All three are written permission to depart from a requirement, and the difference is timing. A deviation is permission given before the product is made, for a set quantity or time. A concession is permission to use or ship product that has already been made and does not conform. Waiver is often used for the same thing as a concession, especially in defense and aerospace. Each one needs an approver, a limit and an end.
The short version
| Deviation | Concession or waiver | |
|---|---|---|
| When | Before the product is made | After the product is made and found nonconforming |
| Typical reason | A known short term change: substitute material, alternate process, temporary tooling | A lot that missed a requirement but is judged fit to use |
| Limit | A set quantity, number of lots, or date range | The specific parts or lots named, nothing more |
| Who approves | Engineering and quality, and the customer when the requirement is theirs | The same, often through the material review board |
| Risk if misused | A temporary change becomes permanent without anyone deciding it | Shipping a problem instead of fixing it |
What every one should contain
- The exact requirement being departed from, with the drawing or specification reference.
- What is different and the evidence it is still fit for use.
- The limit: quantity, lots or end date, whichever comes first.
- How affected parts are identified so they can be traced if something goes wrong later.
- Who approved it, including the customer where their requirement is involved.
- What happens at the end: back to the original requirement, or a permanent change made properly.
Watch for
- Deviations that keep getting renewed. Three renewals means it should be a drawing change or a corrective action.
- Using as is without paperwork. If it does not meet the requirement and it ships, it needs a written concession.
- Customer requirements first. Most automotive and aerospace customers require their approval before nonconforming product ships to them.
Terms vary by company and customer. Some use deviation for both before and after. Use the words in your customer's requirements.