DozyWannabe :
It was safe as long as the aircraft was following Chief Navigator Hewitt's "erroneous" co-ordinates, which were actually safer than the original path he plotted to the TACAN south of Ross Island.
But in a sense, isn't that precisely why INS is not as reliable as ground aides? They can be inadvertently misprogrammed. The crew themselves can mistakenly punch in a wrong coordinate. If you've never been to destination before, wouldn't it also be prudent to check the programmed coordinates you've just entered and make sure they match the actual coordinates for the McMurdo Sound route?
I'm aware the Lewis Bay track and the expected route down McMurdo Sound would have appeared similar. But before the letdown commenced, could the crew really be 100% certain of their position by visual means alone?
Thanks
Chris