Organizing maintenance tasks is a specific and important field of project and production management. Well-planned, properly scheduled, and effectively communicated maintenance tasks result in the accomplishment of more work that is performed more efficiently at a lower cost. In maintenance and production management, agile and lean approaches are becoming more frequently used, where preventive/predictive maintenance (PPM) requires flexible project plans to decide which system components (or equipment) should be maintained to achieve the target system reliability. Maintenance projects have been treated as fixed sequences of corrective/preventive tasks, while the agile/lean approach allows for and usually requires prioritizing tasks and reorganizing the project structure. The fixed structure of maintenance projects and traditional maintenance project scheduling algorithms are not considered representative of these agile properties. The paper models the preventive resource-constrained maintenance project scheduling problem and aims at optimizing its maintainability. A matrix-based algorithm is proposed to apply to both system and project structures that include both traditional and agile/lean project management approaches. Keywords: Maintenance management, Project management, Scheduling, Agile/lean approach, Flexibility