Special Cause Variations
Special cause variation, also known as assignable cause variation, refers to the variation in a process or system that can be attributed to specific, identifiable factors or events that are not part of the inherent, normal variability of the process. In other words, special cause variation represents deviations from the expected or standard performance of a process that can be traced back to specific, often unusual, and non-random factors.
Key characteristics of special cause variation include:
Identifiability: Special causes are specific and identifiable. You can pinpoint the exact reason or event that caused the variation in the process.
Unpredictability: Special cause variation is typically unpredictable and sporadic. It is not part of the regular pattern of variation that a process exhibits.
Infrequent Occurrence: Special causes occur infrequently and are often considered exceptions or anomalies in the process.
Isolation: When special cause variation is detected, the goal is to identify and isolate the cause, so it can be addressed and eliminated to improve process stability and consistency.
To better understand special cause variation, it is often contrasted with common cause variation, which represents the inherent variability in a process that is typically present even when the process is operating under stable conditions. Common cause variation is a result of the natural variation within a process and is expected to occur over time.
In various fields such as quality control, manufacturing, and process improvement, distinguishing between special cause and common cause variation is essential for effectively managing and improving processes. Statistical tools and process control techniques, such as control charts, are often used to detect and address special cause variation and maintain process stability and consistency.
A root cause analysis is required after a special cause variation interrupts or deviate a process. Root cause analysis (RCA) is a systematic process used to identify the underlying or fundamental causes of an issue, problem, or incident. It is a valuable problem-solving technique employed in various fields, including engineering, healthcare, manufacturing, and business, to understand why something went wrong and to develop effective solutions to prevent it from happening again. RCA typically involves the following steps:
Clearly articulate the special cause variation to investigate. This step is crucial because it sets the scope and boundaries for the analysis. It was a special cause variation which lead to an issue, and this cause must be specific and clearly defined in the written text of the background for the root cause analysis.
Collect data and information related to the problem. This can include incident reports, documentation, interviews with involved parties, and any relevant records.
Determine the immediate or proximate causes of the problem. These are the events or factors that directly led to the issue.
Dig deeper to find the root or underlying causes of the problem. These are the systemic or foundational factors that allowed the immediate causes to occur. Common tools used for this step include the "5 Whys" technique, fault tree analysis, fishbone diagrams (Ishikawa diagrams), or process flowcharts.
Not all root causes are of equal importance. Prioritize them based on their impact, frequency, and the feasibility of addressing them. This helps in focusing resources on the most critical issues.
Once you have identified the root causes, devise corrective actions or solutions to address them. These actions should be specific, actionable, and targeted at preventing the recurrence of the problem.
Implement the corrective actions and continuously monitor their effectiveness. Verify that the problem has been resolved and that there are no unintended consequences.
Root cause analysis is a proactive approach to problem-solving that aims to address the source of issues rather than just treating symptoms. It helps SMS enterprises improve their processes, enhance product and service quality, and is designed to prevent costly and potentially dangerous incidents from happening again.
After root cause analysis and the corrective action is implemented, new special cause variations may adapt to processes, and deviate from expected outcome. Special cause variations are independently adaptable to the process. A corrective action plan is designed to correct a known special cause variation, but a new special cause variation will sooner or later integrate itself in a process, interrupt the process, and cause a different outcome. The new process output may be advantageous to the outcome or destructive to the outcome. A special cause variation is neutral without preferences to the outcome.
A corrective action plan (CAP) follow-up is a crucial step in the process of addressing and rectifying issues or problems within an SMS enterprise. It involves monitoring and evaluating the progress of the corrective actions that were implemented in response to identified problems or deficiencies. The purpose of the follow-up is monitoring to assess if actions taken are effective in resolving the issues, that the special cause variation was eliminated, and to analyse if new special cause variations, or drift, are introduced to the process. A CAP implemented does not prevent future special cause variations to be introduced. Here are the key steps involved in a corrective action plan follow-up.
Review the Corrective Action Plan: Begin by revisiting the original corrective action plan to understand the specific actions that were proposed and agreed upon. This should include a clear description of the problem, the root causes, and the steps to address them.
Establish a Follow-Up Schedule: Determine a follow-up schedule that outlines when and how often progress will be assessed. The frequency of follow-ups may vary depending on the nature and urgency of the problem but typically includes regular check-ins.
Assign Responsibility: Clearly define who is responsible for monitoring and overseeing the corrective actions. Assign roles and responsibilities to ensure accountability. This may involve team members, managers, or specialized individuals depending on the complexity of the issue.
Data Collection and Analysis: Gather relevant data and information to assess progress. This may involve collecting metrics, conducting surveys, reviewing incident reports, or other forms of data collection that are pertinent to the issue at hand.
Evaluate Progress: Compare the actual progress made against the objectives and goals outlined in the corrective action plan. Determine if the actions taken have had the desired impact and are effectively addressing the root causes of the problem.
Adjustments and Revisions: If progress is not as expected or if new special cause variations arise, be prepared to make adjustments to the corrective action plan. This may involve revising the plan, changing strategies, or allocating additional resources.
