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

point 30-50 miles in the aircraft direction of flight, and a
5-15 mile radius from the reported position of a crash, are
usually preferred.
3. If the original datum area is too large for search by
available SRUs, the area should be reduced. Information
obtained during the SAR effort may aid in determining what
portion of the area to eliminate.
4. As with point and line datums, drift may be considered in
datum areas. For small or medium-size areas, drift can be
plotted using a single point, relocating the area for drift,
and keeping the original orientation, size, and shape of the
area. If the area is so large that positions have different
drifts, it may be necessary to calculate drift for each
section. Subsequent displaced areas will not keep their
original shape.
F. After each search, a reevaluation should determine whether the
next search should cover the same area, an expanded area, or a different
area. Generally, at least one re-search is desirable.
524 Repeated Expansion Concept
The Repeated Expansion concept is used for successive enlargement
of search areas and is suitable when approximate target datum is known.
It involves up to five successive searches with each search centered on
the datum. As the target is most likely to be near the datum and least
likely to be at the outer edges of the fifth search area, the
concentrated effort is at the most likely target position, while the
search area is expanded by using the search radius safety factors.
After five searches, an area equal in size to the first search area has
been searched five times while the outer edge of the fifth search has
been searched once, resulting in a high cumulative Probability of
Detection (POD) at the center (see paragraph 537).
530 SEARCH PLAN VARIABLES
The goal of search planning is to cover as much of the search area
as possible with a reasonable POD. Area coverage is a function of the
number, speed, and endurance of SRUs used. POD is the measure of
desired search results prior to a search, or the search results actually
obtained, and is a function of sweep width and track spacing. The
planner should balance these variables.
531 Number of SRUs
A. An optimal search plan should be developed assuming that
sufficient and suitable SRUs are available. Every effort should be made
to obtain necessary SRUs.
B. The first SRUs dispatched are usually alert SRUs, and are
normally sent to datum or on a trackline search. Backup and standby