The crashes are at the centre of a $100m (pounds 60m) lawsuit brought by the US government against Boeing, the Chinook's manufacturer, on grounds that it knowingly fitted sub-standard parts and then sought to conceal evidence of this from accident investigators.
Evidence in the case contrasts with Ministry of Defence statements this week following the announcement that faults in a transmission gear had been found. MoD spokesmen said that more inspections were being done as a "strictly precautionary" measure, that there was "nothing to suggest a serious problem" and that "no accidents had been caused by this problem".
They said the fault was in no way connected with the 1994 crash of an RAF Chinook on the Mull of Kintyre, in which 29 intelligence officers and crew died. But fresh evidence from the court case will lead to more pressure for the investigation into that disaster to be reopened. An RAF inquiry blamed the crash on pilot error, accusing the two flight lieutenants of gross negligence. It enraged the men's families, who have campaigned to clear their names.
On Monday the RAF said it had ceased flying its 34 Chinooks after the discovery of cracks in the transmission gear during an inspection by Boeing. The US Army grounded its 466 CH-47 helicopters, and Boeing also advised the many other forces around the world which operate the aircraft to halt flights.
Examination of court papers shows why such swift and drastic action was deemed necessary. The US government case claims that sub-standard engine transmission gears were to fitted to its Chinooks between 1987 and 1995.
It also maintains that these were responsible for a crash in Saudi Arabia in 1991, and another at Fort Meade, Maryland, in 1993, in which a number of soldiers were injured.
A potentially damning list of allegations says Boeing declared the gears safe when it knew they were unsafe; failed to disclose "life-threatening defects" to the US Army; and knowingly used parts that were "susceptible to malfunction or failure in flight". Most alarmingly, it is claimed that Boeing "concealed evidence relevant to the causation of helicopter crashes." Boeing denies all the allegations and the case has become mired in years of legal argument, although there were some signs this week that a settlement may be reached soon.
The case revolves about a company called Speco from Ohio, which produced gears as a sub-contractor to Boeing. The firm has since gone bankrupt, and paid $7.2m to the US government in settlement of the case.
The saga began after Brett Roby, a quality-control engineer for Speco, discovered faults in the finished parts and reported them to Boeing. But, far from being listened to, he said last week, he was told that there was not a problem. When he persisted, he was told he would be sacked for his pains.
Instead of giving up, he launched legal action against Boeing and turned whistle-blower to the federal authorities, who agreed in 1997 to back his case.
Mr Roby was back in court in Ohio on Thursday as the matter dragged through another pre-trial hearing. While conceding that it had all been a "hell of a ride", he said that he had no regrets about getting involved.
"It's a moral responsibility," he said. "This is my final assignment as a quality engineer, and, my God, I'm going to see it through."Reuse content