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We report on the performance of our Airbus 320 during novel advanced required navigation performance (RNP) procedures which contain a fixed radius turn that delivers the aircraft onto a short ILS precision final above aerodrome level. The approaches were flown automatically with guidance and autothrust as computed by the flight management system. Main areas of interest of the flight trials were the performance of the autoland capability, vertical path following during the RNP part of the procedure as well as maintaining an optimized speed profile during the continuous descent approaches Within the PBN concept exists the possibility to incorporate turns with a precise ground track into departure, en-route, arrival and approach procedures called fixed radius transitions or radius-to-fix. They offer the advantage of repeatable ground tracks during the turn and thus more freedom for the procedure designer when route planning in dense traffic, high terrain or obstacle rich environments. Additionally, ARINC 424 allows to specify altitude constraints at waypoints and vertical path angles for each RNP segment terminating at such a waypoint. Whilst offering these benefits such advanced RNP approach operations are still non-precision procedures and automatic landings cannot be performed after their successful completion. Hence, to enable automatic landings and to extract maximum benefits from RNP operations, they must transition into a precision final approach segment provided by any precision landing system (ILS, GLS, MLS) so that the guidance loops for flare and land modes of the auto flight guidance system can activate. This is often called RNP to xLS (or RNP2xLS). Moreover, the vertical path angle feature is currently largely unused and unexplored, except for the final approach segment of an RNP approach. These new options, when properly exercised, would allow any aircraft to benefit from better fuel efficiency during a continuous descent approach and a potentially reduced obstacle clearance due to the fixed vertical RNP profile and RF tracks. Ground tracks are repeatable and could be used for better noise abatement — besides their main purpose, obstruction clearance along the aircraft's path. In this study we investigated the use of the described ARINC424 coding options onto (a) the performance of the speed profile for arrival time optimization (b) the vertical path during the RNP part of the procedure and (c) the performance of the autoland capability after a curved transition onto an ILS. For the trials, we designed five instrument approaches to runway 26 at Braunschweig-Wolfsburg airport, which is equipped with an Instrument Landing System. A RF curve terminates at the ILS intercept point at heights 550ft, 750ft, 1000ft, 1500ft and 2000ft above aerodrome level and each approach had four different initial approach fixes which corresponded to a track angle change of 30,60,90 and 180 degrees during the constant radius turn-to-final. For each initial approach path coded as advanced RNP segments, we programmed different combinations of vertical path angle and height constraints at waypoints. Moreover, as the thrust computer automatically reduces speed to a value suitable for initial approach, we varied the distance of the initial approach fix of one of the approaches from ranging between 3 to 7NM from the FAF in order to allow the aircraft to decelerate as late as possible. For the trials, we used DLR's own Advanced Technology Research Aircraft (ATRA), an Airbus A320 MSN659 with flight test instrumentation and a Thales FMS2. The approaches were entirely flown using the auto flight guidance in managed mode and with auto-thrust activated. The approach mode was armed either at the FAF or before the initial approach fix. We show supporting evidence that RNP2ILS approaches can be safely flown all the way to an automatic landing using the flight management guidance computer and the auto flight control system. In order to fly the desired path with vertical path angle during the RNP initial and intermediate approach, a separate mode (such as LNAV/VNAV) different from the singular approach mode would need to be implemented in the aircraft. Additionally, airlines and other operators currently apply stabilization criteria following which the aircraft must be established on a straight final with the correct sink rate at 1000ft above aerodrome level in order to continue the approach. For landings in low visibility conditions, more stringent criteria are often applied. An operational implementation of RNP2ILS approaches with a curved final intercept would require a rephrasing of the criteria to include a concept such as RNP established.

NextGen terminal airspace operations are expected to operate under a time-based scheduling framework. Key to the success of these operations is the ability of aircraft to realize a Time-Of-Arrival (TOA) assigned by the scheduler. Among other factors, the TOA accuracy achieved by the aircraft depends on the wind uncertainty and the equipage of the Flight Management System (FMS). This paper seeks to characterize the TOA uncertainty associated with different current-day and NextGen FMS features: (i) Lateral NAVigation and Vertical NAVigation (LNAV/VNAV) modes, (ii) Required Time of Arrival (RTA) mode (iii) 4-Dimensional FMS (4DFMS) mode, (iv) LNAV/VNAV with High-Fidelity Wind (LNAV/VNAV-HFW), (v) RTA with high fidelity wind (RTA-HFW), and (vi) 4DFMS with high fidelity wind (4DFMS-HFW). The aforementioned FMS features are evaluated on a high-fidelity commercial aircraft simulation testbed assembled in house. The testbed simulates aircraft point-mass dynamics, bank-angle auto-pilot dynamics, pitch-axis autopilot dynamics, and engine lag dynamics. The simulation environment also employs actual atmospheric forecasts and uses realistic spatio-temporally correlated wind uncertainty models. The TOA uncertainty is characterized using a Monte-Carlo simulation framework. Monte-Carlo simulations are conducted for a total of 864 scenarios composed of 3 types of aircraft (A320, B737, MD82), 4 different speed profiles, flying along 12 routes (5 routes at SFO and 7 routes at LAX), equipped with the 6 kinds of abovementioned NextGen FMS capabilities, and 2 flight segments in descent (Freeze Horizon to Meter Fix, and Meter Fix to Runway). Monte-Carlo simulation for each scenario in turn involves 500 hi-fidelity commercial aircraft simulations with different wind profiles. Overall the results on this paper are based on 432000 hi-fidelity aircraft simulations. Results illustrate the relative benefits of using 4DFMS and high-fidelity wind models.

