An investigation of ‘cannot duplicate’ failures

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.

No Fault Found events in maintenance engineering Part 1: Current trends, implications and organizational practices

“…References Fault diagnostics [1,2,3,6,7,8,9,10,11,12,13,14,15,16,17,18,19] System design [1,13,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32] Human factors [1,20,32,33,34,35,36,37] Data management [1,20,37,38,39] 1 [1,26] are review papers on the NFF.…”

“…Williams et. al (1998) [10] claim that NFF failures can make up more than 85% of all observed field failures within avionics components. They also account for more than 90% of all maintenance costs, which can be can be attributed to:…”

Prognostics and Health Management: A Review on Data Driven Approaches

“…One of the most prominent problems is called No Fault Found (NFF) problem (related terminologies include "cannot duplicate, " "re-test OK, " "trouble not identified, " and "intermittent malfunctions") [10][11][12], particularly in electronic-rich systems. As the name suggests, it refers to the situation that no failure/fault can be detected/replicated during laboratory tests even when the failure has been reported in the field [13]. NFF issues not only make the prognosis and diagnosis extremely difficult, but also can cause skyrocketing maintenance cost.…”

“…NFF issues not only make the prognosis and diagnosis extremely difficult, but also can cause skyrocketing maintenance cost. As reported by Williams et al [13], NFF failures account for more than 85% of all filed failures and 90% of overall maintenance costs in avionics; it is estimated that NFF related activities cost the U.S. Department of Defense 2∼10 billion U.S. dollars per year [14]. Evidently, NFF contributes a lot in operational cost in many different application areas.…”

Data-driven model for maintenance decision support: A case study of railway signalling systems

“…5 The high number of NFF events can be attributed to a limited understanding of the root causes and characteristics of failures in complex systems, inappropriate means of diagnosing the condition of the systems, and the inability to duplicate field conditions. 6 Some research reported in the literature has shown the importance of NFF events, not just technically, but also organisationally and behaviourally, and has proposed addressing this issue as an integrated problem. 5,7-9 Granstro¨m 10 has described how the number of NFF events in railway signalling systems can be reduced by updating the maintenance requirements for these systems.…”