An autonomous navigational system for an airborne vehicle is disclosed which automatically updates its position and heading coordinates at each of a plurality of checkpoints along a preselected flight path. Prestored in a memory of the navigational system is a plurality of reference map images respectively associated with the plurality of checkpoints. Each reference map image is comprised of a plurality of terrain features associated with the terrain about an associated checkpoint. In operation, an acquisition unit senses an image of local terrain at each checkpoint. The relative sizes of reference and sensed map images vary with the mission requirements. A terrain feature extractor detects a plurality of terrain features contained in the sensed map image. The detected terrain features in the sensed map image are selectively matched in a feature pattern matcher against the terrain features of the associated reference map image to determine the position and orientation of the sensed map image within the associated reference map image. The output of the feature pattern matcher comprises error signals which are used by an inertial guidance system to update the position and heading coordinates of the airborne vehicle.