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The traffic density of small aerial vehicles operating within urban environments is expected to increase significantly in the near future. This urban environment is highly constrained due to being limited to the low-altitude airspace directly above the existing road network. Multiple studies have addressed factors influencing the capacity of urban airspace. These have used simulations of aircraft, yet the empirical nature of these simulations limits their use beyond the specific conditions that have been tested. Analytical models would not have this limitation, but they are only developed for general airspace, while the emergent patterns in constrained urban airspace are different than in general, unconstrained conditions. For instance, queuing and local congestion are patterns that are unique to the heavily-constrained environment. Therefore, in this paper, we derive an analytical model for air traffic in a confined airspace to find the influencing factors for its capacity. By means of a simulation of aerial vehicles, we verify the analytical model and show a relationship between the mean flow rate and mean density in a two-dimensional orthogonal grid network airspace. Results show that the entire airspace can become unstable when the maximum capacity of just one intersection is reached. Furthermore, the maximum airspace density is found to be unaffected by cruise speed. The results demonstrate how the derived analytical model provides an effective tool to predict the effect of several design parameters on the capacity of constrained urban airspace. Moreover, this model can form the basis for further extensions, including the altitude dimension and non-orthogonal or non-four-way intersections.

International audience; The Metropolis II project aimed to study the impact of centralised separation management for urban aerial mobility. Three concepts were developed in this study: a fully centralised, strategically separated concept, a hybrid concept featuring centralised strategic separation and distributed tactical separation, and a fully distributed tactical concept. A comparative simulation study was performed, using traffic scenarios based on predicted demand in an urban airspace in the city of Vienna. Simulations were performed with varying traffic densities and situations. Results show that the purely strategic and purely tactical strategies perform comparably in terms of safety, and that further improvements can be achieved with a combination of those strategies.

The Metropolis II project aimed to study the impact of centralised separation management for urban aerial mobility. Three concepts were developed in this study: a fully centralised, strategically separated concept, a hybrid concept featuring cen- tralised strategic separation and distributed tactical separation, and a fully distributed tactical concept. A comparative simu- lation study was performed, using traffic scenarios based on predicted demand in an urban airspace in the city of Vienna. Simulations were performed with varying traffic densities and situations. Results show that the purely strategic and purely tactical strategies perform comparably in terms of safety, and that further improvements can be achieved with a combination of those strategies.

Involving air traffic controllers and pilots into the bird strike prevention process is considered an essential step to increase aviation and avian safety. Prior to implementing operational measures such as real-time warning systems, it is vital to evaluate their feasibility. This paper studies the efficacy of a bird strike advisory system for air traffic control. In addition to the potential safety benefit, the possible impact on airport operations is analyzed. To this end, a previously developed collision avoidance algorithm underlying the system was tested in fast-time Monte Carlo simulations involving various air traffic and bird densities to obtain representative conclusions for different operational conditions. The results demonstrate the strong safety potential of operational bird strike prevention in case of precise bird movement prediction. Unless airports operate close to their capacity limits while bird abundance is high, the induced delays remain tolerable. Prioritization of hazardous strikes involving large individuals as well as flocks of birds are expected to support operational feasibility in all conditions.

Involving air traffic controllers and pilots into the bird strike prevention process is considered an essential step to increase aviation and avian safety. Prior to implementing operational measures such as real-time warning systems, it is vital to evaluate their feasibility. This paper studies the efficacy of a bird strike advisory system for air traffic control. In addition to the potential safety benefit, the possible impact on airport operations is analyzed. To this end, a previously developed collision avoidance algorithm underlying the system was tested in fast-time Monte Carlo simulations involving various air traffic and bird densities to obtain representative conclusions for different operational conditions. The results demonstrate the strong safety potential of operational bird strike prevention in case of precise bird movement prediction. Unless airports operate close to their capacity limits while bird abundance is high, the induced delays remain tolerable. Prioritization of hazardous strikes involving large individuals as well as flocks of birds are expected to support operational feasibility in all conditions.

