Common Mode Analysis vulnerabilities

Step 2 analyse each Common Mode Analysis vulnerability to IdentifyArerify independence criteria... 

Step 1b identify common mode vulnerabilities via the Common Mode Analysis checklist... 

The FTA is the most commonly nsed technique for causal analysis in risk and reliability studies (Nighot, 2003). It should be undertaken as soon as engineers start defining system architecture as it provides the mechanism for them to evaluate the integrity of that architecture. As illustrated in Fig. 4.1, it should be a live document reflecting the evolving system architecture at all times, with an emphasis on ensuring that no common mode vulnerabilities are introduced or missed. 

A preliminary system safety assessment (PSSA) is essential in order to determine (and agree) the depth of assessment needed, the criteria utilised and the manner in which the safety objectives are to be accomplished. The PSSA concentrates on the functions and vulnerabiUties of the system instead of the detailed analysis, and can thus be conducted prior to the definition of the system s architecture. The PSSA remains a live document until the final SSA can be issued. By the preliminary design review (PDR), the PSSA should include functional failure consequences to the aircraft and its occupants consequences of other possible malfunctions of a system (e.g. overheating) and their effects on surrounding systems consequences to the system of failure in other systems or parts of the aircraft, identification of any possible common-mode failures or cascade failures which my need detailed investigation the identification of possible vulnerabilities to flight crew or maintenance error. 

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