Resources

Writing a real root cause (8D)

Customers reject 8D reports for one reason more than any other: the root cause isn't a root cause. "Operator error" and "retrained the operator" tell the customer it will happen again.

Two root causes, not one

A strong 8D answers two questions: why did it occur, and why did it escape (why didn't our checks catch it)? Each needs its own corrective action.

Test your root cause

• Can you turn it on and off? If you put the cause back, would the defect come back?
• Does it explain every unit affected, and why the others were fine?
• Is it about a process, not a person? People make mistakes in systems that let them.
• Did you verify it with data, not just reasoning?

Five Whys, done right

Start from the defect, not the symptom, and ask why with evidence at every step. Stop when you reach something you can control and fix. Example: hole oversize, because the drill wandered, because the spot drill was skipped, because the program was edited to save cycle time, because program changes don't require review. The fix is the change control, not "be more careful".

Prove it worked

Close the 8D only after an effectiveness check: no repeats over a defined period or number of lots, with data. Then update the PFMEA and control plan so the lesson sticks.

General guidance, not legal advice. Standards are referenced by name only. Written by Matt Norman, Norman Quality Tools (Veteran-Owned & Operated).