Der Betrieb unbemannter Fluggeräte (UAS) erfolgte lange Zeit außerhalb der geltenden Regulierungen, wie sie aus der bemannten Luftfahrt seit etlichen Jahren bekannt und europäisch harmonisiert sind. Durch die kommerziell getriebene Entwicklung von UAS, die auch immer mehr Einsatzmöglichkeiten eröffnen, ist der Regulierungsprozess auch hier stärker in den Fokus gerückt. Mit den EU Verordnungen 2019/947 und 2019/945 der Europäischen Kommission ist der von den Joint Authorities for Rulemaking of Unmanned Systems (JARUS) entwickelte Prozess für das Specific Operations Risk Assessment (SORA) als risikobasierter Ansatz zur Beurteilung der Sicherheit des UAS als Leitfaden verankert. Aus diesem Prozess werden missionsabhängige Maßnahmen in Form von Operational Safety Objectives abgeleitet, mit denen die Sicherheit systemseitig nachgewiesen wird. Zusätzlich werden Maßnahmen zur Vermeidung von Risiken im Betrieb (Mitigations) einbezogen. Das Ergebnis des Prozesses sind qualitative Anforderungen an die Mission und das Luftfahrtgerät. Zur Umsetzung der aufgestellten Anforderungen sind, ähnlich dem Vorgehen in der bemannten Luftfahrt, anerkannte Nachweismöglichkeiten, sogenannte Acceptable Means of Compliance (AMC) nötig. Diese Nachweismöglichkeiten bestehen aus unterstützendem Material, meistenteils Standards, die das Vorgehen und die Zielgrößen für Analysen und Tests definieren. Die AMC werden durch die entsprechenden Behörden, im Falle einer Musterzulassung der europäischen Luftfahrt also durch die europäische Luftfahrtbehörde EASA, anerkannt. Im Rahmen des Forschungsprojektes AW-Drones wird das Ziel verfolgt, bestehende Standards als mögliche AMC für die entstehenden Regulierungsprozesse für UAS zu identifizieren und ihrer Eignung nach einzuschätzen. Der Fokus des Projektes liegt in einem schrittweisen Ansatz, der zunächst darauf ausgelegt ist, geeignete AMC für die Risikoklassen SAIL I-IV des SORA Prozesses zu finden. Dieser Ansatz soll später auf Themenbereiche wie U-Space erweitert werden. Der erste Schritt zur Umsetzung der Untersuchungen beginnt mit dem Aufstellen einer Datenbasis UAS relevanter Standards, die zusätzlich nach Themenkomplexen strukturiert ist, um eine grobe Übersicht herzustellen. Anschließend erfolgt eine Bezugserstellung zu den Anforderungen der SORA und als letzter Schritt die eigentliche Analyse der Eignung eines Standards als mögliches AMC anhand verschiedener, gewichteter Kriterien. Daraus werden zum einen potentielle AMC, zum anderen Lücken in unterstützenden Standards identifiziert.

Current investigations into urban aerial mobility, as well as the continuing growth of global air transportation, have renewed interest in Conflict Detection and Resolution (CD&R) methods. With the new applications of drones, and the implications of a profoundly different urban airspace, new demands are placed on such algorithms, further spurring new research. This paper presents a review of current CR methods for both manned and unmanned aviation. It presents a taxonomy that categorises algorithms in terms of their approach to avoidance planning, surveillance, control, trajectory propagation, predictability assumption, resolution manoeuvre, multi-actor conflict resolution, considered obstacle types, optimization, and method category. More than a hundred CR methods were considered, showing how most work on a tactical, distributed framework. To enable a reliable comparison between methods, this paper argues that an open and ideally common simulation platform, common test scenarios, and common metrics are required. This paper presents an overview of four CR algorithms, each representing a commonly used CR algorithm category. Both manned and unmanned scenarios were tested, through fast-time simulations on an open-source airspace simulation platform.

