Apply five whys and fishbone diagrams

Apply classical RCA techniques (5 Whys, Fishbone, FTA, FMEA) with rigor

Linear, single-cause shop-floor incidents (5 Whys), or multi-pathway quality incidents (Fishbone), or safety-critical system design review (FTA/FMEA) where classical techniques have proven power.

• · Incident description or observed failure symptom
• · Contributing factors or potential causes (brainstorm list)
• · Fault modes or component list (for FTA/FMEA)
• · Impact metrics (severity, frequency, detectability for RPN)

• · 5 Whys causal chain (if linear single-cause incident)
• · Fishbone diagram organized by Man/Machine/Method/Material/Measurement/Milieu
• · Fault Tree (top event, intermediate events, basic events) with minimal cut sets
• · FMEA table with Risk Priority Numbers (RPN) and ranked mitigation strategies
• · Doggett's decision matrix selecting appropriate technique per problem type

• · Fishbone/cause-mapping software (optional: Lucidchart, Miro, Excalidraw)
• · FTA solver for cut-set computation (optional: Relyability, OpenFTA)

• · Incident has concluded (or is well-understood while ongoing)
• · Root cause is not known to be multi-pathway (or explicitly scope to single chain for 5 Whys)
• · For FTA: failure modes of components are known upfront
• · For FMEA: design is stable enough to perform proactive review
• · Team trained in the technique (Fishbone is more forgiving than FTA)

• · 5 Whys forced onto multi-pathway incident → misses real causal structure (Card 2017 critique)
• · Fishbone becomes unwieldy with 50+ factors → loses prioritization
• · FTA assumes failure modes are exhaustive → misses rare or novel modes
• · FMEA RPN uses ordinal math (severity × occurrence × detectability) which is statistically invalid (Bowles 2003)
• · Stopping at 'human error' without investigating system design factors
• · Using technique beyond its known boundary (e.g., FTA on dynamic systems with feedback loops)

• · 5 Whys originates from Toyota Production System (Taiichi Ohno, 1988) — foundational to TQM
• · Fishbone (Kaoru Ishikawa, 1960s) standard in manufacturing and service quality for 50+ years
• · FTA developed for Minuteman ICBM (Bell Labs, 1960s) — aerospace/nuclear proven
• · FMEA adopted by automotive (AIAG) and aerospace standards (DO-254, DO-178C)
• · Card 2017 critique explicitly bounds 5 Whys to linear cases, enabling appropriate use
• · Doggett 2005 framework provides empirical meta-selection algorithm