A Methodology for the Quantitative Assessment of the Aircraft Systems Accessibility

A reduction of the maintenance effort of commercial aircrafts caused by changes in the sys- tem architecture results in the opportunity to decrease the direct operating costs. At the Institute of Aerospace Systems, the integration of maintenance aspects into the preliminary aircraft design is being researched within the framework of the AGILE 4.0 project. Thereby, the accessibility of on-board systems and their components significantly influences the maintainability of commercial aircrafts.

In this thesis, a methodology to quantitatively evaluate the accessibility of aircraft systems is developed. With the self-developed methodology 14 different system properties that influence maintainability are evaluated on a detailed scoring scale, in order to allow gradation between the lowest and highest score. Additionally, there exists the option to use weighting factors to allow different properties or components to have a higher influence on the overall result. To validate the developed methodology, the established maintainability prediction methodology Procedure III, which is published in Handbook 472 of the US military, is also implemented. Both methodologies are applied to a reference system, which corresponds to a part of the hydraulic system of a Boeing 777.

The results of this work show that the self-developed methodology provides a more accurate assessment of the maintainability. In addition, it also takes into account the trade-off between opposing system properties. One example is the restricted installation space, which is in con- flict with an increased space between components. Further, the system layout of the reference system is optimized with regard to the maintainability prediction of both methodologies. Here, the advantages of the self-developed methodology also become clear, since a greater improvement in accessibility is achieved, compared to an optimization regarding Procedure III. The weighting factors implemented in the self-developed methodology also allow to target the improvement of certain system properties. Similarly, the component-based weighting can be used to specifically optimize the maintainability of components with higher failure rates.