The ground risk class answers one question: if this aircraft comes down, how likely is it to hurt someone? In SORA 2.5, you first determine an intrinsic class from the aircraft and the area, then apply mitigations to reach the final class.
The iGRC table
Find the column that matches your aircraft’s maximum characteristic dimension and maximum speed. If they point to different columns, use the higher one. Then find the row for your population density.
| Max density (people/km²) | 1 m / 25 m/s | 3 m / 35 m/s | 8 m / 75 m/s | 20 m / 120 m/s | 40 m / 200 m/s |
|---|---|---|---|---|---|
| Controlled ground area | 1 | 1 | 2 | 3 | 3 |
| < 5 | 2 | 3 | 4 | 5 | 6 |
| < 50 | 3 | 4 | 5 | 6 | 7 |
| < 500 | 4 | 5 | 6 | 7 | 8 |
| < 5,000 | 5 | 6 | 7 | 8 | 9 |
| < 50,000 | 6 | 7 | 8 | 9 | 10 |
| > 50,000 | 7 | 8 | Not part of SORA | Not part of SORA | Not part of SORA |
There is one notable shortcut. An aircraft of 250 g or less with a maximum speed of 25 m/s or less has an iGRC of 1 regardless of density, unless it operates over assemblies of people.
Population density
Density is one of the harder inputs in practice. The relevant figure is the maximum density across the entire footprint: flight geography, contingency volume and ground risk buffer. A short stretch over a dense area can set the class for the entire operation.
EASA has published guidelines on static population density data. Check which data your authority accepts.
Mitigations
The final GRC comes from subtracting mitigation credits from the iGRC:
| Mitigation | Low | Medium | High |
|---|---|---|---|
| M1(A) Sheltering | -1 | -2 | Not available |
| M1(B) Operational restrictions | Not available | -1 | -2 |
| M1(C) Ground observation | -1 | Not available | Not available |
| M2 Reduced impact dynamics | Not available | -1 | -2 |
Each credit comes with integrity and assurance criteria you have to meet. A claimed credit is only as strong as the evidence behind it. A parachute without proof of its performance earns nothing.
Final GRC and what it leads to
The result feeds directly into your SAIL. If the final GRC remains above 7, the operation falls outside SORA and belongs in the certified category.
This summary follows the published tables. Always work from the current AMC to Regulation (EU) 2019/947 when preparing a real application.