JP 3-50 National Search and Rescue Manual Vol I - US Navy

should be determined and the assumption made that the crew
rode the aircraft to that altitude before bailout. If highperformance
military aircraft were known to be out of control
(spin, mid-air collision, etc.) prior to bailout, the minimum
safe bailout altitude should be obtained from the parent
agency and used for computations if the actual bailout
altitude is unknown.
3. Winds aloft are usually given in true headings, representing
the direction winds blow from. Data on average winds aloft
between parachute opening altitude and the surface should be
obtained. If wind information is available only for certain
altitudes, a vector solution is used to obtain an average.
The solution assumes the wind is constant above and below a
reported wind to a point midway between it and the next
altitude for which a wind report is available. Figure 5-4
shows a vector solution to a winds-aloft problem where bailout
and parachute opening altitude are 8,000 feet and landing is
at sea level. Wind values for 2,000, 4,000, and 6,000 feet
are used twice for winds from 7,000 to 5,000 feet, to 3,000
feet, and to 1,000 feet, respectively. Values for 8,000 feet
and sea level are used once since each represents only 1,000
feet of altitude. For consistency, downwind vectors are
recommended in plotting. Next, parachute drift due to average
wind is determined, using the parachute drift distance given
in Table 5-1. The value for 8,000 feet and 20 knots is 2.3
miles, which is plotted to determine surface position, as
shown in Figure 5-4C. SMCs should interpolate, as necessary,
to obtain average wind speeds when using Table 5-1.
4. If the parachute opens over terrain, adjustments for the
terrain height should be made. Table 5-1 would be entered
with terrain altitude and interpolated for the average wind
velocity. The difference between the two values is the drift
distance.
5. Glide area for a parachute with a known glide ratio is
determined similar to aircraft glide area. The surface
position is computed assuming the parachute has no glide
ratio. Next, altitude difference between parachute opening
and the terrain is determined, and the no-wind glide distance
computed by multiplying glide ratio by altitude difference. A
circle is drawn around the surface position with radius equal
to glide distance. The enclosed area is the possible landing
area.
514 Maritime Drift
A. Leeway (LW) is the movement through water caused by winds
blowing against the exposed surfaces of the search object. The pushing
force of the wind is countered by water drag on the underwater surface
of the object. Most marine craft have a portion of the hull and
superstructure (sail area) exposed above the water. The more sail area