Analysis of advanced flight management systems (FMSS), flight management computer (FMC) field observations trials: Standard instrument departure with radius-to-fix (RF) path terminators

At the request of The Federal Aviation Administration (FAA), the differences in performance of various manufacturers' Flight Management Systems (FMSs) and their associated Flight Management Computers (FMCs) have been a focus of research by these authors at The MITRE Corporation since 2004. While published Area Navigation (RNAV) and Required Navigation Performance (RNP) procedures and routes are designed according to criteria contained in FAA orders, FMC manufacturers design their systems in accordance with Minimum Aviation System Performance Standards (MASPS) and Minimum Operational Performance Standards (MOPS) for area navigation systems, Technical Standards Orders (TSOs), Advisory Circulars (AC's), and industry characteristics. Because procedure designers may not consider FMS functional characteristics, differences may occur between the intent of a procedure design in accordance with FAA orders and the actual path produced and flown by an aircraft's FMC. Exposing such differences is a derivative of MITRE's research. However, the primary purpose is to research and demonstrate variations in performance of individual FMS products. Another goal of this work is to provide supporting data for the development of instrument procedures where aircraft operations meet expectations for repeatability and predictability to levels of performance sufficient to support Performance-Based Navigation (PBN) worldwide and specifically in the National Airspace System (NAS) and the Next Generation (NextGen) environment. Sometimes, due to the nearly independent development of procedure design criteria and aircraft performance standards, the paths of various aircraft on the same procedure do not coincide and may not match the intent of the procedure designer. This paper explores those paths and complements six previous studies, the first conducted in 2006, (all presented at previous Digital Avionics System Conferences) with the basic title of Analysis of Advanced Flight Management Systems (FMSs), FMC Field Observations Trials. The previous studies have shown that the flight path differences may result from any or all of the following: variations in FMC equipment installed on the aircraft; variations and errors in procedure coding in the FMC navigation database; variations in aircraft to FMC interface and associated aircraft performance capabilities; and variations in flight crew training and procedures. The hypothesis common to all of these papers has been that the FMCs built by the major avionics manufacturers and installed as the core of the FMC/FMS combinations in various airframe platforms will perform differently and each paper has attempted to quantify those differences. This paper explores path adherence of radius-to-fix (RF) leg types (path terminators) in a Standard Instrument Departure (SID). At the time of the trial development in December 2011, the RNAV departure from Amsterdam's Schiphol Airport (EHAM) titled SPIJKERBOOR SPY2KZ Runway 24 Departure was the only public SID that incorporated RF leg types in the design. Subsequent to the initiation of this study, another public SID with RF legs was published in February 2012 at Hong Kong International (VHHH). As airspace becomes more complex, the use of RF legs in other than RNP Authorization Required (AR) procedures such as SID's, Standard Terminal Arrivals (STAR) and non-AR approaches will become increasingly more important as a tool to navigate obstacle rich and environmentally sensitive areas. The FAA has not approved operators to fly procedure designs with RF legs without RNP AR. However, consideration is being given to implementing an "Advanced RNP" concept which would allow RF leg types under certain restrictions. Criteria exists for RF legs in SID's and FAA AC 90-105, [1] addresses RF leg types in non-AR RNP approach procedures. Additionally, the use of RF leg types is encouraged as a key enabler of Performance-based Navigation (PBN) in the FAA [2]. This paper investigates the use of RF legs in departures by testing how FMCs process curved paths with small arc radii close to the departure end of the runway (DER) while accelerating and ascending in various wind conditions. Controlled field observations trials were made using seventeen FMC avionics test benches at seven major FMC manufacturers and four high fidelity flight simulators at three major airlines. The focus on the subject presented follows The MITRE Corporation's previous analysis of manufacturers' FMC lateral navigation (LNAV), vertical navigation (VNAV), radius-to-fix (RF) path conformance on instrument approaches, lateral and vertical path integration, RNAV off the ground SID's, and RNAV holding. This report contributes data, analysis, conclusions and recommendations to industry and the FAA that may influence criteria development to enhance performance-based RNAV and RNP operations. It has been confirmed in previous papers and reconfirmed here that despite FMS differences, the resulting aircraft path performance is generally within the tolerances of the procedure design requirements identified in the FAA criteria.