Through this series of articles, we have gone over all of the components that are necessary to perform a full risk assessment to maximize aircraft wire life extension. These individual components have covered processes involving wire condition assessment, physical routing, failure severity, and the electrical system data components. In this article, we will examine what a comprehensive risk assessment entails.
The first item in the comprehensive risk assessment process is the Risk Hazard Matrix (RHM). The RHM is the first mechanism used for quantifying the risk for the aircraft harnesses. As can be seen in the figure below, the RHM combines the failure probability (as identified by maintenance data and wire degradation assessments) with the failure severity for each harnesses.
By combining the data sets into the RHM, it becomes more apparent which harnesses pose the greatest risk to an aircraft’s airworthiness. In the failure probability rankings, the wire degradation is combined with the environmental conditions to project the relative probability of failure for each harness. What this means is that if all of the wires are in good condition, then the RHM value will not show an overly conservative ranking of the failure probability (as is often the case where the results are scaled to show an even distribution).
If you are interested in wire life extension, you may want to read the other Lectromec articles on this issue (When Should you Consider Adopting a Wire Life Extension Program?) from this series.
An example of an RHM harness evaluation can be seen in the figure below. As each harness is ranked based on the values indicating the loss and severity of failure, a determination can be made as to which harnesses need replacement and/or additional care, or are in good condition and may not require additional actions.
But the RHM alone may not provide sufficient information to make a forecast on fleet reliability. What is also necessary is to understand how the failure probability evolves over time (unless the vehicle is changed, the severity of failure will not change). To address that need, Lectromec developed the Risk Hazard Evolution Assessment (RHEA).
This is a unique assessment available from Lectromec based on extensive research on the wire insulation degradation. The RHEA utilizes the data gathered from the wire degradation assessment and applies it to the wire degradation models. These models, based on years of testing, are used to identify how the EWIS risk evolves over time with the changing failure probability.
This leads to a clear identification of which harnesses need to be replaced, thereby avoiding the high upfront costs of replacing all harnesses. The harnesses can be replaced at the end of a maintenance cycle before the risk to airworthiness becomes too high.