A study of the application of the lognormal and gamma distributions to corrective maintenance repair time data

Abstract

The usual mathematical formulation of availability assumes an exponential distribution for failure and repair times. While this is sometimes correct for reliability, it is not likely to be for maintainability. This study was conducted to verify that the lognormal and gamma distributions are suitable descriptors for corrective maintenance repair times, and to estimate the difference caused in assuming an exponential distribution for availability and maintainability calculations when in fact the distribution is lognormal. Forty-six sets of data of electronic and mechanical systems and equipments were analyzed using the methods of probability plotting and statistical testing for distributional assumptions.