What is Parallel Track Line search as per IAMSAR ?

PARALLEL TRACK SEARCH (PS)

• Used to search a large area when survivor location is uncertain.
• Most effective over water or flat terrain.
• 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 as shown:

• Parallel track search: for use by two ships.
• Parallel track search: for use by three ships.
• Parallel track search: for use by four ships.
• Parallel track search: for use by five or more ships.

In other we can explain this as :

This search pattern is used to search a large area when survivor location is uncertain. When a large area is to be divided into sub areas for assignment to individual search facilities on-scene at the time this search pattern can b used. The commence search pattern 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.