Chinook 240
I'm afraid you're using the same rationale as Cazatou did earlier, in turn reflecting MoD's stance. That is, justifying safety decisions after the event.
"Don't waste money now, let's wait to see if there is an accident before deciding to do anything" is precisely what led to numerous accidents. This is a systemic failure and not just applicable to ZD576 or Chinook. It is what the Haddon-Cave report is all about.
Any Safety Management System, including MoD's, expressly forbids this method of justification so, in this case, Boscombe could only assess safety based on what was put in front of them. At a higher level, even if they had given it the nod "on the bench" they could not test it in a representative Chinook HC Mk2, because they did not have one. (An oft-ignored fact, largely because most don't understand the linkage between Build Standard, Safety Case and RTS). That is, for the RTS to be valid, it must be based on a valid Safety Case which reflects the Build Standard(s). It follows the Build Standard must be known at all times and maintained. THAT is the single biggest airworthiness failing in MoD over the last 25 years - as outlined by the Inspectorate of Flight Safety in his Chinook Airworthiness report of August 1992. As I said earlier, every single technical recommendation could be resolved by maintaining the Build Standard.
In the case of Chinook FADEC, there was no "read across" available from another user as our version was unique. (Despite Dr Reid implying otherwise). The regulations stated what had to be done, and they were ignored. Worse, MoD then lied for many years, claiming the software did not meet the criteria for Safety Critical, when it clearly did. They even lied about the definition of SCS.
What part of these regulations would you be willing to waive if YOU were required to sign for the airworthiness?
There have been two upgrades. I don't know when they were embodied, but neither was in ZD576 (AAIB statement).