Still no-one able or willing to answer my query about ATC in those parts and what sort of service the a/c might have been having.
1) Before we start lambasting the controller, based on what we know the a/c was NOT 'descended' to <2550' by ATC. The crew either deliberately did it (in the wromg place) or some event caused it. To say "ATC should have climbed the flight to 5,400 before they entered the downwind TAA" implies the controller had descended the a/c - which I am not seeing, and also that he/she was aware of its altitude which is not stated.
2) It is to me an unusual 'clearance', but not one that would have caused me any difficulty, merely given me great flexibility in what was, I assume, a quiet piece of sky. 'Downin3' says it was an 'incorrect' clearance ("However, ATC procedures were changed as a result of that accident...When not on a pulbished segment and subsequently being "cleared for approach", the correct phraseology is "Maintain xxx until ESTABLISHED on the approach, cleared for...") - incorrect at all times or only when under ATC control?
3) What is the significance of the min 2000' clearance - does some sort of airfield zone start there?
So - for the 'locals' - what sort of 'control' was this? Would radar be used, a/c identified and full control be expected? Would an altitude squawk be available to whoever was 'controlling'? Can a crew elect in IFR to 'pass;' on a full service?