It has been established beyond doubt that for these ice flights the vis has been amended to read 20km.
How is it possible to be 1,000ft vertically from cloud when after descending to 2,000ft you have to go down to 1,500ft to see further in?.
It is not entirely clear that flight by civil aircraft within the McMurdo airspace was considered "Controlled" or "Uncontrolled". On 13 October 1977 the Commander of the USN Support Force in Antarctica advised in a message (No. 3100) to CAD Christchurch
AIR TRAFFIC CONTROL/FLIGHT FOLLOWING SHALL TAKE THE FORM OF LOCATION ADVISORY OF DEEP FREEZE AIRCRAFT AND POSITION REPORT RELAY ONLY.
Chippindale questioned the briefing failing to mention,
The authority of the US Navy’s Antarctic ATC system to control the civilian Air New Zealand flight.
It would seem quite explicit from the USN message that they would not be providing positive control, hence flight by civil aircraft could be deemed to be in uncontrolled airspace. As with all Deep Freeze functions, it was "use at your own risk" for civilians.
On that assumption, the only element of the VMC rules altered was the visibility requirement increased from 5 km to 20 km. The other rules pertaining would have been below 3,000 AMSL or 1,000 AGL, whichever is higher, you only need to remain clear of cloud and in sight of ground or water.