21-1. To apply the distance and time formulas to GMRS and VIRS, compute the DZ length for a specific mission by using the D = RT formula. (D is the required length of the DZ in meters; R is the ground speed of the aircraft in meters per second; and T is the time required for the aircraft to release its cargo.) To use this formula, some conversions and mathematics are required.21-2. To find the aircraft ground speed, convert aircraft airspeed (expressed in knots) to ground speed (meters per second). Do this by multiplying knots times .51 (knots by .51) (one knot equals .51 meter per second).21-3. To determine the time over the DZ that is needed to release a jumper or equipment, use the following factors:Allow one second for each jumper to exit the aircraft; do not include the first jumper (10 jumpers require nine seconds). Mathematically, this is represented as 9 x 1 second.Allow three seconds per bundle to exit the aircraft; do not include the first bundle (three bundles would require six seconds). Mathematically, this is represented as 2 x 3 seconds.Personnel jumping T-11 ATPS parachutes may exit both doors simultaneously. The door with the most jumper is used to calculate the time required.21-4. For example, what length DZ would eight jumpers require when jumping from an aircraft flying at a drop speed of 90 knots? To solve this question, apply the following steps:Step 1. Solve for R (answer is expressed in meters per second): airspeed by .51 (90 knots by .51)= 45.90 meters per second.Step 2. Solve for T (answer is expressed in seconds): number of jumpers by 1 the first jumper (8 by 11) = seven seconds.Step 3. Solve for D (answer is expressed in meters): 45.90 meters per second by seven seconds =321.30 meters. Always round up to the nearest whole number. Therefore, D = 322 meters, which is the length.Step 4. Always add a 200-meter buffer (100 meters to lead ledge and 100 meters to trail edge) for any drop involving personnel. Therefore, 322 meters + 200 meters = 522 meters, the required DZ length.