Defects are an unavoidable byproduct of any manufacturing process, and most will not affect the overall quality of the finished product. However, if defects in your finished product are severe enough, they can impact consumer safety and lead to costly lawsuits and recalls, so it’s important to define exactly what qualifies as a defect under the AQL Standard so you can identify and prevent them during manufacturing. The following categories cover most of the defects that commonly arise when monitoring your products through an AQL audit.


Quality standards are rules and regulations that suppliers must follow when designing, manufacturing, packaging and shipping products. In most cases, quality standards affect a company’s entire supply chain rather than specific aspects of a business. The International Organization for Standardization (ISO) or ISO 9001 audit  ensures that all members adhere to these rules.

1) Surface Defects

Surface defects are perhaps the most common category of product defects, accounting for roughly 80% to 90% of all product defects. Surface defects include flaws in material or a part’s surface finish, such as marks or scratches; cuts or tears in parts that expose a different material underneath; contamination (outside particles stuck to an otherwise smooth surface); and excessive or insufficient adhesion between two parts. These types of defects can be easily caught during AQL inspection and are typically not expensive to fix.

2) Internal Defects

Internal defects are caused by worker error in production. These defects can be reduced through a supplier audit conducted by a third party or by following an internal inspection process implemented by your company itself. 

Corrective action includes improvement in supplier training and maintenance of standardized processes that minimize human error. 

To ensure suppliers meet these standards, it is recommended to conduct IATF 16949 audits on suppliers to ensure they follow ISO 9001 standards as well as include them in AQL standard for supplier audits for internal product defects.

3) Design-related Defects

The design-related defects are caused by flawed design drawings and computer-assisted designs (CAD). They often cannot be detected until a product has been manufactured. 

Design-related defects may also occur due to miscommunication between designers and engineers. To minimize risks, it is necessary to have a harmonious work relationship between them. In addition, detailed designs should be used to convey information clearly without ambiguity.

4) Non-conforming Documents

Non-conforming documents are documentation items related to production, control and inspection that fail to conform to product requirements or other requirements of an IATF 16949 audit. 

If a non-conforming document is not detected by production control, it can result in a failure by IATF during an audit and may cause customers loss. Therefore, there is a need for companies to pay special attention to review and check non-conforming documents.

5) Non-conforming Production Attributes

These attributes are inherent in parts produced but not apparent to users during assembly, or are apparent but do not affect performance or safety. 

Non-conforming Production Attributes can be detected only during IATF 16949 audit.

6) Incorrect Labeling

In general, a product is considered to be incorrectly labeled if any labeling that is visible when a consumer buys it does not match its contents. Of course, for something to be properly labeled in the first place, it has to meet other requirements as well. 

For example, under federal law any labels must contain enough information so that a consumer can easily read and understand them.

Wrapping up

The standard, known as Acceptable Quality Level (AQL), governs how many product defects are allowable during a supplier audit. While different industries have different limits on these audits, they all look for similar issues in raw materials and other components used to make products. As you can see from our list above, there are six main categories in AQL.