An algorithm for estimating aircraft approach angle using computer vision is proposed in this paper. During the landing of an aircraft, the descent of the aircraft may be approximately considered as a pure translation motion. In this case the epipole has the same coordinates in all images and is called the Focus-of-Expansion (FOE), and the vanishing line of the ground plane is termed the Horizon. Furthermore, how the Focus-of-Expansion and the Horizon are extracted from a few calibrated sequential images is first introduced, then the aircraft approach angle is derived from these parameters. Simulated and real experiments validate this algorithm.