System Testing in the Avionics Domain

Traditionally, avionics systems consisted of several independent or loosely coupled special-topurpose controllers which were each developed by the respective system supplier. To deal with the more demanding requirements and additional feature requests for new aircrafts, current avionics systems are based on the framework of integrated modular electronics which allows to use commercial-of-the-shelf products for less critical functions and uses integrated modular avionics (IMA) technology for safety-critical avionics functions. This integrated avionics architecture is modular, open and highly-flexible. It is based on common standardized platforms (the IMA modules) and standardized aircraft networking technology. For the avionics systems, this means that most special-to-purpose controllers are replaced by shared IMA platforms which are developed independently of the respective systems. Since this evolution affects the entire development, new processes and means for the development and the verification and validation of avionics systems are required. This thesis addresses this evolution from two angles: Firstly, a systems engineering part introduces the general processes and approaches to be considered when developing and testing avionics systems and describes how the technology and the development processes have evolved, particularly with respect to system testing in avionics. Secondly, two case studies detail the described general testing activities during system integration for two newly identified testing areas. In the systems engineering part, this thesis describes how avionics systems are currently developed and discusses the effects of evolving towards integrated modular avionics. To provide an encompassing reflection of system testing in avionics and deliver the conceptual foundation for the case studies, both are addressed from a “system point of view” and a “process point of view”. For the former, this thesis assembles the knowledge about avionics systems with respect to architecture models, redundancy concepts, used platform types, and common aircraft networking technologies and describes how these have evolved. The focus is on IMA-based systems and the specific characteristics of IMA platforms. For the latter, this thesis introduces the development and testing activities from aircraft level to equipment level and elaborates on the differences arising from the chosen avionics architecture model and the used platform types. For IMA-based systems, it reveals two new testing areas which are both independent of specific avionics systems: Testing of single IMA platforms and testing the communication flow in a network of IMA platforms. One possible approach for each of these two testing areas is addressed by case studies in the second part of this thesis. The first case study describes a test suite for automated testing of bare IMA platforms which allows to verify the behavioral compliance with the ARINC 653 specification and with the configurability of the IMAmodule’s operating system, independently of a specific module configuration or the behavior of specific system applications. In particular, this thesis elaborates on the test suite’s approach of providing generic test specification templates which can be instantiated for many different module configurations and discusses the further implementation details. The implementation experience and the final assessment confirm that the approach is well suited for automated hardware-in-the-loop testing of bare IMA platforms and contributes to a significantly higher test coverage (compared to manual testing within the same execution time) – also for each round of regression testing. The second case study presents an approach for testing the communication flow in a network of configured IMA platforms in order to verify that all interactions allowed by the IMA platform specification and the respective combination of IMA platform configurations are possible. The thesis elaborates on an algorithm for test data generation and investigates means for prioritizing those test cases to limit the test execution time. The final assessment of the approach confirms the necessity of an automatable test case generation algorithm but also shows that more effective priorization functions are essential for realistic, i.e., very complex, networks of IMA platforms.