412-420This study presents a comparison of two models to find optimum maintenance policy of complex degraded systems. UsingMarkov processes, optimal value of mean time to preventive maintenance is determined by maximizing availability of completesystems. Models include a stochastic degradation process, random failures and a set of maintenance actions and their effects. A reallife case study is presented to illustrate implementation of models. A two-component transportation system for collecting wasteutilized by Public utility company, Mediana Niš, Serbia, is analyzed