Lower Confidence Limits for Availability Assuming Lognormally Distributed Repair Times

Exact lower confidence limits are established for the availability ratio A where A = ¿y/(¿y + ¿x) and ¿y is the mean time between failures and ¿x is the mean time to repair. It is assumed that the time between failures has an exponential distribution while the time to repair is log-normally distributed, with known variance. A test of the hypothesis A = Ao is also developed and power curves are included. Some results on the comparison of confidence intervals when the time to repair is assumed to be exponentially distributed are given.