Key Factors in the EASA Certification Process for Flight Control Systems in Medium-Risk Operations SAIL III and SAIL IV: MoCs and SORA Methodology

Tue, 09/17/2024 - 08:54

The Specific Operations Risk Assessment (SORA) methodology establishes a crucial framework for risk assessment and management in Unmanned Aerial Systems (UAS) operations. Based on 24 Operational Safety Objectives (OSOs), SORA provides a structured approach to ensure safety in UAS operations within the specific category. In this context, Means of Compliance (MoCs) play a vital role by offering guidelines to meet safety objectives and provide evidence to regulatory authorities.

This article examines key considerations for a guidance, navigation, and control system for unmanned aerial vehicles and how the UAV Navigation-Grupo Oesía flight control system or autopilot aligns with available key MoCs for OSOs related to medium-risk operations (SAIL III and SAIL IV), highlighting its importance for operational robustness and safety.

Understanding MoCs in the Context of SORA

MoCs are guidelines for meeting the 24 established OSOs, offering practical solutions to mitigate risks. Although MoCs are not mandatory, as it’s possible for the applicant to provide alternative means of compliance, they provide a valuable framework for implementing safety measures and generating the necessary evidence for operational approval. The European Aviation Safety Agency (EASA) has published several MoCs that apply to different risk levels. For SAIL III and SAIL IV levels, there are five particularly relevant EASA MoCs that influence the design and operation of flight control systems.

Relevant MoCs for the Design of Flight Control Systems or Autopilots

MoCs for SAIL III

For SAIL III, the MoCs describe accepted means for evidencing compliance with the requirements of OSOs for which an EASA Design Verification is not necessary. For operations classified at the medium-risk level SAIL III, the following MoCs are fundamental:

MoC OSO #5: This MoC focuses on a hazards assessment, highlighting the need to implement effective controls to minimize the risks associated with UAS technical failures. If a quantitative analysis is performed, documentation must show that the probability of loss of control due to technical failures is less than 5x10^-4 per flight hour, with Fault Tree Analysis (FTA), Functional Hazard Assessment (FHA), and Failure Mode and Effects Analysis (FMEA) according to standards such as ED-280. In this regard, the UAV Navigation-Grupo Oesía flight control system incorporates advanced algorithms for risk detection and management, ensuring an effective response to potential failures. Also, the VECTOR autopilots are designed with redundancies and automatic mechanisms that enable safe recovery in unforeseen situations. They have undergone rigorous third-party evaluation, achieving a probability of mission loss of 1.809E-05 per flight hour.
MoC OSO #6: This relates to the Command and Control (C2) characteristics, with the aim of ensuring that they are sufficient and adequate for the operation. In this area, the VECTOR autopilot stands out for employing encrypted communications and robust data protocols to protect the integrity and security of information. Also, configuration for a redundant datalink is possible to enhance the robustness of the communication system.
MoC OSO #18: This MoC addresses the system’s automatic protection of the flight envelope from human error, which can result in loss of control of the aircraft. The VECTOR autopilots also impose flight envelope limitations in terms of maneuverability and performance depending on the specific mode and/or flight condition, minimizing the risk of incorrect control inputs from the remote pilot.
MoC OSO #24: Focused on how the UAS is designed to limit the effect of adverse environmental conditions. Both laboratory and flight tests must be conducted, in addition to meeting standards such as DO-160G and ASTM F3478-20, to demonstrate the UAS's ability to operate safely under non-ideal conditions. In this area, the UAV Navigation-Grupo Oesía flight control system has undergone rigorous integrity and stability tests to ensure its reliability under demanding operational conditions.

MoC for SAIL IV

For the medium-risk level SAIL IV, design-related OSOs need to be verified by EASA through a Design Verification Process according to the Special Condition (SC) for Light UAS. Within the available MoCs, the MoC SC Light-UAS.2510 is especially relevant for the design of a flight control system:

MoC SC Light-UAS.2510: This MoC relates to OSO #5 and establishes that systems and equipment must minimize threats in the event of probable failures, prevent catastrophic failures, and have strategies to detect and manage combined failures. The probability of loss of control must be less than 10^-4 per flight hour and that of technical failures less than 10^-5 per flight hour, with a qualitative or quantitative assessment as needed. The UAV Navigation-Grupo Oesía VECTOR-600 and VECTOR-400 flight control systems are equipped with advanced sensor fusion algorithms and navigation laws that enable safe and efficient operation in complex environments, even in the event of isolated and combined sensor group failures. The UAV Navigation-Grupo Oesía flight control system has been developed to successfully complete missions, ensuring flight safety in the face of any type of operational complication.

Recommendations of Additional Standards and Norms

The following standards are recommended to comply with the described MoCs:

ASTM F3002-14a: For justifying errors in transmitted data.
ASD-STAN PrEN 4709-00011 / ED-325: Protection of the C2 link.
ASTM F3478-20 and ASTM F3298-19: Flight tests.
DO-160: Environmental tests.
ED-280: Safety analysis guide.
ASTM F3309-21: Design and installation evaluation.
ED-135: Methods for safety assessment in aerial systems.

Conclusion

According to EASA, the integration of MoCs derived from SORA into the design of flight control systems is essential to ensure safe operations in compliance with medium-risk levels. UAV Navigation-Grupo Oesía, with its technical expertise, knowledge of the standard and experience in providing robust and safe products, is a valuable partner to accompany our customers in the complex process of authorization of medium-risk unmanned operations SAIL III and SAIL IV. By continuously evaluating and adjusting our system based on these MoCs, we ensure that we maintain the highest standards of safety and operational efficiency.

To ensure the certification of your aircraft for all types of operations, it is essential that you have high-quality control systems like those offered by UAV Navigation-Grupo Oesía. Do not hesitate to contact us to discover how we can help you achieve the highest standards of safety and performance in your operations.