Maintenance planning: Reflections, lessons learned and a novel categorization

Maintenance planning remains a persistent and multifaceted challenge, despite decades of research and industrial advancement. The difficulty spans various scales, from individual components like bearings and relief valves to large machinery such as compressors and boilers, and complex systems including aircraft fleets and power plants. These challenges are intensified by diverse factors such as lifecycle variability, aging assets, fluctuating operational loads, heterogeneous failure mechanisms, and the criticality of component functions. This paper provides a structured approach to tackling these complexities through three key contributions: (1) the introduction of a novel eight-level categorization of maintenance planning eras, contextualize the historical and technological evolution in this field from basic corrective maintenance (CM) to advanced physics-based maintenance (PBM) and provides a strong foundation for both academic analysis and practical application; (2) the formulation of twenty-eight actionable guidelines, clustered into four thematic categories (failure, data, method, and cost) based on decades of industrial experience, case-based learning, and literature synthesis; and (3) a real-world case study involving a six-bearing system is presented to demonstrate the non-universality of optimal maintenance strategies, highlighting how they vary across different eras in order to validate the practical utility of the proposed framework. It not only offers a generalized foundation for maintenance planning under varying operational contexts but also serves as a decision-support tool for industry practitioners aiming to align strategy with system maturity. This research bridges theoretical constructs and field-level execution, offering valuable insights for both academia and industry.