What is the difference between LNAV and VNAV modes?

• A. LNAV handles lateral navigation along the programmed route; VNAV manages vertical profile to meet altitude constraints and optimize performance.
• B. LNAV manages speeds, VNAV manages heading.
• C. LNAV is for takeoff, VNAV for landing.
• D. LNAV uses autopilot, VNAV uses flight director.

Answer: (A)

LNAV and VNAV address different parts of the flight path. LNAV handles lateral navigation, guiding the airplane along the programmed route in the horizontal plane—keeping the track on the course from waypoint to waypoint and making the required turns. VNAV handles the vertical profile, managing climbs, descents, and altitude constraints to meet assigned levels and to follow a speed/altitude plan that optimizes performance.

Together, they let the flight management system fly a complete 3D path: LNAV follows the route geometry, while VNAV follows the vertical constraints and the planned speed schedule. It’s common for pilots to have both modes active so the autopilot or flight director can couple to a precise lateral path and a precise vertical profile simultaneously.

The other descriptions don’t fit because LNAV doesn’t manage speeds, and VNAV doesn’t manage heading as its primary job; takeoff and landing phases aren’t reserved to those modes either, and both LNAV and VNAV can be used with autopilot or flight director depending on how the crew selects guidance.