From memory in the accident report there were 5 factors required by Air NZ SOPs for you to descend below the MSA. You needed all 5, not a couple, not near enough, and they descended without all 5. And yes, the captain has the final authority to operate the aircraft as he sees fit but the SOPs are what the AOC is legally based on in a court of law. When you add in the fact that the US military did an awful lot of training to operate in that environment and had pretty strong reservations about Air NZ doing what they were doing. It was crazy to think that widebody longhaul anywhere else on the Air NZ network could prepare you for VFR polar ops. There were so many holes lined up the second someone in marketing first suggested "let's do antartica" it doesn't bare thinking about.