What is the primary capability of a 2D RNAV system?

The primary capability of a 2D RNAV (Area Navigation) system is to navigate in the horizontal plane. This type of system utilizes navigation sensors and waypoints to determine an aircraft's position and intended flight path primarily in terms of lateral movement.

2D RNAV systems provide the necessary information for an aircraft to navigate along a predetermined flight path, ensuring that it can accurately follow the route defined by waypoints presented in two dimensions—latitude and longitude. While other components of RNAV systems exist for vertical navigation, such capabilities fall outside the scope of a standard 2D RNAV, which focuses exclusively on managing horizontal flight paths.

The options that suggest vertical navigation or a combination of both horizontal and vertical navigation do not accurately reflect the specific functionality of a 2D RNAV. This emphasis on horizontal navigation aligns perfectly with the design and application of such systems in aviation, making this understanding fundamental for pilots and aviation professionals.