Safety Bulletin - Importance of a System Engineering Approach

Following recent incidents and observations the Office of the National Rail Safety Regulator (ONRSR) is reminding all operators of the importance of a system engineering approach.

With various subsystems - such as track, signalling, rolling stock, electrification, stations, depots, and control centres - closely interlinked, any change in one may affect the operation of another. As such, it is important to carefully consider the interfaces and how the subsystems interact with each other (including how these systems work together with people).

It is essential to understand the hazards when making system changes or introducing new products into a system and the effect such a change will have on the overall risk profile of the railway.

One particular area operators should pay attention to is the acceptance of products or systems based on cross-acceptance. That is, where a product or system is deemed safe because it has been applied safely on another railway or because it is compliant with appropriate standards.

Whilst cross acceptance can be an indication of performance, it cannot be taken as evidence that a product will perform safely in the particular railway system it is introduced to. As part of a robust engineering change process it is, therefore, important to understand the potential hazards a product or system may present in the environment it is introduced to - and the effects it might have on the overall safety risk of the railway.

Operators should demonstrate that they use appropriate systems engineering processes and safety assurance processes (e.g. EN50126/8/9 for complex systems) in their design and procurement approach. This can be achieved through the creation of a systems engineering management plan which specifies the procedures to identify and record stakeholders, system requirements and safety needs.

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