Abstract: The present invention discloses an optimization method for minimizing costs of transportation task assignment and maintenance scheduling under constraints of defined target tasks which are to be carried out by different types of transportation devices, each having different capabilities and maintenance requirements. The optimization method is based on an objective formula defined according penalty or costs of calculated deviations from target tasks. The objective formula is activated under constrains rules, which relate to transportation device competence, maintenance requirements, scheduling constrains and target task requirements. The optimization process yields an output list of assignment and scheduling timetables of targeted tasks and maintenance plan for each airplane.