The report is due for publication tomorrow. The 29 dead included senior officers of the RUC, MI5, army intelligence and the Northern Ireland Office, together with four RAF crewmen, on their way from Belfast to a conference in Scotland.
The 400-page report is understood to reach no absolute conclusion on what happened when the helicopter flew into a remote Scottish hillside.
The report suggests a combination of factors may have caused the accident, and that the pilot may have mistakenly entered the wrong co-ordinates on the in-board computer system. This system is used by pilots to help them locate their position to within a few metres.
One informed source said this was a likely mistake, but was only one element of the findings. He added: "The report considers a number of options. Nothing is clear cut. For example, we don't know what happened within the craft."
Investigators were hampered by the lack of a black-box on board and by the fact that there were no survivors. They have ruled out sabotage, mechanical failure and the use of mobile phones on board.Reuse content