A number of points spring to mind.[list=1][*]AIP (Jepp AU-705, para 1.7.5.7) requires a pilot wishing a visual approach
AND satisfied that the conditions at Jepp 1.7.5.1 exist,
MUST report visual. (ie. continuous visual ref to grnd or water, not lesss than 5000m viz, within 30 nm or if being vectored has been assigned the minimum radar LSALT and given heading to intercept final or position the aircraft within 5nm of the aerodrome).[*]From Jepp AU-7 (Definitions & Abbreviations)
VISUAL from a pilot means,
Used by a pilot to indicate acceptance of responsibility to see and avoid obstacles while operating below the MVA or MSA/LSALT.
[*]There is no proscribed distance at which the call of "Visual" shall be made, therefore I don't agree that calling visual at 32 nm is stupid.[*]The CTR boundary to the West of Darwin (approach for RWY11) is aprox 18 DME, this should give ample opportunity to descend from 3000 for a straight in approach.[/list=1]
My guess is that either, the pilot did not fully understand the descent criteria (Jepp AU-705, 1.7.5.5) for a Visual Approach, or, perhaps after gaining clearance to track for a 5 mile final, was uncertain if that clearance voided the Visual Approach clearance.
NFR, to answer your question, I'd descend to the MSA, remaining at or above the CTA LL +500' as I followed the cleared track, until at 5 nm established on the VASIS and aligned with the RWY C/L.
My question to you is, what is a VSA? Visual Straight-in Approach, Visual Sector Approach, ....?