Defining Lines of Defense Against Change Propagation Using Cause‐Consequence Analysis

ABSTRACT Complex engineered systems are the core of modern society. So that engineered systems and infrastructure can be sustainable and offer value over the course of their lifespan, there is a growing need for such systems to be changeable. Yet, establishing and operationalizing changeability can be challenging due to the potential for change propagation. Cause‐consequence analysis is applied to define three lines of defense against change propagation: margin on system parameters, uncoupled design variables, and flexibility of design variables. Changes to a high‐powered rocket are explored as illustrative examples that demonstrate how the lines of defense can help identify efficient redesign strategies and design more changeable systems. By providing a foundation for modeling and analyzing system changeability, the defined lines of defense allow designers to jointly consider how system architecture decisions and margin allocation enable changeability. The lines of defense also support higher fidelity change propagation analyses by enabling quantitative assessment of changeability. Future research should investigate how designers can actively establish the lines of defense and leverage them throughout a system's lifecycle. Significance and Practitioner Points Cause‐consequence analysis is applied to define three lines of defense against change propagation: margin on system parameters, uncoupled design variables, and flexibility of design variables. Change propagation literature provides evidence that each line of defense exists, yet many of these approaches do so without fully accounting for the mathematical relationships between design variables, requirements, and constraints. This work allows designers to jointly consider system architecture decisions and margin allocation strategies as a means of establishing defined lines of defense against change propagation. This is different than many change propagation methods that focus on highlighting where change propagation may occur in the event of a redesign, without providing insight into how that propagation can be prevented. Establishing a formal framework for the lines of defense provides a foundation for quantitatively modeling and analyzing changeability in complex systems. Further, the proposed lines of defense can also support change management practice. By stepping through each line of defense, designers can identify efficient change pathways that mitigate change propagation and limit the scope of the redesign activity. Practitioners could also apply architecture and configuration principles from the lines of defense framework to design more changeable systems.