MOUNTAIN

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MOUNTAIN
OPERATIONS
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• REFERENCES
• FM 3-04.202 (1-202) ENVIRONMENTAL FLIGHT
• AERONAUTICAL INFORMATION MANUAL
• (AIM)

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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

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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.

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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.

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

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PREVAILING WINDS
DEMARCATION LINE
LIGHT WINDS
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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

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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.

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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

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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

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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

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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.

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

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WIND
WIND ACROSS A RIDGE
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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.

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WIND
SNAKE RIDGE
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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.

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WIND
WIND ACROSS A CROWN
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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.

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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.

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FLYING
TECHNIQUES
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FLYING TECHNIQUES

• During Mountain Flying the aviators 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.

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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.

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NORMAL TAKEOFF
AIRSPEED OVER ALTITUDE
MOUNTAIN TAKEOFF
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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

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WIND
DOWNDRAFT TURBULENCE
UPDRAFT
FLIGHT ALONG A VALLEY
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RIDGE CROSSING

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

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RIDGE CROSSING 45 ANGLE
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180 TURN OR EARLY CLIMB
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APPROACH LANDING
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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

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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.

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FIGURE EIGHT
CIRCULAR
LZ
LZ
RACETRACK
LZ RECONNAISSANCE
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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.

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WIND
AREA TO BE AVOIDED
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AREA TO BE AVOIDED
WIND
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WIND
AREA TO BE AVOIDED
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OTHER CONSIDERATIONS
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• 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
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QUIZ

• Click on the link below to access the
• Mountain Flying Techniques Quiz
• http//ang.quizstarpro.com
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• Class Name Mountain Flying Techniques