" Before the 28 November flight the McMurdo NDB was officially withdrawn. Although still operating, it was no longer being maintained and so its accuracy could not be guaranteed. The nearby TACAN was used instead. This was referred to in Company memorandum to AntArctic crews, OAA:14/13/28 dated 8 November 1979. Headed MCMURDO NDB NOT AVAILABLE, it was succinct and unambiguous
Deletev all reference in briefing dated 23/10/79. Note the only let down procedure available is VMC below FL160 to 6,000ft 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 360 grid to 270 grid from McMurdo field, within 20 nm of TACAN CH29.
4. Descent to be coordinated with local radar control as they may have other traffic in area.
A copy of this memorandum was recovered from the cockpit wreckage, so there was no way the crew were not aware of it."