The nav track was an aid, not a railway line
Absolute nonsense. Prior to the unavailability of the NDB (it never was unavailable, it was on air, but expectation was it could fail as maintenance had been withdrawn) and the institution of the VFR procedure the aircraft was to fly Cape Hallett direct to the NDB for an instrument let down, that track led directly over Erebus. There was no instruction to put in any offset or such to avoid overflying Erebus. Para 1.1.1 of Chippendales report.
The briefing gave details of the instrument flight rules (IFR) route to McMurdo which passed almost directly over Mt Erebus, a 12450 ft high active volcano, some 20 nm prior to the most southerly turning point, Williams Field.
He knew he could only go below MSA on instruments
Okihara, this snippet from your quote is incorrect, the only way they could descend below MSA was in visual conditions. The requirements were detailed at 1.17.39 in Chippendales report.
Note that the only letdown procedure available is VMC below FL160 to 6000’ as follows:
1. Vis 20 km plus.
2. No snow shower in area.
3. Avoid MT EREBUS area by operating in an arc from 120° Grid through 360G to 270G from McMurdo Field, within 20 nm of TACAN CH29.
4. Descent to be co-ordinated with local radar control as they may have other traffic in the area.”
Such was the disorganisation within the airline was that the McMurdo controllers had no knowledge of the procedure.