Meadowbank
If you refer to Boeings report (something like “Analysis of Available Data” by Mr Mitchel as I recall without looking it up), this turn was deduced from the last turning rate as recorded in the SuperTANS (again, as I recall off the top of my head) which was consistent with hand calculations and I would suggest that a demanded steer at that time seems far more probable than anything else suggested.
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Reasonable assumption of the conditions ahead and the track taken give a simple picture of their heading to a particular point. As it has rightly been pointed out, if the flight was a routine ferry flight, pressing on closer than waypoint change (look on a chart just how close in waypoint A was) was unnecessary – perhaps some questions should be asked as to whether there was any possible extra task put on that crew – not speculation, but pointedly ask.