SORA Process: A Comprehensive Overview

The SORA process consists of guidelines that are detailed in a document developed by JARUS. This document recommends a risk assessment methodology to establish a sufficient level of confidence that a specific operation of the drone can be conducted safely.

What is SORA

SORA stands for Specific Operations Risk Assessment. SORA is a risk assessment methodology developed by the Joint Authorities for Rulemaking on Unmanned Systems (JARUS) to help operators of unmanned aircraft systems (UAS) identify and mitigate the risks associated with their operations.

How was SORA created?

SORA was created because the absence of safety standards was hindering the introduction of new drone technologies into society.

When there were no safety standards for drones, the Joint Authorities for Rulemaking on Uncrewed Systems (JARUS) came up with the specific operations risk assessment (SORA) methodology. This method allowed for the safe use of drones in society and enabled drone operators to seek authorizations using SORA.

Specific Operations Risk Assessment (SORA) is of great importance in the aviation industry because previous aviation regulations did not adequately address the risks associated with drone operations. Simply we can say that SORA was created to ensure safety in the drone industry.

How is SORA updated?

SORA is updated from time to time. The review process occurs when each working group within JARUS begins to provide comments on the current version of SORA and later discusses those comments.

Applicability of the SORA process

The SORA process is applicable only if:

• The drone operation does not fall under the “open” category.
• The drone operation does not fall under the “certified” category.
• The drone operation does not follow a “standard scenario” approved by the authority.
• The drone operation is not subject to a specific NO-GO directive from the competent authority.
• The competent authority has not determined that the UAS is “harmless” for the ground risk.

The 10 steps of the SORA process

The SORA methodology provides a logical process to analyze the proposed ConOps and establish an adequate level of confidence that the operation can be conducted with an acceptable level of risk. It allows the evaluation of the intended concept of operation and categorization into six different Specific Assurance and Integrity Levels (SAIL). It then recommends operational safety objectives to be met for each SAIL.

There are 10 steps supporting the SORA methodology. Let’s go through one by one.

Step #1: ConOps Description

The concept of operations (ConOps) involves collecting and providing the relevant technical, operational, and system information needed to assess the risk associated with the intended operation of the UAS.

You can find the detailed framework for data collection and presentation in the Annex A of the SORA document. You should provide as accurate and detailed information as possible because the ConOps step is the foundation for all other activities. Along with a description of the operation, you should also provide insight into the operator’s operational safety culture. The relevant authority reviews the ConOps documentation and then decides whether to grant approval or not.

SORA Annex A provides guidance on how to gather and present data and evidence to produce a Concept of Operations (ConOps).

Step #2: Determination of the intrinsic UAS Ground Risk Class (GRC)

This is the stage where an organization assesses the inherent or intrinsic ground risk of their operations. If they are flying over an area without people, buildings, or other structures, they would fall into a low intrinsic ground risk class. Conversely, if the situation is the opposite, they would be categorized into a high intrinsic ground risk class.

The Intrinsic GRC is a classification of the risk that a drone will hit a person on the ground in the case of a loss of control.

Step #3: Final GRC Determination

The final GRC is achieved by implementing risk-reduction measures to the intrinsic GRC established earlier. The goal is to decrease the GRC to a level where the operator can more readily meet all the requirements for obtaining operational authorization.

Mitigations for ground risk

• M1 – Strategic mitigations for ground risk
• M2 – Effects of ground impact are reduced
• M3 – An Emergency Response Plan (ERP) is in place, operator validated and effective

SORA Annex B provides assessment criteria for the integrity (i.e. safety gain) and assurance (i.e. method of proof) of the applicant’s proposed mitigations. The proposed mitigations are intended to reduce the intrinsic Ground Risk Class (GRC) associated to a given operation.

Step #4: Determination of the Initial Air Risk Class (ARC)

Competent authorities, ANSPs, or UTM/U-space service providers may choose to conduct airspace characterization studies to directly assess airspace collision risks. These studies will provide clear maps indicating the initial Air Risk Class (ARC) for a specific airspace. If the competent authority, ANSP, or UTM/U-space service provides an air collision risk map (whether static or dynamic), the applicant should use this service to establish the initial ARC.

