Which statement correctly describes RNAV navigation with an FMS and what LNAV/VNAV provides?

• A. FMS RNAV uses database-driven routes and autopilot navigation; LNAV provides lateral guidance and VNAV provides vertical guidance with speed constraints.
• B. RNAV with FMS ignores autopilot and relies on manual headings.
• C. FMS RNAV relies on pilot-selected headings without a navigation database.
• D. LNAV/VNAV provides only vertical guidance.

Answer: (D)

RNAV navigation with an FMS relies on a navigation database that defines routes, waypoints, and altitude or speed constraints. The FMS computes a path and, when coupled to the autopilot or flight director, it flies the horizontal track along those waypoints (lateral navigation) while also managing altitude and speed along the plan (vertical navigation).

LNAV provides the lateral guidance to follow the programmed route between waypoints, and VNAV provides the vertical guidance to fly the published altitude profile and meet any speed or altitude constraints. When you use LNAV/VNAV, you get both: the aircraft is guided along the horizontal path and along the vertical profile simultaneously.

So, LNAV/VNAV is not solely vertical guidance; it delivers a complete path in three dimensions, combining the horizontal route with the vertical profile to meet the required altitudes and speeds. In practice, you can see this during RNAV approaches or climbs/descents where the system guides you along the route while enforcing altitude constraints and target speeds.