In this paper, an adaptive interval type-2 fuzzy output feedback control (AIT2-FOFC) scheme is developed for flexible air-breathing hypersonic vehicles (FAHVs) in the presence of unknown flexible dynamics and parameter uncertainties. After calculating the derivatives of the velocity and altitude repeatedly, a state feedback dynamic inversion controller is formulated as the basic nominal controller. Then, an adaptive interval type-2 fuzzy logic system (AIT2-FLS) is constructed to approximate the unknown uncertainties in the FAHV longitudinal model. Furthermore, a nonlinear high gain observer is designed to estimate the high order derivatives of the velocity tracking error and altitude tracking error which are unavailable in practice. Based on the separation principle, the overall AIT2-FOFC scheme is finally obtained through combining the state feedback controller and the nonlinear high gain observer. Simulation at last demonstrates the effectiveness of our proposed control scheme.