text: Drop Zones
  PARACHUTISTS OR BUNDLES
  6-31. To calculate the maximum number of either parachutists or bundles that a GMRS or VIRS DZ of
  given length can accept in one pass, use the T=D/R formula (Figure 6-3). You must know the type of
  aircraft and drop speed, and type of exit. The T=D/R formula may also be used to calculate the same
  information for a CARP DZ. In this case, measurement is from the PI to the trail edge of the DZ, minus the
  buffer zone (personnel only). Minimum length for CARP DZ is 3 seconds. In all cases, once the PI is
  established, the DZ time must be recalculated from the PI to trail edge, minus the required buffer.
  Figure 6-3. Example application of T=D/R formula.