CURRENT RESEARCH ACTIVITY ON THE IMPACT OF NO
FAULT FOUND (NFF) ON MAINTENANCE EFFECTIVENESS
THROUGH LIFE
Wg Cdr CJ Hockley OBE, CEng, MRAeS, RAF(Rtd)
EPSRC Centre for Innovative Manufacturing in Through-life Engineering Services,
United Kingdom, Cranfield University, Bedford, MK43 0AL
Telephone: +44 (0) 1793 785337
E-mail: c.hockley@cranfield.ac.uk
Dr Paul Phillips
EPSRC Centre for Innovative Manufacturing in Through-life Engineering Services,
United Kingdom, Cranfield University, Bedford, MK43 0AL
Abstract: Maintenance Effectiveness and Efficiency need to be one hundred percent if
service and availability are to be delivered to customer’s expectations. However, the
occurrence of faults where the cause cannot be determined, usually described in the UK as
No Fault Found (NFF) and in USA as Retest OK (RTOK) can often be a huge and
disruptive pressure on the successful delivery of support to the customer. The NFF
problem affects many industries and often in different ways, yet good lessons are often not
being shared. What is clearly not in doubt is that huge sums of money are still being
wasted by not sharing best practice and not understanding the true cost of the problem.
This paper will provide a summary of the NFF problem and explain the common causes; it
will describe the impact and some of the solutions identified in the project underway at the
EPSRC Centre for Innovative Manufacturing in Through-life Engineering Services at
Cranfield University to research the problem across different industries.
Keywords: Cannot duplicate (CND); Fault-not-found (FNF); Maintenance effectiveness; No-Fault-Found
(NFF); Retest OK (RTOK); Through-life engineering services;
1.
Establishing the Problem: Initially we should understand what the term NFF,
RTOK or Cannot be Duplicated (another common US term) means. Most work in this
area has been done in the commercial airline industry and this is where most research has
been done that provides evidence of the problem. Definitions of NFF, RTOK and CND
differ as to which level and line of servicing or test equipment is involved, so for the
purposes of this paper we will start with a simple definition of NFF provided by current
experts in the field, Cockram and Huby [1]:
A reported fault for which the root cause cannot be found.
Whilst this is straightforward it suggests that NFF is a diagnostic failure and without doubt
many NFF occurrences will fit this definition. However, there is perhaps more to it than
this. For instance we need to include examples for which there never was a root cause in
the first place. Such examples might be described as merely an incorrect interpretation of
1
what was reported ie communication problems where the user perhaps didn’t describe or
report the fault correctly, leading to the maintenance team chasing a spurious fault and
wasting valuable maintenance effort.
Another and well-used definition from the commercial airline industry is defined as:
Removals of equipment from service for reasons that cannot be verified by the
maintenance process (shop or elsewhere) [2]
But it also needs to comprehensively cover the whole logistic support chain where
maintenance and logistic effort might be expended yet yield no results for any number of
reasons. So NFF should also cover any reported fault which has some nugatory
maintenance and logistic cost and effect but where no fault is found.
To return to the aspect of establishing the root causes, means we should consider several
things to achieve diagnostic success, but it needs correct and comprehensive reporting and
interpretation of the reported symptoms in the first place. Given that it will depend on
many other things such as maintenance and test equipment efficiency, technical and
training skill levels and even environment and facilities, it can be seen that the whole
problem is hugely complex. Only if all these factors are in our favour will diagnostic
success be possible.
2.
Background of NFF: The problems and the costs of NFF are difficult to establish.
Some organisations, whilst understanding they have a problem, seem unwilling to
establish actual costs. The reason for this is possibly because of the belief that solutions
are too difficult or elusive, or perhaps too costly to implement. Old data from the
commercial air industry is worthy of mentioning; in 1993 British Airways (BA)1analysed
their NFF costs and highlighted that the major problem was with their older aircraft which
suffered the highest rates - Concorde, Tristar and Boeing 747. The task force that they
then established found that it was not quite as bad as they had initially suspected; it was
thought to be that 33% of all unscheduled removals were NFF where the same fault
reoccurred very soon after. However, for the year of 1992 their data showed that it was
only 13.8% of all unscheduled removals that they could categorise as NFF. The cost
though was still £17.6M per year. Some unsurprising data also emerged; for instance
avionics components made up 80.4% of all NFF which in addition represented 26.6% of
all avionics removals. The task force also established that maintenance personnel were
removing items for the wrong reason and those in the workshops were not repairing the
faults that had been reported but might be repairing something else that they found wrong.
