A flight robust control for a fixed wing Unmanned Aerial Vehicle (UAV) is addressed in this paper. Attitude and airspeed controllers are designed using an Adaptive super twisting control algorithm (ASTA). In order to implement such controller an observer based on super-twisting control algorithm (STO) provide estimation of inertial state vector despite of noisy. Furthermore, this control scheme increase robustness since it is not necessary to know the bound of perturbation. Taking into account modeling uncertainties and external disturbances, simulation tests have been done in order to illustrate performance of proposed control scheme.