text: Chapter 4
  CAUTION
  When fully adapted to the night, the eyes grow extremely sensitive to
  any light. Sudden exposure to a light source causes partial to complete
  loss of night vision. Thus, take care to avoid exposing pilots to light
  sources. Also, if pilots are using NVG, avoid shining a light directly at
  the aircraft, or use light sources compatible with the NVG.
  EXTERNAL LOADS
  4-73. Employing external loads presents a challenge in the dark. Even so, the pathfinder can use one of
  several methods. If he lacks sufficient signalmen, he marks the load by placing three reference lights 25
  meters in front of the load landing and pickup point. He spaces them in a triangle, 5 meters apart. This
  helps the flight crew during hookup, liftoff, and landing. On liftoff, the aircraft climbs vertically until the
  load clears the ground. As the helicopter begins to move forward, the pilot applies enough power to
  maintain a climb that allows the slingload to clear any obstacles on the liftoff path. The shorter the sling,
  the less altitude is required to clear obstacles.
  MULTIHELICOPTER OPERATIONS
  4-74. Only by using NVG can pilots fly safely in formation in a complete blackout and at terrain flight
  altitudes.
  NIGHT VISION GOGGLES
  4-75. To operate at terrain flight altitudes during low- or mid-light levels, pathfinders use night vision
  goggles. If the lights used in the tactical lighting and marking are too bright for night vision goggles,
  pathfinders must place a filter over the light cover, paint the light covers, cover them with plastic tape, or
  use other means to reduce the intensity of the light. The night vision goggles commonly used by aviators
  (AN/PVS-8) generally have a filter to prevent the cockpit instruments and lighting from blinding the
  aircrew. However, these filters also prevent the aircrew from observing green and blue chem-lights. These
  colors might be seen with the unaided eye if the aircrews adjust their goggles to look below them, but they
  will not be able to see the light source through the NVDs.
  WARNING
  When your unit trains with or employs the tactical light set, wear
  a filter over your night vision goggles to prevent eye injury. If you
  do not have a filter, paint the lens cover or cover it with plastic
  tape to reduce light intensity.