There were many reasons identified but the most important were:
• Diagnostic training was not good enough.
• Pressure on quantity of items processed rather than quality of repair.
• Lack of emphasis on the tracking the history of components by serial number.
1
All BA data from a presentation by BA to an ERA Conference (1996). Results and conclusions only
retained in a lecture by the author.
2
•
Data on repetitive defects needed to be shared between user and repair
organisation
Solutions were put in place and one of the most important being to track what they called
“rogue units” [3] which were identified as ones which seemed to rotate from aircraft to
workshop very frequently. Once they had such data they discovered that 360 units could
be described as rogue units as they had been involved in 2300 removals at the aircraft in a
single year. This also highlighted the need to share data between themselves and their
repair contractors.
In 1998 they revisited the study to see how things had improved once the new systems had
been implemented. There had been an improvement in the mean time between
unscheduled removals of 20-30%. They had instituted a robust system to both identify
and track the rogue units, having set specific criteria to identify them. These criteria were:
the component had to have a history of repeated ‘short service’2 periods, demonstrate
repeated, identical system faults, be unable to have the fault detected by standard testing
procedures and a replacement of the same type solved the problem. Rogue units were
quarantined and then put through a detailed testing regime and if a fault identified, other
components that showed the same fault were then tested. Another system introduced at the
same time was aimed at lessening the effect on the repair organisation. This was the
“Subject to aircraft Check” (STAC) which involved authority being given to licensed
engineers to change a component and replace it with a new item. If the aircraft then
suffered the same problem on the next flight it could be assumed that the original item had
not been the problem and that item could be returned to stock as “STAC serviceable”. BA
thought that by adopting this procedure they had saved £17M per year.3 This procedure
was quickly adopted by other airlines and has produced similar savings. However, finding
published data on costs and cost savings has so far been difficult, yet from current
research it is believed that costs in many industries are still a huge problem. In 2007 it was
reported in Aviation Week that avionic problems amounted to 75% of all NFF instances in
the airline industry [4].
In military aviation, the problem is believed to be even bigger. A commercial aircraft is
built to fail-safe design principles so there is an element of redundancy and safety built in
which may alleviate some risk and make a NFF instance a little more acceptable. For a
military aircraft built to safe-life principles there is not the same level of redundancy if at
all, so the risk level is higher and therefore something must be found if at all possible to
minimise the risk. Sometimes this may result in more components being changed as a
form of saturation maintenance, so generating items in the repair pool that were not
originally at fault but with the expectation that the faulty item has been caught.
2
A short service period was defined then as 250 flying hours (approx 25 trips for a 747) however it would
be different for each type dependant on the type of service flown.
3
BA Presentation to ERA Conference (1996). Only results and conclusions retained in a lecture by the
author.
3
From research carried out in the RAF some years ago4 some interesting causes and
conclusions were drawn about causes of NFF in RAF aircraft. Operational pressure to
provide availability was a significant reason in some operational theatres. It could vary
for the same item from 25% where there was little operational pressure to over 90% where
operational commitments were highest. Built-in-Test (BIT) and Built-in-Test Equipment
(BITE) seemed to be responsible for a good proportion of NFF arisings as well. Looking
at particular aircraft fleets also gave different arising rates as might be expected but there
were some more general reasons that could be established. Lack of knowledge and
familiarity, usually when equipment was new into service, was an obvious reason but less
so, were discrepancies in procedures and even in some cases, incorrect techniques. Poor
diagnostic procedures, poor test equipment design and/or tolerances and incorrect software
could also be cited as causes. Another main cause was intermittent faults which
manifested themselves due to environmental conditions and specific usage and these
would invariably be impossible to reproduce and find on the ground.
The research that both BA and the RAF had done into the problem showed that NFF costs
occur throughout the maintenance and supply chain. They are also generated because
poor communication might direct the maintenance staff to the wrong systems and the
system then proves serviceable on the ground because of the inability to simulate the
conditions and environment when the fault occurred. Similarly items may be removed for
the wrong reasons resulting in maintenance work at subsequent levels of the repair
organisation who then fail to find anything, so log it as a NFF; this has all caused further
costs for transport and investigation further down the supply chain..
3.
