Process Improvement for Rotorcraft Tradespace Exploration incorporating Reliability and Availability

Tradespace exploration (TSE) is a Department of Defense (DOD) Engineered Resilient Systems (ERS) (Ref.1) thrust, with overarching goals to develop processes and products capable of performing in a wide range of adverse conditions commonly encountered by military systems. Combined with technology, TSE is modernizing system engineering, facilitating stakeholder value elicitation as well as distributed collaborative environments for design and analysis of alternatives. The majority of existing TSE research emphasizes tradeoffs between functional requirements, especially those pertaining to performance. Our previous work proposed models (Refs. 2, 3) for rotorcraft TSE to quantify the impact of reliability investment at the subsystem level on nonfunctional requirements such as mean time between essential function failures (MTBEFF), fleet size, availability, and program affordability. The present work extends these models to explicitly consider improvement of the reliability engineering process itself. This approach removes the assumption that the parameters of the reliability improvement equations for the subsystems are constant. Instead, our generalized formulation allows a portion of a budget to be allocated to improve these parameters, which represent factors such as the effectiveness of attempts to fix defects. The remaining budget can then be divided among reliability improvement and fleet acquisition. We illustrate the approach through a series of examples in the context of rotorcraft. Our results indicate that this more general optimization framework could lead to additional savings that further promote affordability and other critical nonfunctional requirements related to reliability, availability, and maintainability (RAM).