01Three linked documents
A process flow diagram lists every step from receiving to shipping, including inspection, storage, transport and rework loops. The PFMEA analyses failure modes for each step. The control plan lists, per step, the product and process characteristics, specifications, measurement methods, sample size and frequency, control method and reaction plan.
Consistency between the three is a strong indicator of a supplier's quality planning maturity.
02What a control plan contains
- Process step and machine or tool
- Product characteristics and process characteristics
- Special characteristic classification
- Specification and tolerance
- Evaluation and measurement technique
- Sample size and frequency
- Control method (SPC, check sheet, poka-yoke)
- Reaction plan
Control plans exist for prototype, pre-launch and production phases.
03How to verify a control plan
Take the control plan to the shop floor. At each station check: is the gauge listed present and calibrated, is the frequency followed, are records available, does the operator know the reaction plan? Differences between paper and practice are the most frequent finding in process audits.
04Special characteristics
Characteristics affecting safety, regulation, fit or function are often designated special characteristics with symbols defined by the customer. They require stronger controls, capability evidence and traceability.
Published 2026-11-08 · QUALITAS TR technical team