IRELAND · SORA Air Risk
Understanding the Air Risk Class (ARC) and Its Importance for Drone Operators in Ireland
The Air Risk Class (ARC) is a classification within the Specific Operations Risk Assessment (SORA) that evaluates the risk of encountering manned aviation during drone operations. The ARC is not a separate permit, recognition, or classification granted by the Irish Aviation Authority (IAA). The operator determines and substantiates the initial ARC based on the airspace and expected encounter rate. After accepted strategic mitigations, a residual ARC may follow. This residual ARC then forms the basis for the required Tactical Mitigation Performance Requirement (TMPR).
What Does Air Risk Class Mean?
The ARC describes the air risk: the chance that the UAS will encounter manned aviation during the operation. SORA distinguishes ARC-a through ARC-d. A higher class indicates a higher expected encounter rate and requires more stringent risk management in the air.
The ARC is alongside the Ground Risk Class (GRC). The GRC addresses the risk to people on the ground; the ARC addresses the risk of a collision with manned aviation. Both assessments have different subjects and should not be confused with each other.
From Initial ARC to Residual ARC
The initial ARC results from the characteristics of the operational airspace and the expected presence of manned aviation. The operator must substantiate this with appropriate data and sources, including the relevant airspace, traffic patterns, flight altitudes, usage times, and other operational conditions.
Strategic mitigations can reduce the chance of an encounter. Consider an adjusted operation area, a limited time window, or other demonstrable restrictions before the flight. Only when the chosen mitigations are sufficiently substantiated according to the SORA methodology can a lower residual ARC be used.
What Are the Implications of the Residual ARC?
The residual ARC determines which Tactical Mitigation Performance Requirement applies. The TMPR describes the required performance level for tactical mitigation during the operation, including detection, decision-making, command-and-control, and executing an avoidance action when necessary.
The concrete technical and operational implementation must align with the Concept of Operations (ConOps) and be demonstrably supported with procedures, competencies, configuration data, exercises, and evidence. A mere mention of an ARC class is therefore insufficient.
How Does ARC Appear in an Application?
In a customized SORA, the operator documents the steps taken, input data, initial ARC, strategic mitigations, residual ARC, and associated TMPR in a traceable manner. The competent authority assesses this substantiation as part of the complete dossier for the operational authorization; there is no separate ARC application or ARC granting.
In an applicable PDRA, the risk assessment and conditions are predefined. The operator must then demonstrate that the operation fully fits within those conditions. A PDRA is not a free method by which the operator can independently choose another ARC.
Practical Checkpoints for the Operator
Ensure that the ConOps accurately describes the operation area, vertical boundaries, usage times, and relevant airspace users. Also, document which data for the encounter rate have been used, how current that data is, and what assumptions or uncertainties exist.
Ensure that every strategic and tactical mitigation is reflected in procedures, crew training, technical configuration, and evidence. When the operation area, airspace usage, or operational concept changes, the ARC substantiation must also be reassessed.
- Document the source and reference date of airspace and traffic data.
- Make initial ARC, strategic mitigations, and residual ARC separately visible.
- Link the residual ARC to the applicable TMPR.
- Reference procedures, training, and technical evidence from the analysis.
Frequently asked questions
Is ARC a permit issued by the IAA?
No. ARC is a risk classification within SORA. The IAA assesses the substantiation as part of the dossier for an operational authorization but does not issue a separate ARC certificate.
What is the difference between initial ARC and residual ARC?
The initial ARC results from the operational airspace before applying strategic mitigations. The residual ARC is the class that remains after accepted and sufficiently substantiated strategic mitigations have been applied.
What is the difference between ARC and GRC?
ARC addresses the risk of an encounter with manned aviation. GRC addresses the risk to people on the ground. Both are separate components of the SORA assessment.
Does every Specific-category operation need to determine its own ARC?
Not always. In a customized SORA, the ARC is substantiated according to the SORA steps. In an applicable PDRA, the relevant risk outcomes and conditions are predefined, and the operator must demonstrate that the operation fully fits within those conditions.