Decision support on the three levels of maintenance planning

To simplify the planning process, planning in maintenance management is typically divided into three levels: strategic, tactical and operational. The three planning levels are closely interrelated. On the one hand, strategic planning provides the strategies that form the framework for tactical planning, and the scheduling of the tactical level is an input for operational planning. On the other hand, the operational implementation of the plans in turn provides information for the first two planning levels that should be considered in the future. In addition, it is necessary to be able to react dynamically to unexpected and unforeseen failures or changes during the execution of the plans.

At this level, long-term effects of strategies and technologies are analyzed. A maintenance strategy is required that takes into account the achievement of long-term goals and compliance with defined parameters (RAMS and LCC), as well as risk classes (criticality). The result is strategies and specifications that form the framework for the two lower planning levels.

Typical decisions of the strategic planning level:

• Subdivision and grouping of components by categories.
• Selection of maintenance strategies for different component categories
• Selecting the best technology for renewals
• Determination of control parameters
• Setting thresholds and maintenance intervals

The tactical level of maintenance planning covers a medium-term time horizon. Based on the strategies and specifications of strategic planning, complex maintenance activities are initially planned, which require a long lead time. To determine the time windows for the maintenance activities, knowledge of the planned utilization of the system is necessary (for example, in rail networks the timetables, in road networks traffic flows and in production systems production planning). The disruptions to the system caused by maintenance should be minimized. The result is a mid-term rough schedule and resource planning, which form the basis for operational planning. These schedules also help to make the necessary resources and time windows available.

Typical tactical planning level decisions:

• Analysis of the necessary scope of maintenance work for the components (modernization/renewal) and rough time classification
• Determination of the required long time windows for maintenance on specific sections of the infrastructure (determination of possible detours)
• Estimation of the costs incurred and resources required

Required maintenance activities are planned according to their priority, taking into account the availability of the required maintenance teams, materials and machines. Operational planning is a dynamic process. It is necessary to react quickly to unexpected situations, such as when maintenance takes more time than planned or when crews, machines, or materials are down or unavailable. Robust optimization methods are used to reduce the impact of such disruptions.

Operational planning of maintenance activities often involves decisions about:

• Specific timing of maintenance activities, taking into account the utilization of the system.
• Scheduling of team and machines
• Work equipment planning (availability of material)

The last step is the operational implementation of the maintenance plans. On the one hand, this generates new information for dynamic operational planning, and on the other hand, feedback can be given to the two higher planning levels. At the strategic level, for example, measurements of the asset condition as well as the costs of the performed maintenance tasks should be used to adjust the control parameters in order to verify whether the strategies are working as anticipated. At the tactical level, the information of the implementation phase can be used, for example, to better evaluate the impact of maintenance activities on the condition of the system.