Quality · continuous improvement
Root cause analysis: a worked example with the 5 Whys
Root cause analysis (RCA) means asking why a problem happened until you reach a cause you can actually change, then changing it. It is the difference between fixing the symptom every week and fixing the system once.
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The 5 Whys on one problem
Customers in Germany are returning headphones that stop charging.
- Why are they returned? The battery fails after a few weeks.
- Why does the battery fail? The cells in those units come from one batch with a high failure rate.
- Why did that batch reach customers? The lab sampled too few units from it, and it was released.
- Why so few samples? Inspection was cut to save time during a busy week.
- Why was that batch bought at all? The supplier was chosen on unit price alone, with no quality score in the decision.
The symptom is returns. The root causes are a purchasing rule that ignores quality and an inspection plan that bends under pressure. Replacing the returned units treats the symptom. Changing how suppliers are scored and protecting the sampling plan fixes the system.
Tools that help
- 5 Whys: fast, good for one clear problem.
- Fishbone (Ishikawa) diagram: sorts possible causes into people, method, machine, material, measurement and environment.
- Pareto chart: shows the few causes behind most of the cost.
- Traceability: being able to follow a failure back to the lot, batch and order it came from. Without it, RCA is guesswork.
Common mistakes
- Stopping at the first answer, usually a person (“the inspector missed it”).
- Fixing the symptom and calling it closed.
- Not checking later whether the fix worked.
Practise it
In Cargo & Consequence, Customer Care can trace any complaint back to the purchase order, batch and shipment behind it. The bad-batch challenge is a root cause exercise: a cheap batch of cells fails about one time in seven and is already in the factory, the stores and the European warehouse. Testing at the factory alone passes 0 times in 10. Tracing, stopping and sorting the stock already in Europe passes about 8 in 10.
In a real plant the data is spread across machines, quality records and ERP. Finding the constraint or root cause worth fixing is what Vrolen is built for.
Questions
What is root cause analysis?
It is a structured way to find the underlying cause of a problem, the one that, if changed, stops the problem from coming back, instead of only fixing its symptoms.
What are the 5 Whys?
A root cause technique where you ask why a problem happened, then ask why again about each answer, usually about five times, until you reach a cause you can act on.
What is an example of root cause analysis in supply chain?
Tracing product returns back through a failed battery batch and a skipped inspection to a supplier chosen on price alone, then changing the supplier scoring and the sampling plan.