NO FAULT FOUND (NFF)
The maintenance of aircraft electronic Line Replaceable Assemblies (LRUs) and Weapon Replaceable Assemblies (WRAs) pose an ever increasing challenge. Much of the challenge is related to intermittent faults which occur due to aging wiring and inter-connections.
These intermittent problems manifest themselves as "bad actor" LRUs and WRAs. Intermittence is known by many names in the maintenance community, including:
No Fault Found (NFF)
Can Not Duplicate (CND)
No Trouble Found (NTF)
Retest OK (RTOK)
No Evidence of Failure (NEOF)
Intermittent faults are a growing problem in electronic equipment. As integrated circuits (ICs) and other electronic discrete parts become increasingly capable and reliable, an ever growing portion of the electronic equipment maintenance problems encountered are not component failures, but rather inter-connectivity problems between the electronic piece parts.
Intermittent faults can be caused by:
loose or corroded wire wraps
cracked solder joints
corroded connector contacts
loose crimp connections
hairline cracks in a printed circuit trace
vertical interconnect accesses (vias)
other phenomena common in electronic equipment
An intermittent fault will often manifest itself during an initial troubleshooting test, such as in the electronic back shop of a commercial repair facility or military flying wing, but by the time the equipment item has been transported to a commercial or military depot for repair, the intermittent circuit is no longer manifesting. This results in NFF. LRUs and WRAs test NFF roughly 50% of the time when inducted into repair facilities.
Intermittent Fault Detection and Isolation System 2.0 (IFDIS 2.0), which augments traditional testing methods, is used to detect and isolate intermittent faults as well as any other wiring problems in complex LRU and WRA chassis.
Intermittent Fault Detector (IFD) is the portable variant used to detect and isolate intermittent faults in Electronic Wiring Interconnect Systems (EWIS) and cable harnesses.