The airspace is categorized into 13 aggregated collision risk categories. These categories were characterized by altitude, controlled versus uncontrolled airspace, airport/heliport versus non-airport/non-heliport environments, airspace over urban versus rural environments, and lastly atypical (e.g. segregated) versus typical airspace.

To find the proper ARC for the type of UAS operation, the applicant should use the decision tree provided in the SORA document.

The ARC is qualitatively assessed at four levels (from lowest to highest risk): ARC-a, ARC-b, ARC-c, and ARC-d.

ARC-a is generally defined as airspace where the risk of collision between a UAS and manned aircraft is acceptable without the addition of any tactical mitigation. ARC-b, ARC-c, and ARC-d are generally defining airspace with increasing risk of collision between a UAS and manned aircraft.

Step #5: Application of Strategic Mitigations to determine Residual ARC (optional)

ARC is a generalized qualitative classification of the rate at which a UAS would encounter a manned aircraft in the specific airspace environment. However, it is recognized that the UAS Operational Volume may have collision risk different than the generalized Initial ARC assigned.

If an applicant considers that the generalized Initial ARC assigned is too high for the condition in the local Operational Volume, then refer to SORA Annex C for the ARC reduction process. If the applicant considers that the generalized Initial ARC assignment is correct for the condition in the local Operational Volume, then that ARC becomes the Residual ARC.

For example, if a drone is water resistant, it would be a strategic mitigation for bad weather conditions.

Step #6: Tactical Mitigation Performance Requirement (TMPR) and Robustness Levels

There are two classifications of Tactical Mitigations within the SORA, namely:

• VLOS, whereby a pilot and/or observer use human vision to detect aircraft and take action to remain well clear and avoid collisions with other aircraft.
• BVLOS, whereby an alternate means of mitigation to human vision, as in machine or machine assistance, is applied to remain well clear and avoid collisions with other aircraft. (e.g. ATC Separation Services, TCAS, DAA, UTM, U-Space, etc.)

Under VLOS the pilot/operator accomplishes “see and avoid” by keeping the UAS within their Visual Line-of-Sight (VLOS). The UAS remains close enough to the remote operator/observer to allow seeing and avoiding another aircraft with human vision unaided by any device other than, perhaps, corrective lenses. VLOS is generally considered an acceptable means of compliance with the “remain well clear” and “avoiding collisions” requirements of ICAO Annex 2.

Different states may have other rules and restrictions for VLOS operations (e.g. altitudes, horizontal distances, times for relaying critical flight information, operator/observer training, etc). In some situations, the competent authority and/or ANSP may decide that VLOS does not provide sufficient mitigation for the airspace risk, and may require compliance with additional rules and/or requirements. It is the operators’ responsibility to comply with these rules and requirements.

Since VLOS has operational limitations, there was a concerted effort to find an alternate means of compliance to the human “see and avoid” requirements. This alternate means of mitigation is loosely described as “Detect and Avoid (DAA).” DAA can be achieved in several ways, e.g. through ground-based detect and avoid systems, air-based detect and avoid systems, or some combination of the two. DAA may incorporate the use of varying sensors, and architectures, and even involve many different systems, a human in the loop, on the loop, or no human involvement at all. Tactical Mitigation Performance Requirement (TMPR) provides tactical mitigations to assist the pilot in detecting and avoiding traffic under BVLOS conditions.

Annex D of SORA provides the tactical mitigation used to reduce the risk of a Mid Air Collision (MAC).

Any given risk mitigation or operational safety objective can be demonstrated at differing levels of robustness. The SORA proposes three different levels of robustness: Low, Medium and High, commensurate with risk.

The robustness designation is achieved using both the level of integrity (i.e. safety gain) provided by each mitigation, and the level of assurance (i.e. method of proof) that the claimed safety gain has been achieved.

A Low level of assurance is where the applicant simply declares that the required level of integrity has been achieved. A Medium level of assurance is one where the applicant provides supporting evidence that the required level of integrity has been achieved. This is typically achieved by means of testing (e.g. for technical mitigations) or by proof of experience (e.g. for human-related mitigations). A High level of assurance is where the achieved integrity has been found acceptable by a competent third party.

