I use 3 way 5 why to not only address the specific issue but also address why it wasn't detected and any systemic causes. A lot of failures may have multiple root causes and by using 3 way you can address those as well and reduce reoccurrence of repeat CARs. Some may argue if you get to the root cause it will addresses all, but I believe it is important to address all failure points.
I find it the traditional 5-Why or even 3-Legged 5-Whys are incomplete. I have dealt with several methodologies of corrective actions in the past several years and the method that made the most sense (which was much easier to understand for more people in our organization) was the methodology introduced by former Denso employee. It's similar to 5-Why, but it's not necessarily asking 5 "why" questions." The reason for this is because some questions cannot be asked 5 times - instead the original "why" splits and create additional "whys," so the diagram will look more like a tree instead of 5 lined up questions of "whys." I would say this is a combination of traditional 5-Why and fishbone, but more in-depth. When people are stuck with traditional 5-Why method, they only think to come up with 5 "Why" questions and answers, and it can become like an obligation or purpose to come up with 5 "why" questions and answers instead of actually doing the in-depth investigation, and once they can come up with 5 "why" questions and answers, their mind stops. In reality, when nonconformance occurs, there's layers and combination of bad things that causes an incident and it's usually more complex than 5 "whys." This is why the traditional 5-Why or 3L5W is incomplete method.
I think a lot of people get a hang-up in 5-Why method because when you do the discussions in the multi-disciplinary team, it won't fit in that 5-Why format. There should be more in depth discussion that spreads out from the initial "why it happened," and people are encouraged to discuss freely without that format, and it should create several more "whys" that do not necessarily line up in the first 5-why line but may be related.
I also find that when the root cause analysis is done, there aren't very many good training material out there that explain how it should be done other than doing traditional 5-Why, 3L5W, or fishbone. It finally made sense to me after I read the book written by the former Denso employee who had step by step instruction on how it should be done along with several examples.
It is in my personal opinion that
8D still should be utilized to ensure that all corrective action activities are recorded in one place; however it is the very last thing to summarize the root cause investigation and corrections made.
- Create a multi-disciplinary team
- Look for data and records at the time of the incident
- Interview employees
- Brainstorm what you can think from evidence and write down questions
- Reorganize the questions written down and discuss what each team member had thought and wrote down
- Start organizing what's been discussed in "Why" question trees (write question in the top half of the box and write answer at the bottom half)
- Keep discussing and split "why" boxes until there's no answers - some "whys" may stop at the first or second time if the direct answer answers "why," and write the conclusion and solution at the end of each thread
- Make actual corrections to the problem
- Finalize and summarize the corrective action in 8D, attach all the evidence of investigation and root cause analysis.
Problem solving is the top major nonconformance in IATF audits as well (
https://www.iatfglobaloversight.org...023/06/2023-05_TopTenMajorNC-12MonthMD-EN.pdf). It's that much people are struggling to do the thorough problem solving. I think the part of the cause is the traditional 5-Why or 3L5W methodology that everyone is trying to fit into that format.
