For me all the evidence points to a navigation error...........if the crew thought they had open sea ahead of them when they entered cloud , they would have initiated a gentle climb to break through on top . the cloud/fog was localised and they could continue at low level after resuming vmc .
..there are references to errors on the Racal nav box , including a possible erroneous entry....and I am sure they did not realise that their first checkpoint was 300 feet up a cliff ......
Does anyone know if any of the flight planning documents survived..?????...
On a clear day any error would have been obvious , but in the localised greyout conditions they had no chance........