In het boek The Toyota Way to Lean Leadership beschrijven Jeffery LIker & Gary L. Convis het nut en de noodzaak van de A3-methode:

A3 Problem Solving Makes the Thinking Proces Visible

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Mr Fumitake Ito became president of NUMMI and was not satisfied with the uptime of the body shop. He also noticed the body-shop engineers spending too much time in the office, which of course meant the problems were not going to get solved. In one meeting, he asked Gary to start a new practice. Whenever equipment was shut down for 30 minutes or more, he wanted a personal report from the engineers, with Gary present. The report should be on one piece of paper, the famous Toyota "A3 report" (after the A3 paper size used in the metric system). Ito did not offer a training course on A3, but rather asked for a 'breakdown report' for each instance and suggested that the Japanese engineers in the body shop would be able to show the American engineers how to prepare it.

The purpose of the report is to produce, in a single page, a 'problem-solving story' that summarizes the problem, its root cause, and the countermeasures taken to solve the problem. ... The single-page report details the problem, the gap between the current and the ideal state, the countermeasures tried, the results, and further actions required. The engineers' job was not only to fix the breakdown but to identify why the breakdown happened and to address the root causes so that the breakdown would not be repeated. The engineers were to present the report personally to Ito and Gary within a week of the breakdown.

By approaching the situation this way, Ito was addressing several needs at once. First, he was addressing the production problems that NUMMI was having in a sustainable way (rather than putting production goals first and just letting the Japanese engineers solve the problems). Second, he was creating a development opportunity for the American engineers to practice their problem-solving skills. By instituting the policy of having the American engineers take the lead and be responsible for the A3 reports, Ito-san was focing them to learn problem solving and learn the value of genchi genbutsu. Third, he was gving Gary an opportunity to be engaged in the problem-solving process and creating an opportunity to coach Gary in his responsibility to develop engineers.

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The goal of filling out the A3 report, of course, is not to fill out the form perfectly, but to serve as an aid to clear thinking and learning in the problem-solving process. ... As every developing leader at Toyota learns, the reports are a powerful technique for developing problem-solving ability. (...) Any individual report was relatively unimportant in the grand scheme of developing leaders. The steady improvement in the reports showed the more important progress in developing the engineers and to see how they thought, how they reasoned, how they were going to prevent problems, and how they were going to sustain that prevention.

Bron: The Toyota Way to Lean Leadership, Jeffery Liker & Gary L. Convis