This paper presents a collision avoidance algorithm to prevent bird strikes for aircraft departing from an airport. By using trajectory-information of aircraft and birds, the algorithm predicts potential collisions. Collision avoidance is performed by delaying departing aircraft until they can follow a collision-free trajectory. An implementation of this concept has the potential to increase aviation safety by preventing bird strikes but might reduce runway capacity due to delaying aircraft. As a precursor to the feasibility, this study investigates the maximum achievable safety effect at minimum delay costs of such a system by assuming a deterministic world. Therefore, no uncertainties regarding bird and aircraft positions were considered to enable the system to prevent all bird strikes for departing traffic while causing the smallest possible delay. The anticipated effects were studied by running fast-time simulations including three air traffic intensities at a single-runway airport and bird movements from all seasons. The results imply a high potential for the increase in safety at a reasonable reduction in runway capacity. An initial cost-estimate even revealed a strong saving potential for the airlines. Based on these results, a feasibility study of implementing a bird strike advisory system including uncertainties in bird movements as well as probabilistic effects will be performed.

Bird strikes have the potential to cause severe damage to aircraft. Therefore, measures to reduce the risk of bird strikes are performed at airports. However, this risk is not limited to the airport but is increased in the arrival and departure corridors as well. Consequently, a significant amount of bird strikes occurs outside the direct airport area. To estimate the risk of bird strikes in this extended airport area, a fast-time simulation environment was developed, representing air traffic as well as bird movement. It was verified by performing Monte-Carlo Simulations including real flight plans, a model for realistic bird movements and a comparison to real bird strike data.In this study, the simulation results were evaluated considering the impact of bird strikes. For this purpose, the kinetic energy of the bird strikes that occurred within the simulation was calculated. Based on the international certification requirements for the impact resistance of engines, windshields and structure, the potential for severe damage was analysed. Finally, the results were compared to a long-term study of damaging bird strikes of the US aviation authorities. The results indicate that the simulation environment allows a reasonable estimation of the damaging potential of bird strikes. The simulation data derives from the Netherlands, while the real bird strike data originates from the US. For further validation and enhancement of the simulation’s bird model, European data from multiple years would be required.

International audience; The work that is presented in this paper is part of an ongoing study on the relationship between airspace structure and capacity. The present paper investigates the degree of structuring needed to maximize capacity for decentralized en route airspace. To this end, four decentralized en route airspace concepts, which vary in terms of the number of constrained degrees of freedom, were compared using fast-time simulations, for both nominal and non-nominal conditions. The airspace structure–capacity relationship was studied from the effect of multiple traffic demand densities on airspace metrics. The results indicated that structuring methods that overconstrained the horizontal path of aircraft reduced capacity because traffic demand displays no predominant patterns in the horizontal dimension for decentralization. The results also showed that capacity was maximized when a vertical segmentation of airspace was used to separate traffic with different travel directions at different flight levels. This mode of structuring improved performance over completely unstructured airspace by reducing relative velocities between aircraft cruising at the same altitude, while allowing direct horizontal routes.

In the context of decentralized separation, airspace stability pertains to the propagation of con?ict chain reactions as a result of tactical con?ict resolution maneuvers. This notion of airspace stability has been used in previous literature to develop a semi-empirical method for determining the capacity of a decentralized direct-routing airspace concept in the horizontal plane. The present paper extends this method by explicitly mod-eling: a) the effect of a given Con?ict Detection and Resolution (CD&R) strategy on the stability of the airspace; b) the in?uence of direct-routing on instantaneous con?ict probability; and c) the impact of ?nite-time measurements on the determination of airspace states. To validate the resulting analytical capacity model, fast-time simulations were performed. The results indicate that the predictions of the analytical model are close to that of the previous semi-empirical approach. Thus, the analytical model can be used to obtain a ?rst-order estimate of the maximum theoretical capacity, as along as simulation settings do not cause the ‘local’, or per aircraft, con?ict rate to deviate signi?cantly from assumptions made during the model derivation. Future work will focus on relaxing model assumptions, and extending the modeling approach to three-dimensional airspace.

