I initiated the Antarctic flights and went on the 9 Qantas ones I chartered.
I was always on the flight deck when at low level and personally marked the lat and longitude from the INS on the ONC chart. In those days the aircraft operated at low levels - as low as 500 agl over the pack ice.
One of the flights was on the 17 TH Nov 1977 and was an attempt to get to the South Geographic pole but adverse winds meant a change and we overflew McMurdo at low level. Descent was in IMC using guidance from the McMurdo radar operator . I marked all the positions on the chart so there was a backup.
It's clear that no one in the accident aircraft marked positions on a visual chart as a safety backup.
Just on that last point, it was speculated that the crew were confirming their current position using a map (the atlas) with a line drawn on it and the distance to go.
"Where's Erebus in relation to us at the moment"
"Left about (twenty) or (twenty) five miles"
"Left do you reckon"
...
"I think it'll be left yes"
"Yes I reckon about
here"
You'd use "here" if pointing at a map, "there" if pointing out the window
The problem being that a) the line would have been drawn using the briefing co-ordinates, not the co-ordinates given to the crew that day, and b) unfortunately for them the geography of the bay they were entering being a good match for the bay they thought they were entering so they weren't getting a visual clue to contradict the picture in their minds.