Closing the loop on Root Cause Analysis

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Closing the loop on Root Cause Analysis

Conducting Root Cause Analysis is not an easy task and whilst tools like the 5 Whys in particular, and Fault Tree Analysis help to a large extent, one of the most common pitfalls in RCA is not testing the Corrective and Preventative Actions taken to address the Root Cause. Likewise, not collecting test data or sufficient data to verify the effectiveness of the Actions before formally closing out the RCA is another common pitfall.

Root Cause Analysis should always be based on evidence backed up by a credible set of data and in fact the real test of whether you have established the true root cause is that one should be able to recreate the problem………i.e. switch it on and switch it off.  In some cases this is not feasible from a cost, time or operational perspective but if the situation warrants it this is indeed the ultimate test of true root cause.

Let’s take this example below where the Primary Metric is OEE (Overall Equipment Effectiveness) being impacted by intermittent unplanned downtime as a result of bottles being jammed in the Corker (i.e. where corks are being inserted into the bottle head after product filling).

5 Whys Project Example

Problem: Corker Machine has unplanned downtime affecting line OEE

WHY          Because corker is intermittently stopping and not releasing bottles

WHY          Because the bottles are jamming in the corker head

WHY          Because contour and variation in geometry of shoulder of bottle is causing jamming

WHY          Because corker head is not suitable for current bottle design (in particular neck & shoulder)

WHY          Because corker head was designed for an older version of bottle

ROOT CAUSE:    Corker head not modified to suit new bottle design

Action:     Modify corker head design to allow bottle enter and exit corker head without jamming


The 5 Why established the root cause as the Corker Head Design not being suitable for the current Bottle (i.e. the neck and shoulder) and the Preventative Action taken was to modify the corker head as illustrated above to prevent the jamming. A series of trials were then conducted to verify the effectiveness of the design modification with the result being zero jamming on the Corker Head. More importantly the Team saw a reduction in the unplanned downtime and an increase in OEE within a number of shifts and a clear sustainable trend over 6 weeks for unplanned downtime.

In terms of the big Picture

  • We all know hindsight is a great thing but if one wanted to go to the next ‘Why’ in the 5 Whys one could argue that the real root cause is the inadequacy of the Change Control System i.e. when the bottle design changed it should have triggered an assessment and redesign of the Corker Head Design!
  • Emanating from the RCA and Preventative Actions the obvious thing to do is to establish if a similar phenomenon was occurring on other Lines (jamming due to the Corker Head Design) and Redesign the other Corker Heads accordingly.

Submitted by our Expert Lean Six Sigma Tutor, Eamon O’Bearra

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