Previous research relating airspace structure and ca-pacity has shown that a decentralized layered airspace concept, in which each altitude band limited horizontal travel to within a prede?ned heading range, improved safety when compared to unstructured airspace. However, the extent of the safety bene?ts of such layered airspace designs were not quanti?ed. To this end, in this paper, con?ict rate models are developed to determine the intrinsic safety of unstructured and layered airspace designs. In comparison to previous work, the present models consider con-?icts between aircraft in different ?ight phases. Thus, con?icts for climbing and descending traf?c, as well as for cruising aircraft, are taken into account when computing the total con?ict rate. To validate the models, fast-time simulations were performed for several different layered airspace concepts, and for unstructured airspace. The results indicate that the models are able to estimate the con?ict rate for high traf?c densities using a model ?t for low densities. When comparing the different layered airspace concepts tested, the model predicted, and the simulation results con?rmed, a clear safety improvement when the permitted heading range per altitude band is reduced. Thus the models can be used to study the effect of airspace design parameters on the safety of unstructured and layered airspace concepts.

The occurrence of pop-up flights negatively affects the (extended) arrival manager. This issue is known already for a long time by operational experts, but the extent thereof has now been assessed during experiments. An arrival manager research model was developed and integrated in BlueSky, an open-source air traffic management simulator. Fast-time simulations showed that extended arrival management is significantly negatively affected by pop-up flights, in terms of flight crew and air traffic control task load, sequence stability and delay (cost). Simulations also indicated that this impact could be mitigated by pre-planning pop-up flights prior to departure, using their take-off time estimates. This will, however, only be beneficial when these estimates are sufficiently accurate. With currently achievable accuracies, and using currently available systems, it is better to discard these estimates in the context of extended arrival management.

Best paper award for the Network Management track; International audience; Airspace structure can be used as a procedural mechanism for a priori separation and organization of en-route air traffic. Although many studies have explored novel structuring methods to increase en-route airspace capacity, the relationship between the level of structuring of traffic and airspace capacity is not well established. To better understand the influence of traffic structure on airspace capacity, in this research, four airspace concepts, representing discrete points along the dimension of structure, were compared using large-scale simulation experiments. By subjecting the concepts to multiple traffic demand scenarios, the structure-capacity relationship was inferred from the effect of traffic demand variations on safety, efficiency and stability metrics. These simulations were performed within the context of a future personal aerial transportation system, and considered both nominal and non-nominal conditions. Simulation results suggest that the structuring of traffic must take into account the expected traffic demand pattern to be beneficial in terms of capacity. Furthermore, for the heterogeneous, or uniformly distributed, traffic demand patterns considered in this work, a decentralized layered airspace concept, in which each altitude band limited horizontal travel to within a predefined heading range, led to the best balance of all the metrics considered.

International audience; Airspace structure can be used as a procedural mechanism for a priori separation and organization of en-route air traffic. Although many studies have explored novel structuring methods to increase en-route airspace capacity, the relationship between the level of structuring of traffic and airspace capacity is not well established. To better understand the influence of traffic structure on airspace capacity, in this research, four airspace concepts, representing discrete points along the dimension of structure, were compared using large-scale simulation experiments. By subjecting the concepts to multiple traffic demand scenarios, the structure-capacity relationship was inferred from the effect of traffic demand variations on safety, efficiency and stability metrics. These simulations were performed within the context of a future personal aerial transportation system, and considered both nominal and non-nominal conditions. Simulation results suggest that the structuring of traffic must take into account the expected traffic demand pattern to be beneficial in terms of capacity. Furthermore, for the heterogeneous, or uniformly distributed, traffic demand patterns considered in this work, a decentralized layered airspace concept, in which each altitude band limited horizontal travel to within a predefined heading range, led to the best balance of all the metrics considered.

