Reliability analysis of phased-mission systems: A correct approach

At the 2006 RAMS Conference, a paper entitled Reliability Analysis of Phased-Mission Systems: A Practical Approach [1] was presented. This paper established an alleged novel and simple approach to reliability analysis of phased-mission systems. The technique presented in that paper transformed a phased-mission system into several nonphased systems, thus allowing for each phase to be analyzed independently. The paper then presented a method for combining the individual results into a composite solution that spanned all the phases of the system in question. Unfortunately, we discovered that the paper contained grave errors in its methodology, leading the authors to draw inaccurate conclusions. The paper determined a reliability time function for each phased topology, which were then combined into a so-called exact solution. This approach did not take into account the critical question of what happened to the system in the previous phases. Our paper will demonstrate a mathematically accurate solution for the main example of the previously presented paper in addition to a simulation solution to verify our own methodology. Moreover, our paper presents a solution for the examples shown in the previous paper that are mathematically intractable. In summary, the ultimate objective of this paper is to correct the errant phase-dmission methodology presented at the last RAMS Conference.