Unmanned aerial systems (UASs) have recently enabled novel applications such as passenger transport and package delivery, but are increasingly vulnerable to cyberattack and therefore difficult to certify. These applications require robust positioning, communciations, and time synchronization services. Legacy systems such as GPS provide these capabilities extremely well, but are sensitive to spoofing and hijacking cyberattacks. In a previous study, we developed a local GPS alternative that provides highly secure communications, positioning, and timing synchronization services to networks of cooperative RF users. In this study, we consider this Communications and High-Precision Positioning (CHP2) system in the context of safety-critical transport applications and urban air mobility. We demonstrate rapid (< 100 ms) and precise (< 1cm) positioning capabilities in over-the-air experiments using flexible ground stations and UAS platforms using limited bandwidth (10 MhZ). We compare several position estimation algorithms in simulation and experimental test environments to identify suitable approaches for different applications. We discuss how the integrated communications link secures the system from spoofing and hijacking cyberattacks. We assert that the these capabilities make CHP2 a suitable candidate to provide both communications, navigation, and surveillance (CNS) and alternative positioning, navigation, and timing (APNT) services for safety-critical transport applications on a variety of vehicular platforms.