Originally Posted by
henry crun
...and you will have some trouble convincing me he would have been influenced by the very brief flickering of the transponder light in the manner which Dozy Wannabe suggests...
How do you know it was "brief", or indeed how brief it may have been? It could have been coding for several minutes while the decision-making process was happening.
Imho there was no room for any shade of grey in his (Collins) situation.
Let's talk about mental models for a second. As far as Collins is aware, the radar controller will not approve a let-down until they are positively identified - also as far as he is aware, the radar controller will have an exact copy of the flight plan that he was given along with the co-ordinates, so even if identification is sporadic, the controller will know where he is at a given point in time. He's also used to radar control as it exists in the civilised world, where things are indeed "black-and-white". This is Collins' mental model, and as such he was entitled to take the controller's assent to the let-down as confirmation that everything is safe for him to do so.
The controller's mental model is somewhat different, because unbeknownst to Collins, the flight plan sent to Mac Central by ANZ was incomplete and in fact lacked the all-important changed co-ordinates for the McMurdo waypoint. So it's possible that the controller approved the let-down based on a calculated position in turn based on the flight plan, which may have been the plan from the previous flight which had the (original, "false") co-ordinates used as a reference (because the co-ordinates were missing from the new one). In "black-and-white" terms the controller should not have approved the let-down for this reason, but this is not your usual radar-controlled airspace - it is in fact a sparsely-populated bit of airspace on the edge of the known world and things tend to be a little less rigid here. The controller is also aware that TE901 is not the average hoary old military propliner with decades-old nav equipment that he is used to handling, it is a state of the art jetliner festooned with gadgetry that is probably better at calculating their current position than he is.
The difference in these mental models could well carry the genesis of the physical reasons for the let-down being approved when perhaps it should not have been. As I did before, I must ask myself - if the controller had done things by the book and the aircraft crashed, then why destroy a segment of the radar trace that would have erased all doubt?