by a downdraft.
RIDGE CROSSING
   45° ANGLE
180° TURN OR EARLY CLIMB
APPROACH
           &
               LANDING
         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
         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.
FIGURE EIGHT                    CIRCULAR



    LZ                     LZ



               RACETRACK

                  LZ




     LZ RECONNAISSANCE
       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.
         WIND




AREA TO BE AVOIDED
        AREA
        TO BE
WIND   AVOIDED
      WIND




 AREA
 TO BE
AVOIDED
OTHER CONSIDERATIONS
                SETTLING WITH POWER
             •Vertical / Near Vertical Descent
                      at least 300fpm
                 •Low Forward Airspeed
         •Using some of available Engine Power
                         20%-100%




HOVER IGE                                  HOVER OGE
-Reduced rotor tip                      -Large blade-tip
vortex                                         vortexes
-Reduced velocity of                   -High velocity of
induced airflow                         induced airflow
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Class Name = Mountain Flying Techniques