The common perception regarding drone classification typically categorizes unmanned aerial system  (UAS) according to their size as «small,» «medium,» or «large.» However, aviation authorities—particularly the European Union Aviation Safety Agency (EASA)—classify drones based not on their physical dimensions but on their operational risk levels. EASA regulates UAS through a risk-based approach instead of the traditional «small–medium–large» weight classification. In this context, EU Regulation 2019/947 categorizes UAS operations into three categories: «Open,» «Specific,» and «Certified.»

The Open category covers the lowest risk flights, typically involving simple visual line-of-sight (VLOS) operations with lightweight drones (e.g., class C0–C4). This category includes only subcategories A1, A2, and A3; for example, in A1, drones cannot fly over people, whereas in A3, flights must maintain a distance of at least 150 meters from people. 

The Specific category includes riskier flights not permitted under the Open category. For instance, drones over 25 kg, beyond visual line-of-sight (BVLOS) flights, or flights over crowds fall into this category. In the Specific category, safety levels are determined according to the risk of each operation. The classification considers not just drone weight but also the operational scenario, airspace type, and population density beneath the flight path.

SORA (Specific Operations Risk Assessment) and SAIL Levels

For every drone operation conducted in the Specific Category, the operator must perform a detailed risk assessment. To this end, EASA offers the «Specific Operations Risk Assessment (SORA)» methodology.

SORA calculates the ground and air risks of an operation step by step, and primarily includes the following aspects:

• Ground Risk: The potential impact on people or property on the ground in case of drone crash or loss of control. Main factors influencing ground risk include population density, type of operation (VLOS or BVLOS), and drone size. For example, a BVLOS operation in a densely populated urban area generates significantly higher ground risk compared to a flight in an isolated rural setting.
• Air Risk: The likelihood of collision between a drone and manned aircraft. Air risk is determined by factors such as traffic density in the operational airspace and existing traffic separation measures.

These risks are expressed quantitatively and combined to determine the SAIL (Specific Assurance and Integrity Level). Lower SAIL levels (e.g., I–II) represent relatively safe operations, while higher SAIL levels (V–VI) denote high-risk flights. Operational and technical requirements increase accordingly with SAIL level. For instance, compliance through manufacturer declarations may suffice at SAIL I–II levels, whereas SAIL V–VI requires compliance with EASA’s Part-21 type certification standards.

Table: Risk Calculation (Example)

Operation Type	Drone Size	Final  GRC	Final ARC	Resulting SAIL  (Risk) Level
Visual Line of Sight (VLOS), Rural, in Atypical Airspace	Small (1 m)	6	ARC A	SAIL I (low risk)
Beyond Visual Line of Sight (BVLOS), Urban, in Controlled airspace under 500 ft AGL	Medium (3 m)	6	ARC C	SAIL V (high risk)

As seen in the table, a small drone flying VLOS in a rural area corresponds to SAIL I due to its low ground and air risk. The same drone, if flown BVLOS over a populated area and controlled airspace, incurs a higher ground and air risk and may be classified as SAIL V.

Factors Affecting Classification

Under the SORA method, the main factors that determine a drone operation’s risk classification are:

• Drone Mass/Size:
  Larger, higher-energy drones can cause greater damage if they fall. In SORA’s tables the drone’s characteristic size is used to compute its Intrinsic Ground Risk Class (iGRC) based on potential kinetic energy.
• Operational Scenario:
  The nature of the flight (e.g. VLOS vs. BVLOS, altitude, speed) and the number of people involved. For example, flying over a densely populated area yields a higher GRC than a sparse rural environment. Operations within a controlled area (e.g. fenced off) reduce risk; conversely, flying over crowds increases GRC.
• Airspace & Traffic:
  Whether the flight takes place in controlled or uncontrolled airspace, and the density of manned traffic there. High traffic density makes BVLOS operations more complex (higher air risk).
• Ground Risk & Population Density:
  The concentration of people, buildings, critical infrastructure, etc., beneath the flight path. Flying over empty fields or remote areas carries a much lower ground risk than over a city center.
• Ground Risk Buffer:
  The safety margin around the flight area to protect people if the drone deviates. SORA typically applies a 1:1 rule—i.e. buffer distance ≥ flight altitude. For rotorcraft (e.g. helicopters), a ballistic model may be used to calculate the buffer.
• Containment Measures:
  Precautions to prevent the drone leaving its designated area in an emergency (e.g. signal loss or runaway). In the final SORA step, measures must protect neighboring areas and safely confine the drone—examples include geo-fencing, physical nets, or flight-limit sensors.

