8.8 Incoming Inspection (AQL & Sampling)

It is statistically impossible to inspect 100% of incoming components (e.g., a reel of 10,000 resistors). Therefore, Incoming Quality Control (IQC) relies on statistical sampling plans defined by ISO 2859-1 (ANSI/ASQ Z1.4).

8.8.1 The AQL (Acceptable Quality Limit)

AQL is the maximum percent defective that can be considered satisfactory for a process average.

• Critical Defects (Safety/Regulatory): AQL 0.01 (effectively Zero Defects).
• Major Defects (Functional Failure): AQL 0.65 or 1.0.
• Minor Defects (Cosmetic): AQL 2.5 or 4.0.

8.8.2 Execution of the Plan

1. Lot Size: Determine total quantity received.
2. Inspection Level: Standard is Level II. (Use S-1 through S-4 for destructive testing).
3. Code Letter: Use ISO 2859 table to find the sample size code (e.g., Lot of 5,000 = Code "L").
4. Decision Rule: Code "L" requires inspecting 200 units.

• Scenario: AQL 0.65. Accept on 3 defects, Reject on 4.
• Outcome: If 4 defects are found, the entire lot is rejected and returned to the vendor (RTV) or 100% sorted at the vendor's expense.

Final Checklist