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

Figure 5-39. Parallelogram Search Patterns
b. Cross-Over Barrier Pattern (B). These patterns have
search legs perpendicular to the expected relative movement of
targets. The three types of barriers -- depending on
relationships of search speed, search leg length, and target
speed -- are advancing, stationary, and retreating barriers
(see Figure 5-40). Most barrier patterns executed by aircraft
will be advancing. If multiple barrier patterns are used,
search areas should be joined only along sides parallel to
search legs. All SRUs should creep in the same direction,
with aircraft given altitude separation. Barrier and
parallelogram patterns should never be used in adjacent areas.
A barrier pattern is more sensitive than a parallelogram
pattern to differences between the computed rate of target
drift and target rate of drift.
c. Expanded Area. Circumstances may not permit use of
parallelogram or barrier patterns for drift compensation. The
search area size and number of SRUs may preclude establishing
adjoining search areas. If so, the planner should expand the
area and plan a search with non-compensated patterns. The
amount and direction(s) of expansion should be consistent with
expected target drift. Figure 5-41 illustrates a case of
drift direction reasonably well known, but a search area
grouping requiring the expanded area technique. In this case,
search areas are oriented in the direction of drift. Figure
5-42 illustrates a similar case where the search area cannot
be oriented with the drift direction. When the search is