Originally Posted by
FGD135
(Re : AINS vs. ground aids)
Agreed, and I don't believe anybody in this thread has stated anything to the contrary.
The issue in this case is that while the withdrawal of the Williams Field NDB effectively reduced the available ground aids by 50%, the airline did not treat it as such. The written materials were in the briefing, but aside from that nothing had changed. The dispensation to descend to any level specified by the McMurdo Station controller (and the assertion that as far as the company was concerned, it superceded the 6,000ft NZCA limit) remained unchallenged. I'd bet any money you'd care to name that any disquiet on the part of the NZCA was never relayed in the briefing. As far as the company was concerned, the AINS and radar tracking from McMurdo Station provided enough defence in depth against a mistake. Unfortunately - because the change of waypoint was never communicated to the crew, and the co-ordinates of the new waypoint were never transmitted to Mac Central - both those safeguards were defeated and that left the lives of everyone on board in the hands of a crew who was navigating visually to the best of their ability but who did not know that the starting point of their descent had changed, nor did they know that the overcast they were trying to avoid was capable of hiding the mountain that had unwittingly been placed in their path. If everyone involved had followed procedure then it is likely the accident would have been avoided - unfortunately a desire on the part of the Chief Navigator to correct a mistake as quietly as possible led to disaster.