mm flynn:
this could equally have happened in Class D airspace (operated to ICAO standards), and it could have happened regardless of which flight rules the 402 was following
Exactly. The "separations" between IFR and VFR - or VFR and VFR - on final approach in Class D are in effect the same as in Class G. They rely on what IO540 has dubbed "grey areas". There is one other thing though. Aircraft in contact with Tower and operating in the vicinity of an ATZ are receiving an ATC service and are expected to comply with ATC instructions - even if they're in Class G.
clearly if the 402 was receiving a RAS service he would be separated from everything
Not in this case. Coventry can't provide a RAS below 1700 feet in this area and in any case if he's been transferred to Tower he's effectively (another grey area...) no longer in receipt of a radar service.
NS