We had a Sim detail which brught this out. the senerio was dispatch with one A/P U/S (Quite ok by the MEL) than thick cockpoit smoke making it virtuallu impossible to see out (happened to Value-jet).
A single A/P Approach and autoland was the best soution.
Topslide, it's silly to suggest that ANY capability the aircraft has, whether certified or not, should not be understood and available in an emergeny as per above.