quality-nonconformance

Select the method based on complexity: 5 Whys for simple single-cause failures, Ishikawa plus 5 Whys for multi-factor issues, 8D for recurring process problems, and Fault Tree Analysis for safety-critical events. Verify each cause with data rather than opinion, and never accept human error as a root cause.

Corrective action addresses an existing non-conformance and prevents its recurrence, while preventive action addresses a potential non-conformance identified through trend analysis or risk assessment. FDA expects both under 21 CFR 820.100, and conflating them is a common audit finding.

Rule 1 (one point beyond 3 sigma) demands immediate action, while Rules 2-4 (runs, trends, alternating patterns) indicate systematic causes requiring investigation before the process goes out of spec. A process within specification limits can still be out of control, so do not adjust for common cause variation.

Use 5 Whys for single events with a simple linear causal chain, budgeting 1-2 hours. Use the full 8D team-based methodology for recurring process issues or when automotive customers mandate it, budgeting 20-40 hours across all eight disciplines.

The Material Review Board can disposition material as use-as-is (with engineering justification), rework to full conformance, repair with permanent deviation, return to vendor with a SCAR, or scrap with documented approval. Safety-critical characteristics cannot be used as-is without formal risk assessment and regulatory notification.

CAPAs typically fail because the original root cause analysis stopped at symptoms, such as blaming operator error and retraining as the fix. Verification confirms the action was implemented, but validation requires monitoring data over at least 90 days or three production lots showing zero recurrence.