The product life cycle of a technical system is often longer in practice than the availability of spare parts. Every day, manufacturers worldwide are discontinuing products, so their end of life is announced. This affects not only the systems manufacturer but largely the operator of the plant. The machine down risk for a defective component within the system increases. While it was common practice a few years ago to stock critical components, it was soon removed in respect of warehouse costs and the tied-up capital and replaced by just-in-time inventory availability by the manufactures or distributors.

 I would like to take you on an excursion into the world of numbers and statistics. Statistically, German companies spend 6 -10% of their gross fixed assets on annual maintenance. This currently amounts to about 250 billion in the Federal Republic of Germany [1] Euro annually. If we take the indirect costs of machine failures, delivery shortfalls, quality problems and short-term replacement investments into account, we talk about a value of 750 billion euros per year.