Abstract: This paper discusses the use of an on-board radar altimeter and Digital Elevation Model (DEM) for terrain referenced integrity monitoring during an Unmanned Aircraft Systems precision approach and landing. For operation of commercial UAS in the National Airspace System (NAS), a Performance Based Navigation (PBN) system applicable to all phases of flight is needed for unrestricted airspace and airport access. Methods, such as Radar Altimeter (RALT) Aiding, are currently being researched to create a Global Navigation Satellite System (GNSS) based navigation system with sufficient positional accuracy for a CAT-IIIc like precision approach and landing. While these systems have successfully addressed the vertical accuracy, horizontal accuracy, and vertical integrity requirements, further development for horizontal integrity is needed. This paper builds on previous work by the authors on radar altimeter augmentation to GNSS and discusses additional measures to improve the horizontal integrity of the navigation system. Performance of the proposed system is assessed in nominal and off-nominal conditions using data collected with a DC-3 aircraft at the Ohio University airport.

Abstract: In aeronautical navigation the use of Global Navigation Satellite Systems (GNSS) is becoming ever more important. GNSS are one of the cornerstones of the performance based navigation (PBN) concept. They are currently used for navigation en-route, as well as during arrival procedures and for lateral approach guidance. Together with satellite-based or ground-based augmentation systems (SBAS, GBAS) satellite navigation can provide precision approach guidance down to CAT-I minima. In order to ensure sufficient global availability of these services and enable new services, such as Advanced Receiver Autonomous Integrity Monitoring (ARAIM) for providing services with higher performance levels, including in regions with active ionospheric conditions, existing integrity concepts and augmentation systems are upgraded to incorporate not only GPS but multiple GNSS constellations and also navigation signals on a second frequency. On the side of GNSS, all GPS satellites since the Block IIF generation with currently 12 operational satellites provide signals in the L5 band (in addition to the most commonly used signals in the L1 band), a second frequency band usable for aeronautical applications. The Galileo constellation has currently 22 operational satellites in orbit that all provide signals on the E1 and E5a frequency bands. Other constellations, such as Glonass and BeiDou are also launching further satellites so that a large number of navigation satellites are available to users. The use of dual-frequency and multi constellation techniques will mitigate the impact of most ionosphere-related disturbances, significantly increasing service availability. All GNSS-based navigation methods have in common that they need appropriate integrity concepts safely bounding any residual errors that may prevail in the position solution. With the ionospheric errors largely addressed by dual-frequency and multi-constellation methods, the residual noise and multipath becomes the most significant contributor to the residual errors. In order to bound these errors, standardized error models are used. The existing multipath model was developed based on extensive data analysis, however, using only the legacy GPS signal in the L1 band. Galileo is using a different modulation for the E1 signals which is less susceptible to multipath. The GPS and Galileo signals in the L5/E5a band are using a 10-times higher chipping rate than the L1/E1 signal. Therefore, also for these signals, the multipath envelope is significantly smaller, potentially allowing to have smaller error models for these signals. When using dual-frequency methods to remove the ionospheric delay, the receiver tracking noise and multipath error from the signals on both frequencies are combined. For all these cases the existing model is not well suited for error modelling. Within the frame of the DUFMAN project funded by the European Commission new multipath models for the new signals are developed in order to be able to exploit the potential benefits for aviation users. Previous papers on the project were addressing the methodology, described the results of the studies and the influence of the antenna. This paper explains the standardization activities and discusses choices that were made in setting up the data collection campaign and the subsequent steps to standardized models. Regarding standardization, the International Civil Aviation Organization (ICAO) is producing Standards and Recommended Practices (SARPS) for DFMC SBAS which will make use of the DFMC multipath models. Further requirements on the hardware exist e.g. in form of Minimum Operational Performance Standards (MOPS) that specify performance of certain components, such as the airborne antenna. A variety of antennas differing significantly in performance is available on the market. Furthermore, the airborne receiver hardware may use different correlator spacing and receiver bandwidth settings which may also have an impact on the results. In the effort to characterize the multipath errors, hardware and processing choices had to be made taking into account all those requirements and the impact on the final models. The paper discusses the interdependency between different standards and explains the choices that were made in the project, as well as results in terms of standardization.

Abstract: Over the past decade, the proliferation of Performance Based Navigation (PBN)-enabled diverging departure procedures has increased departure capacity, reduced delay, and lowered aircraft emissions at major airports across the National Airspace System. However, increasing departure capacity at airports with narrow departure corridors remains challenging as implementations of additional departure paths and the current requirement for immediate divergence may markedly change an airport's noise footprint. This paper explores options for capacity-enhancing application of divergence-based initial spacing without requiring aircraft to diverge immediately after departure. It presents the analysis approach taken to characterize departure performance of aircraft observed in actual operations and the simulation model developed to estimate collision risk. The results indicate that the proposed operations meet target level of safety requirements for aircraft on PBN procedures that diverge within 10 miles after departure and suggest the feasibility of realizing departure capacity benefits while minimizing changes to the noise footprint of the operations.