This paper seeks to characterize the temporal spacing errors resulting from the use of Interval Management (IM) algorithms. The focus of the current paper is IM concepts and algorithms that realize a specified temporal spacing between a Target aircraft and an Ownship aircraft at the runway threshold. The paper presents an IM algorithm consisting of the following four modules: (i) Target-Landing-Time Estimation Module, (ii) OwnshipLanding-Time Estimation Module, (iii) Ownship Speed Command Computation Module, and (iv) Ownship Thrust Command Computation Module. The overall guidance module is evaluated on a simulation that models aircraft point-mass dynamics, bank-angle auto-pilot dynamics, pitch-axis auto-pilot dynamics, and engine lag dynamics. The simulation environment also consists of actual atmospheric forecasts and realistic spatio-temporally correlated wind uncertainty models. Results obtained from single case simulation as well as Monte-Carlo simulations are presented in the paper. The modeled scenario consisted of an A320 Target equipped with “Lateral Navigation”/“Vertical Navigation” (LNAV/VNAV) capabilities followed by an A320 Ownship equipped with the IM algorithm. Both aircraft fly the BIGSUR route to SFO airport using a RAP-13 1-hr wind forecast. 500 Monte-Carlo simulations were conducted with realistic wind uncertainty models. The IM algorithm for this case is seen to have a 90% probability landing time error range of 5.9 seconds, compared to the no-IM solution, which has a 90% probability landing time error range of 33.4 seconds.

This paper develops 3D-path tracking algorithms to simulate the Lateral NAVigation (LNAV) and Vertical NAVigation (VNAV) capabilities found in current day aircraft flight management systems. The LNAV/VNAV capability is realized using two modules: (i) Reference Trajectory Synthesis Module, and (ii) LNAV/VNAV Guidance Module. A separate paper deals with the Reference Trajectory Synthesis Module. The focus of the current paper is the design and evaluation of LNAV/VNAV Guidance Module. The guidance module is formulated as a reference-trajectory tracking controller. The control laws are based on single-input single-output linear feedback control principles. The outputs from the guidance module are: (i) bank-angle command, (ii) coefficient-of-lift command, (iii) thrust command, and (iv) spoiler drag command. The guidance module is evaluated on a simulation that models aircraft point-mass dynamics, bank-angle auto-pilot dynamics, pitchaxis auto-pilot dynamics, engine lag dynamics, atmospheric forecast model, and a realistic forecast uncertainty model. Test scenarios include A320 and MD82 aircraft flying along different arrival routes into San Francisco and Los Angeles International airports. MonteCarlo simulation framework is used to estimate the time-of-arrival uncertainty associated with a A320 LNAV/VNAV flight.

This paper evaluates the effect of Lateral NAVigation (LNAV) and Vertical NAVigation (NAV) equipage on the performance on time-based scheduling. The paper relies on two companion papers: (i) the first paper develops a high-fidelity simulations model of LNAV + VNAV, and (ii) the second paper develops a realistic spatio-temporally correlated model of wind uncertainty. Two different Monte Carlo simulation frameworks are used to evaluate the effect of LNAV + VNAV equipage on time-based-scheduling. The first Monte Carlo simulation framework is used to evaluate the time-of-arrival uncertainty for flights equipped with LNAV + VNAV capability. This Monte Carlo simulation uses a point-mass simulation model of the aircraft equipped with LNAV + VNAV and flying through spatio-temporally correlated wind uncertainty fields. The second Monte Carlo simulation evaluates the effect of LNAV + VNAV equipage on the performance of time-based scheduling. NASA's Stochastic Terminal Area Scheduling and Simulation (STASS) software is used for timebased scheduling and terminal area traffic simulations. Terminal-area traffic Monte Carlo simulations are conducted for 1.0x, 1.5x, and 2.0x demand ratio at San-Francisco International Airport (SFO), Los Angeles International Airport (LAX), and Dallas Fort Worth International Airport (DFW). Results illustrating the effect of LNAV + VNAV equipage level (0%, 25%, 50%, and 75%) on delay, throughput, and the number of separation violations are presented in the paper.

