significantly aging the UUT. Note: Types and levels of testing may have to be increased if infant mortality failures are occurring in operational use. Conversely, if a statistically significant sampling demonstrates that infant mortality failures are not occurring, ESS tests may be reduced or eliminated. Functional Testing is still required. Note: Testing must strike a balance between the probability that the repairs have induced a defect, and the probability that the testing can detect that defect. For example, a reduced number of temperature cycles has a lower probability of detecting a defect, but may be appropriate if the repair is minor and has little risk of inducing a defect. Note: Repaired 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 repaired units or from the original Production Unit Acceptance Test data shall require rejection of the UUT. Reliability ESS This should be part of the Qualification and Acceptance ESS when verification of reliability is required. Reliability Qualification Testing Purpose: Done on the production qualification UUT to demonstrate life-cycle compliance with the reliability specifications per Mil-Std-781, and the original manufacturer's development specifications. Method: Use Mil-Hdbk-781A. The UUT is usually tested to actual environmental levels, but margin is added if accelerated aging is required. Note: Must do Acceptance Testing including Pre-Conditioning first. This is because these tests are done on all production units and so become parts of the environmental stress profile. Note: The presence of redundancy in the design is not reason to eliminate reliability tests. Redundancy is used to compensate for any unknown and untested failure modes, and for damage tolerance. Redundancy only increases reliability by a small amount. Reliability Acceptance Testing Purpose: Done on all production units to find any unit with reliability degradation due to daily variations in the production process and workmanship. Method: Vibration (typically 0.04 G2/Hz for 5 minutes/axis) and temperature for 3+ cycles, last one failure-free. Note: Usually only done on high reliability (3-sigma) and safety of flight items. Pre-Conditioning Testing. Also called Burn-In Testing Purpose: Done on all active unit LRUs, SRUs, and piece parts (production, spare, and repair) to find ‘infant mortality’ of parts and workmanship. Method: per Mil-Std-750D, Mil-Std-883E, and Mil-Std-202G. Note: Most mil-spec piece parts have not been pre-conditioned by the part manufacturer. UUT Categories Passive Unit Examples: chassis, antenna coupler,