Investigation of APNT optimized DME/DME network using current state-of-the-art DMEs: Ground station network, accuracy, and capacity

An optimized DME/DME network is one of the Federal Aviation Administration's (FAA) proposed Alternative Position, Navigation, and Timing (APNT) architectures. In comparison to other FAA-proposed APNT architectures, namely DME pseudolite network and passive Wide-Area Multilateration, airline operators find DME/DME more attractive for navigation back-up, as this solution requires no change to avionics used by nearly all commercial aircraft, thus reducing equipage costs to private companies. It is also advantageous because the absolute DME range measurements likely require a lower number of stations than the other architectures, thereby minimizing the cost to the public of installing new infrastructure. However, the insufficient range accuracy of the traditional DME (DME/N) has caused hesitation in actively pursuing this solution. U.S. and ICAO DME range accuracy standards of 0.2 nm is insufficient to support RNAV/RNP 0.3 nm operations, the performance the FAA has defined as needed for APNT. However, these standards are based on antiquated DME designs and have failed to account for advancements in both aircraft and ground station radio designs and performance. Recent flight inspections of DME range determined that the accuracy of the current state-of-the-art DME (DME/N) ground transponder is much better than 0.2 nm using current-day DME avionics. This enhanced accuracy presents an opportunity to leverage this technology and the network of DME ground stations for APNT. The DMEs in most stations in the National Airspace System (NAS) have been in service for more than 20 years and are due for replacement. It is thought that replacing DME legacy radios with modern state-of-the-art DMEs could support RNAV/RNP 0.3 operations, as well as optimize coverage with minimal addition to the DME network. This supposition leads to the feasibility study of the proposed APNT optimized DME/DME network. Using the expected range accuracy of the state-of-the-art DMEs, this paper investigates the feasibility of this proposed APNT solution by answering the following two key questions. First, what would be the optimal DME/DME ground station network that enables RNAV/RNP 0.3 operation for navigation and surveillance? Second, will the DME/DME network have sufficient capacity to support high density air traffic such as the 2020 LA basin model? The paper provides preliminary research results, by evaluating selected areas of the continental United States. Recommendations for network operation are based on the sample areas.