An investigation of ‘cannot duplicate’ failures

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.     

Human error risk management for engineering systems: a methodology for design, safety assessment, accident investigation and training

The objective of this paper is to tackle methodological issues associated with the inclusion of cognitive and dynamic considerations into Human Reliability methods. A methodology called Human Error Risk Management for Engineering Systems is presented that offers a ‘roadmap’ for selecting and consistently applying Human Factors approaches in different areas of application and contains also a ‘body’ of possible methods and techniques of its own. Two types of possible application are discussed to demonstrate practical applications of the methodology. Specific attention is dedicated to the issue of data collection and definition from specific field assessment.     

Purple plague: Eliminated or just forgotten?

The reappearance of ‘purple plague’ as a reliability and failure risk in current IC devices has led to renewed interest in the precise failure mechanisms and eventual failure mode. These are outlined and illustrated with examples of recent failures in plastic encapsulated integrated circuits, hermetically sealed integrated circuits and hybrids. The reasons for the reappearance of this type of failure are discussed, and it is shown that the problem may be expected to increase in future generation devices.     

An Experimental Study of the Mechanical Behaviour of the ‘Conchyliates’ Shell‐Stone: Some Irregularities of the Size Effects

Abstract: A detailed experimental study of the size effect, i.e. of the dependence of the mechanical properties on the size of the (self‐similar) specimens used for the laboratory tests is presented in this paper for the case of a relatively soft natural building stone called ‘conchyliates’ (shell‐stone). ‘Conchyliates’ was used by ancient Greeks for the erection of the Zeus Temple at the Olympia archaeological site. The motive of the study was the need of the scientists working for a partial restoration of the monument for an in‐depth knowledge of the mechanical behaviour of both the original building material of the monument as well as of the material that could be used for the completion of damaged structural elements. During the study various classes of cylindrical ‘conchyliates’ specimens were subjected to uniaxial (unconfined) compression. It was concluded that the dependence of the peak stress of the material on the size of the specimen is not only very strong but it appears to be, also, non‐monotonous. In addition it was indicated that the size of the specimens also influences the elasticity modulus as well as the strain energy density in a more or less similar manner. On the contrary it is concluded that the slope of the strain energy density plotted versus strain is not seriously affected by the size of the specimen, at least for the working‐load portion of the stress‐strain graph.     

The failure characteristics of mechanical equipment which receives comprehensive maintenance overhaul

Research into the failure and repair characteristics of such diverse mechanical equipment as centrifugal pumps and compressors, comminution machinery, electrical generators and offshore pipelines has shown that their repairs and overhauls seldom return their performance to a condition which is ‘as good as new’ in a reliability sense. The research reported here was commissioned to test whether this conclusion applied to mining machinery, which was overhauled to exacting maintenance standards. The results showed that these machines eventually exhibited a similar deterioration, which was statistically, significant. Furthermore, the escalation in their real costs of overhaul was of such a magnitude as to justify their systematic and frequent replacement. The evidence suggested that this deterioration in life performance resulted from the wear out of machine components and the bodies of these machines, which could not be remedied properly by successive overhauls.     

Effects of Packaging Liners on Cooling Rate and Quality Attributes of Table Grape (cv. Regal Seedless)

Table grapes are commonly packed in multi‐layered packages consisting of cardboard carton, plastic liners and carry bag/pouch to maintain product quality along the cold chain. Each liner is characterized by the number and the size of perforations, which influence the environmental conditions around the produce inside the package. This study investigated the effects of different carton liners on the cooling rate and quality attributes of ‘Regal Seedless’ table grapes. Fruit quality attributes measured include weight loss, stem dehydration and browning, SO₂ injury, decay, berry firmness and colour. Non‐perforated liners maintained relative humidity (RH) close to 100% during cold storage and during a 7 day shelf life period, which resulted in delaying the loss of stem quality but significantly (p ≤ 0.05) increasing the incidence of SO₂ injury and berry drop during storage, as compared with perforated liners. Perforated liners improved fruit cooling rates but significantly (p ≤ 0.05) reduced RH. Low RH in perforated liners resulted in significant (p ≤ 0.05) increase in stem dehydration and browning as compared with non‐perforated liners. Berry firmness decreased by 78% after 42 days of storage at ?0.5°C. Significant (p ≤ 0.05) differences in berry firmness between the different packages were observed only during the first 7 days of storage. Berry colour changed from greenish‐yellow to yellowish‐green in all types of plastic liner during the storage period. Fruit decay occurred in all packages after a 7 day shelf life, with the highest incidence of decay occurring in liners with less perforation. Copyright © 2011 John Wiley & Sons, Ltd.     

The NRC Bell 412 ASRA safety system: a human factors perspective on lessons learned from an airborne incident

The National Research Council (NRC) Bell 205 Airborne Simulator is a full authority fly-by-wire (FBW) research helicopter. On 24 May, 1996 this aircraft underwent a failure which drove all four flight control actuators to full extension shortly after engagement of the FBW system, with nearly catastrophic results. The sound design inherent in the original Bell 205 safety system allowed the safety pilot to override the FBW system and prevented the loss of aircraft and crew. This incident, however, led to the realization that the existing safety system configuration in the Bell 205 was only marginally acceptable, and that this same system would be inadequate for the next generation FBW aircraft, the NRC Bell 412 Advanced Systems Research Aircraft (ASRA). Experience gained from the Bell 205 incident, and historical experience, has driven the design process of the safety systems for ASRA, with a particular view toward the capabilities and limitations of the operators.     

New Observations on a Geological Hotspot Track: Excursions in Madeira and Porto Santo (1825) by Mrs T. Edward Bowdich

This paper works with the modern concept of the geological hotspot track – the building processes and movements of volcanic island chains – applied strategically to one of its illustrative formations, the Madeira Archipelago. By analogy, however, the concept works equally well to describe the important early 19th‐century scientific knowledge‐building activity that produced Charles Lyell's On the Geology of Some Parts of Madeira (1854). A central section of the paper uncovers the contributions to knowledge of this geology before Lyell's, and in particular, Excursions of Madeira and Porto Santo (1825) by Mr [sic] T. Edward Bowdich. A thorough examination of this text then constitutes an important case study for literal and figurative investigation of geological hotspot tracks. The main argument proposed is that current specialist research forgets its submerged and longer histories to its detriment. Insights contained in older information often supply reminders of the key questions and contributions from the past that provide checks and balances for further developments of a field. By promoting multi‐level, multi‐stranded and multi‐lingual investigation of the history of 19th‐century geology in Madeira before Lyell ( 1854 ) as central to hotspot track research, this paper marks nodal conditions that constitute advancement in critical knowledge‐building within and outside the discipline of geology.