## 2 Basis for Planning the Logistical Support of the Operation Process  
The intensity of the spare parts supply stream should fully satisfy the user's demand for consumable materials while maintaining a safe quantity as a fixed stock as a safety buffer (non-rotating stock). An example of a needs planning methodology in a manufacturing company is presented in work [20] and mainly focuses on the issue of scheduling supplies necessary for the production process. While planning the replenishment of material or technical resources, consideration should be given to, among other things [14; 20; 21]:  
* the type and number of technical facilities;
* the standards and limits of consumption, e.g., oil, lubricants, and fuel;
* the intensity of using the technical facilities;
* current stock levels;
* experience from previous operations;
* planned additional maintenance, modifications, and upgrades. In the case of aviation, the planning of material and technical needs, e.g., spare parts and consumables, is carried out for each calendar year. The accurate planning of purchases makes it possible to avoid aircraft downtime associated with the search for parts at take-off. In planning purchases, four phases can be distinguished in establishing a complete list of needs:  
Phase I--based on the planned number of flight hours per aircraft type in the planned calendar year, an \"Airframe Plan\" is prepared, in which the expected intensity of aircraft utilization is entered and broken down into individual quarters and months, as well as a \"Schedule of Periodic Maintenance and Engine Replacements\" [22], in which all types of maintenance resulting from the \"Air flight plan\", as well as from the time intervals (calendar) independent of the completed air flight. Based on information regarding the number and type of individual maintenance operations, it is possible to analyze the range of individual maintenance and the necessary consumables needed for each type of maintenance. A list of technical and material supplies (broken down by P/N--part number identification), e.g., washers, gaskets, pins, filters, etc., for a particular service can be called a logistics or maintenance package, which represents the minimum necessary list of materials to be consumed during a particular service. Depending on the level of service and its scope, the logistics packages will have a differentiated list of assortments. In this stage of planning activities, the total number of assortments defined is determined by multiplying the number of services by the service packages [23]. The result of this procedure gives us the total number of consumables required to secure the assumed list of planned maintenance [23]. The next step (Phase II) in logistical planning is the analysis of components with a limited calendar or technical life (LLP--life-limited parts), and there is an obligation to replace them within the planning period. The list of such components is another set to the comprehensive set of needs in the logistics planning process. The next phase (Phase III) is the identification of technical bulletins (SB--service bulletins), which must or can be performed by the forces of the own maintenance organization, e.g., modifications to aircraft equipment. The list of material and technical provisions for these activities is another set in determining the comprehensive logistics need. In determining this list, a methodology identical to Phase I is used. All the activities described above (Phase I, II, and III) are activities resulting from the planning. Determining the material and technical provision is not a major problem, but it consumes a significant part of the man-hours of those involved in the planning process. In the operational process, the so-called unplanned failures and breakdowns are very common and cannot be predicted. At the Phase IV stage of planning, it is necessary to analyze the service life, identify the most frequent faults, determine their causes, and estimate the needs arising from the service life.