Tex Johnston describes the Dutch Roll as, "...an inherent characteristic of swept-wing aircraft. It starts with a yaw. In a 35-degree swept-wing airplane, a yaw is accompanied by a simultaneous roll in the direction of yaw. The roll is caused by changing lift factors as the airflow path over the wing changes. For example, in a left yaw the left wing slews toward the rear so that airflow is displaced spanwise from its normal front-to-rear path over the airfoil section. That reduces lift. Simultaneously, the advancing right wing gets more chordwise flow, and so its lift is increased. In combination the two conditions create a left roll. Similarly, a yaw to the right results in a roll to the right. An oscillation is set up."