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System Safety Assessment
Reliability Engineering
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Quoting from ARP4761: "Independence between functions, systems or items may be required to satisfy the safety requirements. Therefore, it is necessary to ensure that such independence exists, or that the risk associated with dependence is deemed acceptable. Common Cause Analysis (CCA) provides the tools to verify this independence, or to identify specific dependencies. In particular the CCA identifies individual failure modes or external events which can lead to a catastrophic or hazardous/severe-major failure condition. Such common cause events must be precluded for catastrophic failure conditions and must be within the assigned probability budget for hazardous/severe-major failure conditions". |
 For example, the circuit comprised of L27, C27, U1 and U2 must be independent from that of L32, C32, U3 and U4 to validate the AND condition shown above. CMAs are performed for each unique AND condition (i.e. AND gate) contained in all CATastrophic fault trees (FTA). |
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