ONEPOSTONLY -
A few points regarding your post,
I believe that the IFR ILS approaches you fly differ from the VFR ILS approaches being flown here. Stay with me on this...
When I first started flying in Inverness I was treated to a discussion with the SATCO about the difference between VFR, IFR and VISUAL approaches. As I understand if you started out IFR and want to make a VISUAL approach then you will still be treated in the eyes of ATC as being an IFR (and still expected to fly the published missed approach if you went around) despite being able to see where you are going.
If you 'cancel IFR' (normally using that phrase) you are now treated as a VFR flight (because you now are!) and seperation now VFR against VFR, ie not given. You are now responsible for see and avoid, although of course FIS may be provided with traffic info given. (if you go around you will be expected to fly a visual circuit by the way).
The relevance of this is that although we believe the 402 (not a 406 by the way, there is quite a difference) was flying practice ILS approaches for CALIBRATION purposes, therefore I believe that the purpose of the two pilots up front was to provide safety pilot look out whilst the other was busy. Remember this is a single crew aircraft and will be flown as such with single crew SOPS, there will be no challenge and response stuff and the HP (or PF if you prefer) will be doing it all. The second pilot in this case was probably also acting in an instructing capacity too as he/she was a CRE/line trainer.
Incidentally it is not unusual for aircraft to fly ILS approaches as VFR traffic for several reasons, most commonly for training OPC LPC stuff. In Inverness we choose to do this when the conditions allow of course, because otherwise the slots available for IFR training (as a pukka IFR flight with seperation) are much harder to get.
I believe this accident would be highly unlikely to happen with larger IFR commercial traffic because that aircraft would retain its IFR status down to the ground and ATC seperation would apply. Of course there is nothing to stop anyone flying across the path of an ILS outside the ATZ, but that is not peculiar to CVT, try Blackpool, Filton, Cambridge, and Cranfield for starters...
I have worked for the Atlantic Group (and spin off companies) for 12 years and have flown over 200 hours in EYES. I am very sad for those affected by this accident.
CRX.
Ps: ATC comment about my understanding of the above is welcome.