No Fault Found Working Group

Tackling 'No Fault Found' in Maintenance Engineering

No Fault Found

The phenomenon of No Fault Found (NFF) is known by a variety of names, and is a problem which has plagued operators and maintainers in technology-dependent sectors from automotive to telecommunications. In- service faults which are detected by operators or faults recorded by Built-In Tests (BIT) will be investigated and are likely to result in a subsequent product removal.  After troubleshooting activity, product removal events are grouped into either ‘Confirmed Fault’ or ‘No Fault Found’ categories.  NFF will contain ‘fault isolation failures’ where the actual fault exists in another product which has been missed due to poor troubleshooting or attributed to a hidden fault undetectable during testing. Recent research investigations show that improving the system to reduce the number of product removals with no apparent failure will have far more effect on improving the overall business impact than a corresponding improvement in the product reliability.  Some notable causes that contribute to NFF problems include cultural factors, inadequate systems design, repeated down-time, fault isolation methods and their cost, reduced availability, increased burden on TES.

The NFF Research Programme

In 2011, the EPSRC Centre undertook a 5 year research programme to provide solutions for the NFF problem across industries including defence, aerospace, marine and rail.  The root cause and influencing drivers toward NFF form a complex coupling between electronic, mechanical and software interactions mixed with organisational, procedural and human errors.  The EPSRC Centre aims to take a systems based approach to understand this coupling in order to provide research solutions to address related strategic industry problems.
Currently several projects are being undertaken in this area:

The Reduction of NFF through Improved System Design

The EPSRC Centre for Through-life Engineering Services core NFF research project is a 3 year full-time project which will address the inherent causes of NFF resulting from inadequacies in equipment design. An example is the design of a Built-In-Test-Equipment (BITE) which relies upon an in-depth knowledge of all system interactions. There also is the inevitable case where failure mechanisms only manifest themselves during a limited envelope of operation. These scenarios may not be recognised during design due to limits on system understanding resulting in the selection of inappropriate detection and confirmation strategies leading to a NFF susceptible design. Other areas which are of importance include inappropriate designed limits, software coding errors, inadequate procedures and the situation when the process depends on human judgement for design and validation activities.
The core deliverables include:
• Established generic causes of NFF for candidate groups.
• Identification of individual solutions for candidate items selected for investigation.
• Established cross discipline features and design improvements to solve in-service occurrence of NFF.
• Publication of a handbook and set of design rules to act as expert guidance to better inform designers on how to avoid NFF through the life of a product.
Project team: Paul Phillips, Chris Hockley, Ian Jennions and Samir Khan

Predicting the Burden of NFF in Avionics Through-life

This BAE Systems sponsored project aims to identify equipment design features (i.e. functions/components, measures of complexity or BIT/BITE) and correlate these to NFF attributes (i.e. fraction of faults detected / isolated, fraction of false alarms and rate of false alarms) in order to develop a NFF rate/burden predictor.  The overall impact of such a NFF rate/burden predictor is that it will be used at the design phase, or to verify a proposed modification, to aid in developing equipment which is increasingly immune to NFF throughout its operational life. 
Project team: Tabassom Sedighi, Paul Phillips, Peter Foote

Intermittent Failures in Electronic Systems

The reduced size of electronic chips and increases in their interactions and complexities have led to difficulties in diagnosing system faults; in particular when these faults occur at the component level and are intermittent in nature. The purpose of this project is to investigate the Tools &Techniques which can be used to successfully diagnose intermittent faults and to provide intelligent reasoning on intermittent fault progression.  The aim of the project is to develop in-situ health monitoring technology to detect and characterise intermittent failures arising from such causes as dry solder joints, loose connections, damaged wiring and enviromental degradation,  which heavily contribute to the burden of NFF.
Project team: Wakil Ahmad, Samir Khan and Suresh Perinpanayagam


The No Fault Found Working Group

The ADS MRO & Logistics Network has established a No Fault Found Working Group (NFF WG) with a view to cutting across organisational boundaries in pursuit of a joined-up approach to solving NFF across the industry. From the outset support from the EPSRC TES Centre and industrial partners Copernicus Technology Ltd has been instrumental in the formation of the NFF WG The decision follows a strategic review of the UK MRO sector by members of ADS (the UK trade association for aerospace, defence and security industries) and the Aerospace, Aviation & Defence Knowledge Transfer Network.  It was recognised that there is an opportunity to strengthen the UK MRO sector's capabilities and competitive edge by making step-change improvements to solving No Fault Found (NFF) problems.

In addition to obvious aspirations to share knowledge and best-practice among the group, there has been an unequivocal appetite to deliver tangible outcomes rather than just being a ‘talking shop’.  Consequently the WG will examine the potential to use members’ maintenance data to identify opportunities for NFF improvement case studies and, in parallel with that, it will work with the TES centre at Cranfield to peer-review a proposed taxonomy of NFF terminology to 'get everyone on the same hymn sheet'.  Beyond that plans are also afoot to use the WG as a forum for cross-sector NFF bench-marking, and for reviewing the progress of and lessons from related research in other industry and academic projects


It has been agreed that the formation of the NFF WG has been an important step and that it should continue rather than being a one-off meeting, and so the WG shall meet 3 times a year.


Dr Paul Phillips
Mobile: 07557 386509
Direct Line: 01234 750111 ext 2282



ADS report of 1st NFF WG meeting - 03 July 2012

Minutes of 2nd NFF WG Meeting - 07 Nov 2012

Minutes of NFF WG Meeting - 13 March 2013