The air risk class looks at the chance of meeting a crewed aircraft. It runs from ARC-a, for airspace where encounters are not a realistic concern, to ARC-d, where they are most likely.
Initial ARC
You determine the initial ARC by asking where you fly. In broad terms:
| Where you fly | Typical initial ARC |
|---|---|
| Atypical or segregated airspace | ARC-a |
| Below 150 m (500 ft) in uncontrolled airspace over rural areas | ARC-b |
| Below 150 m in uncontrolled airspace over urban areas | ARC-c |
| Below 150 m in controlled airspace | ARC-c |
| Above 150 m in uncontrolled airspace | ARC-c |
| Airport environment, class E, F or G | ARC-c |
| Above 150 m in controlled airspace | ARC-d |
| Airport environment, class B, C or D | ARC-d |
Treat this as a guide to the logic. The method and your national airspace set the final answer, and local factors such as military low-flying areas or helicopter routes can matter a great deal.
Strategic mitigation and residual ARC
If you think the real risk is lower than the generic class suggests, you can argue for a reduction. Strategic mitigations include limiting your operation to certain times, boundaries or volumes where traffic density is demonstrably low. The outcome is the residual ARC.
This usually takes supporting data. Ask yourself what evidence shows that traffic really is lower in this volume at this time.
Tactical mitigation
Whatever remains has to be managed during flight. The tactical mitigation performance requirements (TMPR) set how well you need to detect and avoid traffic:
- Under ARC-a there is no specific requirement.
- For higher classes, the expectations rise steadily, from basic traffic awareness to systems and procedures with demonstrated performance.
Operations in visual line of sight can usually meet this through the pilot’s own see-and-avoid responsibility. BVLOS operations have to make the case some other way, for example with airspace observers or detection systems.
Why it matters
ARC is a blunt tool in the SAIL table. Moving from ARC-c to ARC-b can bring a low-GRC operation from SAIL IV to SAIL II, and ARC-d always means SAIL VI. A small change to where and how high you fly can pay off more than any piece of equipment.