Relationship of Field Reliability to AGREE Bench-Test Reliability

The purpose of this test was to establish a quantitative relationship between AGREE bench-test results and field-test results, as measured in terms of mean time-between-failures (MTBF). The scarcity of field data on AGREE-tested equipments and the variations in field conditions and definitions of failure prevented direct comparison of field and bench results. Therefore, AGREE results were compared with composite field data on many airborne equipment types, the comparison being made in terms of a factor reflecting the relationship between equipment complexity and observed MTBF. The comparison took into account 1) two levels of test severity, 2) two degrees of optimism in interpretation of test results, and 3) differences between tubed and transistorized equipments. Comparison shows that the observed field MTBF was generally higher than the observed bench MTBF for similar equipment types. These findings are reasonably indicative of what might be expected when additional AGREE and field test data are accumulated. In order to improve feedback of information to AGREE, it is recommended that methods and definitions used in military-sponsored field tests be standardized. These changes would appreciably increase not only the predictive value of bench tests but also the usefulness of future field evaluations to all users of field data.