text: Air Traffic Control
  know if an aircraft fails to arrive at its destination on time. When this happens, they contact intermediate
  stop points to identify the last known location, and to aid in search-and-rescue operations.
  Color And Type What This Means to an What This Means to an
  of Signal Lights Aircraft on the Ground Aircraft in Flight
  Steady green Cleared for takeoff (or liftoff) Cleared to land
  Flashing green Cleared to taxi Return for landing (followed
  by a steady green light at the
  proper time)
  Steady red Stop Give way to other aircraft
  and continue circling
  Flashing red Taxi clear of landing area of Airport unsafe—do not land
  runway in use
  Flashing white Return to starting point (on NA
  airfield)
  Alternating red and green Use extreme caution Use extreme caution
  (general warning signal)
  Red pyrotechnic NA Do not land for the time
  (red flare) being, despite previous
  instructions.
  Table 3-6. Light signals on or near a landing zone.
  GROUND-TO-AIR TRANSMISSIONS
  3-54. The pathfinder might encounter endless situations while using GTA. If he can master the
  following four most common ones, he can handle most situations:
  SITUATION 1, KNOWN AIRCRAFT LOCATION
  3-55. Known aircraft location is the simplest of the GTA transmissions.