Please try to get it right. Boscombe Down did not "Ground" the Mk2 Chinook; it ceased Trials Flying until such time as clarification was provided in respect of engine control malfunctions that had occurred on the ground during start up checks. Such clarification was completed and accepted by Boscombe Down on 24 October 1994 and Test flying recommenced without any changes to the FADEC system.
MoD have long acknowledged Boscombe, properly, stopped flying on airworthiness grounds. The many incidents occurred both on the ground
and in the air. MoD at first denied the latter, but were soon found out. To quote MoD, Boscombe acted
"within the proper exercise of airworthiness considerations".
And from the same letter (15.9.96) -
"In the period up to 2nd June 1994 there were a number of incidents involving AIRBORNE HC Mk2 of which approximately 5 (five) were due to FADEC malfunction whilst operating in normal mode. There had also been other incidents on the ground (since April 1994). The MoD(PE) Project Office sought explanations of the various incidents from the aircraft and engine manufacturers but in the absence of satisfactory explanations Boscombe Down suspended trials flying".
That is, the PE project offfice (Director Helicopter Projects) and Boscombe Down acted together when suspending flying. Given the grounded aircraft was PE's, not the RAF's, it would be highly unusual if they did not act together. This makes it all the more bizarre that DHP did not recommend the same action to the RAF, given the requirement of such trials is to present the aircraft at the in-service build standard; or as near as possible.
As ever, this is also important because MoD lied about it.
That there were (apparently) no subsequent changes to the FADEC system is completely and utterly irrelevant. The important and over-riding factor is that there did not exist the mandated degree of validation or verification of the software, nor a full understanding of how the system behaved (i.e. on the day of the crash the aircraft build standard was immature and still in the development phase). That uncertainty was seen, quite correctly, as a significant flight safety (and, by definition, airworthiness) risk by both PE and Boscombe; especially given the long history of unexplained incidents. That risk was, in time, mitigated by experience bringing a better understanding of what the malfunctions meant and how they affected the aircraft. This understanding was, presumably, translated into later amendments to the FRCs. The important point here is that, at the time of the crash, the FRCs did not contain any relevant information to help the pilots. (A significant breach of the airworthiness regulations).
MoD has consistently tried to shift the blame to Boscombe, claiming they “wanted to assess the design” (Lady Symons, March 2000) of the FADEC software; implying this was an unnecessary extravagance or they did so of their own volition. This, of course, is absolute bollox. The software is Safety Critical (eventually acknowledged by John Spellar, April 1999), therefore the regulations mandated Boscombe be tasked by MoD(PE) to do this. I don’t know if they were properly tasked, but they certainly did their job properly. The PE and RAF staffs who ignored them did not. And it is the protection afforded these staffs that has prevented an overturn. (Who was the Air Marshall who threatened to resign in early 2002, when MoD were seriously contemplating an overturn?).