Reliability Calculation for Dormant k-out-of-n Systems with Periodic Maintenance

James Li
James Li is a Lead RAMS Engineer in Bombardier Transportation, AME Division, Kingston, Ontario, Canada. He has more than twenty years of experience in Mass Transit Industry including RAMS Engineering, Mass Transit Vehicle Engineering and Project Management. His interests are in the fields of Reliability Calculations, FMECA, FTA and Electric Circuit Reliability and Safety Analysis. His experience more


This presentation introduces a reliability calculation methodology for a dormant k-out-of-n redundant system. In reliability engineering, dormant failure is a failure that cannot be detected when it occurs because of the nature of the failure characteristic. Therefore, a dormant failure becomes the blind point to the design for reliability, maintainability, and safety because of its inability to be detected. One of the common approaches in detecting a dormant failure is to carry out a scheduled periodic inspection, test and maintenance. The applied scheduled maintenance could prevent an unexpected dormant failure that could lead to an unsafe condition, or costly corrective maintenance. In this presentation, a methodology is introduced on how to calculate the effective Mean Time Between Failure (MTBF) for a dormant k-out-of-n redundant system. The study also includes the examination of mathematical relationships between the effective MTBF of a dormant k-out of-n redundant system and the inspection or maintenance interval. This could help determine the inspection or maintenance interval for a dormant k-out-of-n redundant system to prevent the system from entering a dangerous failure state. Case studies are also employed to illustrate the application of this methodology in the reliability and safety design in the development of the Bombardier Innovia monorail train.


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