SORA Air Risk Class (ARC) Explained for UK Operators

Air Risk Class — ARC — is the other half of the SORA risk picture alongside Ground Risk Class. Where GRC asks "what harm could an impact cause on the ground?", ARC asks "how likely is a collision with a manned aircraft in this airspace?". Getting the ARC right is central to operations such as beyond visual line of sight (BVLOS).

What the ARC represents

The ARC is a qualitative measure of the risk of a mid-air encounter. It runs from ARC-a (lowest risk) to ARC-d (highest risk). It reflects the density and predictability of manned traffic in the volume of airspace you intend to use, rather than the consequences of a collision, which are assumed severe in all cases.

Setting the initial ARC

The initial ARC is read from the airspace environment. The key factors are:

• Altitude — operations close to the ground generally meet less manned traffic than those higher up.
• Airspace classification — controlled versus uncontrolled airspace.
• Proximity to aerodromes — airspace near airports and airfields carries far higher traffic density.
• Environment type — atypical or segregated airspace, where manned aircraft are not expected, carries the lowest ARC.

So a low-level operation in a remote, segregated volume may sit at ARC-a, while an operation in busy airspace near an airport could begin at ARC-d.

Reducing ARC: strategic mitigations

Strategic mitigations are applied before the flight and reduce the chance of encountering manned aircraft. They fall into two broad types:

• Operational restrictions — limiting altitude, time of day, or the geographic volume to avoid known traffic.
• Common structures and rules — using airspace arrangements such as segregation, a temporary danger area, or coordination with airspace users to keep manned aircraft out of your volume.

Strategic mitigations can lower the initial ARC to a lower residual class if they are robust and credible.

Reducing ARC: tactical mitigations

Tactical mitigations operate during the flight to avoid a collision once the residual encounter risk is known. They include:

• Detect and avoid (DAA) — onboard or ground-based systems that detect intruder aircraft and enable avoidance.
• Visual observers — for operations where airspace observers can see and respond to approaching traffic.

The required tactical mitigation performance is driven by the residual ARC: a higher residual ARC demands more capable detect-and-avoid measures.

How ARC feeds the SAIL

The residual ARC is combined with the final GRC to produce the SAIL. A lower residual ARC can reduce the SAIL and therefore the overall robustness you must demonstrate. This is why operators planning BVLOS work invest heavily in either segregating their airspace (strategic) or fielding capable detect-and-avoid (tactical) — both pathways lower the air-risk contribution.

Practical points for UK operators

When building the ARC part of a SORA: characterise your airspace honestly using current aeronautical information, identify whether segregation is realistically achievable, and be clear about what your tactical measures can and cannot detect. Overclaiming detect-and-avoid performance is a common weakness that CAA assessors will probe.

As with the rest of SORA, the ARC tables and mitigation expectations are refined between methodology editions. Always work from the version the CAA currently references, and treat earlier worked examples as illustrative rather than definitive. A well-reasoned ARC, grounded in real airspace data and honest mitigation claims, is the foundation of a credible higher-tier operation.