Reduction of ‘No-Fault Found’

Reduction of ‘No Fault Found’ through System Design

The 'No Fault Found problem'

The phenomenon of No Fault Found is known by a variety of names, and is a problem which has plagued operators and maintainers in all technology-dependent sectors from automotive to telecommunications. In- service faults which are detected by operators or faults recorded by built-in tests 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.  No Fault Found 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. NFF can be seen to have more significance upon the overall removal reliability. Recent research shows that improving the system to reduce the number of product removals with no apparent failure will have far more effect on the overall reliability than a corresponding improvement in the product failure rate.  The main causes can be  categorized into system design, inadequate troubleshooting and diagnostics, fault isolation methods and their cost, repeated down-time, reduced availability and increased burden on Through-life Engineering Services.   

The NFF Research Programme

The EPSRC Centre is undertaking 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, software interactions mixed with organisational, procedural and human errors.  The EPSRC Centres aims to take a systems based approach to understand this coupling in order to provide research solutions to address related strategic industry problems.  There are currently several projects 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:

  • Establishing generic causes of NFF for candidate groups
  • Identifying individual solutions for candidate items selected for investigation
  • Establishing cross discipline features and design improvements to solve in-service occurrence of NFF
  • Publishing a handbook and set of design rules to act as expert guidelines to better inform designers to avoid NFF through-life

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.   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.

The NFF Research Team


The NFF team organised a one day symposium on 18th March 2013, co-sponsored by the Institute of Engineering & Technology (IET) Manufacturing TPN and the Aerospace, Aviation & Defence KTN (AAD KTN). It was aimed at bringing together practitioners from across various industrial domains to share their experiences, best practices and ideas for future solutions in order to address the problem of NFF. The event attracted approximately 145 delegates from 60 companies and successful in estabilshing the key research themes which were identified as being the most influential contributors to the problem. To more information about the day and to download keynote presentations, please go the 1st Annual Symposium page, the symposiums report is also available.

Due to the success of the event and the 2nd Annual Symposium is scheduled for Wednesday 28th May at the Shrivenham Campus.  For more information and to register please visit the NFF Symposium Event page.