ABSTRACT
The main objective of the paper was to initiate a discussion on the accuracy of the calculation of the MTTF, MTTR and other measures of reliability and maintainability because they are the basis for a large number of decisions made during the life cycle of an engineering system. The accurate analytical way for calculating the expected (mean) value of the probability distribution of the random variable which represents the complex event has been developed and demonstrated through several numerical examples related to engineering systems which consist of several subsystems, modules, units and components connected in series, from the point of view of reliability.
