Control plan explained
A control plan is a written summary of the control methods used to maintain process performance and product quality. It tells operators and inspectors what to check, how to check it, how often, and what to do when something is out of control.
The control plan is not a list of specifications—it is a living operations document. It references the process flow and PFMEA and is updated whenever the process changes.
Key columns in an AIAG control plan
| Column | What it captures |
|---|---|
| Part / process name | The step or component being controlled |
| Characteristic number | Links back to the drawing or PFMEA item |
| Product / process characteristic | The specific dimension, attribute, or parameter being controlled |
| Special characteristic | Flagged with symbols (e.g., △ for safety, ◆ for key product characteristic) |
| Specification / tolerance | The acceptance limit (from the drawing or standard) |
| Evaluation measurement technique | Gage, fixture, test method, visual standard |
| Sample size and frequency | How many parts and how often to check |
| Control method | SPC chart, attribute chart, go/no-go gage, 100% inspection |
| Reaction plan | What the operator must do when the characteristic is out of control (contain, tag, call supervisor, stop production) |
Three types of control plan
- Prototype control plan: covers prototype builds in APQP Phase 2. Less formal; focus is on development learning.
- Pre-launch control plan: used during the production trial run (APQP Phase 4). More rigorous; all characteristics identified.
- Production control plan: the live document used every day on the shop floor. Updated when process or design changes occur.
Common exam traps
- The reaction plan is not optional. Every controlled characteristic needs a documented reaction plan. “Stop and call supervisor” is a valid reaction plan; blank is not.
- Control plans do not replace work instructions. A control plan says what to control; a work instruction says how to do the operation. They are complementary.
- Special characteristics always appear in the control plan. Any characteristic flagged in the DFMEA or PFMEA as safety-critical or key must appear in the control plan with an appropriate control method.
- The control plan is updated after every change. Process change approval is not complete until the control plan reflects the new state.
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