Banking (roll) control affected by aileron movement  A Directional (yaw) control affected by rudder movement  C Climb and dive (pitch) control affected by elevator movement  B Normal altitude Longitudinal axis Longitudinal axis Lateral axis Normal altitude Lateral axis Vertical axis Normal altitude Aileron Rudder Elevator Aileron Vertical axis Figure 2-10.  Motion of an aircraft about its axes.  Directional Stability Stability about the vertical axis is referred to as directional  stability. The aircraft should be designed so that when it is  to motion in pitch. The horizontal stabilizer is the primary  surface which controls longitudinal stability. The action of  the stabilizer depends upon the speed and AOA of the aircraft.  2-10