The insufficient and excessive indications of the measured angle of attack (AOA) are experimentally observed in takeoff and landing phases, corresponding to the fast pitching up and down processes, respectively. This paper studies the effects of lever-arm and unsteadiness on measurements of AOAs of a certain aircraft through theoretical analysis and numerical simulations, where the former is applied for the lever-arm effect and the latter is adopted in the unsteady effect analysis. It validates that the existence of lever-arm and aerodynamic unsteadiness are two main reasons leading to the inaccurate AOA measurements by the weathercock sensor mounted at the front fuselage. Additionally, through the quantitative results of insufficient and excessive indications, an accurate method is proposed to correct the effects of lever-arm and unsteadiness. Applying this correction method, the accuracy of AOA measurements in the takeoff and landing phases is improved. This method is also suitable for other stages of aircrafts maneuvering in the air with arbitrary angular rates.