This study introduces the system dynamics model that simulate total operational availability when 10 equipments made of 3 major components are serviced under the constrains of the maintenance capacity level and the number of spare parts. This simulation is designed on the base of reliability engineering concept so failures of components happens with the rule of engineering factors like the mean time between failure(MTBF) of component and the next failure time of one component is effected by the conditions of other components. We analysed availability of 10 equipments under 121 constrains and executed multiple regression analysis with the simulation result. The analysis provide the managerial insight in the service fields with operation many equipments.