Production systems are becoming increasingly complex, for example due to digitalization, new technical possibilities and smaller batch sizes. This means that the main task of industrial maintenance, ensuring technical availability of a production system, is also becoming increasingly difficult. The previous focus of maintenance efforts on individual machines and plants must give way to a holistic view encompassing the whole production system in order to meet the requirements of interlinked production. Against this background, the technical availability of a production system must be redefined. Different definition approaches range from focusing on the respective availability of individual machines and adding them to an overall key figure without attention to their context in the production system to only focusing on the output quantity of the production system. The incompatibility of these definitional approaches can be well illustrated by contrasting extreme types of production systems such as a full concatenation without intermediate buffers or systems with very large buffers between two consecutive machines. The aim of this publication is to present definition approaches of the technical availability of production systems and to demonstrate the effects of random machine failures on the key figure. The demonstration is based on discrete event simulations of production systems with different levels of complexity to show how each definition approach reacts to different complexity levels. Based on the simulation results, a recommendation is developed as to which definition approach of technical availability of production systems should be employed depending on the individual focus and complexity.