No fault found

{{short description|Term used in technical maintenance}}

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.{{cite journal|last1=Söderholm|first1=Peter|title=A system view of the No Fault Found (NFF) phenomenon|journal=Reliability Engineering & System Safety|date=January 2007|volume=92|issue=1|pages=1–14|doi=10.1016/j.ress.2005.11.004}}{{cite book|last1=James|first1=I.|last2=Lumbard|first2=D.|last3=Willis|first3=I.|last4=Goble|first4=J.|title=Annual Reliability and Maintainability Symposium, 2003 |chapter=Investigating no fault found in the aerospace industry |date=1 January 2003|pages=441–446|doi=10.1109/RAMS.2003.1182029|isbn=978-0-7803-7717-2|s2cid=109886043 }}{{cite journal|last1=Qi|first1=Haiyu|last2=Ganesan|first2=Sanka|last3=Pecht|first3=Michael|title=No-fault-found and intermittent failures in electronic products|journal=Microelectronics Reliability|date=May 2008|volume=48|issue=5|pages=663–674|doi=10.1016/j.microrel.2008.02.003}}

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:{{cite journal|last1=Khan|first1=Samir|last2=Phillips|first2=Paul|last3=Jennions|first3=Ian|last4=Hockley|first4=Chris|title=No Fault Found events in maintenance engineering Part 1: Current trends, implications and organizational practices|journal=Reliability Engineering & System Safety|date=March 2014|volume=123|page=183|doi=10.1016/j.ress.2013.11.003|hdl=1826/9947|url=https://pure.coventry.ac.uk/ws/files/3999358/J1_R.PDF |hdl-access=free}}

  • 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

File:NoFaultFoundCycle.pdf

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.{{cite news|last=Werner|first=Debra|title=Aerospace America|url=http://www.aerospaceamerica.org/Documents/Aerospace%20America%20PDFs%202015/February2015/Feature1_AA_Feb2015.pdf|archiveurl=https://web.archive.org/web/20170510083521/http://www.aerospaceamerica.org/Documents/Aerospace%20America%20PDFs%202015/February2015/Feature1_AA_Feb2015.pdf|date=February 2015|archivedate=2017-05-10|accessdate=2020-01-01|issue=2|publisher=AIAA}}

See also

References