Don't get confused here. The trap in the DC10 and I think the Alaskan incidents was "sector whiteout". In the DC10 incident the flight visibility was in excess of 150 miles. The FMS was programmed so that they were'nt where they thought they were which is really incidental. The whole crew thought they were in the clear and could see the coastline and several other features clearly. They were well below the cloudbase. The white cloudbase, white mountain covered in white snow was undetectable to the capabilities of the human eye. During all the investigations the same course was flown in a US military 212 from Mc Murdo about a year (I think) later to the day. The same conditions existed and said mountain was not visible. The conditions of sector whiteout are never apparent and you have no reason to even think about using instruments unless you know the symptoms that cause it. The conditions were VMC and the aircraft were not in any sort of precipitation.
Unless you have experienced it yourself it is difficult to appreciate or describe to someone else how deceptive it is.