Acceptable Quality Limit - AQL Wikipedia
What is AQL?
The acceptable quality limit (AQL) is the worst tolerable process average (mean) in percentage or ratio that is still considered acceptable; that is, it is at an acceptable quality level.
Closely related terms are the rejectable quality limit and rejectable quality level (RQL).
In a quality control procedure, a process is said to be at an acceptable quality level if the appropriate statistic used to construct a control chart does not fall outside the bounds of the acceptable quality limits. Otherwise, the process is said to be at a rejectable control level.
In 2008 the usage of the abbreviation AQL for the term "acceptable quality limit" was changed in the standards issued by at least one national standards organization (ANSI/ASQ) to relate to the term "acceptance quality level". It is unclear whether this interpretation will be brought into general usage, but the underlying meaning remains the same.
What are Critical/Major/Minor defects?
For example: “I want no more than 1.5% defective items in the whole order quantity, on average over several production runs with that supplier” means the AQL is 1.5%. In practice, three types of defects are distinguished. For most consumer goods, the limits are:
•0% for critical defects (totally unacceptable: a user might get harmed, or regulations are not respected).
•2.5% for major defects (these products would usually not be considered acceptable by the end user).
•4.0% for minor defects (there is some departure from specifications, but most users would not mind it).
These proportions vary in function of the product and its market. Components used in building an airplane are subject to much lower AQL limits.
Note that this tool is used mostly during final outgoing inspections (when the products are ready to be shipped out), and sometimes during production (when the number of products is sufficient to have an idea of the batch’s average quality).
In quality management, a nonconformity (also known as a defect) is a deviation from a specification, a standard, or an expectation. Nonconformities are classified as either critical, major, or minor.
In software engineering, ISO/IEC 9126 distinguishes between a defect and a nonconformity; a defect is the nonfulfilment of intended usage requirements, whereas a nonconformity is the nonfulfilment of a requirement. A similar distinction is made between validation and verification.
- Minor nonconformity – Any nonconformity which does not adversely affect the performance, durability, interchangeability, reliability, maintainability, effective use or operation, weight or appearance (where a factor), health or safety of a product. Multiple minor nonconformities when considered collectively may raise the category to a major or critical nonconformity.
- Major nonconformity – Any nonconformity other than critical, which may result in failure or materially reduce the usability of the product for the intended purpose (i.e. effective use or operation, weight or appearance (where a factor), health or safety) and which can not be completely eliminated by rework or reduced to a minor nonconformity by an approved repair.
- Critical nonconformity – Any nonconformity which may result in hazardous or unsafe conditions for individuals using, maintaining or depending upon the product or prevent performance of a vital agency mission.