Root Cause Analysis: A Worked Manufacturing Example

Worked RCA example: six packaging jams

This is a fictional teaching example, not a Vrolen customer result. A packaging line has six jams totaling 46 minutes during ten runs of product B. Product A runs without the same jam. The first report says “operator setup error.” That label is too broad to tell us what to fix.

The investigation compares the jam timeline, product setup records and maintenance observations. It considers low air pressure, faulty packaging material and an incorrect guide setting. The table separates observations from conclusions.

Define the problem before explaining it

Describe the gap in observable terms: what happened, where, when, how often, how large the effect was, and what should have happened instead. Avoid causal language in the problem statement. “Filler 2 is unreliable” already assumes the answer; “unplanned stops exceeded 46 minutes on SKU B during night shift” can be tested.

Freeze the relevant evidence early: event logs, alarm sequences, sensor trends, quality records, operator observations, maintenance work, product mix, and recent changes. Synchronize timestamps before reconstructing the sequence.

• Contain immediate safety or customer risk under the approved procedure.
• Separate an observation from the explanation you still need to test.
• Record evidence for and against each candidate in the worksheet above.

Choose an RCA method for the problem

Use the tools to ask better questions. A fishbone diagram is useful when several explanations remain plausible. A 5 Whys chain helps explore one explanation in detail. Stop when you run out of evidence, even if you have asked fewer than five questions.

ASQ describes RCA as part of a larger problem-solving process. Protect people and customers first. Urgent containment can run alongside the investigation, but record it separately from a permanent corrective action.

Where RCA fits within DMAIC

ASQ describes DMAIC as Define, Measure, Analyze, Improve and Control. Root-cause analysis mainly supports Analyze: test explanations against a defined problem and reliable measurements. Improve tests a corrective action; Control checks whether the change holds. A fishbone diagram or a fifth why does not complete those later steps.

Choose a tool for the uncertainty you need to resolve. Use 5 Whys for a traceable causal sequence, a fishbone to collect competing possibilities, change analysis for a changed condition, and A3 or 8D to coordinate a broader investigation. The table above groups useful approaches; it does not claim a universal list of seven RCA methods. See Lean Six Sigma for the wider improvement sequence.

Test causal candidates against evidence

For each hypothesis, state the expected signature: what should be present if the cause is true, what should be absent, and what observation would disprove it. Check timing, mechanism, dose or frequency, and consistency across affected and unaffected runs.

Operational models and simulation can test whether a candidate cause is capable of producing the observed system effect. This is a counterfactual check, not proof. Confirmation still requires physical evidence, a controlled trial, inspection, measurement, or recurrence data.

• Did the candidate precede the effect?
• Is there a credible physical or process mechanism?
• Does the pattern appear when the candidate is present and disappear when absent?
• Can the observed magnitude and timing be reproduced?
• What alternative explanation fits the evidence equally well?

Follow the loss across the system

Production systems propagate effects. An upstream micro-stop can starve a downstream constraint minutes later; a quality hold can appear as low performance; a scheduling rule can create apparent equipment downtime. Align events on one timeline and distinguish the origin of the disturbance from the location where the KPI moved.

Constraint context helps prioritize the investigation. A frequent fault on a protected, non-constraint process may be less urgent than a smaller recurring disturbance at the system constraint. This does not make the first fault acceptable, it clarifies impact and sequencing.

Design corrective action and prove it held

Corrective actions should remove or control the verified cause, strengthen detection, and avoid transferring risk elsewhere. Assign an owner, due date, verification metric, and observation window. Training alone is weak when the process, control, design, or workload still makes the failure likely.

After implementation, verify both the local mechanism and the system outcome. Confirm that the failure signature disappeared, the target metric improved under comparable conditions, and no new safety, quality, or flow problem emerged. Update standard work, maintenance logic, alarms, and the operating model with what the team learned.

1. Contain

   Protect people, customers, and production while preserving evidence.

2. Explain

   Build and test competing causal chains.

3. Correct

   Remove or control verified causes and failed barriers.

4. Verify

   Observe performance over a defined window and comparable conditions.

5. Standardize

   Update controls, work, training, and monitoring.

Use the RCA worksheet and verify the action

Use the blank RCA worksheet and filled teaching record above to follow the example. Keep unchecked explanations separate from rejected causes.

In the example, the proposed action is to add the product-specific width check to the approved changeover process and verify it before release. Observe ten comparable product-B runs, recording running hours and jam duration as well as jam count. Zero jams in a short test would be encouraging, but would not prove the fault can never return.

Use a downtime Pareto to choose the next recurring loss. For a problem needing several teams, the A3 worked example shows how to keep the investigation and follow-up together. Software selection belongs in the separate RCA software guide.

A five-part RCA and the questions inside it

A practical five-part grouping is: define the problem and contain immediate risk; collect facts; test possible causes; implement an approved corrective action; verify the result and update the working method. These are groupings for this guide, not a universal five-step standard. Containment may begin before the investigation is complete.

For 5 Whys, ask why the observed problem happened, then ask why the preceding condition existed. Check each answer against evidence before following it further. Five is a prompt to look beyond the first explanation, not a quota. Branch the investigation when several causes are plausible; do not end at a person’s name.

Lists of five RCA principles vary. The useful checks here are a precise problem, preserved facts, tested causal links, actions aimed at confirmed causes and a follow-up under comparable conditions. ASQ describes several RCA approaches rather than one mandatory list. A completed diagram cannot establish that a cause is true.