Managing Risk Reduction using a Relative Risk Prioritization Tool

The Safety Management System (SMS) provides an environment where undesired events (proactively or reactively identified) are evaluated for the effect on safety using Risk Analysis. When the risk is evaluated, an interim risk reduction (mitigating action) may be applied to reduce the risk to a level that allows operations for a longer period before the safety issue is fully resolved. The risk assessment provides a means of evaluating the risk level and it may be difficult to quantify the “benefit” of interim mitigations that will reduce the risk. Prioritization of issues in the same risk category of the Risk Matrix is often simplified to a schedule and logistics basis of the final corrective action and often does not adequately show the benefit of the interim mitigating actions taken. Employing a concept used in System Reliability Analysis, the Design / Process Failure Modes and Effects Analysis (Design FMEA as defined in SAE J1739) uses a Risk Priority Number as a tool to identify the most significant failure modes that need to be evaluated in order to determine if redesign can mitigate the risk to a lower level. This paper will develop this concept in conjunction with an Aircraft / System Functional Hazard Assessment and acceptable level of risk (certification levels) to formulate a Risk Priority Number as a tool to rank the risks while taking into account the effectiveness of mitigating actions. A means to baseline the product acceptable level of risk / safety is also proposed in order to determine the relative risk increase from the as certified risk level.