IAMSAR Search Patterns

Most effective when the location of the search object is known within relatively close limits.
The commence search point is always the Datum Position.
To be used by a single ship during a search.
Often appropriate for vessels or small boats to use when searching for persons in the water or other search objects with little or no leeway.
Accurate navigation is required.
The first leg is usually oriented directly into the wind to minimize navigational errors.
All course alterations are of 90^O.
Two first two legs will be of same length ‘d’. ‘d’ will depend upon the visibility and the height of eye of the lookouts and the swell and sea height.
- Legs 3 and 4 will be a length of 2d.
- Legs 5 and 6 will be a length of 3d.
- Legs 7 and 8 will be a length of 4d.

Most effective when the position of the search object is accurately known and the search area is small.
Used to search a circular area centered at the datum.
Can be used by only one craft at a time at a certain location.
An aircraft and a vessel may be used to perform independent sector searches of the same area.
A suitable marker may be dropped at the datum and used as a reference point.
The commence search point is where the ship or aircraft enters the area to be searched.

Used to search a large area when the location of the search object is uncertain.
Most effective over water or flat terrain.
Usually used when a large search area must be divided into sub-area 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.
The main legs indicate the direction of drift.

Multiple vessels may be used as shown opposite:

Normally used when an aircraft or vessel has disappeared without a trace along a known route.
Often used as initial search effort due to ease of planning and implementation.
Consists of a rapid and reasonably thorough search along intended route of the distressed craft.
Search may be along one side of the track line and return. in the opposite direction on the other side (TSR).
Search may be along the intended track and once on each side, then search facility continues on its way and does not return (TSN).
Aircraft are ‘frequently used for TS due to their high speed.

Used around mountains and in valleys when sharp changes in elevation make other patterns not practical.
Search is started from highest peak and goes from top to bottom with new search altitude for each circuit.
Search altitude intervals may be 150 m to 300 m (500 ft to 1,000 ft).
The aircraft may make a descending orbit away from the mountain before resuming the contour search at the lower altitude.
The aircraft may spiral downwards around the mountain at a low but approximately constant rate of descent when there is not enough room to make a circuit opposite to the direction of search.
If the mountain cannot be circled, successive sweeps at the same altitude intervals as listed above should be flown along its side.
Valleys are searched in circles, moving the centre of the circuit one track spacing after each completed circuit.

Normally used only if there is an OSC present to give direction to and provide communications with the participating craft.
Creeping line search, co-ordinated (CSC) 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 so that the aircraft can use it as a navigational checkpoint.
The aircraft, as it passes over the ship, can easily make corrections to stay on the track of its search pattern.
Gives a higher probability of detection than can normally be attained by an aircraft searching alone.
Ship speed varies according to the speed of the aircraft and the size of the pattern.
The relationship among the speed of the surface facility, the aircraft’s speed, the track spacing and the length of the search legs is defined by the following equation:

Vs = (5 x Va)/ (L + 5)

Where,

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