A helicopter returning from an oil platform has gone down in the North Sea with 16 on board, the UK coast guard agency said Wednesday. There was no immediate word on survivors after the helicopter ditched off the northeast coast of Scotland. The Maritime and Coastguard Agency said two Royal Air Force helicopters and a Nimrod airplane were heading for the area, along with ships in the vicinity. The accident was the second such incident this year. A Super Puma helicopter crashed into the North Sea in February, but everyone was rescued in that incident. Helicopters have been used to ferry workers to and from the oil and gas fields off the Scottish coast since the construction of platforms there in the 1970s.