Robust message integrity for FANS 1 and CNS/ATM

The International Civil Aviation Organization (ICAO) is developing a Communication, Navigation, and Surveillance/Air Traffic Management system (CNS/ATM) to provide advanced data link services between aircraft and ground hosts. These services will be provided over the Aeronautical Telecommunications Network (ATN) infrastructure, which is yet to be fully implemented. In the interim, the FANS 1 (Future Air Navigation System) program was developed, which offers valuable intermediate data link services over the existing ACARS network as a first step toward a full CNS/ATM system. Of paramount importance in both systems is the robustness of the Air Traffic Services (ATS) message transfer integrity. This paper describes and documents the ATS message integrity across the interim FANS 1 system, and its logical extension to the end state CNS/ATM environment. We will show that the interim system offers robust message integrity, assuring very low (and very acceptable) undetected error rates for ATS messages. It is shown that the FANS 1 implementation benefits from an end-to-end CRC, augmented by multiple levels of subnetwork CRCs to achieve this high-level of integrity. This robustness is further augmented by other error detection processes used in the FANS 1 Flight Management System (FMS). In this paper, the worst case probability of undetected errors for the interim system, considering multiple CRC´s across each subnetwork, is calculated. Additional error detection mechanisms used in airborne ATS end systems are also considered. Finally, these concepts are expanded to encompass the enhanced error detection processes for future CNS/ATM applications over the ATN