Prospector. You are correct re being on the wrong side of Beaufort Island. Photos recovered showed the island was clearly indentifiable.
What is doubly strange is that Antarctic veteran and close friend of Ed Hillary , Peter Mulgrew was on the flight deck and did not mention that they were clearly on the east of the island not the west .
Re accuracy of the INS. On the Qantas flights I checked the accuracy when we overflew at low altitude indentifiable places like Mawsons Hut or Cape Adare. The INS was within a mile at these locations.