MIL-STD-690D
5.2.4 Extension of failure rate (optional). Manufacturers may designate, at their option, specific samples to load on life test for the sole purpose of accumulating hours to extend a failure rate. These samples must be randomly selected from the manufacturer's production and cover the full range of values that, upon successful completion, will provide for failure rate extension. The test hours accumulated for this test cannot be used by manufacturers as part
of their failure rate maintenance testing (see 5.2.2). If this option is chosen, the manufacturer shall notify the qualifying activity:
a. That this option is being used prior to loading samples.
b. Details of the sample parts that will be used in the upload (date codes, values, and styles).
c. Prior to discontinuing the test for any reason. NOTE: The qualifying activity has the option of requiring the manufacturer to do a complete failure analysis on failed test samples and require the manufacturer to notify customers of affected products.
5.3 Procedure III, "Maintenance of FR level qualification":
a. Maintenance of qualification at the qualified FR level shall be predicted upon compliance with the requirements of 5.3.2. The qualification maintenance period shall be specified in the ER specification, and is not an option to be selected by the manufacturer. At the beginning of each qualification maintenance period, the manufacturer shall elect and record the unit-hour requirements ("C" number) that will be met within the qualification maintenance period specified and notify the qualifying activity. If a manufacturer selects a different unit-hour "C" requirement than used during the previous qualification maintenance period, the manufacturer is required to notify the qualifying activity of this change at the beginning of, or prior to, the new maintenance period.
b. The maintenance period in effect shall not be changed, regardless of the unit-hours accumulated. Unit- hours that exceed those required for the maintenance period shall be at the manufacturer's risk (within the original "C" number). However, these unit-hours may be used for failure rate extension.
c. Qualification shall be maintained periodically, in accordance with 5.3.2, as long as the product remains qualified at any given FR level.
d. The same combination of data permitted in establishing lower FR levels (see 5.2) may be used in maintaining these FR levels. However, the FR level established in accordance with Procedure I shall be maintained separately for each style qualified, unless otherwise specified. If qualification has been granted at the "R" or "S" level and production is not sufficient on each style to maintain the unit hours required by table IV, the minimum number of unit hours required for any one style would be the unit hours required to maintain that style at the "P" FR level. These unit hours may be obtained from units which are on extended
FR tests or from parts manufactured for test. Data may be combined from all similar styles for the remaining unit hours required for the "R" or "S" FR level. In instances where qualification by similarity is not detailed in the applicable specifications, determination of similarity and information regarding consolidation of data is to be obtained from the applicable military specification and the qualifying activity. The qualifying activity has the option of style groupings if excessive failures occur in one particular style.
e. Where the manufacturer determines that they will not meet the minimum unit hours required during the maintenance period, the qualifying activity shall be notified immediately.
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