The following commentary appears in The Erebus Papers which is quoted elsewhere on this website and is included here to assist with linking the times as shown in the above diagram with relevant portions of the cockpit voice recorder transcript.
43:27 Mulgrew: There you go. There’s some land ahead.
Believing he was pointing to Cape Bernacchi but in fact he was looking at Cape Bird. Had Mulgrew correctly identified it as Cape Bird, then he would have known they were some 26 miles east of where he believed and headed for Mt Erebus.
45:36 Mulgrew: Taylor on the right now.
[Washington transcript] Mulgrew is referring to Taylor Valley being on the right Mulgrew is in fact looking at the cliffs in Lewis Bay which were not in sector whiteout and mistakenly identifying them as the Taylor Valley. Mulgrew seated on the left behind Collins can now see to the right since the aircraft is no longer banked left.
46:39 Brooks: Where’s Erebus in relation to us at the moment?
Mt Erebus is concealed in sector whiteout giving the illusion it is part of the flat expanse of McMurdo Sound. The question is asked by the engineer, not by the pilots who are navigating and flying the aircraft. It is directed to either Moloney or Mulgrew
Moloney or Mulgrew: Left (about four or five miles) about eleven o’clock... yep.
Paper rustling, suggests Moloney or Mulgrew handling map they are reading from. This answer would accurately locate Mt Erebus supposing the DC10 had been on its plotted track in McMurdo Sound on the left.
Mulgrew: Yes [pause] no, no, I really don’t know.
If Mulgrew displays a momentary hesitation with this remark, he dispels it seconds later with his next identification.
47:02 Mulgrew: That’s the edge.
Meaning the dangerous edge of Ross Island namely Cape Royds but in fact he is looking at the cliffs left of Lewis Bay which are not in sector whiteout.
48:10 Mulgrew: Ross Island there. Erebus should be here.
This was spoken in a confirmatory tone. Both Collins and Moloney appear to concur.
48:55 Collins (to Cassin): What’s um [pause] have we got them on the tower?
Not a landmark observation but included to show first expression of concern shown by flight crew. But concern only in the sense that the tone of voice shows Collins is merely puzzled, not anxious.
48:59 Cassin: No [pause] I’ll try again.
Replying to Collins’s puzzled tone, Cassin’s tone of voice reveals he also is puzzled but not anxious.
49:08 Mulgrew: Looks like the edge of Ross Island there.
Still believes he’s on the expected track in McMurdo Sound which he has mistakenly identified from the landmarks and still believes he is looking at the cliffs around Cape Royds. The direction is exactly the direction which you would expect Cape Royds to be in. In reality he’s looking at the area of Lewis Bay just left of the insidious fog ramp concealing the coast of Ross Island. If Mulgrew had not mistakenly identified Cape Tennyson as being Cape Royds but had correctly identified it as Cape Tennyson, then Mulgrew would have known he was in Lewis Bay heading directly towards Mount Erebus.
49:35 Mulgrew or Moloney: You can see (Ross Island).
Because Mulgrew and Moloney had similar voices the Washington transcript marked the speaker as unidentified. Vette attributes it to Mulgrew and logic supports him. The comment merely indicates that Ross Island is on the left and the DC10 is flying safely past it.
49:50 End of Recording
Now the shifting of the track did not in itself cause the accident: many things combined to make the accident happen, as they tend to do with all high-technology accidents. But, according to the Royal Commission of Inquiry, this was the most dominant and effective factor that made the accident possible.
The vertical path
Discussion of the aircraft’s flight path would not be complete without consideration of the vertical aspect of the path. The minimum safe altitude over Mt Erebus was 16,000 feet. Descents below this altitude could only be conducted visually, that is clear of clouds and with good visibility, or by radar from McMurdo air traffic control. The former was used, although to be absolutely correct the aircraft should have requested, and been cleared for, a “visual approach.” Instead, the clearance was for a “descent maintaining VMC,” which means “visual meteorological conditions,” that is, clear of clouds and with good visibility. Since the requirements for maintaining VMC are similar to those for a visual approach this anomaly was not a factor in the accident.
According to the airline and the Civil Aviation Authority, descents below 16,000 feet required operation in an arc around the southern flanks of the mountain and only to a minimum altitude of 6,000 feet. If that is true, then the airline failed to communicate this effectively since it was known that many of the preceding flights operated much lower than that, with the knowledge of airline management. This “low flying” was written about extensively in tourist publications and in in-house journals, some of which are shown elsewhere on this website. In dismissing the Royal Commissioner’s appeal of the Court of Appeal’s finding that the Royal Commissioner was not entitled to claim that there had been a “litany of lies” the Judicial Committee of the Privy Council stated obiter dictum that the airline’s executives were aware of this low flying and did nothing about it, and therefore could not subsequently claim that the accident aircraft was inexplicably low.