The same radar was also used for the PAR approach, so it may have been that the azimuth portion was centred on traffic coming down the sound to the Bryd waypoint to feed traffic into the PAR. In the PAR mode the azimuth only swept plus/minus 15°. I've asked experts on the radar what it's capabilities were, as it was widely used by the RAAF in the past. No reply as yet.
It really, really, doesn't matter. The point is, Captain Collins was offered a radar descent, said "Crikey, that's what we want"...... and then proceeded to descend "VMC" without one. End of story. He never went down the road of ascertaining whether a radar descent would even be possible.
3 Holer.
You've interpreted my post incorrectly. Fantome might be able to help as he seems to be expert with language.
A comment from you on Delziell's crew plotting from the INS would be appropriate.
3-Holer will simply say "Mahon, guided by the erudite wisdom of Vette, is uncontested...crew made no error... but he never said they were blameless....not that they were in any way to blame either.......", but I'm going to go in to bat for Collins here. Yes, with the benefit of hindsight, continual plotting from the INS onto a topo would have added a layer of safety and probably would have saved the aircraft. But to do so was not a regulation or SOP; no crew member offered to do it, so the fact that Collins did not do so doesn't make him negligent - it just makes Dalziell, to his credit, extra vigilant.
The chain of errors Collins made has been well described. I don't think that the absence of continual plotting on a topo is one of them.