text: Drop Zones
  DETERMINATION OF RELEASE POINT LOCATION
  6-89. To determine a release point on a GMRS drop zone, Air Force fixed wing VIRS drop zone, or
  Army rotary wing VIRS drop zone, complete the following steps (Figure 6-8):
  Figure 6-8. Release point location.
  STEP 1--DETERMINE DROP HEADING
  6-90. If the drop zone was surveyed and an AF IMT 3823, Drop Zone Survey, was published for the
  drop zone, then the DZSTL uses the magnetic course indicated. The drop zone might have been surveyed
  as a circular DZ, or a tactical assessment might have been done on it. It might be established as an ARMY
  VIRS. In the latter case, the DZSTL determines the drop heading based on the long axis, wind direction,
  and obstacles on the approach and departure ends of the DZ.
  STEP 2--DETERMINE POINT OF IMPACT
  6-91. The PI for personnel is the centerline of the drop zone 100 meters from the leading edge. The PI
  for bundles is the centerline of the DZ, but on the leading edge. These points may be adjusted forward, left
  or right. For CDS and heavy equipment, the DZSTL uses the surveyed PI locations shown on the
  AF IMT 3823. If a tactical assessment was done in lieu of an AF IMT 3823, he uses the standard PI
  locations for CDS and heavy equipment from the CARP dummy tree.
  STEP 3--DETERMINE WIND DIRECTION AND SPEED
  6-92. The DZSTL uses the PIBAL to determine the MEW. If he has no PIBAL, then he must use the
  surface wind direction and speed. Once he determines the wind direction and speed, he calculates a D = K
  x A x V formula for drift in meters.