Safety is crucial in aviation. This includes the category of General Aviation, which consists of flights that are not performed by commercial airliners. Many of these vehicles are small in comparison to the aircraft used for commercial transport, providing seats for two or four persons. Despite their limited size, accidents involving General Aviation aircraft can be costly or even lethal. Therefore, a high priority is placed on the prevention of accidents in General Aviation. The importance of Situation Awareness In order to prevent collisions, a pilot needs to have an accurate and complete situation awareness, so that he or she can take appropriate action to avoid hazardous situations. This awareness includes knowledge about the own aircraft, as provided by the flight instruments in the cockpit. Besides this information, the pilot needs to have information about the immediate environment. This immediate environment can contain many different objects of which the position relative to the aircraft needs to be known. Stationary obstacles such as towers, windmills and other buildings are relevant when flying at low altitudes. Also the curvature and elevation of the landscape are relevant for a pilot flying near the ground, such as when taking off or landing at an airfield. Dynamic obstacles can also pose threats to a pilot. These obstacles can be other aircraft, and birds are also known to cause dangerous situations for aircraft. And the development of unmanned air vehicles also leads to more conflicts between drones and aircraft. Situation Awareness Limitations in Visual Flights For flights taking place in Instrument Flight Rules, a situation awareness solution is guaranteed and enforced; all aircraft must be equipped with the correct transponders and aircraft that do not comply are tracked down by military radar. But for flights under Visual Flight Rules, there are no such regulations, for various reasons. In these flights, which make up the majority of General Aviation flights, the pilot relies on eyesight in order to guarantee separation with other aircraft and the ground. At times, human eyesight is insufficient to guarantee safety. This can be a consequence of a high workload for the pilot, changing weather conditions, the direction of where an object is coming from, and other reasons. This can lead to unsafe situations for the pilot and for others, both in the air and on the ground. Technical solutions have been developed that can assist the pilot in his or her situation awareness tasks. Unfortunately, these solutions all involve the use of transponders of some kinds, which makes them dependent solutions. These soluxitions can only provide an indication of safety, but no guarantee, because aircraft without transponders cannot be detected. An independent sensing solution in General Aviation for purposes of detect and avoid can contribute significantly to safety in the air. The aim of the research in this dissertation is to contribute to the actualization of such a solution… @en

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.@en

Both U-space in Europe, as well as UTM in the USA, develop concepts and tools for UAV airspace. Enabling highdensity operations is one of the goals of these studies. Past and recent studies have analysed which factors affect the capacity of a UAV airspace. An improved understanding of this can lead to control methods for capacity management. Two general principles for capacity management can be distinguished: controlling the traffic density, and controlling the traffic complexity. The first approach can be achieved using geofencing or geocaging, which is foreseen for UAV airspace. The second approach is hardly addressed in the planned concepts. In this paper a new, general concept, called geovectoring, is proposed which could increase the capacity by reducing the traffic complexity for U-Space and UTM. This paper therefore proposes to add geovectoring as a third service to the already planned concepts of geofencing and geocaging. @en

Several conflict resolution algorithms for airborne self-separation rely on principles derived from the repulsive forces that exist between similarly charged particles. This research investigates whether the performance of the Modified Voltage Potential algorithm, which is based on this algorithm, can be improved using bio-inspired swarming behavior. To this end, the collision avoidance function of the algorithm is augmented with the velocity alignment and flock centering swarming traits displayed by animals such as birds and fish. The basic and swarm augmented versions of the algorithm were compared using large-scale fast time simulations, for multiple traffic demand scenarios. For ideal conditions, the results show that the process of aligning with neighboring traffic triggered a large number of conflicts. However, when noise was added to scenarios, swarming led to a lower increase in the number of intrusions, which could indicate that it can be used to improve the robustness of the Modified Voltage Potential algorithm. Furthermore, the stability results suggest that both versions of the algorithm could reduce the number of conflict chain reactions with respect to simulations without resolution. Future research will further explore the effect of conflict resolution on airspace stability, as well as whether varying the relative weights of swarming elements can improve the safety of swarm augmentations.@en

The work that is presented in this paper is part of an ongoing study on the relationship between structure and capacity of decentralized airspace concepts. In this paper, the effect of traffic stability, which considers the occurrence of conflict chain reactions as a result of conflict resolution maneuvers, on capacity is examined closely. Using the domino effect parameter as a measure of traffic stability, a model relating stability and capacity is derived. Although the derivation of this model is not complete, its current form shows that traffic stability, and therefore capacity, is also affected by the safety and efficiency characteristics of decentralized concepts. This suggests that the capacity measurement of decentralized concepts must consider the variation of intrinsic system-wide properties with density, using a minimum of safety, efficiency and stability metrics. Future work will continue the development of the model, and its validation using large-scale simulation experiments.@en

Object tracking is performed when surveillance applications have multiple observations of an object over time. An example of such a surveillance application is mounting a wideangle Frequency Modulated Continuous Wave (FMCW) radar system on board of a General Aviation aircraft. This is done in order to observe its environment in detail, including noncooperative objects such as birds and windmills. Data generated by such a system follows different physical laws than the images of standard visual applications. In this paper, a novel tracking algorithm is introduced which is tailor-made for FMCW applications. The algorithm is tested in a simulated crowded general aviation airspace, and the resulting tracks are qualitatively and quantitatively analysed. The proposed algorithm performs better than a traditional algorithm on all aspects, but tracking errors can still be made in rare cases. The proposed algorithm can be used in conjunction with research focusing on observation quality or assignment problems. @en

