Massive MIMO technology stands poised to revolutionize the transmission capabilities of broadband communication systems. Nevertheless, in the context of aeronautical multi-user air-to-ground communications, conventional user selection algorithms encounter formidable obstacles, including pronounced self-interference, resource-intensive operations, and burdensome computational overhead, all stemming from the escalating tally of antenna components and users. This paper investigates a positioning-assisted massive MIMO user selection algorithm specifically designed for aeronautical applications. By leveraging real-time user location information obtained by the base station, the algorithm optimizes the conventional Greedy User Selection (GUS) algorithm by enabling real-time beamforming design and channel capacity calculation without the need for complex instantaneous channel state information acquisition. This approach avoids high-dimensional matrix inversions. Simulation results demonstrate that the proposed algorithm, applied in aeronautical multi-user air-to-ground communication scenarios, achieves comparable performance to traditional greedy user selection algorithms while offering excellent interference suppression and capacity performance. Moreover, the algorithm significantly reduces the computational complexity, making it highly valuable for practical engineering applications.