What is parallel sweep search as per IAMSAR?

Parallel sweep search (PS): 
  • Used to search a large area when survivor location is uncertain.
  • Most effective over water or flat terrian.
  • Usually used when a large search area must be divided into sub areas for assignment to individual search facilities on scene at the same time. 
  • The commence search point is in one corner of the sub area, one half track space inside the rectangle from each of the two sides forming the corner.
  • Search legs are parallel to each other and to the long sides of the sub area.
  • Multiple vessels may be used for
  •  parallel sweep by 2,3,4 and 5 or more ships.