What are different search patterns as per IAMSAR ?

CONTOUR SEARCH (OS)

• 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.