This research project investigated and identified under which conditions the assumption is valid that any internal failure of the COTS component can be identified when evaluating the output of the component. Therefore the objective of the study was to provide the Agency with sufficient data and analysis on the subject of COTS Airborne Electronic Hardware components fault symptoms and related generic detection means in safety-critical airborne systems. These systems would be of Development Assurance Levels (DAL) A in compliance with CS 25.1309(a) and (b), ED-79A / ARP4574A, ED-80 / DO-254 and EASA Certification Memoranda (EASA CM-SWCEH–001 issue 01 Rev 01) for Airborne Electronic Hardware (AEH). The scope of the study covers all kinds of complex and highly complex digital electronic hardware COTS components used in airborne safety critical applications