Abstract: Methods and apparatus are provided for indicating safe or potentially hazardous operating conditions of an aircraft in a required navigational performance (RNP) environment. The apparatus comprises a course deviation display field with first and second markers defining outer boundaries of the RNP width and a central marker indicating the desired course within the RNP width, an aircraft estimated position uncertainty (EPU) marker in the display field whose size corresponds to the EPU relative to the RNP and a current aircraft position marker coupled to the EPU marker and moving therewith as the aircraft position changes with respect to the RNP width. The display desirably changes color and/or flashes to alert a pilot to a potentially hazardous condition when an outer boundary of the EPU marker approaches to within a predetermined guard-band distance of or overlaps either of the first or second markers. An audible warning can be included.