Which term describes stability about an aircraft's vertical axis, also called yawing or directional stability?

• A. Vertical speed indicator
• B. Vertical stability
• C. Vertical axis
• D. Very-high frequency

Answer: (B)

Stability about the vertical axis is the aircraft’s tendency to resist yaw and return to straight flight after a sideslip or a rudder input. This yaw or directional stability comes from the aircraft’s tail configuration and fuselage shape, with the vertical stabilizer producing a restoring moment that tends to align the aircraft with the oncoming airflow, like a weather vane. That is why describing this as vertical stability fits: it denotes stability about the vertical axis. The other terms don’t describe this behavior: a vertical speed indicator shows climb or descent rate, not stability; the vertical axis is simply the axis around which yaw occurs, not a stability term; very-high frequency refers to a radio band.