AINS
I’m not suggesting that the crew couldn’t trust the three gyroscopes and the computer hardware in the AINS. Pieces of steel and silicon do not tend to make mistakes. But the AINS required input from a human being or two at various stages, and it’s the human input that created the potential for the AINS to be wrong. The Navigation Section might have made an error. The crew might have made an error when entering the coordinates. The crew might have made an error while fiddling around with the AINS on the way down from NZ.
There’s probably no need for any evidence to back up your reconstruction of the decision to descend, because that’s probably exactly what happened. But what was the basis for the crew believing that they were in the middle of McMurdo Sound? It was the AIMS – and only the AIMS. There was nothing else. Could they see the high ground and get a visual fix? No. Did the ATC have them on radar? No. Did they have both NBD and TACAN? No. All they had was the AINS.
It’s obviously not practical to continually verify one’s position for the whole flight. But what about landing? And what about going down to 2000 feet when there’s a 13000 foot mountain around? You may think it’s 20 miles left of track, but why do you think that? Because of the AINS. Anything else? No. So wouldn't the average commercial pilot, exercising a reasonable amount of care and attention, stay at the safe altitude until his position had been verified?