Taming the Complexity Beast

Increasing system complexity poses a threat to the continued safety of manned and unmanned aircraft in the NAS. Testing alone cannot establish strict bounds on all the behaviors that may occur during operation of these software-intensive systems. New approaches to verification based on logic and mathematical analysis are needed to tame the "complexity beast" and support continued innovation in aircraft systems. This article will briefly describe sources of complexity in modern aircraft software and the limitations of test-based verification methods. The role of software testing in the certification standards for civil aircraft will be described next, as well as how this domain is beginning to embrace new verification approaches based on formal methods. The article concludes with several examples of formal methods that have been used to verify complex software.