This paper reports on in-flight tests conducted to evaluate a method aimed at controlling the formation of autonomous unmanned aerial vehicles (UAVs) in a leader-follower configuration. The study introduces a two-stage formation flight controller designed to address the challenges encountered in controlling the position and velocity errors inherent in the leader-follower formation flight. In particular, difficulties arise when activating the formation flight mode with considerable distances between the leader and the follower, as well as substantial disparities in their heading angles. The proposed formation flight control scheme comprises two stages: coarse guidance on the leader and precise leader following. The efficacy of this control system was assessed by in-flight testing, in which flight parameters of both the leader and the follower were recorded and scrutinized. The analysis demonstrates that the proposed control algorithm significantly enhances the organization of formation flight. The results obtained from the tests validate the effectiveness of this method, showcasing improvements in formation flight organization and ensuring collision-free conditions. The described algorithm presents a promising approach toward enhancing formation flight control for autonomous UAVs.