SORA 2.5 · ARC
ARC and Air Risk Mitigations: Worked Example of SORA 2.5
In the United Kingdom's regulatory framework for Unmanned Aircraft Systems (UAS), the Specific Operations Risk Assessment (SORA) is a crucial tool for assessing and managing air risk in specific operations. The Air Risk Classification (ARC) within SORA 2.5 provides a quantitative estimation of the likelihood of encountering manned aviation in the operational airspace. Assigning an ARC category involves more than just selecting a letter; it requires a thorough analysis of the airspace, data sources, and the effective application of strategic and tactical mitigations to ensure a coherent and controllable outcome.
Justifying the Initial ARC: Comprehensive Airspace and Traffic Analysis
The first step in determining the ARC is to establish the Initial ARC based on a detailed description of the operational airspace. This includes identifying the airspace class (such as Class C or D in the UK classification system), defining the vertical and lateral boundaries of the operation, and considering information about nearby aerodromes and commercial air routes. It is essential to analyse the traffic patterns and density during relevant time periods to understand the potential for encounters with manned aircraft. Authoritative sources like the UK Aeronautical Information Publication (AIP), UK CAA geozones, and official aviation charts should be utilised for this evaluation.
Selecting the appropriate Initial ARC category (labelled a to d in UK SORA) must be grounded in the collected data, assumptions, and clearly documented uncertainties. The justification should demonstrate that the ARC applies uniformly to the entire operational volume and assumes optimal operational conditions at the time of flight.
- Identification of UK airspace classification and operational limits
- Assessment of traffic volume and mix, including peak periods
- Use of official sources: UK AIP, UK CAA geozones, ATC data
- Documentation of assumptions, uncertainties, and date of assessment
Strategic Mitigations and Derivation of the Residual ARC
Strategic mitigations are pre-planned measures designed to reduce the probability of encounters with manned aircraft. Examples include scheduling the operation during low traffic periods, restricting the operational volume to reduce exposure, or coordinating with air traffic control (ATC) and other relevant service providers to manage traffic effectively.
The effectiveness and applicability of these mitigations must be substantiated with operational evidence. Only when their impact is sufficiently justified can the Residual ARC be determined. Any desired ARC reduction without supporting evidence is not acceptable. The Residual ARC therefore reflects the quantifiable reduction of air risk after the implementation of these strategic mitigations.
- Time and spatial restrictions limiting flight exposure
- Pre-operation coordination with UK ATC and stakeholders
- Evidence-based justification of mitigation effectiveness
- Clear and traceable derivation of Residual ARC as per SORA 2.5
Tactical Mitigations and Tactical Mitigation Performance Requirement (TMPR)
Tactical mitigations are active measures applied during flight operations to detect and avoid both cooperative and non-cooperative manned aircraft. This involves using certified detection systems, established communication protocols, decision-making procedures, and clear avoidance manoeuvres. UK SORA requires these to meet the Tactical Mitigation Performance Requirement (TMPR) appropriate to the operation's risk level.
Comprehensive documentation must link these resources and procedures to the TMPR, covering roles and authorities for decision-making, reaction times, communication standards with ATC and other traffic participants, and fallback procedures should primary mitigations fail. Training and scenario simulations help ensure operational reliability and compliance.
- Certified detection technologies with verifiable coverage
- Prompt and clear decisions by qualified remote pilots
- Robust communication and deconfliction procedures with third parties
- Contingency plans including fallback and failure management
Frequently asked questions
Is a low flight altitude sufficient to reduce the ARC?
No, flying at low altitudes alone does not guarantee a lower ARC. UK SORA 2.5 requires that any strategic mitigations be convincingly justified and supported by evidence. Without demonstrable risk reduction, the ARC cannot be decreased based solely on altitude.
What is the difference between Initial ARC and Residual ARC?
The Initial ARC is the risk classification based solely on the airspace environment prior to applying any mitigations. The Residual ARC is the adjusted risk level after validated strategic mitigations have been implemented, reflecting a demonstrated reduction in the likelihood of encounters with manned aviation.
How do I prove the effectiveness of strategic mitigations?
Effectiveness can be shown with traffic statistics, confirmation of coordination with ATC, operational agreements, and monitoring results. Any ARC reduction must be supported by verifiable data; without this, mitigations cannot justify a lower ARC.
When are tactical mitigations mandatory under UK SORA?
Tactical mitigations are required when the Residual ARC indicates a remaining risk of encounter that must be actively managed during flight. Compliance with the Tactical Mitigation Performance Requirement (TMPR) ensures adequate detection, communication, and decision-making capabilities to mitigate this risk.