Thanks for the reply, I'm still reading but can only get online when I've kicked the kids off!
The FADEC problem seems to me to be the most likely. I agree that initially they were flying at a sensible height and speed for the weather conditions at the time. But a high side FADEC failure at the turn point would have increased the work load ten fold. While all pilot training deals with a "traditional" engine failure - that is the engine ceases to produce power - do we know from the training records for the pilots concerned, if they received any training in "other kind of engine failure" or did they expect the failed FADEC to freeze? Did the Flight Reference Cards contain any info about High and Low side FADEC failures?
I'm sure Wessex pilots would like to jump in here, but it is a sad fact of life that sometimes experience and knowledge can get lost over time and lessons have to be relearned. I of course refer to the Gnome twin pac and it's fuel computers.