Abstract: In this paper, we propose a flush air data sensing system for subsonic aircraft. Firstly, a pressure database for the FADS system was established by modeling and numerical simulations, and the corresponding error bounds in the range Ma = 0.2～0.4 were analyzed based on the model accuracy and wind tunnel calibration. Secondly, a real-time algorithm for the FADS system was developed and integrated into a prototype. Finally, a systematic evaluation of the real-time algorithm and the prototype of FADS was conducted through wind tunnel and flight tests. The angle of attack value was recalculated through post-model algorithm reconstruction to evaluate the reliability of the real-time algorithm for the angle of attack in flight tests. The results show that: (1) Compared to other systems, such as the initial navigation system, the real-time calculation method for the angle of attack adopted by the FADS system has high accuracy in flight tests, with an error of less than 0.5°. In addition, the angle of attack values obtained by the FADS system based on different models are consistent, confirming the reliability of the real-time calculation algorithm; (2) The fluctuation of the calculated real-time angle of attack in the initial stage of the flight test is caused by the large error limit of pressure input. The large amplitude of pressure fluctuation at high altitudes and low speeds is the main reason for the large deviation in real-time angle of attack calculation. The angle of attack calculation method established by numerical modeling technology for the FADS system has little effect on the angle of attack calculation within the algorithm error limit. However, excessive pressure fluctuation beyond the algorithm error limit significantly affects the angle of attack calculation. The FADS system for high-altitude and low-speed aircraft has high requirements for the accuracy level of pressure sensors and engineering implementation, so the accuracy level of pressure sensors should be guaranteed as much as possible in practical engineering applications.