<p>Overcoming the impacts of model uncertainties and external disturbances is a common challenge in fixed-wing UAV control system design. This paper introduces a novel fixed-wing UAV attitude control framework that integrates Barrier Function Super-Twisting Control (BFSTC) with Single-loop Incremental Nonlinear Dynamic Inversion (SINDI). By leveraging SINDI to linearize second-order attitude dynamics, we apply a BFSTC strategy featuring an adaptive gain that dynamically responds to disturbance magnitudes. This integrated approach exhibits heightened robustness against internal and external disturbances compared to the standalone INDI or Sliding Mode Control (SMC) schemes, while simultaneously achieving faster response and reducing the parameter tuning burden. Additionally, we provide a rigorous stability analysis under the saturated control gain and offer systematic guidelines for barrier function parameter selection. Comprehensive validation through numerical simulations and real-world flight experiments confirms that the proposed method delivers exceptional tracking precision, robustness and adaptability across diverse flight paths and disturbance scenarios.</p>