You have done some terrific analysis, but you are failing to see the wood for the trees. The message from this accident is very clear and very valuable: don't press on in dodgy weather towards and through mountains. Even if it looks like it might be OK, it also might not and unless you are an experienced mountain pilot who knows these particular mountains very well then the Plan B which you think you can depend on may not turn out so dependable after all.
I do hope I am not!
I wanted to understand better why this pilot did what he did and where it all went wrong.
I dont agree it was a case of pressing on in dodgy weather - that is far two simple - although that was obviously what ultimately lead to the accident.
I think the weather in which he departed was more than good enough for the sector proposed - although perhaps not for his level of experience.
What I couldnt understand is why he pressed on at Bathesda over the mountains when he could so easily have turned north without adding hardly any time to his journey. Pilots usually make those sort of decisions for a reason and particularly one who had already demonstrated he was prepared to turn back as he did earlier in the day. Remember he wasnt in a rush it would seem, he was prepared to turn back, he had flown the same route earlier that day and I am sure he knew he could track along the coast over low ground and in reasonable weather.
I could be wrong, but I now think he saw a clear route through the valley - maybe the same way as he had come. That was poor judgement but at least I can understand why he did it.
That is a subtely different message becasue it illustrates how easy it is even when there is a very simple alternative for pilots to be attracted into flying up a valley.
I suspect this pilot really believed that he could continue up one of the valleys shown in the graphic and over, otherwise I dont think he would have done so. Had the valleys not been there, or had they presented in a different way, I believe he would have "diverted" to the north.
.. .. .. so in short there are lots of message in aviation that are clear and most pilots could resite them till the cows come home, but accidents like this continue to happen. Understanding why the pilot decided to ignore something he knew well I think is equally as important. For me at least this accident illustrates just how enticing on that day flying up the valley must have seemed and that in spite of your message how many other pilots might have been tempted, unless they had read this thread.