Although the main goal of a newly developed Collision Alert Radar is to observe airborne targets, it was found that reflections of the ground are received by the radar. The radar is carried on board of the aircraft, and the ground reflections may be used to detect flight information with respect to the terrain, something which is not possible with existing hardware. In this paper a method is developed which makes use of range and Doppler information from ground reflections, in order to provide the pilot with height and velocity information. The method was tested on a local flight in the Netherlands, with a prototype of the radar on-board. State results were compared to those of a GPS tracker on board. It was found that the horizontal and vertical components of the velocity were found with a standard deviation of about 3m/s, and the height estimates had a standard deviation of 23m. Also, a discrepancy of 36m between the GPS and radar height estimates was found, which was caused by a fault in the GPS earth surface model, which was no problem for the radar. It is concluded that the quality of radar state estimates is approaching that of GPS measurements. The rapid developments in microwave sensing techniques can help the radar to surpass the quality of GPS in the coming years. If that happens, state estimation by radar can become an option for pilots who do not want to be dependent on the correctness of a terrain model, but who measure the terrain shape independently. @en

This paper presents analytical models that describe the safety of unstructured and layered en route airspace designs. Here, ‘unstructured airspace’ refers to airspace designs that offer operators complete freedom in path planning, whereas ‘layered airspace’ refers to airspace concepts that utilize heading-altitude rules to vertically separate cruising aircraft based on their travel directions. With a focus on the intrinsic safety provided by an airspace design, the models compute instantaneous conflict counts as a function of traffic demand and airspace design parameters, such as traffic separation requirements and the permitted heading range per flight level. While previous studies have focused primarily on conflicts between cruising aircraft, the models presented here also take into account conflicts involving climbing and descending traffic. Fast-time simulation experiments used to validate the modeling approach indicate that the models estimate instantaneous conflict counts with high accuracy for both airspace designs. The simulation results also show that climbing and descending traffic caused the majority of conflicts for layered airspaces with a narrow heading range per flight level, highlighting the importance of including all aircraft flight phases for a comprehensive safety analysis. Because such trends could be accurately predicted by the three-dimensional models derived here, these analytical models can be used as tools for airspace design applications as they provide a detailed understanding of the relationships between the parameters that influence the safety of unstructured and layered airspace designs.@en

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. @en

In many ATM studies experiments are performed to determine the capacity. This paper looks at the effect of airspace design on the capacity. Using an algebraic approach a relation is derived between the design parameters of a layered airspace design and the capacity of the airspace. The validity of the assumptions which are used in this derivation are tested experimentally. This airspace lay-out proved to be the airspace design which had the highest capacity for the unstructured, extremely high traffic demand used in an earlier experimental study. The result is both a method to relate an airspace design to the capacity as well as a relation which shows the effect on the airspace capacity for an airspace design where different levels or layers are defined each with their own segment of heading angles. @en

Many pilots in General Aviation use electronic add-ons aids in flight, which rely on satellite navigation information. This navigation information is often a single point of failure which is undesirable since the pilot relies on the information. This paper presents the results of research whether a novel mobile radar station can be used to validate the navigation results from the GPS. The radar transmits signals to the ground, and compares the locations of the reflections to a digital map such as Google maps. A test flight was performed with a radar system on board. Fifteen different methods for processing the images were investigated, and it was found that Ridge Operators and Entropy Detection are good methods to extract similar features in Google and radar images. These algorithms were always successful in picking the single correct GPS coordinate out of a pool of 300 false ones within 150m of the correct answer, except when the aircraft was making a turn and the radar was pointed to the sky. It is concluded that a ground-scanning radar on board can be used to validate the results of a GPS, provided that the radar can observe recognizable features that can be compared to a digital map. The type of image processing used to extract the data is crucial for the application. @en

A detailed situation awareness of the local environment is essential for safe flight in General Aviation. When operating under Visual Flight Rules, eyesight is crucial for maintaining situation awareness and objects may be overlooked. Technical solutions such as Flarm have been sought, but they only work on a basis of co-operation: obstacles without the proper equipment are invisible. Recent developments in the field of radar technology, partly empowered by the demand for sensors for autonomous cars, have improved the size and power consumption of available hardware. Today, the hardware exists to build a portable primary radar system for situation awareness. In this paper the results are presented of efforts to build the first portable primary radar for general, which has to be lightweight, cheap and have a low power consumption. The focus in this paper is on the software design of such a radar system. The physical principles of radar sensing are described, as well as the scientific steps needed to provide situation awareness. The hardware and software for the radar are both built and tested, and the results of these tests are presented. A flight experiment is performed with a small aircraft flying past a stationary radar on a small hill. It is found that the radar is capable of detecting the aircraft up to a distance of at least 3 kilometers. 3D localization is performed and the location determined by the radar was on average 46 meters away from the aircraft position as measured by satellite navigation, relative to a total distance of about 1000 meters from the radar. A low-pass filter can be applied on the raw results in order to improve the location estimation further. Future research will focus on bringing the portable radar in motion while operating.@en

It was found that a newly developed portable collision alert radar receives reflections from the ground while flying. In this paper a method is developed that uses range and Doppler information from these reflections. This information is used to compute height and velocity information relative to the terrain, something which is not possible with existing hardware. The method was tested on a local flight in the Netherlands, with a prototype of the radar. Flight state results were compared with those of a GPS tracker on board. It was found that the velocity can be computed within meters-per-second accuracy. Height differences are due to the measurement method, measuring directly from the ground surface (radar) or relative to a database (GPS). If developments in microwave sensing techniques continue to improve the hardware, flight state estimation by radar can become an option for pilots who do not want to be dependent on the correctness of a terrain model, but who measure the terrain shape independently.@en