No abstract

Various terms such as ‘cannot duplicate (CND)’, ‘re‐test OK (RTOK)’, ‘no fault indicated (NFI)’, ‘no fault found (NFF)’, and ‘no trouble found (NTF)’, are used to describe the inability to replicate field failures during laboratory assessment. This paper uses CND to refer to all such failures. CND failures can make up more than 85% of all observed field failures in avionics and account for more than 90% of all maintenance costs. These statistics can be attributed to a limited understanding of root cause failure characteristics of complex systems, inappropriate means of diagnosing the condition of the system, and the inability to duplicate the field conditions in the laboratory. This paper addresses CND issues with reference to research carried out on samples of an electronics board used as the seat‐back processor modules on board the Boeing 777. The boards were monitored continuously using existing on‐board comprehensive built‐in test equipment. It was found that the hot temperature operating limits of the board decreased by up to 70°C during highly accelerated environmental stress. Furthermore, improperly seated connectors were found to result in spurious component failure reports from the built‐in test equipment. This paper suggests that the observed drift in operating limit and connector issues are two likely root causes of CND failures and makes recommendations for addressing them. © Crown Copyright 1998. Reproduced with the permission of the Controller of Her Majesty's Stationery Office.

This report was prepared as ^n ati^ount ot work sponsored by the United btateb oovernmtnt NLither the United States nor the United State^ AtLnit, Energ^> Commission, nor any of their epiployees, no^ 3n> of their contractois subcontractor^ or their emplo>e>,s makes any vvarrarit> express or implied or a^sum s any legal liability or rtsponsibility foi ihe dcturdc> corn plefeness o-jsefulness of anv r lorrr itioii rtj^pai I'ui product or process disclut.'-d, or rt.pre'-ents that 's i e would not infringi-privately c-v^nt j rigliis

This report describes the expected performance of the XECF test assembly. Predictions are presented and discussed for all tests outlined in RN-S-0314, XECF Test Specification., and in modifications No. 1 and 2 thereof. The test-prediction analysis indicated that, under all test conditions considered5 the test-parameter limits would at no time be exceeded; and no unsafe conditions were disclosed that could result in damage to-the test article or facility. Descriptions of the engine system, the test facility, and the instrumentation system are included so the report can be used as a comprehensive reference document during quick-look analyses of test results.