CWD, now now, play nicely! One for us, one for you!!
The Mk6 is not 'common' to either the CH47F or the Mk2/3/4 as it has the DAFCS. The UK has not adopted a standard 'F' for a number of good reasons. CAAS, at the time, had a HMI optimised for US Army ops and would have required a complete change in RAF SOPs - for example, the UK use crewmen in the cabin extensively for navigation and data entry, none of which are (were) possible with CAAS when we looked at it. When I asked for some necessary changes the answer from US Army was 'when you've got 2500 cockpits running this system we'll listen to you...' Airworthiness, as CWD mentioned, was also tricky because CH47 didn't have the best rep (MoK, Mk3 AU fiasco) so getting a nascent MAA and reluctant RTSA to buy into US Army airworthiness regs was a step too far at the time. There are other important changes in avionics and mission kit and the Mk6 also has a rotorbrake to help with ship ops.
A2QFI,
The original Mk3 purchase was a dreadful mess, and has been thoroughly rodded-out by the NAO. Suffice to say, in the finest traditions of procurement, no senior hands were sacked or even reprimanded; indeed, several involved were still in post when I arrived at ABW a decade later. The cost to 'put it right' is misleading as it involved several upgrades that would have to have been put onto the ac even had it entered service on time - in many respects they were just catching up with their sisters. The real irony is that the 8 Mk3s were built by Boeing with legacy cockpits then flown to Honeywell to have the glass cockpit installed; they are now on 'legacy' cockpits again until the Mk5 programme...therefore some ac will have had 3 cockpits by 100hrs TT and some will be on number 4 by about 1000hrs....
MGD,
Mk6 is a Combined Test Team from day 1 with Boeing, Boscombe and RWOETU crews involved; never say never, but hopefully even QQ can't put unnecessary delays into this programme. Oh, I'm aware of the potential irony of what I've just said......