The UK Air Accident Investigation Branch has released initial information about the Eurocopter Super Puma AS332L2 accident off Sumburgh, in the Shetland Isles, Scotland.
The statement does not venture any explanations for the crash. It says: "Preliminary information indicates that the approach proceeded normally until approximately three miles [4.8km] from the runway, when there was a reduction in airspeed accompanied by an increased rate of descent. The helicopter struck the sea approximately two miles west of the runway 09 threshold."
This happened, said the report, at 18:20 local time on 23 August 2013. Four of the 18 occupants lost their lives. But the agency adds: "At this early stage it is not possible to identify the causal factors leading to the accident."
It says: "The evidence currently available suggests that the helicopter was intact and upright when it entered the water. It then rapidly inverted and drifted northwards towards Garths Ness.
"The helicopter was largely broken up by repeated contact with the rocky shoreline. Some items of wreckage have already been recovered and will be transported to the AAIB's HQ in Farnborough," it says.
It initially struggled to find the combined cockpit voice and flight data recorder but later located the device which has been recovered and sent to its Farnborough headquarters for analysis.