the Production Unit Qualification Testing. Sequence of PreQual Repaired Article / First Repaired Article testing: Visual Inspection & Functional – Preconditioning – Acceptance ESS – Visual Inspection & Functional – Gov't Inspection & Functional. Note: Due to Diminishing Manufacturing Sources (DMS), substitutions of piece parts are often necessary. Substitute parts that appear under ambient test bench conditions to function like the original parts can exhibit unsatisfactory performance in the operational environment. Qualification by Similarity. Qualification of a replacement or repaired unit by similarity to the original unit requires that the units are essentially identical. In addition, the replacement unit must have previously been qualified by testing to environmental and operational performance requirements meeting or exceeding the environmental and operational requirements of the original unit. Acceptance ESS Formal tests conducted to demonstrate acceptability of the individual unit for delivery. They demonstrate performance to purchase specification requirements and act as quality control screens to detect deficiencies of workmanship and materials. The successful completion of such tests denotes acceptance of the unit by the procurement agency. Production Unit Acceptance Testing Purpose: Done on 100% of new units to detect workmanship and process errors. Inspection of some microelectronic devices is destructive so lot sampling is used for acceptance testing (see paragraph 8.3.2). Method: Tailored down from applicable Production Qualification Test but done to workmanship levels, no more severe than actual environmental levels and of shortened duration. Usually these tests are structured to include the Pre-Conditioning and Reliability Acceptance Testing requirements. Sequence for Components testing: Visual Inspection & Functional – Preconditioning – Acceptance ESS – Acceptance Reliability – Visual Inspection & Functional. Note: Production Unit Acceptance Testing performance data is also used to evaluate "in-family" performance. While a UUT may meet all other Acceptance Test pass/fail criteria, results which deviate significantly from other units within the production lot shall require rejection of that unit. Repaired Unit Acceptance Testing Purpose: Performed on 100% of repaired units to detect workmanship and process errors. Method: Tailored down from applicable Production Acceptance Tests. To maintain the specified reliability criteria, Pre-Conditioning Testing should be included if the repair parts are not pre-conditioned or the repair workmanship can be expected to induce failures. Sequence for Components testing: Visual Inspection & Functional – Preconditioning – Acceptance ESS – Visual Inspection & Functional. Note: Test levels are low and not destructive so testing may be repeated for test failures and subsequent repairs without