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

640 ON SCENE SEARCH
641 Operations
A. Search Techniques
1. SRUs execute assigned search patterns making every effort to
locate and to be visible to the search object. A distressed
craft has only a limited supply of expendable visual detection
aids, and survivors usually do not activate these devices
until they either see or hear an SRU. SRUs should use audible
signals when searching for survivors in a canopied life raft
or similar craft, or when visibility is poor. For night
searches, as much lighting as possible should be kept on.
2. During daylight searching the use of a whistle, horn, smoke,
or other signaling device by an SRU to make its presence known
may cause those in distress to set off detection aids. In
using such devices, however, care should be taken not to
confuse other SRUs.
3. For night searching SRUs should increase self-illumination by
turning on navigation and other lights if this does not
detract from the night vision efficiency of scanners.
a. Turning on aircraft landing lights when established
on a new search leg will sometimes assist a survivor in timing
the firing of a pyrotechnic signal to ignite ahead of the
aircraft, rather than behind or to the side.
b. During night surface searches for survivors known to
be without any type of electronic or luminous detection aid,
audio reception becomes important. The survivor might have a
police whistle, or may have to rely entirely on voice to
attract attention. This situation is most common with a
person overboard or a person lost in difficult terrain.
4. SRUs are most effective in audio searching when they are
downwind of a sound source. With winds up to 10 knots, the
upwind sound range may be only one-fourth of the downwind
range. SRUs should concentrate on listening on the upwind
side.
5. SRU background noise should be reduced as much as possible
during audio search. If possible, marine SRUs should stop
engines occasionally to permit low-decibel sounds to be heard.
6. While every search radar and SRU has unique features,
capabilities, and limitations, some general radar search
guidance applies.
a. Search leg alignment. Optimum target detection is
obtained when the radar signal is aimed downwind or crosswind