Analysis of advanced flight management systems (FMSS), Flight management computer (FMC) field observations trials: Performance based navigation to X landing system (PBN to xLS)

The differences in performance of various manufacturers' Flight Management Systems (FMSs) and their associated Flight Management Computers (FMCs) have the potential for significant impact on the air traffic control system and as such need to be examined and reexamined. While Performance Based Navigation (PBN) 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 build their systems in accordance with Minimum Aviation System Performance Standards (MASPS) and Minimum Operational Performance Standards (MOPS) for area navigation systems, Technical Standard Orders (TSOs) and Advisory Circulars (ACs). It has been shown in previous papers on this subject that the resulting performance of the aircraft FMC will generally meet the procedure design requirements identified in the FAA criteria. However, there are notable differences. A goal of this paper is to provide supporting data for the development of instrument procedures and associated criteria where aircraft operations meet expectations for repeatability and predictability to levels of performance sufficient to support 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 closely match the intent of the procedure designer. This paper is an addition to eight annual studies which began in 2006, (all presented at previous Digital Avionics System Conferences) with the basic title of Analysis of Advanced Flight Management Systems (FMSs), Field Observations Trials. The hypothesis of these papers has been that the FMSs produced by the major avionics manufacturers and installed in various airframe platforms will perform differently and each paper has attempted to quantify those differences. This paper studies Performance Based Navigation to x Landing System (PBN to xLS), where xLS includes instrument (ILS) or Ground Based Augmentation System (GBAS) landing systems (also referred to as GLS), or Space Based Augmentation System (SBAS) landing systems (also referred to as LPV) through analysis of data collected from a series of trials where FMS bench testing devices and high fidelity simulators fly an RNP to ILS approach at selected temperatures. The paper analyzes differences between aircraft models (with specific avionics equipage) and how they transition from Lateral Navigation/Vertical Navigation (LNAV/VNAV) to the ILS Localizer/Glideslope (LOC/GS) given temperature deviations. In addition, MITRE will investigate differences and relationships between what is expected by procedure design and charting and the conditions under which they can be successfully executed by the FMSs and autopilot. The results support the validation of a Matrix Laboratory (MATLAB) [1] tool which has been developed to study the characteristics of such approach designs relative to current aircraft/avionics that might be used to fly them over a range of design and environmental conditions. The approach chosen for this exercise is the RNP to ILS approach, PAKT ILS Z RWY 11, at Ketchikan, Alaska. There are also EUROCONTROL, International Civil Aviation Organization (ICAO) and FAA PBN to xLS projects all over the world and there are reported to be over 200 RNP to ILS approaches published in China, but they are all special procedures coded for specific airlines. For MITRE's purposes, a public procedure that is already coded in Jeppesen, Lufthansa Systems (LIDO) and European Aeronautical Group (EAG) aircraft navigation databases is required and to date, the PAKT procedure is the only public RNP to ILS approach identified by Jeppesen and LIDO. Controlled field observations trials were made using fourteen FMS avionics test benches at seven major FMC manufacturers, and five high fidelity flight simulators at three major airlines. The focus on the subject presented follows The MITRE Corporation's previous analysis of manufacturers' FMSs. 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 and to help the FAA establish criteria for PBN to xLS. Some conclusions in this paper propose that a continuously descending path definition for these procedures would be problematic operationally. For high International Standard Atmosphere (ISA) deviations, captures necessarily will be from above, which is behavior that flight crews deem unsatisfactory. It also can cause the systems to capture the GS before the LOC, which is another undesirable consequence. It was further observed that some systems automatically insert a shallower vertical path segment prior to the expected GS capture point which allows for deceleration. Relative to temperature variation in the barometric path however, this segment allows even hot day GS captures to be from below the GS, widening the temperature range over which capture can occur. This was unexpected but a very positive finding. Complete conclusions and recommendations are presented at the end of this paper.