Following our previous discussion on Step 4 of SORA: Initial Air Risk Class (ARC) Determination, we now focus on Step 5, which involves the application of strategic mitigations to reduce the risk of mid-air collisions.

This step is essential for reducing the initial Air Risk Class (ARC), making drone operations safer and ensuring regulatory compliance. Strategic mitigations are applied before the flight to proactively limit the exposure to risk, either by operational restrictions or by utilizing airspace structures and rules.

What Are Strategic Mitigations?

Strategic mitigations are pre-flight risk reduction measures aimed at lowering the probability of a UAS encountering a manned aircraft in the operational airspace. These mitigations modify the Initial ARC and result in a Residual ARC, which determines the necessary level of tactical mitigations in subsequent steps.

Strategic mitigations can be classified into two main categories:

1. Operational Restrictions – Measures that the UAS operator directly controls.

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3. Common Airspace Structures and Rules – Measures that are controlled by the Competent Authority or ANSP (Air Navigation Service Provider) and must be followed by all airspace users.

Strategic Mitigation by Operational Restrictions

Operational restrictions are mitigation strategies that limit the operational exposure of the UAS, thereby reducing the likelihood of encounters with manned aircraft. These mitigations include:

1. Geographical boundaries

• Limiting the operational volume to specific areas where manned aircraft operations are rare.

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• Operating away from high-density airspace, such as airport control zones or busy flight corridors.

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• Flying in segregated or restricted airspace to reduce collision risk.

Example: A UAS operation within Class C airspace near an airport may be limited to a defined sector where no regular manned aircraft traffic is expected.

2. Time-based restrictions

• Restricting operations to specific time periods when manned air traffic density is lower.

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• Conducting night-time operations in airspaces where manned aircraft predominantly operate during the day.

Example: A drone operator intending to fly over a port area may restrict operations to late-night hours when helicopter traffic is minimal.

3. Limiting time of exposure

• Reducing the total operational duration within airspace where manned aircraft operate.

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• Minimizing transition time in high-risk areas, such as flying a shorter route through controlled airspace.

Example: A drone performing a powerline inspection near a busy flight corridor might be required to quickly transit through risk areas, rather than operating there for extended periods.

Strategic Mitigation by Common Airspace Structures and Rules

Unlike operational restrictions, common structures and rules apply to all aircraft within a given airspace and are enforced by authorities like ANSPs or U-Space providers.

1. Common Flight Rules

• Right-of-way rules that establish priority between manned and unmanned aircraft.

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• Requirements for electronic conspicuity, such as ADS-B transponders.

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• Mandatory flight planning and submission to a central ANSP system.

Example: Some controlled airspaces require all manned aircraft to use electronic conspicuity to improve detectability.

2. Common Airspace Structures

• Designated UAS corridors to separate drone traffic from manned aircraft.

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• Predefined airways or procedural routes for safer integration.

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• Mandatory participation in UTM/U-Space services, ensuring dynamic air traffic awareness.

Example: A country might implement dedicated drone transit corridors near urban areas to safely integrate drone operations without affecting general aviation.

Lowering the Initial ARC Using Strategic Mitigations

The Initial ARC is assigned based on Airspace Encounter Categories (AECs), which define operational environments and their respective air traffic densities. The ARC can be lowered through strategic mitigations by demonstrating that the local air traffic density is lower than the generalized risk assumptions.

Understanding the AEC and Density Rating

• The AEC classification assigns a density rating to airspace based on the probability of encountering manned aircraft.

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• Density ratings range from 1 (low) to 5 (very high).

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• The Initial ARC is based on these ratings and can be found in standardized tables.

Steps to Lower the Initial ARC

1. Identify the AEC applicable to the operation (e.g., operating near an airport, in uncontrolled rural airspace, in segregated airspace, etc.).

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3. Determine the initial ARC based on the AEC and generalized air traffic density rating.

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5. Apply strategic mitigations to justify a lower local air density rating, such as:

   • Operating in a restricted time window when fewer manned aircraft are present.

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   • Using airspace segregation or pre-coordination with ATC/ANSP.

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   • Providing traffic studies, radar data, or operational assessments to validate reduced encounter rates.

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7. Submit evidence to the Competent Authority for approval of the adjusted ARC level.

What If Strategic Mitigations Are Not Sufficient?

If strategic mitigations alone do not sufficiently reduce the ARC, operators will need to apply tactical mitigations (Step 6), such as:

• Detect and Avoid (DAA) systems.

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• UTM-based conflict resolution tools.

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• Real-time pilot intervention measures.

Conclusion

Step 5 of the SORA process helps operators implement strategic mitigations to proactively manage air risks before flight. By applying operational restrictions and common airspace structures, operators can potentially lower the required safety measures in subsequent steps.

At AirHub Consultancy, we specialize in risk assessments, airspace integration, and strategic planning for enterprise drone operations. Our AirHub Drone Operations Platform provides tools to analyze operational airspaces, manage air risk, and ensure compliance with SORA.

Stay tuned for our next blog, where we explore Step 6 of SORA: Tactical Mitigations and Detect & Avoid Requirements!

Need help with your SORA application? Contact AirHub Consultancy for expert guidance on navigating the SORA process and ensuring compliance with UAS regulations.