In this paper, a backstepping sliding mode flight controller with adaptive function approximation for heavyweight airdrop operations is proposed in consideration of aerodynamic uncertainty. The complex nonlinear uncertainty is first factorized into a known matrix and an uncertainty parameter vector, and the difficulties of the controller design are reduced. On this basis, an adaptive law is designed to estimate the uncertainty parameter vector, and the problem of the switching gains of the sliding mode controller selected according to the bounds of the uncertainty is solved. Lyapunov based analysis indicates that the proposed method can ensure the air speed and pitch angle of the aircraft converge to an arbitrary small area.