A Ministry of Defence investigation into the crash on 2 June 1994, which killed 25 military and civilian anti-terrorist experts, blamed the accident on the negligence of the four-man crew.
But the fatal accident inquiry report, and due to be published this morning, will say it is unable to determine the cause of the tragedy.
The accident killed many of the key figures in the fight against terrorism in Northern Ireland, including the army's head of intelligence in the province, senior RUC officers and several members of the Security Service, MI5. They were en route from Belfast's Aldergrove airport to a conference in Scotland when the US-built Chinook helicopter slammed into a mountainside, killing all on board.
The report of the 18-day fatal accident inquiry held in January this year, which was chaired by Sir Stephen Young, the Sheriff of North Strathclyde, is to be released in Paisley this morning.
The inquiry is broadly equivalent to a coroner's inquest in England and Wales and its findings are not binding on the MoD or the RAF. However, it is likely to prove embarrassing for the MoD because it is expected to contradict the findings of their official inquiry published on 25 June last year.
The latter concluded that the pilots, Flight Lieutenants Jonathan Tapper and Richard Cook, were negligent because they continued to fly towards the high ground of the Mull of Kintyre in unsuitable weather conditions.
The weather forecast at the time of take-off from Northern Ireland was suitable for the route flown but the weather deteriorated during the approach to the Mull of Kintyre.
RAF personnel were also witnesses at the Sheriff's inquiry, which it is understood concluded they could not be blamed. The pilots' families have accused the RAF of making them scapegoats for the crash.Reuse content