manufacturing and repair entities are accountable for delivering quality products, and to provide selection and qualification criteria for new sources of supply. Determinations of product quality and source capabilities usually require ESS testing. While considerable information concerning ESS methods and procedures is available including United States Military Standards, handbooks, guides, and the original equipment manufacturer's test plans, often these publications use differing and confusing definitions for the testing phases where ESS is applied. Lengthy explanations were needed to clarify contract clauses citing these publications. This paper ensures testing requirements are uniformly applied and clearly understood in writing source qualification requirements and contracts. Visual Inspection Purpose To ensure that good workmanship has been employed and that the UUT is free of obvious physical defects. Method Visually inspect UUT before and after each manufacturing, repair, and test operation. Verify proper labeling, weight, and dimensions. With the unaided eye, inspect all accessible areas of the UUT. Under 10X minimum magnification, inspect all critical surfaces and interfaces of the UUT. Pass/Fail Criteria Workmanship shall meet the applicable standards including T.O. 00-25-234 and shall be free of obvious physical defects. A unit that exhibits any sign that a part is stressed beyond its design limit (cracked circuit boards, loose connectors and/or screws, bent clamps and/or screws, worn parts, etc.) is considered to have failed even if the UUT passes the Functional Testing. Functional Testing Purpose Done before, during, and after ESS testing to verify that the UUT is functioning within design tolerances. Method Applying an input signal or stimulus and measuring the output. Pass/Fail Criteria Output responses/signals must be within technical data specifications, and the UUT must operate satisfactorily in the next higher assembly. Environmental Stress Screening (ESS) Purpose Testing at the physical environmental conditions (shock, vibration, temperature, altitude, humidity, etc.) that simulate those encountered over the operational life of the component. Random vibration and temperature cycling have proven to be the most successful forms of ESS in terms of effective flaw precipitation. Method A stress profile is developed and applied to the UUT. The profile simulates the environmental conditions encountered during transportation, storage, handling, and operational use phases. The UUT is configured to match the phase, e.g. transportation shocks are applied with the UUT in the shipping container, operational use temperature cycles are applied with the UUT operating. Pass/Fail Criteria The UUT (Unit Under Test) must pass Functional Testing and Visual Inspection before, during,