Using these inputs, you calculate the drone’s Intrinsic Ground Risk Class (iGRC) and Final Ground Risk Class (fGRC), as well as the Intrinsic and Final Air Risk Classes (iARC/fARC). The combined GRC and ARC values then determine the operation’s SAIL level.

Standard Scenarios (STS) and PDRA Approaches

Rather than carrying out a full SORA from scratch for every Specific operation, EASA supports the use of Standard Scenarios (STS) and Pre-Defined Risk Assessments (PDRA):

• Standard Scenarios (STS):
  These are pre-defined rule sets for particular flight types. For example, STS-01 covers VLOS operations in an open rural environment with a C5-class drone. An operation that fully complies with an STS is deemed low-risk and may be approved quickly. STS-01, for instance, specifies not only the drone classes allowed (C5 or C6) but also technical limits (e.g. maximum speed < 5 m/s).
• Pre-Defined Risk Assessments (PDRA):
  These are EASA-provided templates for common operations. For example, PDRA-S01 covers activities such as agricultural spraying or short‐range flights, while PDRA-G02 addresses long-range operations. If an operation fits a PDRA template, the operator simply fills out the corresponding tables to document compliance and can obtain accelerated approval. For each PDRA scenario, a specific risk category is measured based on the SAIL level.

Operator’s Precautions and Mitigations and their effects on classification 

The technical and operational measures proposed by the operator in the Specific category directly influence the calculated risk. Accordingly, the strategic and tactical mitigations in SORA can lower the operation’s risk class and thus the drone’s risk-based classification. For instance:

1. Strategic Measures:
   • Completely clearing the flight area in advance or prohibiting unauthorized persons from entering the area
2. Energy-Reduction Measures on Impact:
   • Parachute systems or ballistic protective systems or Impact-attenuation designs that do not significantly increase drone weight
3. Organizational and Procedural Measures:
   • Operator holds approved training and certification levels or comprehensive emergency procedures and recovery plans

When these mitigations (classified by EASA as M1, M2, M3) are implemented, the final Ground Risk Class (GRC) may decrease and the required SAIL level may drop accordingly. For instance, equipping a drone with a robust parachute system or deployable safety sensors reduces its risk score. As a result, the same operation can be approved under a lower SAIL, reducing both the operator’s exposure to risk and the risk level used for the drone’s classification.

FAA Approach to the classification: Part 107 and Categories

The U.S. Federal Aviation Administration (FAA) does not apply as detailed a risk-based assessment as EASA when classifying drones; instead, it regulates primarily by weight and operation type. The FAA’s principal commercial regulation is Part 107, which applies only to “small UAS” with a takeoff weight of 25 kg (55 lb) or less. Under Part 107, these drones must be flown by a remote pilot holding a Part 107 certificate and comply with general requirements such as VLOS operations and a maximum altitude of 400 ft AGL.

Part 107 also defines special categories for flights over people via four subcategories (Category 1–4):

• Category 1: Drones weighing 0.55 lb (0.25 kg) or less with no exposed rotating parts. These very light, toy-sized UAS may be flown safely over people.
• Categories 2–3: Drones weighing more than 0.55 lb but not exceeding 25 kg, lacking a Part 21 aircraft certificate. These must meet FAA limits on injury energy in the event of failure and implement specific safety measures. Category 2 allows looser thresholds, while Category 3 imposes stricter limits and prohibits sustained flight over assemblies of people.
• Category 4: Drones that hold a Part 21 type or special airworthiness certificate. These fully certified UAS may carry people on board (or fly over people) but must operate within the limitations of their flight manuals.

For UAS over 55 lb, the FAA requires either obtaining a type certificate under Part 21 or operating under a waiver/exemption process established by Section 44807 of the Modernization Act. In the U.S., therefore, larger UAS are controlled through traditional airworthiness certification processes. Uncertified drones (i.e., those without an FAA airworthiness certificate) are not permitted to fly over people, as they cannot demonstrate compliance with national safety and design standards.

