How do LNAV and VNAV operate during cruise in the A320?

• A. LNAV provides lateral navigation along the route; VNAV manages vertical profile and speed constraints to meet altitude and fuel objectives.
• B. LNAV, VNAV are autopilot modes that only help with the flight plan.
• C. LNAV and VNAV only control the engines.
• D. LNAV provides vertical guidance; VNAV provides lateral guidance.

Answer: (A)

In cruise, LNAV and VNAV work together as the FMS/autopilot’s managed navigation. LNAV handles the lateral path, following the route from waypoint to waypoint and making the necessary turns to stay on course. VNAV takes care of the vertical side, following the defined vertical profile and any altitude constraints, while also juggling speed to meet targets and optimize fuel burn. Put simply, LNAV keeps you on the right line left to right; VNAV controls how high you go (or remain at) and how fast you fly to meet constraints and efficiency goals. The other options mix up these roles or describe engine control, which is not what LNAV/VNAV do.