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As of January 26, 2023, the U-space regulatory framework will become effective in Europe. However, the designation of U-space will not immediately follow. It is important for local governments, Air Navigation Service Providers (ANSPs), and Unmanned Aircraft System (UAS) operators to consider the effects of U-space airspace. This article focuses on the relationship between U-space and the Specific Operations Risk Assessment (SORA).
The SORA approach includes the Air Risk Model, which assesses the risk of an encounter with manned air traffic. The principle is based on defining the initial Air Risk Class (ARC) of the operational volume, while proper mitigations can reduce the initial ARC to a residual (final) ARC. Together with the Ground Risk Class (GRC), the final Specific Assurance and Integrity Level (SAIL) is determined. This outcome represents the risk of the UAS operations and the corresponding requirements (Operational Safety Objectives, OSOs) for the operation.
The European Union Aviation Safety Agency (EASA) defines the ARC as a ”qualitative classification of the rate at which a UAS would encounter a manned aircraft in typical generalized civil airspace.” The ARC can be divided into four levels (ARC-a, – b, -c, -d) with an increasing risk of a collision between a UAS and a manned aircraft. It can be determined using the decision tree as published in Regulation EU 2019/947 (Unmanned Aircraft Systems).
Reducing the initial ARC can be achieved by applying strategic mitigations through operational restrictions (on the side of the UAS operator) or common structures and rules (e.g. airspace structure and/or traffic procedures). The residual risk can be further mitigated by means of tactical mitigations, which apply to Beyond Visual Line of Sight (BVLOS) operations. For (Extended) Visual Line of Sight flights, the ‘see and avoid’ principle can be maintained by keeping an eye on the UAS.
U-space within the SORA model
Within the SORA methodology, the Air Risk Model allows for mitigations that come from the services provided within U-space airspace. Since SORA 2.0 was published in the early stages of U-space development, the model did not further address the role of U-space within SORA. However, with the implementation of Regulation EU 2021/664 (U-space regulation) and the corresponding Acceptable Means of Compliance (AMC) and Guidance Material (GM), EASA provides a recommendation for the residual ARC after implementing U-space: ”It is recommended to apply a residual ‘ARC-b’ for U-space in both controlled and uncontrolled airspace.” The competent authority will decide whether or not to adopt the recommendation.
Without U-space, ARC-b is defined as the airspace below 500 ft in uncontrolled airspace over rural areas. The recommendation of ARC-b for U-space is based on having applied the strategic and tactical means that support the implementation of U-space airspace. Therefore, it must be demonstrated that the U-space airspace volume including the services is comparable to ARC-b operations to take advantage of the ARC reduction (a similar approach of reducing the ARC without U-space services).
This operational condition (the reduction to ARC-b) will be determined through the U-space Airspace Risk Assessment. The risk assessment covers both ground and air risks and takes into account safety, privacy, security, and environmental aspects. The output of the risk assessment, including the output from stakeholder hearings, will result in a U-space Deployment plan to the Member state which includes the performance requirements of the U-space airspace.
The following sections will further address the relationship between U-space and the SORA mitigations.
Strategic U-space mitigations by common structure and rules
The U-space flight authorization service (which is a mandatory U-space service) can be used as a strategic mitigation to separate UAS and manned aircraft (and other UAS flights). Since the UAS operator does not control the airspace volume, the operator must file a flight plan, which will be checked against planned and already airborne flights by the U-space Service Provider (USSP). It is an example of a mitigation through common airspace (U-space) structure. Based on the flight authorization process, the USSP guarantees separation through procedural control in the airspace.
Tactical U-space mitigations
While U-space is used as the traffic management system for UAS operations, initially below 500 ft, traditional manned aircraft may still operate within U-space if they comply with Regulation EU 2021/666 for e-conspicuity. The 666 Regulation requires manned aircraft, operating in U-space airspace, to make themselves electronically conspicuous to the USSP. This principle applies to uncontrolled airspace.
For controlled airspace, Regulation EU 2021/665 is applicable. Since traffic in U- space airspace will be known (through the Network Identification service and detection systems), the risk of encounters with manned traffic can be mitigated by the Dynamic Reconfiguration concept. The concept aims to segregate manned and unmanned traffic within U-space airspace. It requires cooperation between the USSP (or multiple USSPs if applicable) and the ANSP.
Tactical Mitigation Performance Requirements (TMPR)
For BVLOS (Beyond Visual Line of Sight) operations, the UAS operator is required to demonstrate that it fulfils the TMPRs. U-space does not change this process, however, it provides additional ways and means of fulfilling the requirements for detection. The operator can rely on the U-space Traffic Information Service as a means to detect traffic in the area, so it supports UAS operators in avoiding collisions with manned (and unmanned) traffic. It, therefore, highlights the importance of the Traffic Information Service provided by the USSP to the UAS operator in relation to the air risk mitigation within the SORA.
However, the service does not give the USSP (or ANSP) responsibility for the operation. The UAS operator remains responsible for the safety of the flight and for meeting the U-space operational conditions. U-space is a way of mitigating the risk of a collision, but it still requires operators to apply for an operational authorization with the SORA approach.
Based on the U-space Deployment plan (the result of the risk assessment and the output from the stakeholder hearings), the Member State may define additional, more demanding performance requirements than the TMPRs. This means that UAS operators should demonstrate the most demanding requirements (TMPRs or the U- space performance requirements) to the competent authority (as per SORA application) to obtain a European authorization to fly.
The SORA model allows for U-space as a way of mitigating the initial ARC. EASA recommends defining the residual ARC for U-space airspace as ARC-b, which represents the risk of encountering manned traffic below 500 ft in uncontrolled airspace over rural areas. The U-space services will allow for this way of mitigating the initial ARC, both strategically and tactically. Therefore, it is important to consider the performance criteria in relation to the SORA and TMPRs during the U- space Airspace Risk Assessment and to continuously monitor the performance criteria. This way, UAS operators are able to take advantage of the U-space services in relation to their SORA application.