Sector search (VS)

  • Sector searches are most effective when the position of the search object is accurately known and the search area is small. Examples of this situation include a crew member seeing another crew member fall overboard from a ship or a reported distress from a craft which provides a very accurate position. Sector searches are used to search a circular area centred on a datum point, as shown in figure 5-1. They are easy to navigate and provide intensive coverage of the area near the centre, where the search object is most likely to be found. Due to the small area involved, this procedure must not be used simultaneously by multiple aircraft at the same or similar altitudes or by multiple vessels. Instead, an aircraft and a vessel may be used together to perform independent sector searches of the same area.

Figure 5-1 Sector pattern: single-unit

  • A suitable marker (for example, a smoke float or a radio beacon) may be dropped at the datum position and used as a reference or navigational aid marking the centre of the pattern. Each search leg should then pass the marker at close range or directly overhead. When the sector search is used over a marker at sea, adjustment for the effects of total water current on the search object’s motion during the search is easier. The first leg should usually be down-drift. For aircraft, the search pattern radius usually lies between 5 NM and 20 NM. The angle between successive search legs will depend on the radius used and the maximum track spacing at the ends of the search legs. For vessels, the search pattern radius is usually between 2 NM and 5 NM, and each turn is 120°. Normally, all turns in a sector search are made to starboard.

  • If the search object is not located by the time the sector search pattern has been completed one time ,it should be rotated and repeated with the second set of search legs falling half-way between the search legs followed during the first search, as indicated by the dashed search legs in figure 5-1.

Read More: IAMSAR – I

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