A factory shipping casual trousers to Europe fails a final inspection with 8% defect rate. The team blames sewing operators and adds extra inline checks. Defects drop for two days, then return at 7%.
A manager starts collecting evidence: stitch photos, machine settings, needle logs and operator rotation records. The 5 Why chain reveals that needle heat rises after three hours of continuous sewing, causing skipped stitches that look like operator mistakes. Operators were also rotated every two hours on other lines but not on this style.
Containment is immediate: sort already-sewn pieces, replace needles every two hours, and add a short cooling pause. Correction is longer term: update the needle-change standard for this fabric and train supervisors to read heat-related stitch defects. The root cause was not carelessness; it was a missing process control.