As far as they knew they were VMC (see Vette's sector whiteout material)...and had possibly confirmed their position visually (if mistakenly). And in order to confirm this they elected to re-establish on the briefed track up McMurdo Sound after each orbit. When they (possibly) became uneasy with the situation they elected to climb out, again straight up McMurdo Sound.
Disagree. As Vette showed you needed a cloud layer above you to get the whiteout conditions that lead them to believe that they didn't have terrain in front of them. They were uneasy before descent, in descent and for some time at the lower level. They shouldn't have commenced descent in the first place. There is no point in blaming the company, the crew elected to descend themselves. They were slow to react to a worsening situation and slow to react to the GPWS. Having blind faith in the INS, below MSA in a completely unfamiliar environment?
Vette further highlighted what a completely unfamiliar environment it was so what were they doing there? LA three times a month isn't going to give you preparation for VFR around Antartica.
Lets say the company didn't give them the changed co-ordinates but the INS developed a xtrack error instead, without tacan they still would have hit the mountain. Whose fault then? Chippendale would still have come to the same conclusion.
What would Mahon have said then?