Root cause analysis
A structured method for finding the underlying cause of a failure so it does not recur.
How it works
A repair fixes the symptom. Root cause analysis (RCA) asks why the failure happened, and keeps asking until it reaches a cause that you can change. A bearing failed. Why? It ran hot. Why? It was short of grease. Why? The lubrication task for that machine was missing from the PM plan. The fix is the plan, not only the bearing.
Common methods include:
- 5 whys: ask "why" repeatedly, usually around five times.
- Fishbone diagram (Ishikawa): sort possible causes into groups such as machine, method, material, people, and environment.
- Fault tree analysis: work backwards from the failure through the combinations of events that could cause it.
Why it matters
Without RCA, the same fault comes back, and the team gets good at fixing it instead of preventing it. Repeat failures are a large share of corrective work in many plants, and they are the cheapest kind to eliminate once the cause is known.
In practice
RCA takes time, so teams pick their targets: failures with safety impact, long downtime, high cost, or a pattern of repeats. The analysis relies on facts from the floor. What did the technician see? What was replaced? What did the old part look like? Work orders closed with "fixed" leave nothing to analyze.