CAPA: Investigating the Root Causes of Process Failure


September 22, 2015

Layered Process Audit Questions

In a routine audit one of your auditors discovers that during a recent production shift a seasoned employee used fastener B, despite a work instruction for the process that calls for the use of fastener C. A typical investigation of this type of nonconformance would likely note operator error as the cause.

While concluding that this was a case of operator error is an accurate description of what happened and how it happened, if you accept this conclusion you probably haven’t probed deeply enough to understand the root cause. According to the American Society for Quality (ASQ), a root cause is “a factor that caused a nonconformance and should be permanently eliminated through process improvement.”

Getting to the Root of the Issue

Uncovering the reasons why a nonconformance occurred is essential for developing effective recommendations for improvement. Generally, mistakes don’t just happen but instead can be traced back to some well-defined causes. In this case, you don’t really know what corrective actions are necessary to prevent this error from happening again and potentially affecting product quality. You might ask, “Was the procedure confusing? Were the fasteners clearly labeled? Was the operator familiar with this particular task?”

The answers to these and other questions will help determine why the error took place and what you can do to prevent a reoccurrence. In the case of the fastener error, potential recommendations might include revising the procedure or performing procedure validation to ensure references to fasteners match the fastener labels found in the field.

You may find it useful to incorporate Lean tools such as the 5 Whys approach, which, as the name implies, involves the repeated use of “Why” questions in your investigation. By asking “why” at least five times, you can drill down more easily to the root of the nonconformance. This tool is also useful for discovering relationships between various root causes of a single nonconformance, and it is a simple, easy-to-use method that does not involve statistical analysis.

Scenarios such as the fastener example demonstrate that a robust corrective and preventive action (CAPA) program is a key element in creating a culture of continuous improvement. When you are able to utilize your CAPA system to identify root causes, you are able pinpoint opportunities for improvement and thus prevent problems before they affect production and your bottom line.

If your auditors uncover a nonconformance, here are some tips to keep in mind when searching for the root causes to the issue:

  • Root causes are underlying causes. Your goal should be to identify specific underlying causes. The more specific you can be about why an event occurred, the easier it will be to arrive at recommendations that will prevent reoccurrence.
  • They are issues over which management has control. You should avoid using general cause classifications such as operator error, equipment failure, or external factor because such causes are not specific enough to make effective changes. You should know exactly why a failure occurred before action can be taken to prevent reoccurrence.
  • You can identify root causes within a reasonable timeframe and cost. It is not practical to keep valuable manpower occupied indefinitely searching for root causes.
  • If identified correctly, you should be able to generate effective corrective actions. Recommendations should directly address the root causes identified during the investigation. If you generate vague recommendations such as, “improve adherence to written policies and procedures,” then you likely haven’t found a basic and specific enough cause and need to conduct further analysis of the nonconformance.

Root Cause Analysis

One of the most effective ways to determine root causes is through root cause analysis (RCA), a process for investigating and categorizing the root causes of events with safety, health, environmental, quality, reliability, or production impacts. Using a structured RCA approach as part of your CAPA protocol allows you to maximize the human and financial resources that are devoted to the investigation.

RCA is typically a four-step process involving the following activities:

  1. Collecting data: Gather all of the pertinent information surrounding the nonconformance.
  2. Charting causal factors:  Select the appropriate quality tool or tools to determine causal factors. Popular and easy-to-use tools include fishbone diagrams, Pareto charts, and scatter diagrams, to name a few. Define your causes as direct, contributing, or as root causes.
  3. Identifying the root cause(s): Once you correctly determine why an event or failure occurred, then you can focus your CAPA efforts on creating specific and effective corrective actions.
  4. Generating and implementing solutions: Develop a specific corrective action plan to address the root cause and fix the nonconformance.

What tips can you share for strengthening your CAPA system by correctly uncovering the root causes in your nonconformances?