[en] Based on the original five-dimensional drift kinetic equation, a three-dimensional reduced drift kinetic equation has been obtained to describe the neoclassical transport of helical plasmas in ultra-low collisionality regime where the collision frequency is much lower than the poloidal bounce frequency of the super banana particles. The reduced drift kinetic equation describes the evolution of the distribution function in terms of three independent constants of motion. In contrast to the conventional neoclassical theory, this reduced drift kinetic equation includes the effects of finite super banana width and the effects of finite aspect ratio. Therefore, this reduced drift kinetic equation is suitable for studying the collisional transport of fast ions in helical magnetic confinement systems. (author)