A Root Cause(s) may be below the first level cause. For example, consider the illustration:
For failure modes whose effects have a severity rating of 9 or 10, identify the Root Cause(s) of the failure mode. Root Causes are sometimes below the first level cause, and there may be more than one lower level root cause. Techniques such as TOPS (8D), Cause and Effect Diagram, or Fault Tree Analysis (FTA) can be used to help determine Root Causes.
Design Deficiency Equipment Process Variation
Switch rocker cracked Inadequate or no lubrication