Abstract: We studied how pilots handle operational variations during arrival and approach instrument flight procedures (IFPs), focusing on factors that may be related to performance-based navigation (PBN). PBN is a key enabler of the Next Generation Air Transportation System (NextGen). We developed a factor rubric based on an iterative review of events in the Aviation Safety Reporting System (ASRS) public database and prior research. We coded 164 ASRS reports selected for relevance to PBN. We identified where each event occurred relative to the route of flight, tallied the coded factors and event outcomes, and gathered data on crew actions that indicated resilience to operational variations such as unexpected behavior of aircraft automated systems. We conclude that PBN appears to magnify the effects of operational complexity for these events. Pilots would benefit from training that provides opportunities to experiment with new situations they could encounter in PBN scenarios.

Abstract: EUROCONTROL, the Technical University of Berlin and Lufthansa Aviation Training conducted a series of flight tests in the frame of Horizon 2020 SESAR PJ.14-1.1 “CNS Environment Evolution” using CS-FSTD Level D certified Full Motion Flight Simulators to analyse the Path Steering Error (PSE) and budget allocation for this error in the computation of the navigation Total System Error. Additionally, the performance and behavior of aircraft while executing turns in the trajectory was analysed. To make the analysis as broad as possible with an optimal coverage of investigated navigation and flight guidance-systems used in ECAC, the tests were performed in a range of different aircraft types including Airbus A319, Airbus A340-300, Airbus A220-300, Boeing 737-300, Boeing 777-200, Boeing 747-400, Embraer E190, De Havilland Canada DHC-8-Q400, Embraer E145 and Bombardier CRJ-200. In each aircraft, two different trajectories were flown under known operating conditions using both the autopilot and manual flight using Flight Director. Recorded data was used to deduct the resulting Path Steering Error and turn performance indicators (bank angle and turn radius). The generated data provides valuable information about the actual navigation performance of modern aircraft, in contrast to the assumed PSE values and turn performance requirements in the current standards (MOPS DO-283B & MASPS DO-236C). A lower assumed PSE could allow using less accurate navigation sensors for certain PBN applications while maintaining the same overall TSE. For example, if the adjusted PSE is low enough, ground based DME-DME sensor combination could be used to serve Performance Based Navigation (PBN) operations with a Required Navigation Performance of 0.3NM. The demonstrated PSE was in the order of magnitude of 0.1NM for both the trajectories flown using autopilot and manual flight with Flight Director, which is a reduction compared to the values from DO-283B. A wide spread of tracks was observed in the turns, which were all executed as “fly-by” turns. Depending on the track change and aircraft type, applied bank angles ranged from 5 to 30 degrees, with resulting turn radii ranging from 38 to 1 NM. All the tracks were within the fly-by transition area defined in DO-236C. The huge spread of tracks in the turns makes revision of the conservative definitions of the fly-by transition area challenging but not impossible.

Abstract: Flight arrival and departure scheduling (FAADS) problem, one of the critical tasks in terminal air traffic operation, faces new challenges as the terminal air traffic management has transformed to adapt to the performance-based navigation (PBN) environment; beside of that, the terminal system uncertainties which are usually due to the time-varying interference of the convective weather and flight arrival time will also exacerbate the difficulty to realize an efficient terminal air traffic operation. In order to effectively address the above issues, we propose the formulation and solution approach for a stochastic terminal FAADS problem under PBN environment. The proposed FAADS problem formulation combines the flexible 4-dimensional trajectory requirement under PBN environment and the stochastic quantifications both from the convective weather and flight arrival time uncertainties, which can finally make the FAADS results realize the avoidance of the convective weather and immunity of the flight arrival time variations within tolerable risk probabilities. We provide an efficient solution approach to tackle this problem with complex mixed integer and nonlinear programming basics and illustrate the capabilities of the solution approach by a test case on real terminal system in Shanghai Metroplex. Numerical results demonstrate the effectiveness of proposed problem formulation and solution approach.

Abstract: Recent evolutions of the Unmanned Aircraft Systems (UAS) Traffic Management (UTM) concept are driving the introduction of new airspace structures and classifications, which must be suitable for low-altitude airspace and provide the required level of safety and flexibility, particularly in dense urban and suburban areas. Therefore, airspace classifications and structures need to evolve based on appropriate performance metrics, while new models and tools are needed to address UTM operational requirements, with an increasing focus on the coexistence of manned and unmanned Urban Air Mobility (UAM) vehicles and associated Communication, Navigation and Surveillance (CNS) infrastructure. This paper presents a novel airspace model for UTM adopting Performance-Based Operation (PBO) criteria, and specifically addressing urban airspace requirements. In particular, a novel airspace discretisation methodology is introduced, which allows dynamic management of airspace resources based on navigation and surveillance performance. Additionally, an airspace sectorisation methodology is developed balancing the trade-off between communication overhead and computational complexity of trajectory planning and re-planning. Two simulation case studies are conducted: over the skyline and below the skyline in Melbourne central business district, utilising Global Navigation Satellite Systems (GNSS) and Automatic Dependent Surveillance-Broadcast (ADS-B). The results confirm that the proposed airspace sectorisation methodology promotes operational safety and efficiency and enhances the UTM operators’ situational awareness under dense traffic conditions introducing a new effective 3D airspace visualisation scheme, which is suitable both for mission planning and pre-tactical UTM operations. Additionally, the proposed performance-based methodology can accommodate the diversity of infrastructure and vehicle performance requirements currently envisaged in the UTM context. This facilitates the adoption of this methodology for low-level airspace integration of UAS (which may differ significantly in terms of their avionics CNS capabilities) and set foundations for future work on tactical online UTM operations.