Expanding square search (SS)

  • The expanding square search pattern is also most effective when the location of the search object is known with relatively good accuracy. The commence search point (CSP) for this pattern is always the datum position. The pattern then expands outward in concentric squares as shown in figure 5-2, providing nearly uniform coverage of the area around the datum. If the datum is a short line instead of a point, the pattern may be changed to an expanding rectangle. Due to the small area involved, the same cautions about the use of multiple search facilities as previously mentioned for the sector search also apply to the expanding square pattern.

Figure 5-2 Expanding square search (SS)


  • The expanding square pattern is a precise pattern and requires accurate navigation. To minimize navigational errors, the first leg is usually oriented directly into the wind. The lengths of the first two legs are equal to the track spacing and the lengths every succeeding pair of legs are increased by another track spacing. For successive searches in the same area, the direction of the search legs should be changed by 45° as shown in figure 5-3.


Note: Expanding square patterns are often appropriate for vessels, small boats or helicopters, but not necessarily fixed-wing aircraft, to use when searching for persons in the water or other search objects with little or no leeway as compared to the magnitude of the total water current. In such cases, it may be appropriate for the vessel or small boat to navigate the pattern by careful dead reckoning rather than by precise electronic or visual navigation. Just as a sector search pattern automatically compensates for total water current when using a floating marker as a navigational reference, a vessel’s DR navigation of an expanding square also automatically compensates for the effects of total water current.


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