Analysis of Advanced Flight Management Systems (FMS), Flight Management Computer (FMC) field observations trials: Area Navigation (RNAV) holding patterns

The differences in performance of various manufacturers' Flight Management Systems (FMSs) and their associated Flight Management Computers (FMCs) have the potential for significant operational impact on the air traffic control system and as such require continuous examination. While Area Navigation (RNAV) and Required Navigation Performance (RNP) procedures and routes are designed according to criteria contained in Federal Aviation Administration (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 Standard Orders and Advisory Circulars. It is anticipated that the resulting performance of the aircraft FMC will meet the procedure design requirements identified in the FAA criteria. The resulting variation however has posed a challenge for the criteria development and Air Traffic operations. A goal of this paper is to provide supporting data for the development of instrument flight 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 overlap and do not match the intent of the procedure designer. This paper is a continuation of five studies, beginning 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. They have shown that these 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 of this paper is 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 with respect to the construction and execution of holding patterns. The paper will attempt to identify and quantify those differences. As airspace becomes more complex, the use of RNAV and RNP holding patterns will become increasingly more important as a tool to reduce the size of holding protected areas. Today, there are no FAA criteria for RNP holding and there are many questions unanswered about RNAV holding. Some of these questions relate to how FMC's build a holding pattern path, how they compute holding pattern entries, how the FMC computes holding pattern time, and how they determine miles from the holding fix for a Distance Measuring Equipment (DME) hold. Controlled field observations trials were completed using fourteen FMC avionics test benches at seven major FMC manufacturers and two high fidelity flight simulators at a major airline. This year's analysis of holding patterns follows The MITRE Corporation's previous analyses of FMC lateral navigation (LNAV), vertical navigation (VNAV), radius-to-fix (RF) path conformance, lateral and vertical path integration and RNAV off the ground Standard Instrument Departures (SIDs). The intent of this report is to contribute data, analysis, conclusions and recommendations to industry and the FAA that may influence criteria development to enhance RNAV and RNP operations.