Toshirozero: The point of the extract is to demonstrate that the “eyeballing” evidence relied on by D. Dingo was not convincing, to say the least.
As to the decision to lock the aircraft back onto the nav track, that doesn’t dispose of anything.
Assume that at the briefing on 9 Nov the pilots were told that the track was direct to McMurdo Station but were not told that this track went over Erebus (which is, basically, what Mahon found).
Assume that the Capt. Collins retained one of the flightplans, or else noted down the co-ordinates.
Three weeks later, the night before the flight, he gets out his charts. He would have noted that a direct track from Cape Hallett to McMurdo Station went over Erebus. On plotting the track using the co-ordinates, he would have noted that the track went down McMurdo Sound, with the high ground of Ross Island (including Erebus) to the left. Assuming that he remembered what was said at the briefing, he would have noted the contradiction re the track. He resolved the contradiction by assuming that the track shown by the co-ordinates would be the track that the aircraft would fly, without conducting any further check. That was an error, and a reasonably bad one. He had received contradictory information re the final waypoint, so he should have checked that waypoint as it was entered the following morning. Instead, he simply assumed that the final waypoint was the same as the one he had plotted the night before. It doesn’t mean he was suicidal or insane. It just means that he made an error.
After completing the descending orbits, he locked the aircraft back on the nav track, obviously, as you say, under the assumption that the track was down McMurdo Sound, with the high ground of Ross Island to the left.
Then F/E Brooks says “I don’t like this” and a few seconds later, the Captain decides to climb out. F/O Cassin, in the right-hand seat, says that its clear to the right for a 180 degree turn. The Captain says “No negative”, then pulls out the Heading Select knob and initiates a left-hand turn using the autopilot (refer page 99 in the Chippindale report). Then the impact.
Why did he decide to turn left? If he was certain that he was in McMurdo Sound, with the high ground of Ross Island to the left, then he would have turned right, as the F/O had recommended. One explanation is that he recalled what he was told about the track at the briefing and the pennies started to drop. The fact is that in his actual position (at 1500 feet in Lewis Bay with Erebus dead ahead and Cape Bird to the right and behind), the only way out was to the left.