At least eight people were killed on Wednesday and eight more are missing after a helicopter crashed into the North Sea as it returned from an offshore oil rig.
Oil company BP said the Super Puma helicopter had been carrying 14 passengers and two crew from its Miller platform some 270km offshore.
The aircraft went down in the sea about 55 km east of the Crimond coast between Fraserburgh and Peterhead.
The coastguard said all those on board the Super Puma had been wearing survival suits.
It said rescue vessels had spotted two overturned life rafts and that weather conditions in the area were calm and dry.
Two Royal Aircraft helicopters and a Nimrod marine patrol aircraft were assisting the search, and had been joined by 11 other ships and lifeboats.
The crashed aircraft was operated by Bond Offshore Helicopters, which runs a fleet of Super Puma twin-engined helicopters to supply sea-based oil rigs.
The crash comes less than two months after a Bond Super Puma helicopter crashed into the North Sea just 500 metres from a BP platform in an area known as the Eastern Trough Area Project.
On that occasion all 18 passengers were rescued, 15 by the platform's own lifeboat and three by air rescue.
One of Britain's worst North Sea helicopter accidents happened in 1986 when 45 oil workers died after a Chinook crashed near the Shetland Islands to the north of Scotland.