The Privy Council bid not uphold Mahon's finding about the culpability of the crew, because it was not at issue. Don't believe me? Try reading quite a lot of words. I know it's scary, but give it a go:
Mahon v Air New Zealand Limited [1983] NZPC 3; [1983] UKPC 29; [1984] AC 808; [1983] NZLR 662; [1984] 3 WLR 884; (1983) 4 NZAR 33; (1983) 50 ALR 193; [1984] 3 All ER 201 (20 October 1983)
Who cares about where Mahon's findings stand or sit or whatever? That's like quoting the findings of the Warren Commission to a Kennedy conspiracy theorist. The issue is not what Mahon found. It's whether he was correct. Does this relieve the feigned bafflement?