Former Defence ministers are calling for a new inquiry into the crash of Chinook 576, after new disclosures of a "positively dangerous" flaw in software that was installed in the helicopter and others of its type.
Malcolm Rifkind who was the Secretary of State for Defence at the time of the crash of Chinook ZD576, and former Conservative Defence minister James Arbuthnot are among senior politicians calling for a new investigation.
The RAF blamed the crash on the two dead pilots, Flight Lieutenants Rick Cook and Jonathan Tapper.
But yesterday the BBC and Computer Weekly reported on the contents of two newly-disclosed MoD documents, one of which described a flaw in the "Fadec" fuel control system installed in the Chinook Mk2 as positively dangerous.
In the months before the crash of helicopter ZD576 on the Mull of Kintyre in June 1994, problems with the Chinook Mk2's Fadec had caused engines to behave erratically and unpredictably, according to the RAF Board of Enquiry.
After the crash, which killed all 29 on board, including 25 senior police and intelligence officers, Computer Weekly has learned that the software and hardware used in the Chinook Mk2 was changed.
There is no evidence that software failings caused the crash but an RAF Board of Inquiry did not rule out the possibility. Two air marshals, however, found that the pilots had been grossly negligent.
Evidence suggests that the air marshals, and the RAF Board of Inquiry, were unaware of the extent and seriousness of the software problems which afflicted the software-controlled Fadec system.
Now several former Conservative ministers have voiced their concerns about the refusal of the Ministry to reopen an inquiry into the blaming of the pilots.
Malcolm Rifkind told the BBC "Today" programme that when he was Defence Secretary at the time of the crash, the MoD did not tell him about problems with the Fadec system.
"Neither I nor ministers had been informed of these [Fadec-related] concerns. When the RAF had been asked that very question in recent years they had said that they had already concluded that the software problem, although it existed, couldn't have been a possible explanation for the Chinook disaster and that's why they did not draw it to the attention of ministers or the wider public.
"I think that was an error of judgment. I think that was a serious mistake."
He said that newly disclosed documents added weight to the argument that the finding of gross negligence against these two pilots simply is unsustainable.
"We do not know the cause of that accident. It might have been negligence. It might have been technical failing in the helicopter equipment, and the evidence that has come into the public domain in recent years gives much greater weight to the possibility that it was technical malfunction, either in the software or some other part of that helicopter, that caused the events themselves.
"When you are faced with a situation, as you sometimes are in this imperfect world, that you just don't know what caused an accident, the one thing you shouldn't do is blame human error on the part of the pilots, because that is unfair to their reputations."
James Arbuthnot, a former Conservative Defence minister, who now chairs the House of Commons' Defence Committee, described the newly-disclosed documents as "very significant".
He responded to claims by the Mod that a document which highlighted problems with the Fadec was available to the RAF Board of Inquiry into the crash of Chinook ZD576.
"The warnings about the Fadec system should have been taken seriously by the Board of Inquiry and the fact that it [the document warning that the Fadec had a dangerous flaw] was available to the Board of Inquiry doesn't mean that they read it. And so it seems to be that the MOD should definitely reopen the inquiry."
Another former Conservative minister David Davis, who chaired a Parliamentary inquiry into the accident, said: "Under the circumstances of this crash, the finding of gross negligence amounts to a conviction for manslaughter on the basis of very little evidence at all, and in defiance of their own documentary evidence."
"I would ask the Ministry of Defence to quash this finding of gross negligence which smears the reputation and honour of two brave, young, and very capable pilots who served in the RAF Special Forces Squadron."
John Major, the prime minister at the time of the crash, writing in the Times in 2004, said that the horror of the accident has "never left me". He said: "We may never know what truly caused this tragedy. It follows therefore that there is no justification for blaming pilot error to let posterity do so would be a harsh verdict that is not justified on the evidence and is cruel in its impact upon the families of the pilots who perished."
Lord Chalfont who campaigned successfully for a Lords inquiry into the crash said: "The RAF put into service on a very important mission an aircraft which they knew perfectly well was not fit for purpose. I think that all has happened ever since is a cover up and a saving of face."
Menzies Campbell, former Liberal Democrat leader, said: "This fresh information confirms my view that an injustice has been done in this matter and at the very least the board of inquiry should be reopened."
The MoD said: "It has been reported in various media that new evidence has emerged that computer software faults may have caused the 1994 Chinook helicopter crash on the Mull of Kintyre.
"This latest information is from an RAF document; it was available to the inquiry team and is not new evidence. Since this tragic incident, the Chinook Mk2 has had a remarkably safe and successful service history, often under the most trying operational conditions, with no history of any incidents that would call the aircraft's airworthiness into question.
"Ministers have repeatedly stated that they would reopen the Board of Inquiry if any new evidence is raised. Despite numerous representations over the years, nothing has been presented to successive Secretaries of State that would justify reopening the inquiry. Our thoughts remain with the families of those who tragically lost their lives when ZD576 crashed in poor visibility on the Mull of Kintyre in June 1994."