text: Helicopter Landing Zones
  DENSITY ALTITUDE
  4-117. In the mountains, density altitude can vary a lot between PZs and LZs. It can also vary greatly from
  one time of day to another. It normally peaks in the late afternoon, and drops to its lowest point at dawn.
  NAVIGATION
  4-118. In the mountains, the helicopter offers the best way to rapidly move forces. In the offense, air
  assault operations can insert forces into the enemy's rear area and bypass or envelop his defenses. In the
  defense, helicopters can move reinforcements and reserves rapidly.
  LANDING SITES
  4-119. Mountainous regions offer few, if any, airfields for fixed-wing aircraft, and few LZs suitable for
  multiple helicopters.
  4-120. If the enemy situation allows, pathfinders set up LZs on the windward side of the mountain
  because that side offers more stable winds.
  4-121. When they can only find LZs designed for single aircraft, planners increase in-flight spacing. This
  places an extra load on each crew. When conducting multiship operations into a small LZ, the pathfinder
  controller should allow sufficient time between liftoff and landing for the turbulent air generated during the
  departure of the previous helicopter to stabilize. Otherwise, the pilot of the incoming craft will experience
  that turbulence and lose lift.
  4-122. A pilot must touch down very carefully on the typical small, rough, sloped mountain LZ.
  Depending on the angle of the slope and on the aircraft's available torque, the pilot might be able to make a
  normal slope landing. Pilots of larger craft, such as cargo helicopters, might have trouble positioning the
  entire fuselage in the available area. Once the cockpit extends over the landing area, the pilot cannot see
  the ground. He must rely on the crew chief and signalman to direct him.
  4-123. During a mountain approach to an LZ surrounded by uneven terrain, the pilot has a hard time
  determining the actual aircraft altitude and rate of closure. Where the terrain slopes up to the LZ, a visual
  illusion occurs. The pilot might think he is flying too high and closing too slowly. If the terrain slopes
  down to the LZ, he might feel he is flying too low and closing too fast. Employing a signalman on the
  ground gives the pilot a visual reference to adjust his controls. He might need more than one signalman.
  SITE ASSESSMENT
  4-124. Pathfinders should determine the following information while reconnoitering and selecting a
  mountain site:
  y The size, slope, amount of surface debris, and the area covered by shadows and obstacles in and
  around the site.
  y The approximate direction, speed, and characteristics of the wind.
  y The inbound route, if necessary. When the pilot cannot land due to a steep slope, the aircraft
  might terminate at a hover to off-load troops and supplies.
  y The departure route. Departure routes should orient into the wind and over the lowest obstacles.
  SECTION VII. APPROACH PATH CONSIDERATIONS
  Pilots should try to land their aircraft into the wind; however, the terrain and its effect on the wind might
  require a crosswind landing. If so, the pilot for single-rotor helicopters should plan the approach so that the
  wind blows from the left side of the aircraft. This helps the pilot overcome the effects of torque, reduces power
  requirements, and helps him control the heading. Other considerations include vertical air currents, escape
  routes, terrain contour and obstacles, and the position of the sun.