No fault found
No fault found (NFF), no trouble found (NTF) or no defect found (NDF) are terms used in the field of maintenance, where a unit is removed from service following a complaint of a perceived fault by operators or an alarm from its BIT (built-in test) equipment. The unit is then checked, but no anomaly is detected by the maintainer. Consequently, the unit is returned to service with no repair performed.[1][2][3]
If there is an underlying fault that has not been detected the unit may be returned for repair several times with no fault identified. Alternative descriptors include:[4]
- No fault found (NFF)
- Cannot duplicate (CND)
- Fault not found (FNF)
- No trouble found (NTF)
- No defect found (NDF)
- Hidden failures
- False failures
The NFF problem
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As the figure shows once a fault has been reported, investigated, and no fault found any future problems caused by the fault cause additional work which is a waste of maintainer time. Different causes have been suggested for this issue.
- Some can be attributed to the way a possible fault is perceived by the user.
- Some can be attributed to the diagnostic methods available to the maintainer.
The fact remains that no fault found causes a cost to industry. NFF is thought to cost the United States Department of Defense in excess of US$2 billion per year.[5]
See also
[edit | edit source]References
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