Families of the pilots of the Mull of Kintyre Chinook helicopter crash have renewed calls to clear their names on the 11th anniversary of the tragedy.
The crash on the Mull of Kintyre killed 29 people
The 1994 crash killed 29 people, 25 of whom were senior members of Northern Ireland's intelligence community.
An inquiry blamed "gross negligence" by the pilots, who died in the crash, but a 1996 inquiry concluded it was not possible to be certain of the cause.
Relatives have fought to clear pilots Richard Cook and Jonathan Tapper.
The helicopter, based at RAF Odiham in Hampshire, was flying from Belfast to Fort George, near Inverness when it crashed on 2 June 1994.
John Cook, the father of pilot Richard Cook, who was from Church Crookham, Hampshire, died last month after a long battle with emphysema.
He had fought along with his other son, Chris, to clear Richard's name.
Mike Tapper, the father of the other pilot, Jonathan Tapper, who was from Burnham Thorpe, Norfolk, said he would not rest until both pilots had been proved innocent.
He said: "Recent overtures to the prime minister have borne no fruit whatsoever.
"I remain astonished that he cannot see that the burden of proof against our sons was not met and could never be met.
"They were and are innocent, and neither Chris nor myself will rest until our argument prevails."
James Arbuthnot, Conservative MP for North East Hampshire, has repeated calls for the government to overturn the verdict against the pilots.
He said: "The recent death of John Cook has strengthened our determination to see justice done.
"That it was not during his lifetime is a cause of deep sorrow for all those who supported him throughout his 11-year fight to clear his son's name.
"Chris Cook, John's other son, now leads the Cook family's campaign for the exoneration of his brother Rick, who was blamed posthumously, along with Jonathan Tapper, when their RAF Chinook helicopter crashed."
Sir John Major has backed the families' campaign
An all-party House of Lords select committee unanimously concluded in February 2002 that the MoD's finding of gross negligence was not justified.
The RAF found the pilots had put the helicopter into a long, fast and shallow climb over Kintyre, misjudging the speed and position of their machine.
The Board of Inquiry said that technical malfunction was unlikely, but could not be disproved.
The Mark 2 Chinook involved in the tragedy was the first of its type in Northern Ireland and had more sophisticated computerised systems than the Mark 1 model.
Relatives, MPs, peers, and journalists have accused the RAF of being unfair to the dead pilots.
The families' case has been supported by three major independent inquiries - a Scottish fatal accident inquiry in 1996, a Public Accounts Committee Inquiry in 2000, and a Lords Select Committee Inquiry in 2001/02.
The government has disagreed with the findings of all these inquiries.
Last year, former Prime Minister Sir John Major added his voice to those calling for the pilots to be cleared and the Church of Scotland urged the MoD to reconsider its judgment over the crash.
Families of the 29 people who died gathered to mark the 10th anniversary of the disaster last year.
No official ceremony is planned this year.