IRELAND · SORA Risk Classes
GRC and ARC within SORA: What is the Difference?
Ground Risk Class (GRC) and Air Risk Class (ARC) are two distinct risk classes within the Specific category of the Specific Operations Risk Assessment (SORA) methodology. GRC pertains to the risk to people on the ground, while ARC addresses the risk of collision with manned aviation in the operational airspace. These are not alternative authorisation routes and are not used to classify operations in the Open category.
Ground Risk Class (GRC): Risk to People on the Ground
The SORA first determines the intrinsic Ground Risk Class (iGRC) based on the operational scenario, the characteristics of the Unmanned Aircraft System (UAS), and the area over which the flight is conducted. Factors include Visual Line of Sight (VLOS) or Beyond Visual Line of Sight (BVLOS), population density, the presence of a controlled ground area, and the maximum characteristic dimension of the UAS.
When acceptable ground risk mitigation measures are applied, a final GRC can be established. The justification and required robustness must align with the chosen measure.
- iGRC: intrinsic Ground Risk Class before ground risk mitigation measures
- Final GRC: ground risk class after accepted mitigations, if applicable
- GRC is a step within SORA and not a classification for the Open category
Air Risk Class (ARC): Collision Risk in the Airspace
The Air Risk Class describes within SORA the risk of an encounter with manned aviation in the operational airspace. The operator determines and substantiates the initial ARC based on the aviation environment and the expected encounter rate.
After accepted strategic mitigations, a residual ARC can be established. This residual ARC forms the basis for the required Tactical Mitigation Performance Requirements (TMPR).
- Initial ARC: starting class for the air risk
- Residual ARC: remaining class after accepted strategic mitigations
- ARC-a to ARC-d: ascending air risk classes within the SORA methodology
GRC and ARC are Two Axes of the Same SORA
GRC and ARC are not chosen against each other. A SORA application addresses both the ground risk and the air risk. Together with the other SORA steps, they lead to the Specific Assurance and Integrity Level (SAIL) and the applicable operational safety objectives.
A Pre-Defined Risk Assessment (PDRA) is a pre-developed risk analysis with established conditions. An EU Standard Scenario (EU-STS) is a declaration process with fixed conditions. Only when a bespoke SORA is necessary, the applicant goes through the full GRC and ARC substantiation.
- GRC: consequence for people on the ground
- ARC: risk of encounter with manned aviation
- SAIL: follows from the SORA combination of ground and air risk
Application in Ireland
Irish operators can, depending on the operation, use an EU-STS, an operational authorisation based on a PDRA, or an operational authorisation based on a full SORA risk assessment. The Irish Aviation Authority (IAA) recognises STS-01 and STS-02 as available standard scenarios in line with EASA lists.
The chosen route determines the necessary risk substantiation and supporting documentation. Therefore, present GRC and ARC only as integral SORA concepts and not as standalone permits or authorisation routes.
- STS-01: VLOS over a controlled ground area in a populated environment, meeting the relevant C5 requirements
- STS-02: BVLOS with airspace observers over a controlled ground area in sparsely populated environment, meeting the relevant C6 requirements
- For operational authorisations, a suitable PDRA or a complete SORA may be used
Frequently asked questions
Does GRC stand for Ground Risk Class?
Yes. Within SORA, GRC stands for Ground Risk Class. The intrinsic variant is often referred to as iGRC.
Does ARC stand for Air Risk Class?
Yes. ARC stands for Air Risk Class and within SORA describes the risk of encounter with manned aviation.
Do I need to choose between GRC and ARC?
No. A full SORA process assesses both ground risk and air risk as two complementary components.
Is GRC used for the Open category?
No. The Open category follows predefined operational limitations set by EASA, and GRC is a risk classification within the Specific category SORA methodology.
Can I use STS in Ireland?
Yes, provided the operation fully complies with conditions for STS-01 or STS-02 and relevant IAA rules, a declaration can be made to the Irish Aviation Authority.