This ruling was overturned by two senior reviewing officers, who stated that the pilots were guilty of gross negligence for flying too fast and too low in thick fog.

In 2011, an independent review of the crash cleared the crew of negligence and accepted that the RAF had falsely declared compliance with regulations in relation to the aircraft's authority to fly.

At the time of the accident, Air Chief Marshal Sir William Wratten called it "the largest peacetime tragedy the RAF had suffered".

The points of impact were shrouded in local cloud with visibility reduced to a few metres, which prevented those witnesses who had heard the aircraft from seeing it.

[6]In the immediate aftermath of the accident, one commentator stated that the loss of so many top level Northern Ireland intelligence officers in one stroke was a huge blow to the John Major government, "temporarily confounding" its campaign against the IRA.

[7] That the crash killed so many British intelligence experts, without any witnesses in the foggy conditions, led to considerable speculation and conspiracy theories being devised regarding the potential of a cover-up.

Among these were accusations that wake turbulence from a top-secret hypersonic US aircraft had been responsible for the crash,[8] while another postulated that it was a deliberate assassination of the intelligence operatives on board in order to facilitate negotiations with republican factions during the then on-going Northern Ireland peace process.

An immediate suspicion that the helicopter could have been shot down by the Provisional IRA, with their known Strela 2 surface-to-air missile capability, had been quickly ruled out by investigators.

The 2011 Parliamentary report found the reviewing officers to have failed to correctly adhere to the standard of proof of "absolutely no doubt" in deciding the question of negligence.

The campaign for a new inquiry was supported by the families of the pilots, and senior politicians, including former prime minister John Major and former defence secretary Malcolm Rifkind.

[15][16] On 8 December 2008, Secretary of State for Defence John Hutton announced that "no new evidence" had been presented and the verdicts of gross negligence against the flight crew would stand.

Issued in November 1993, the Controller Aircraft stated that the entire navigation and communications systems used on the Chinook HC2 were not to be relied upon in any way by the aircrew, and therefore it had no legitimate clearance to fly.

Knowledge of this had been withheld from the pilots; by withholding this when issuing their Release to Service (RTS) (the authority to fly), the RAF had made a false declaration of compliance with regulations.

In December 2012, the Minister for the Armed Forces, Andrew Robathan, confirmed such a false declaration did not constitute "wrongdoing", despite it leading directly to deaths of servicemen.

[28] The Board of Inquiry had identified that several factors may have sufficiently distracted the crew from turning away from the Mull, and upon entering cloud, failed to carry out the correct procedure for an emergency climb in a timely manner.

[24] In October 2001, Computer Weekly reported that three fellows of the Royal Aeronautical Society had said that issues with either control or FADEC systems could have led to the crash.

[42] The main submission to Lord Philip (see above) revealed that the FADEC Safety Critical software did not have a Certificate of Design, and was therefore not cleared to be fitted to Chinook HC2.

It further revealed that John Spellar MP had been wrong when claiming the software was not Safety Critical, providing the original policy document governing this definition to Lord Philip.

[43] The investigation observed that it was possible for some of the avionics systems to interfere with the Chinook's VHF radio, potentially disrupting communications.