Bird strikes have operational impacts and cause economic loss to the aviation industry. In the worst case, the damages resulting from bird strikes lead to crashes. The highest risk for bird strikes lies in the area below 3000 ft and thus mainly in airport environments. Despite intense efforts from the airports in controlling the local bird populations, the number of bird strikes in these environments is still very high. Usually, Air Traffic Control is neither integrated into the process for reducing bird strikes nor do the controllers receive any specific information about the current bird traffic situation at the airport. For the project described in this paper, we assume a different situation: Air Traffic Control is provided with a tool supporting the controller with advisories to prevent bird strikes. The advisories are based on the current and predicted bird movements and the anticipated risk for air traffic. Potential advisories include rerouting or delaying of traffic. Especially when applying the latter, a reduced runway capacity could result. However, the effects of a bird strike advisory systems for Air Traffic Control have never been studied. The project in this paper therefore aims at investigating the consequences on an airport's safety and capacity when implementing such a system. For this purpose, fast-time simulations including varying conditions considering bird densities and air traffic volume will be performed. This paper describes the proposed research concept and the chosen simulation environment.

Most Free-Flight concepts rely on self-separation by means of airborne Conflict Detection and Resolution (CD&R) algorithms. A key enabling technology for airborne CD&R is the Automatic Dependent Surveillance-Broadcast (ADS-B) system, which is used for direct state information exchange between aircraft. Similar to other communication systems, ADS-B is affected by a number of limitations which can be broadly classified as system and situation related deficiencies. This re- search investigates the impact of these limitations on the viability of using ADS-B for airborne CD&R within the Free-Flight context. Here, ‘state-based’ conflict detection and the modified voltage potential conflict resolution algorithm are used as a case- study. An ADS-B model is developed, and its effect on the aforementioned CD&R method is measured using three fast- time simulation experiments. The experiments studied overall safety with ADS-B, as well as the specific effect of situation related characteristics, i.e., transmission range and interference, on safety. The results indicated that the overall safety with ADS- B was comparable to the case where perfect state information was assumed. Additionally, it was found that increasing ADS- B transmission range also increased signal interference, which in turn lowered safety. This suggests that the degrading effect of ADS-B signal interference should be considered in future airborne CD&R research, particularly for high traffic densities.

This paper presents a fast-time simulation environment for assessing the risk of bird strikes in aviation. An existing air traffic simulator was enhanced in order to simulate air and bird traffic simultaneously and to recognize collisions between birds and aircraft. Furthermore, a method was developed to generate bird movement information from different radar sources. The resulting set-up represents the first simulation environment to perform fast-time simulations including air traffic and bird movements. A verification with real data revealed that approximately thrice as many bird strikes occur in the simulation as in reality. When considering bird reaction to approaching aircraft, which is not covered in the simulation as well as unreported strikes, this implies an adequate result. For this reason, the simulator can serve as valuable tool to analyse the risk of bird strikes and to evaluate new Air Traffic Management concepts to reduce the number of these events.

Bird strike prevention in civil aviation has traditionally focused on the airport perimeter. Since the risk of especially damaging bird strikes outside the airport boundaries is rising, this PhD thesis researches the safety potential of operational bird strike prevention involving pilots and controllers. In such a concept, controllers would be equipped with a bird strike advisory system, allowing them to delay departures which are most vulnerable to the consequences of bird strikes. However, the introduction of take-off delays reduces the maximum capacity of a runway. This PhD thesis investigates the feasibility of a bird strike advisory system with regard to safety and capacity by performing fast-time simulations including different air traffic intensities and bird abundance. In a first step, a system assuming perfect predictability of bird movement is developed, demonstrating a strong safety potential. However, when preventing all bird strikes, the induced delays can exceed tolerable limits for high air traffic intensities. In a second step, the system includes the limited predictability of bird movement. Bird tracks are predicted based on a simple linear regression model, considering variability of velocity and heading. To limit the negative effects on runway capacity, delays are only imposed on aircraft, for which strikes are predicted with a high probability and a damaging potential. The number and duration of delays remains reasonable even for airports operating at their capacity limits. However, linear regression proves insufficient to suitably evaluate the risk of collisions. To achieve reliable predictions, in-depth studies of multi-year bird movement data from various sensor types are recommended to develop site- and species-specific bird models. As such, the concept of a bird strike advisory system can be further developed to exploit the entire safety potential demonstrated by the initial study of the thesis.