Step #7: SAIL (Specific Assurance and Integrity Levels) determination

After determining the Final GRC and Residual ARC, it is now possible to derive the SAIL associated with the proposed ConOps.

The SAIL parameter consolidates the ground and air risk analyses and drives the required activities. The SAIL represents the level of confidence that the UAS operation will stay under control. The SAIL is not quantitative but instead corresponds to Operational Safety Objectives (OSO) to be complied with.

	Residual ARC
Final GRC	a	b	c	d
≤2	I	II	IV	VI
3	II	II	IV	VI
4	III	III	IV	VI
5	IV	IV	IV	VI
6	V	V	V	VI
7	VI	VI	VI	VI
>7	Category C operation

A drone operation can fall under one of six SAILs. The risk increases with higher SAIL and decreases with lower SAIL.

Step #8: Identification of Operational Safety Objectives (OSO)

Use the SAIL to evaluate the defenses within the operation in the form of operational safety objectives (OSO) and to determine the associated level of robustness.

This is a consolidated list of common OSOs that historically have been used to ensure safe UAS operations (as described in the SORA document). It represents the collected experience of many experts and is therefore a solid starting point to determine the required safety objectives for a specific operation. Competent authorities may define additional OSOs for a given SAIL and the associated level of robustness.

There are six different SAILs that a drone operation can fall into, and the higher the SAIL, the higher the associated risk. Conversely, a lower SAIL indicates a lower risk level.

Currently, most organizations aim for SAIL IV but often end up settling for SAIL II since it’s easier to obtain approval for. SAIL V and SAIL VI represent highly risky operations, and the level of risk associated with them is currently challenging to accurately assess. Many companies striving for SAIL IV are unable to achieve that and must operate at SAIL II to eventually reach SAIL III. Therefore, SAIL V and VI are largely considered future-oriented.

Technical issue with the UAS

• OSO#01: Ensure the operator is competent and/or proven
• OSO#02: UAS manufactured by competent and/or proven entity
• OSO#03: UAS maintained by competent and/or proven entity
• OSO#04: UAS developed to authority recognized design standards
• OSO#05: UAS is designed considering system safety and reliability
• OSO#06: C3 link performance is appropriate for the operation
• OSO#07: Inspection of the UAS (product inspection) to ensure consistency to the ConOps
• OSO#08: Operational procedures are defined, validated and adhered to
• OSO#09: Remote crew trained and current and able to control the abnormal situation
• OSO#10: Safe recovery from technical issue

Deterioration of external systems supporting UAS operation

• OSO#11: Procedures are in-place to handle the deterioration of external systems supporting UAS operation
• OSO#12: The UAS is designed to manage the deterioration of external systems supporting UAS operation
• OSO#13: External services supporting UAS operations are adequate to the operation

Human Error

• OSO#14: Operational procedures are defined, validated and adhered to
• OSO#15: Remote crew trained and current and able to control the abnormal situation
• OSO#16: Multi crew coordination
• OSO#17: Remote crew is fit to operate
• OSO#18: Automatic protection of the flight envelope from Human Error
• OSO#19: Safe recovery from Human Error
• OSO#20: A Human Factors evaluation has been performed and the HMI found appropriate for the mission

Adverse operating conditions

• OSO#21: Operational procedures are defined, validated and adhered to
• OSO#22: The remote crew is trained to identify critical environmental conditions and to avoid them
• OSO#23: Environmental conditions for safe operations defined, measurable and adhered to
• OSO#24: UAS designed and qualified for adverse environmental conditions

Step #9: Adjacent Area/Airspace Considerations

This step address the risk posed by a loss of control of the operation resulting in an infringement of the adjacent areas on the ground and/or adjacent airspace. These areas may vary with different flight phases. Where adjacent areas are gatherings of people unless already approved for operations over gathering of people OR ARC-d unless the residual ARC is ARC-d. In populated environments where M1 mitigation has been applied to lower the GRC.

Step #10: Comprehensive Safety Portfolio

Once all steps of the specific operations risk assessment (SORA) are completed, an organization can compile all the information into a comprehensive safety portfolio.

Satisfactory substantiation of the mitigations and objectives required by the SORA process provides a sufficient level of confidence that the proposed operation can be safely conducted.