I have a foot in both camps. I largely agree with the faults identified by Mahon concerning organisational factors, however with qualification. Chippendale was succinct. I don't think I can fault their two coexistent causes of the accident being those detailed in paras 393 and 3.37 of their respective reports. Mahon overreached in other areas, Chippendale didn't quite go far enough, IMHO.
But given that the forecaster said at McMurdo
1.7.4 'We have low overcast in the area at about 2000 feet and right now we have some light snow but our visibility is still about 40 miles.
Why would the captain decide to descend and establish below that weather given what he knows about whiteout and that he would be navigating visually without any ground aids, knowing that under his flight rules he could not operate below MSA purely by reference to the INS?
Mahon's report also contains this assertion; para 28
'To the left, clearly visible under low cloud, was the thin strip of black rock indicating the shoreline of Cape Tennyson about 13 miles away. To the right, also clearly visible under cloud, was the strip of black rock and the lower slopes of Cape Bird, indicating its shoreline about 10 miles away. It therefore followed that as the aircraft had approached Mt. Erebus it was flying in skies in which there was perfectly clear visibility for at least 23 miles'.
It appears he simply added the distance L & R to reach the conclusion that there was 23 miles of visibility. Notwithstanding that, although the visibility is claimed left and right it refers to ground features and vertical visibility is often better than the horizontal visibility so I'm not sure the inferred visibility was as good as stated and if it was then this calculation is questionable.
I've no doubt the whiteout phenomenon prevented anyone on the flight deck seeing the mountain which they did not expect to see. But I also tend to agree with Mahon that they were not uncertain of their position. They were exactly where they 'thought' they were, hence no alarm.
I've learnt a great deal reading this thread. Thank you for the ongoing discussion, it has opened my eyes on a great number of issues.