European researchers start work to develop CONOPs for U-space separation management

A consortium comprising the Polytechnic University of Valencia, the University of Coimbra, the University of Rome La Sapienza, EUROCONTROL and Indra, is starting work to develop and validate a concept of operations (CONOPs) for separation management in U-space, Europe’s framework for safe and secure drone traffic management in Europe.

The BUBBLES programme will develop Artificial Intelligence (AI) based algorithms to compute the collision risk of UAS leading to separation minima and methods so that a Target Level of Safety (TLS) stated in terms of overall probability of collision can be defined and maintained.

According to a consortium statement: “To develop the CONOPs for separation management for UAS, BUBBLES will use an innovative performance-based approach not applied yet to the U-space. This approach is inspired by the methodology used by EUROCAE to develop the ED 261 (GEN-SUR-SPR) standard, which the consortium will adapt to the unique features of the U-space. The BUBBLES consortium will apply the methodology to a generic VLL airspace and will start by identifying the set of possible UAS missions that can take place therein. These operations will be represented by a reduced set of generic UAS CONOPS detailed enough to cover all envisaged applications but, at the same time, generic enough that their number does not make infeasible the computation of a global frequency of collisions for the whole volume. BUBBLES will conduct pre-defined risk assessments (PDRA) for each generic UAS CONOPS using SORA, as well as pair-wise PDRA for all the possible combinations of UAS CONOPS. Using the single UAS PDRA and the estimated traffic density, the consortium will compute the frequency of conflicts within the generic VLL volume, while with the pair-wise PDRA, the researchers will calculate the conditional probability of collision in case of conflict.

“A generic operation services and environment description (OSED) will be defined by the aggregation of the expected CONOPS and the available U-space services. The consortium will develop new intelligence (AI) techniques to determine the separation minima needed to guarantee a particular target level of safety (TLS) stated in terms of frequency of collision taking into account the results of the PDRA. Once the OSED is completed with the applicable separation minima, an innovative operational performance assessment (OPA) and an operational safety assessment (OSA) that will take into account the performance of the communication and surveillance systems in nominal and faulted modes will be performed to derive required performance specifications. In line with the ED 261, BUBBLES will also define the general principles and functionality of tools needed for demonstrating compliance with the performance requirements and will outline methods to compute the various performance metrics.

The consortium statement says: BUBBLES outcomes will support the competent authorities designated by the Member States to perform risk assessment and to identify the required U-space services and systems performance prior to designate a particular VLL volume as a U-space airspace. They will also support U-space service providers (USSP) to demonstrate they have achieved and maintain the required levels of safety performance.

“European citizens will benefit from the high levels of safety and efficiency attained by applying conflict management methods inspired in well-established aeronautical concepts and developed leveraging cutting-edge technologies such as AI. This will unleash a market valued at several billion euros annually in the next decades, leading to the creation of more than 400 000 highly skilled jobs by 2050. In addition to the positive impact on the economy, it is expected that these unmanned aircraft when powered using clean electricity will offer alternative greener mobility option in large cities.

“According to the 2016 SESAR Drones Outlook Study, it is expected that by 2035 the total flight hours of unmanned air systems (UAS) flying over dense populated areas will exceed of 75% of the flight hours of the rest of the fleet. That leads to a rough estimate of up to 10 000 UAS overflying a 1 million inhabitants city at any moment of the day.”


Separation minima are needed to define safety and performance requirements for U-space services and systems.

In manned aviation, separation management (also known as separation provision) is the second layer of conflict management within the ICAO ATM Operational Concept. The goal of conflict management is to limit the risk of collision between aircraft and hazards to an agreed level deemed as acceptable. The first layer of conflict management is the strategic conflict management, based on a pre-flight analysis of flight plans. When strategic conflict management cannot reduce the risk to an acceptable level, separation provision has to define a separator (the aircraft or a ground-based service) and a set of agreed procedures (separation mode) to be applied by the separator so as to keep aircraft beyond a minimum distance from hazards (separation minima) when a conflict is detected within a pre-defined conflict horizon. That process, well established in the manned aviation framework, is what BUBBLES intends to adapt to the particular features of UAS.

To face the challenge posed by such huge numbers of UAS traffic, the European Commission appointed SESAR Joint Undertaking to develop U-space, a safe and secure drone traffic management for Europe. The U-space consists of a set services relying on a highly automated systems to support the access of a large number of UAS to the airspace, especially very low level (VLL) (i.e. approximately 400 ft. below).  To this end, SESAR JU has been fostering since 2015 the development of research projects targeting at developing and demonstrating U-space services within the SESAR 2020 programme. Among these projects, CORUS proposed a concept of operations (CONOPs) for U-space that pointed out that within VLL volumes within medium operational risk, pre-flight (strategic) conflict resolution has to be provided, whereas within high operational risk volumes there must be also a ground-based tactical (in-flight) conflict resolution service.  Other SESAR projects (CLASS, SAFIR and DOMUS) investigated technologies and architectures to provide conflict resolution. However, the separation minima that have to be applied, as well as the separation mode (advisories or ATC-like instructions), are still to be determined. And although some separation minima have been proposed in the context of detect and avoid (DAA) systems, they cannot be easily extended to ground-based tactical conflict resolution systems.



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