WingoWango
My expertise is on 737, A320 and A330 so I am not familiar with the BQ400. However the general procedure is the same with any aircraft for the LVP's for that particular aircraft.
Clearly in the case of the BQ400 if the autopilot is only authorised for use down to 80ft then that is the minimum for the BQ400. Of course 80ft is substantially lower than the normal ILS minima of 200ft and therefore to legally achieve an 80ft minimum low visibility procedures would have to be used.