In the A321, what is the function of VNAV during climb?

• A. Manage lateral route deviations only.
• B. Manage vertical profile to meet altitude constraints and optimize performance.
• C. Provide weather avoidance guidance.
• D. Disable autopilot during climb.

Answer: (B)

VNAV during climb is responsible for the aircraft’s vertical path, using the flight plan’s altitude constraints to shape the climb and optimize performance. It calculates when to start the climb, how fast to climb (the target climb speed), and how much thrust to use so you reach required altitudes at the designated fixes while keeping fuel burn and engine limits in check. The autopilot and autothrust work with VNAV to follow this vertical profile, adjusting pitch and thrust as needed to stay on the programmed path and meet constraints on time or altitude.

This function is not about steering the airplane sideways or avoiding weather. Lateral navigation and weather avoidance use other systems and modes, while VNAV’s job is the vertical path. It also doesn’t disable autopilot; VNAV is designed to be active with the autopilot guiding the aircraft along the managed climb profile.