Application of Area Navigation (RNAV) and Required Navigation Performance (RNP) to aircraft separation continues to be a point of difficulty which frequently centers on defining statistical models for Performance-Based Navigation (PBN). Given that questions of the statistics associated with position estimation error are fairly well known, and that path definition error is near zero in modern RNP avionics, this paper will focus on path steering error, which has not been studied using operational data. We propose analysis methods that can be applied to analyzing large volumes of recorded, in-service data to answer the questions of statistical modeling for the path following behavior of these systems. Preliminary analysis results derived from partner airlines' RNAV and RNP equipped aircraft flying in revenue service are presented. Answers to key questions related to the Flight Management System's (FMS) Path Steering Error (PSE, also known as Flight Technical Error, or FTE) will be presented. This paper will characterize any variations that might exist in the distributions due to flight phase (climb, level or descent), flight path characteristics (turning or straight) and piloting mode, e.g., flight director or autopilot coupled with Lateral Navigation (LNAV). Results are presented as sample statistics, cumulative distributions, and Q-Q plots.

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.

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 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 Service Orders and Advisory Circulars. Despite the disconnect it is anticipated that the resulting performance of the aircraft FMC will meet the procedure design requirements identified in the FAA criteria. The goal is procedures where aircraft operations meet expectations for repeatability and predictability to levels of performance sufficient to support performance based operations in the National Airspace System (NAS). 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 expectancy of the procedure designer. Studies referenced in this paper such as Assessment of Operational Differences Among Flight Management Systems, Analysis of Advanced Flight Management Systems (FMSs), Analysis of Advanced Flight Management Systems (FMSs), FMC Field Observations Trials, Lateral Path, and Analysis of Advanced Flight Management Systems (FMSs), FMC Field Observations Trials, Vertical Path 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 basic FMCs built by the major manufacturers and installed as the core of the FMC/FMS combinations in various airframe platforms will perform differently and this paper attempts to quantify those differences. It focuses on standard performance-based public RNAV (RNP) instrument approach procedures with coded ARINC Navigation Systems Database Specification 424, Radius-to-Fix path terminators (RF), also labeled as RF leg types, and their variations in performance. Criteria currently allows the use of RF leg types only in RNP Special Aircraft and Aircrew Authorization Required (SAAAR) procedures. A Trial Plan was developed and controlled field observations trials were made using eleven test benches at seven major FMC manufacturers. The focus is on RF path terminators used in public procedures at Long Beach Daugherty Airport, California, and follows previous analysis of manufacturers' FMC lateral navigation (LNAV) path conformance described in Analysis of Advanced Flight Management Systems (FMSs), FMC Field Observations Trials, Lateral Path and analysis of vertical navigation (VNAV) path conformance described in Analysis of Advanced Flight Managements Systems (FMSs), FMC Field Observations Trials, Vertical Path. It is hoped that the results of this research will contribute to the eventual acceptance of RF usage in Basic RNP and RNAV criteria.

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. While area navigation (RNAV) and required navigation performance (RNP) procedures and routes are designed according to criteria contained in Federal Aviation Administration (FAA) orders, FMCs are built to meet minimum aviation system performance standards (MASPS) (RTCA, 2003) and the minimum operational performance standards (MOPS) (RTCA, 2003) for area navigation systems, technical service orders and advisory circulars. The expectation is the resulting performance of the aircraft FMC will meet the procedure design requirements identified in the FAA criteria. The airspace design goal is procedures where aircraft operations result in repeatable and predictable paths. However, actual aircraft performance frequently does not match the expectations of the procedure designer. Studies referenced in this paper such as assessment of operational differences among flight management systems (Steinbach, 2004), analysis of advanced flight management systems (FMSs) (Herndon et al., 2005) and analysis of advanced flight management systems (FMSs), FMC field observations trials (Herndon et al., 2006) have shown that these differences result from variations in FMS equipment; variations and errors in data collection and processing; variations in pilot training and airline operating procedures; and variations in aircraft performance. This paper presents the hypothesis that given a standardized performance-based (RNAV/RNP) procedure with coded altitudes, variations in vertical path performance will exist among the various FMC/FMS combinations that are tested. Controlled observations were made using twelve test benches at five major FMC manufacturers and three full-motion simulators at the FAA and two airlines. This focus on vertical navigation (VNAV) path conformance follows the MITRE Corporation's analysis of lateral navigation (LNAV) path conformance described in analysis of advanced flight management systems (FMSs), FMC field observations trials (Herndon et al., 2006).