5 WHY A method for rapidly determining the root cause of a problem Summary The “Five Why’s” is a method for rapidly determining the root cause of a problem popularized by Taichi Ohno, the father of the Toyota Production System. His technique was to approach any problem and keep asking “Why” until he was satisfied that the answer showed him what was really the source of the problem. In doing so, he then had a good idea of what needed to be fixed to prevent the problem. He called it the “Five Why’s” because he found over time that by asking “why” five times he usually ended up with the right information to go and fix the problem. The Five Why’s should be used by individuals and teams when trying to quickly assess and determine source of problems. Most problems can be handled this way, however more complex or life/mission critical problems typically require a more formal root-cause methodology including documenting the analysis. However, even the formal methodology requires asking “why” over and over again. Example Problem: High reject rate of parts used by downstream aircraft assembly process 1) Why? - There is bare material exposed 2) Why? - The primer paint coating does not cover the whole part 3) Why? - The priming process does not ensure full coverage 4) Why? - The priming process is never done the same way twice 5) Why? - The priming process has always relied on word-of-mouth training and has no standard process defined To improve, get the primers together to create a standard work method that defines the exact sequence and tools for priming the parts. This will significantly improve the process yield. They can then explore further improvements using their standard work as the baseline.