Common Cause Analysis
CCASection 06: System Safety & Functional Safety
Definition
A set of safety analysis methods that evaluate the susceptibility of a system to events or conditions that could simultaneously affect multiple items or functions, defeating architectural features such as redundancy and independence. CCA encompasses three complementary analyses: (1) Zonal Safety Analysis (ZSA) — evaluates physical proximity and installation-related common causes; (2) Particular Risk Analysis (PRA) — evaluates external hazards such as fire, bird strike, tire burst, uncontained engine rotor failure, and lightning; (3) Common Mode Analysis (CMA) — evaluates systematic common causes such as common hardware, common software, common requirements errors, common manufacturing processes, and common maintenance errors.
Where This Shows Up
Common cause analysis is critical because redundancy is ineffective against common causes. If two redundant channels can both fail from the same cause (e.g., both routed through the same zone where a fire could damage both, or both running the same software that contains a bug), the redundancy provides no protection against that cause. CCA ensures that the architectural assumptions made in FTA — particularly the assumption of independence between parallel elements — are valid.
Primary Sources
Addresses common cause analysis as a required element of the 25.1309 compliance demonstration.
Related Terms
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