BOAC
(Dare I suggest?) If you read the thread regarding the wx, I think you will find that I don't believe that they were in IMC until the very last seconds, as they entered the ground mist, which hardly counts. I have repeatedly suggested that anyone interested in this case should actully go up there at the right time of year and see such weather for themselves – it is quite consistent. At low level on that day (from what was expected and eyewitnesses I have spoken to) they would have been able to see the Mull from quite a way off (including the shoreline) but it would have been bereft of familiar objects or ground texture that could have helped their visual judgement of closing range while they were approaching at speed.
In those conditions, my view is that at the position of waypoint change they had already come in too close to have relied safely on SuperTANS or visual judgement and so, if you argue that they were not negligent, you need to dig deeper to explore the possibilities for equipment or procedures that they may have been reliant upon to excuse them.