A control plan is the document that shows which characteristic is measured by which method, at what frequency, by whom, and what is done in the event of a deviation.
It is one of the documents most frequently examined in audits and most frequently found nonconforming. Since March 2024 it has been published by AIAG as a standalone manual, separated from the APQP manual.
Three types
Prototype, pre-launch and production control plans correspond to different maturity stages and have different control intensities.
Content
Process step, product and process characteristics, special characteristics, specification, measurement method and equipment, sample size and frequency, control method and reaction plan.
Three common mistakes
No PFMEA link. No measure is defined in the control plan for a failure mode found to be high-risk in the PFMEA.
Sampling without rationale. The frequency is written down, but there is no logic showing why it is that frequency.
Vague reaction plan. Who decides, how far back suspect product is traced, whether the process stops — not defined.
It must be updated when the process, equipment or measurement method changes.
Preparing a control plan, transferring from the PFMEA and writing the reaction plan are practised on your own plans in the Control Plan training. For the sampling logic, see the SPC training.