Click here for the full text of RAF Justice
The Lords committee report, which names Computer Weekly as having provided information to Parliament, found that there is doubt about the cause of the crash because of the possibility of a technical malfunction, such as a jam of the pilot's controls or a sudden engine surge, caused by the Chinook's safety-critical full authority digital engine control (Fadec) system.
"Any of these events could have had a serious effect upon the crew's ability to control the aircraft," says the report.
The committee found that two air marshals, including John Day, commander in chief, Headquarters Strike Command, were not justified in stating that the two pilots of ZD576 were grossly negligent beyond any doubt whatsoever. All 29 on board ZD576 were killed, including 25 senior police and intelligence officers.
The Lords committee, comprising a judge, three QCs and a qualified engineer, was convened especially to investigate the justification for finding the pilots guilty of gross negligence but it does not have the power to overturn the RAF's verdict.
The Ministry of Defence (MoD) said this week that the Lords report was thorough but insisted that it did not raise any new evidence. A spokeswoman said we "stand by the air marshals".
In 1999 new evidence of software problems was disclosed in Computer Weekly's 140-page report, RAF Justice. This week's Lords report cited much of the new material introduced in RAF Justice and said that this evidence had not been available at the time of the original RAF board of inquiry in 1995.
But since Labour came to power in 1997 six defence ministers have denied that there is any new evidence: John Reid, Doug Henderson, Lewis Moonie, Geoffrey Hoon, John Spellar and Baroness Symons have all backed the air marshals and said that no information had emerged to justify reopening the RAF board of inquiry.
Large sections of this week's Lords report are given over to discussion of problems with the procurement, testing and faults involving the Fadec system. It says that a Fadec-related engine surge could not be ruled out as a cause of the crash. "In short it has not been established to the required standard of proof that it was the voluntary actions of the pilots which caused the aircraft to fly into the hill."
Questions about the performance of Fadec have been at the centre of Computer Weekly's campaign for a new investigation. Before the crash trials pilots had twice halted flying Chinooks over concerns about Fadec.
The campaign led to crossbench peer Lord Chalfont winning a vote in the House of Lords to set up the select committee.
Did MoD keep Blair in the dark about software?
Handwritten notes by the prime minister, Tony Blair, denying that there is new evidence about the 1994 Mull of Kintyre Chinook crash, are in direct conflict with the House of Lords select committee report.
Blair's note to the relative of one of those who died in the crash rejects the need for a new inquiry into the accident and says, "I have looked into this personally. I know my conclusion will disappoint you but I wanted to set out the reasons in detail."
The disclosure of Blair's letters will make it more difficult for him to accept the Lords report. If he does so he will, in effect, be accepting the evidence he has already rejected.
The committee highlighted new evidence that was known to Downing Street and the Ministry of Defence when Blair wrote three letters about the crash, two of which have his personal notes appended, dated July 1999 and July 2000.
In May 1999, some of the new evidence accepted by the committee was published in RAF Justice, Computer Weekly's 140-page report on software problems that might have contributed to the accident. The MoD conducted an appraisal of RAF Justice at the time but said it represented "nothing new".
The Lords report may suggest to Blair that the MoD has not briefed him fully on the potency of the new evidence.
In a letter in 2000 to the then MP Martin Bell, Blair said that, "No evidence has ever been put forward which would provide any justification for reopening the inquiry."
A Downing Street spokesman said it needs time to study the report but it did not appear that any new evidence had emerged.
The Lords committee's verdict
"We have considered the justification for the air marshals' finding of negligence against the pilots of ZD576 against the applicable standard of proof, which required 'absolutely no doubt whatsoever'. In the light of all evidence before us and having regard to that standard, we unanimously conclude that the reviewing officers were not justified in finding that negligence on the part of the pilots caused the aircraft to crash."
"It is clear that at the time of the crash there were still unresolved problems in relation to the Fadec system of Chinook MK2s."
"We consider that Boeing's conclusions cannot be relied upon as accurate." (Boeing's simulation was crucial to the 1995 enquiry's conclusion that the pilots were in control.)
"Sir John Day's [one of the air marshals who accused the pilots of negligence] conclusions on this matter must be weakened by his reliance on matters which he treated as facts but which have been demonstrated to our satisfaction to be not facts but merely hypothesis or assumptions."
Fadec damaged beyond repair
"The Air Accidents Investigation Branch were unable to assess the functionality of number 1 Digital Electronic Control Unit [the Fadec software] owing to gross fire damage."
Were the pilots in control?
"... the Air Marshals were not justified in concluding that the pilots were in control four seconds before impact..."
"How could it be that a very experienced crew... flew into the Mull? We shall never know."
Click here for the full text of RAF Justice