Ampan
If the crew couldn't verify their position visually, the only other available method was radar
Sorry, can’t agree with that.
They were locked on to their Nav track until the orbits started, and then again when the orbits were completed.
I’ll bet (without any evidence to back it up, unfortunately
) that one of the crew looked at the NAV distance to run, stuck his finger on the track line on the famous never-to-be-recovered map and thought “with xx miles to run, we are about here in the middle of McMurdo sound with no high ground within about 20 miles, and it looks OK outside, so I’m happy with a VMC descent”.
You are implying that they could not trust the phenomenal accuracy of their 3 NAV systems.
It all gets back to the fact that they were relying on the McMurdo waypoint they were using, and it had been changed without their knowledge.
Perhaps we all should never accept or trust our flight plan data unless we have personally verified every digit on it. Hardly a practical proposition, I think.