What is System Safety?

Imagine a world where flying taxis and drone deliveries are a part of our daily lives. This vision is becoming a reality with the rise of Advanced Air Mobility (AAM) vehicles. These novel aircraft concepts involve intricate, complex and interconnected systems. But how do we ensure that these intricate systems remain safe throughout their lifecycle?

To get an understanding how this safety is ensured, we will delve into the concept of system safety in this post. Follow along to learn more.

Understanding System Safety

System safety combines the concepts of "system" and "safety." A system is made up of multiple sub-systems, units, assemblies, and components working together towards specific functions. Safety is defined as freedom from harm or unacceptable risk. Thus, system safety focuses on preventing and managing hazards and risks within interconnected systems.

As defined by MIL-STD-882, system safety is the application of engineering and management principles, criteria, and techniques to achieve acceptable risk within the constraints of operational effectiveness, suitability, time, and cost throughout all phases of the system life-cycle. System safety emphasises building safety within the system rather than retrofitting protection measures.

Early identification of hazards allows for risk elimination and mitigation strategies to be included early in the design phase. It considers systems as a whole rather than individual components, understanding safety to be an attribute of the system. One of the objectives is to evaluate interfaces between systems and determine the effects of both component/sub-system interactions and effects of their failures. For better understanding, lets try to apply this to an aircraft design.

Integrating in an Aircraft Design

For instance, determining whether an aircraft design is safe cannot be achieved by examining the failure of a single valve in isolation. System safety focuses on the complex interactions among various components and subsystems, which are systematically analysed through processes such as Aircraft Functional Hazard Assessment (AFHA) and System Functional Hazard Assessment (SFHA). A single failure could have cascading effects, influenced by equipment design, maintenance practices, human factors, and control systems.

Therefore, achieving system safety necessitates a holistic approach that includes thorough Validation and Verification (V&V) of all requirements. This ensures that all elements of the aircraft interact effectively to prevent and manage potential hazards.

Conclusion

Ensuring aircraft safety involves more than just preventing individual component failures—it requires a deep understanding of how these components interact within the entire system. System safety in aerospace emphasizes this interconnectedness, beginning with a top-down approach to analyse hazards early in the design stage.

As the system evolves, measures to eliminate, control, and manage hazards are integrated throughout its lifecycle. In a rapidly advancing technological world, system safety isn't just a technical requirement—it's the foundation that ensures we can trust these innovations with our lives.

System Safety is a superset of Functional Safety, functional safety focuses only the system functions that has electrical and/or electronic (E/E) elements. Refer to our post on "What is Functional Safety?" where we try to define it with respect to ISO 26262.

In a highly regulated environment, every new concept must be certified by airworthiness regulators (such as FAA, EASA, Transport Canada, etc). The regulators certify based on whether the product is compliant with system safety standards (such as: ARP 4761, MIL-STD-882, etc). These standards outline a comprehensive approach to be followed where safety requirements are derived and fed into the design to manage hazards.

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Finally, we would like to leave you with the thoughts of Jerome Lederer, Former Director of NASA Manned Flight Safety Program for Apollo, who wrote:

System safety covers the total spectrum of risk management. It goes beyond the hardware and associated procedures of system safety engineering. It involves: attitudes and motivation of designers and production people, employee/management rapport, the relation of industrial associations among themselves and with government, human factors in supervision and quality control, documentation on the interfaces of industrial and public safety with design and operations, the interest and attitudes of top management, the effects of the legal system on accident investigations and exchange of information, the certification of critical workers, political considerations, resources, public sentiment, and many other nontechnical but vital influences on the attainment of an acceptable level of risk control.