EASA and FAA Approach Differences

• Classification Criteria:
  EASA determines a drone’s category based on the operation’s risk level. FAA, on the other hand, categorizes by weight and operation type—small (≤ 25 kg) vs. large, and special “over-populated environment” categories. EASA’s risk-based approach allows a drone of the same weight to be subject to different rules in different scenarios. For example, a 3 meter dimension drone flying over a crowd may require a high SAIL under EASA, whereas the FAA would still treat it as a “small UAS” under Part 107 due to the less weight.
• Drone Categories:
  EASA has three categories—Open, Specific, Certified—that cover a wide range of concept of operation. The FAA’s classification essentially splits UAS into those under Part 107 (small UAS) and ever operation else, with special subcategories only for operation like “flight over populated area.”
• Assurance Levels:
  Under EASA, high-risk flights require internationally recognized approvals such as a Design Verification Report (DVR). The FAA likewise requires either a type certificate or a special Certificate of Waiver or Authorization under 49 USC 44807 for larger drones. Both regulators demand certification for very risky operations, but EASA ties it to the SAIL level, whereas the FAA ties it to weight and operation type.
• Operational requirements:
  FAA Part 107 allows operators to apply for waivers to exceed standard limits (e.g., BVLOS, night operations). In EASA, if an operation does not fit a Standard Scenario (STS) or Pre-Defined Risk Assessment (PDRA), the operator must obtain approval via a full SORA risk assessment. In both systems, offering additional safety mitigations (like additional sensors or notification procedures) can gain more flexible permissions.
• Overall Objective:
  EASA’s new regulations aim to harmonize rules across the entire EU for seamless cross-border operations, having built in a minimum-risk framework (STS/PDRA) from the start. The FAA remains more open to state-by-state or bilateral coordination with other authorities, issuing incremental rules as technology evolves.

Conclusion

Under the EASA framework, a drone’s classification flows directly from the risk its operation presents. The FAA, by contrast, classifies mainly by take‑off weight (≤ 55 lb / > 55 lb) and operation type (e.g., Part 107 Categories 1‑4 for flight over people), with comparatively little granular risk scoring. When setting insurance terms, it is therefore essential to reference the criteria each authority actually applies. Assuming that any drone above 25 kg is inherently more hazardous than the one below that threshold is a mistake: true risk hinges on the platform’s technical specification and, above all, on the effectiveness of its mitigations. A 28 kg multirotor equipped with a certified parachute recovery system may pose less residual risk than a 20 kg aircraft lacking impact‑attenuation features. Likewise, a 30 kg drone fitted with an approved detect‑and‑avoid (DAA) suite could be safer in controlled airspace than a 15 kg drone that relies only on visual “see and avoid.” Insurers—and operators—should therefore weigh mitigation capabilities alongside weight and mission profile when determining coverage and compliance.

References

• European Commission. (2019). Commission Implementing Regulation (EU) 2019/947 of 24 May 2019 on the rules and procedures for unmanned aircraft operations.
• EASA. (2020). Acceptable Means of Compliance (AMC) and Guidance Material to Commission Regulation (EU) 2019/947 – Article 11 (Specific Category Risk Assessment).
• EASA. (2022). Specific Operations Risk Assessment (SORA) – EASA Guidelines and Workshop Material.Retrieved from EASA website.)
• JARUS. (2019). JARUS Guidelines on Specific Operations Risk Assessment (SORA) v2.0. Joint Authorities for Rulemaking of Unmanned Systems. 
• JARUS. (2021). JARUS SORA 2.5 (Draft Edition) – Update Summary. Joint Authorities for Rulemaking of Unmanned Systems.
• del Estal Herrero, A., Apter, N., & Hristozov, S. (2025). A Parametric Comparison of JARUS SORA 2.0 and 2.5 Ground Risk Models. Engineering Proceedings, 90(1), 47. 
• FAA. (2016). Operation and Certification of Small Unmanned Aircraft Systems – Part 107 Final Rule. Federal Aviation Administration, 14 CFR Part 107 (Federal Register Docket No. FAA-2015-0150).
• FAA. (2021). Revision of Part 107 – Operations Over People and at Night; Final Rule. Federal Aviation Administration (Federal Register Docket No. FAA-2018-1087).