The Exponential Repair Assumption: Practical Impacts

For repairable systems, we assessed the impact of assuming that the repair follows an exponential distribution versus a lognormal distribution for systems with various ratios of MTBF to MRT and various levels of redundancy. Real repair times, as a rule, generally curve fit to the lognormal distribution. We analyzed the system reliability parameters of R(t), Ao, and MTBDE. We found that reliability was sensitive to low values of the ratio MTBF to MRT, and to moderate and low redundancies. In all cases that displayed a statistically significant difference, the exponential repair assumption inflated system reliability