In the Specific Operations Risk Assessment (SORA), determining your intrinsic Ground Risk Class (iGRC) is a foundational step toward gaining operational authorization. A key factor in calculating this ground risk is the Critical Area - a concept that’s often misunderstood but carries significant implications for your approval pathway, especially as operations grow in complexity and scale.

So, what is the Critical Area? How is it calculated? And how can drone operators use it to their advantage without compromising safety or compliance?

Let’s break it down.

What Is the Critical Area?

The Critical Area represents the surface on the ground that could be affected in the event of a drone crash - essentially, it’s an estimate of how much ground would be exposed to potential harm from an impact. It’s a crucial input to determine the iGRC in Step 2 of the SORA process, before any mitigations like parachutes or strategic ground risk reductions (M2) are applied.

In practical terms, the larger your Critical Area, the more people might be at risk in a crash scenario, and the higher your baseline ground risk. That means higher regulatory scrutiny, possibly higher SAIL levels, and more complex mitigations.

Two Models, One Objective

To calculate the Critical Area, EASA provides two models - each suited for different types of aircraft and crash dynamics:

1. The JARUS Model

   This is the default model and assumes a fixed-wing drone with glide and slide characteristics. It calculates how far a drone could travel after losing power, factoring in things like cruise speed, mass, glide angle, and surface friction.

2. The High Impact Angle Model

   Designed for rotorcraft and multirotors, this model assumes a steep, ballistic descent - common for vertical takeoff and landing (VTOL) platforms. If your impact angle exceeds 60°, this model is typically more accurate and less conservative than JARUS.

Operators can use the Critical Area Assessment Tool on the EASA website to determine which model applies and to calculate their Critical Area accordingly.

Why Calculation Matters

Here’s the nuance: the standard iGRC table assumes default Critical Area thresholds based on the maximum characteristic dimension (e.g., wingspan) of your drone. But that can be overly conservative. For instance, a 3.4 m drone automatically places you in a higher iGRC bracket - unless you calculate your actual Critical Area and demonstrate that it falls below the default threshold for a smaller class.

This allows operators to “down-class” their ground risk assessment and avoid unnecessary mitigations or documentation. But you need to do your homework: gather accurate specs, apply the right model, and document your assumptions.

Calculating the Critical Area

For the JARUS Model, the calculation considers:

• Maximum characteristic dimension

• Cruise speed

• Mass

• Impact angle (typically assumed at 35°)

• Glide and slide distances

• Friction coefficients and restitution

For the High Impact Angle Model, the main inputs are:

• Mass

• Characteristic dimension

• Minimum flight altitude

• Cruise speed (used to calculate terminal velocity)

The model estimates the kinetic energy at impact and then applies a safety factor to account for secondary effects (bounce, splatter, blade throw). The resulting area is defined as a circular zone around the impact point.

Both models use conservative assumptions to comply with the SORA principle of “worst credible failure.” That means that if you’re aiming to reduce your Critical Area for a lower iGRC, you must limit minimum flight altitudes and document it in your operational manual - especially if using the high impact angle model.

How AirHub Helps You Get It Right

Navigating Critical Area calculations can be complex, especially if you’re scaling operations across different platforms or mission types. AirHub supports you on both fronts:

With our Consultancy

We help operators:

• Choose the right model based on aircraft type and flight profile

• Use the EASA tool effectively and interpret the results

• Incorporate altitude and operational limitations into your OM and SORA

• Submit updates when changing platforms or expanding to new locations

With our Software

AirHub lets you:

• Store aircraft specs, OM, and SORA documentation in one place

• Link operational limits directly to mission planning workflows

• Monitor real-world flight profiles and validate against iGRC assumptions

• Easily export compliance reports for audits or authorization renewals

The Bottom Line

Understanding the Critical Area isn’t just a paperwork exercise - it’s a way to align your safety case with the real-world behavior of your drones. And in many cases, it’s an opportunity to optimize your iGRC, reduce approval burdens, and scale smarter.

Want to know if your operations could benefit from a Critical Area reassessment? Let’s talk.