Loss Scenario Tree

A Loss Scenario Tree is a risk-modeling tool derived from System-Theoretic Process Analysis (STPA) that describes specific scenarios leading to system loss. Unlike Fault Tree Analysis (FTA) which focuses on component failures, Loss Scenario Tree captures unsafe or unsecure control actions resulting from system interactions. This aligns with ISO 26262's functional safety principles and ISO/SAE 21434's cybersecurity requirements. It allows engineers to map causal paths for each loss scenario, ensuring that control measures are both necessary and sufficient to mitigate risks. In the context of Intelligent Connected Vehicles (ICVs), it bridges the gap between safety and security analysis, preventing redundant efforts while ensuring comprehensive coverage of emerging threats and system complexities.

Implementation typically follows three steps: 1. System-level definition of control structures, including actors, controllers, actuators, and processes. 2. Scenario-based analysis, where each control action is evaluated for unsafe or unsecure control actions (e.g., action not taken, action taken too late, action based on incorrect information). 3. Risk-adjusted control measures, where each scenario is mapped to specific technical or organizational controls. For example, a Taiwanese autonomous driving supplier implemented Loss Scenario Tree during the concept phase, reducing late-stage design changes by 40% and achieving 100% compliance with ISO/SAE 21434's threat analysis requirements. Key performance indicators (KPIs) include Scenario Coverage Ratio and Risk-Adjusted Control Effectiveness.

Three primary challenges exist: 1. Technical Expertise Gap—STPA is a non-intuitive methodology for engineers trained in traditional FMEA. Companies must invest in structured training and pilot projects. 2. Tooling Incompatibility—Many enterprises use static spreadsheets, which cannot be easily updated as system architectures evolve. Transitioning to dynamic modeling tools is essential. 3. Regulatory Pressure—With the enactment of the Taiwan AI Basic Law and tightening of international standards like UN R155, companies face increasing pressure to demonstrate rigorous risk analysis. The solution is to integrate Loss Scenario Tree into the early stages of the V-model, ensuring risks are mitigated before mass production. Priority should be given to high-risk components, such as ADAS and V2X modules, with a 6-month implementation roadmap.

Winners Consulting Services Co., Ltd. specializes in Loss Scenario Tree for Taiwan enterprises, delivering compliant management systems within 90 days. We provide end-to-turn consulting, from methodology training to tool-chain integration. Our expertise in ISO 26262 and ISO/SAE 21434 ensures your organization meets international standards with confidence. Free consultation: https://winners.com.tw/contact