Communication: Keep all relevant stakeholders informed about the progress of the corrective action plan. Effective communication is crucial to ensure everyone involved is aware of the status and any changes that may occur.
Documentation: Maintain detailed records of the follow-up process, including meeting minutes, data collected, and any changes made to the plan. Documentation is essential for transparency and accountability.
Closure: Once the corrective actions have successfully addressed the special cause variation, and it is unlikely to recur, formally close the corrective action plan. This involves obtaining final approvals and ensuring that the issue is resolved to compliance with the SMS policy and expected outcomes.
Continuous Improvement: Use the insights gained from the corrective action process to improve organizational processes and prevent the same issue from occurring in the future. Encourage a just culture of continuous improvement. The difference between continuous and continual improvements is that continuous improvement is the change, or repair to current process for the purpose of maintaining a known process, while continual improvement is to abandon the current process an implement a new process. Example of a continuous improvement process is to change from verbal format recording to written format reporting. Example of a continual improvement process is to change from paper format process to a web-based electronic format such as SiteDocs. (www.sitedocs.com – offroadpilots@gmail.com)
Special cause variation occurs in processes due to specific, identifiable factors or events that are not part of the inherent, normal variability of the process. These factors or events can be categorized into various reasons.
External Factors: Special causes can be introduced by external influences that are beyond the control of the process. For example, changes in environmental conditions, equipment malfunction, power supplies, external supplier issues, human factors, organizational factors, supervision factors and environmental factors can lead to special cause variation.
Human Errors: Mistakes made by individuals involved in the process can introduce special cause variation. This includes errors in data entry, measurement, or operation of machinery.
NOTE: Human error is a sub-category of Human Factors, which are integrated, or built into a system for a desired process output. Human errors may not necessarily cause an accident, it could also improve a process reliability.
Process Changes: Any deliberate or unintentional changes made to the process can introduce special cause variation. This includes adjustments to process parameters, changes in raw materials, or modifications to equipment. A complete system analysis for planned process changes is needed, while unintentional process changes are drift, or introduction of other acceptable work practices.
Equipment Failures: Mechanical or technical failures of equipment used in the process can lead to special cause variation. For example, a machine breakdown or a sensor malfunction can disrupt the process.
Outliers: Occasionally, extreme or rare events can occur that disrupt the process. These events might include accidents at arriving or departing airport, extreme weather conditions, or other unforeseen circumstances.
Variability in Input: Variability in the inputs or materials used in a process can result in special cause variation. For instance, if the quality of raw materials varies significantly, it can lead to variations in the output. New personnel hired are special cause variation, which could lead to unplanned outputs.
Inadequate Training: Insufficient training or skill level of personnel involved in the process can lead to errors and special cause variation. Training serves two purposes. One is to detect drift in operational control by flight crew or mechanics, the second is to detect organizational drift. A potential issue with assigning training tasks to a person who does not hold a position to train as a regular trainer is that there is often not enough time to do so adequately and introduce a special cause variation. In preparation for training an instructor needs to do research, design a training plan, scheduling g, and develop target specific training goals to conform to an SMS enterprise’s safety policy and training objectives. There are SMS enterprises, both large and small, that believe training is busy-time, or waste of time since their personnel was already trained. In addition, refresher training that is not a part of a regulatory requirement are discouraged and not allowed during regular working hours. When an SMS enterprise, or a person in a leadership position does not seek or take advantage of all training opportunities available to their personnel, their skills become stale.
Design Flaws: Sometimes, special cause variation can be traced back to design flaws in the process or equipment, which can lead to unexpected performance issues. Some years ago, a flaw was discovered in compressor turbine disk by applying non-destructive testing of the CT disk. This test was the first test after the final production stage and after it had left the production line. The test discovered a flaw in the material and was reported. There was no safety management system reporting avenue at that time, just an inspection report. This material flaw was the very first flaw in a CT disk that management new of. At some point during the manufacturing process a special cause variation was introduced. There have been several CT disk failures in turbine engines and Sioux City IA is the best high-profile accident known.
It's important to note that the identification of special cause variation is a critical step in process improvement and quality control. By identifying and addressing the specific causes of variation, organizations can work to eliminate or mitigate these factors to achieve more consistent and predictable processes. This, in turn, leads to improved product or service quality and overall operational efficiency. Statistical methods, such as control charts, hypothesis testing, and root cause analysis, are often used to detect and address special causes in various industries and processes.
Special cause variations are common process variations in the aviation industry. For our own comfort and safety while flying, we like to believe that established processes and checklists are fail-free, and when adhered to, there will be no longer be any aircraft accidents. We also like to believe that 100% of pilots adhere to 100% of processes 100% of the time. However, here is the news, special variations in aviation will always exist, which is one reason to run with a healthy safety management system which includes a daily rundown quality control system.
Super Centers normally have automatic walk-in doors and walk-out doors. As long as the automatic doors are functioning as expected, everything is fine and without scuffles. When the walk-out door malfunction and remains open, there is a special cause variation. This special cause variation is a causal factor for scuffles. The special cause variation is not the root cause, but a variation interrupting the designed process.
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