If these were so watertight as you seem to be suggesting,
They were watertight, as has been posted numerous times in this thread
They also had company memorandum that covered requirements for descent OAA:14/13/28 dated 8th November 1979.
There was a copy recovered from the cockpit so the crew were aware
will post it again, though it seems quite straightforward to me.
Delete all references in briefing dated 23/10/79. Note that the only let down procedure available is VMC below FL160 (16,000ft) to 6,000ft as follows:
1. Vis 20km 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 the area.