Andon (Visual Control)

Definition

The andon is a board hung above the production line, visible from any work station, that shows the status of every point on the line at a glance: green for normal operation, yellow when a worker needs help adjusting something, red when the line must stop to fix a problem. It is Ohno's clearest instance of "management by sight" — a control system that works because anyone looking up can instantly see where trouble is, rather than a report or a supervisor having to go find out.

In the Book

Ohno introduces the andon in Chapter 2 alongside standard work sheets as the visible surface of the Toyota production system: "When one looks up, the andon (the line stop indication board) comes into view, showing the location and nature of trouble situations at a glance." The glossary entry spells out the three-light protocol explicitly and closes with the operating principle behind it: "workers should not be afraid to stop the line." This is not incidental — it connects directly to autonomation (Chapter 1), where Ohno argues that a machine or line that keeps running through an abnormality mass-produces defects, while one that stops the instant trouble appears forces the problem into view where it can be fixed rather than quietly patched over and repeated. The andon makes that stop-on-abnormality principle collectively visible: instead of one worker or one supervisor quietly knowing there's a problem, the whole floor sees it the moment it happens.

Why It Matters

Most organizational problems are invisible until someone goes looking for them, which means small deviations compound before anyone acts. Andon inverts that: it puts the current state of a whole system into a single glance, ambient and public, so a deviation gets noticed and addressed at the moment it appears rather than at the next status meeting or the next audit. The design principle — make abnormal state impossible to miss, and make raising it low-cost and blame-free — generalizes to any system where the person closest to a problem is not the person with authority to escalate it: build states dashboards, service alerts, or the norm that anyone can "stop the line" are all andon in a different medium.