IAMSAR Search Patterns with diagrams
Track Spacing (S)
The distance between adjacent tracks in a search pattern of a rescuing ship is called track spacing. The distance ‘S‘ between tracks is found out from the table given in IAMSAR based on object of search and the visibility. An appropriate weather correction factor is applied depending on prevailing wind force. Radius is normally taken as 10 NM if search is to be commenced immediately otherwise it is calculated.
Expanding Square Search (SS)
Used when the search area is small. The location of the search object is known within relatively close limits, but some doubt exists about the distress position, and a concentrated search is desired. Not too many vessels/crafts can take part due to small area involved.
Sector Search (VS)
Used when the search area is small and location is known. Must not be used by multiple aircraft/vessels. An aircraft and a vessel may be used together to perform independent sector searches of the same area.
Parallel Sweep Search (PS)
Used when the search area is large, location uncertain. Area to be subdivided for assignment to other SRUs( Search & Rescue Units). Multiple vessels can be used. Search commences from one end of the sub-area and search legs are parallel
Trackline Search, Return (TSR/TSN)
Used when an aircraft or vessel has disappeared without a trace along a known route. Often aircrafts used as initial search effort due to ease of planning and implementation. A rapid and reasonably thorough coverage of the missing air craft’s/vessel’s intended.
Creeping Line Search (CS)
Used when the search area is large. Creeping line search, co-ordinated is often used. The aircraft does most of the searching while the ship steams along a course at a speed as directed by the OSC(On-Scene Coordinator) so that the aircraft can use it as a navigational checkpoint.
Ref: 2MFG Fn-1 App