An ongoing investigation into a North Sea helicopter crash which killed four oil workers has found the engines were still working when it hit the water and there is no evidence so far of technical failure.

Three men and a woman died when a Super Puma plunged into the sea off Shetland on 23 August. There were 14 survivors.

The Air Accidents Investigation Branch (AAIB) said in a report that both the helicopter's engines were giving out power when the aircraft hit the water. "The rate of descent remained constant for a period, before increasing rapidly. Shortly thereafter the helicopter, which was intact, struck the sea in a near-level pitch attitude with a slight right bank. Both engines were delivering power until impact," the report said.

It said that "no evidence of a causal technical failure has been identified" to date, but added that a detailed examination of the combined voice and flight data recorder and wreckage was continuing.

The helicopter was travelling from the Borgsten Dolphin support vessel when it came down on the way to Sumburgh airport with 16 passengers and two crew on board.

Pat Rafferty, the Scottish secretary of the Unite union, said: "The AAIB report does nothing to alleviate offshore workers' fears about the safety of the Super Puma fleet, nor does it provide any further detail into why four people could not escape the crash with their lives."

Source: PA