The ministry is accused of suppressing information that would have shed new light on the disaster, which killed 25 anti-terrorist experts and four crew. On 2 June 1994 Chinook ZD 576 crashed on the Mull of Kintyre on the way to a secret conference in Scotland. The MoD report blamed pilot error. An RAF board of inquiry posthumously convicted the two pilots of gross negligence.
But, according to an inquiry by Computer Weekly and Channel 4 News, the verdict has diverted attention from the fact that the helicopter should not have been allowed to fly at the time. They say the MoD knew there were problems with Chinook software.
The families of the pilots, Flight Lieutenants Jonathan Tapper and Richard Cook, have campaigned against the MoD verdict. Mr Cook's father, John, said yesterday: "We are very pleased with the investigation."
John Cook, a former RAF and Concorde pilot, said that in the week before the crash, his son had three times expressed concern at the safety of the Chinook Mk2 and asked his father to look after his wife and child if anything happened.
Key evidence concerns the computer system, called Full Authority Digital Electronic Control (Fadec),which controls the Chinook engines. There has been concern over it for some years and campaigners said problems with it may have led to the crash. The MoD denied this and MPs were told the system was not critical to the safety of the helicopter.
Ian Mitchell, of Computer Weekly, said the investigation showed the MPs were misled. "Fadec is capable of causing a catastrophic accident. We found the technical investigation into the cause of the crash was partly based on incomplete information and did not review potentially vital evidence, because crash investigators had not been given all the facts." Mr Cook added: "This ... lays to rest one lie of the MoD that Fadec had nothing to do with the accident. This is not saying Fadec caused the accident but that it could have done."
Newly obtained MoD documents show there were concerns over Fadec before the crash: in certain circumstances the system could power the engines up or down without instructions from the pilot.
The papers also show that at the time of the crash the MoD was suing the Fadec contractor, Textron Lycoming, largely over a design fault. This was unknown to the investigators. Nor did the the RAF tell them about an incident involving ZD576, which led to an engine being replaced six weeks before the crash.
Last night the MoD said: "The circumstances of the ... tragedy have been rigorously examined on no less than five occasions. Each time the original verdict of the RAF board of inquiry has been upheld."Reuse content