Pre-shipment inspection: how to read an AQL sampling plan
Sampling inspection is not a random look at the goods: it is a standardised statistical method whose result only means something if the thresholds were set in the contract.
The SELA International team
The question addressed
How does an AQL pre-shipment quality inspection work?
Key takeaway
An AQL inspection draws a sample whose size depends on lot volume and the chosen inspection level, then counts defects by severity — critical, major, minor. For consumer goods, an AQL of 2.5 for major defects and 4.0 for minor defects is common, with critical defects governed by a contractual zero-tolerance rule. The lot is accepted or rejected against the ISO 2859-1 tables, not on the inspector’s judgement. Those thresholds must appear in the purchase contract: without them, an inspection report is hard to enforce against the supplier.
AQL stands for Acceptance Quality Limit — known as Acceptable Quality Level before the 1999 revision of ISO 2859-1. The principle: inspecting a fraction of the lot is enough to rule on the whole, provided the sample is drawn according to a recognised table and the tolerance threshold is defined in advance.
The three defect levels
- Critical — the product is unsafe or unlawful to sell. Zero tolerance: a single critical defect fails the lot.
- Major — the product is usable but would likely be refused or returned by the end customer.
- Minor — a visible deviation from specification, with no effect on use or saleability.
What the report must contain
- The production progress at the time of the visit — an inspection carried out at 40% packing proves nothing about the rest of the lot.
- The sample size drawn, the inspection level and the thresholds applied, explicitly quoted.
- The defect count by severity, each photographed and traced back to its original carton.
- Checks outside the sampling plan: markings, barcodes, carton dimensions, drop test, unit weight.
- A binary conclusion — pass or fail — rather than a narrative assessment.
The costliest mistake is booking the inspection too late. A check triggered the day before loading leaves no room for rework: the choice narrows to shipping non-conforming goods or losing the vessel slot. A during-production inspection (DUPRO), at around 60 to 80% completion, leaves time to correct.
SELA INTERNATIONAL LTD has inspections carried out by independent third-party bodies and passes the full report to the buyer, including where its findings are adverse. Where the purchase contract so provides, the report gates release of the balance payment to the supplier.