Can NFF be Classified? It is clear that a great many NFF occur in avionics,
electrical and electro-mechanical, but initial research shows that software is also causing
problems. Mechanical systems and structure do not give rise to many NFF and are usually
confined to maintenance actions such as Non-Destructive Testing (NDT) inspections.
NDT checks range from simple visual inspections to much more technical ones such as
eddy-current and ultra-sonic inspections. A NFF in these cases will be caused by lack of
skill or training but also perhaps by a badly designed inspection. The issue here is that
whilst we usually think of NFF as applied to avionics, electrical and electro-mechanical, it
can indeed be much wider and demands solutions.
Consequently the earlier simple definition of NFF as a “reported fault for which the root
cause cannot be found” suggests it is merely a diagnostic failure and therefore needs some
expansion. Relating symptoms to the root cause is clearly important to ensure the right
maintenance activities are set in motion, but the causes of NFF and the solutions are not
always quite that simple. It is thus vital to understand first the causes and to see if they
can be classified into groups that will aid our understanding and lead to the best solutions.
In the past it has been accepted that there are three main categories or classes of faults that
are prevalent in the study of NFF:
4
The investigation was carried out by the Central Servicing Development Establishment at RAF Swanton
Morley under direction of the author but the report is unfortunately no longer available. The results and
summary conclusions though have been retained by the author in a lecture prepared at the time.
4

Intermittent – This category is fairly obvious and describes the fault in a component
or system that only occurs infrequently. It manifests itself as some loss of function or
disruption of a connection and may only occur for a minimal or limited time. The
causes can be diverse but are usually caused by vibration or flexing of the mountings
or possibly through corrosion.

Integration – This category describes components and system that work effectively
when tested in isolation but demonstrate a fault when they are integrated into another
system. The most obvious example is a bent pin on an electrical connector plug.
Integration problems may occur as a result of the way the components or subsystems
have been built, or as a result of software compatibility and are often not a fault in the
original component or subsystem itself; nevertheless the component or subsystem
often takes the blame resulting in wasted maintenance and logistic effort.

Testing – The final generally accepted category concerns BIT/BITE and testing in
general. Tests may be done as part of the system routine checks within the equipment
itself or as part of the diagnosis when a fault is reported. The effectiveness and success
of the BIT/BITE then becomes important in that it needs to be able to assist the
technician in diagnosing the cause and identifying the necessary maintenance action.
In the same way testing in the workshop needs to be able to isolate the cause
successfully and the correct repair required. Test effectiveness and efficiency are
therefore important and the tests have to be designed correctly in the first place. In
addition the alarm rates need to be set at the correct level because if they are too low,
faults will not be isolated and if too high, too many faults that are of little consequence
or effect perhaps will cause a spurious alarm to be triggered.
These three categories or classes, however, appear to be too narrow from the initial
research underway at the EPSRC Centre for Innovative Manufacturing in Through-life
Engineering Services. For instance there are many causes that do not fall into the above
three categories and there are some that might only be relevant to particular industries. For
instance we need to consider other causes such as poor design, lack of communication,
mis-communication, wrong diagnostic methods and processes being specified, poor
training, wrong processes applied and operational pressure. Categorising these is
necessary if we are to comprehensively solve this costly problem. All will generate NFF
which do not fall into one of the generally accepted three classes. Consequently it may be
necessary to generate other specific categories or classes in due course. Perhaps the issue
is not can we categorise all NFF into three or more classes, but can we relate causes,
solutions and classes as an aid to understanding how to solve or reduce the cost of the
problem?
4.
Additional causes of NFF: It is necessary therefore to look at all the other causes
that can be identified to see how they can be grouped. Initial work shows that there are
many additional causes that must be considered if total and effective solutions are to be
provided. These additional causes are broadly grouped under organisational and culture,
procedures and rules, technical inefficiencies, and finally workforce behaviour. However,
within each of these there are many sub-sets and causes and they are briefly mentioned
below.
5
Organisational and culture. Some organisations are too big and often therefore too
bureaucratic to recognise or admit that they have a problem and even when they do, there
is a reluctance to grasp the need for fundamental change. Often in these situations the
there is a lack of evidence on the true cost of the problem. Certain levels in the
organisation know of the problem but do not have the authority or motivation to help solve
the problem. Some organisations have a structure that doesn’t allow good communication
between maintenance teams and between the different technical trades. The organisation
does not have culture that encourages solutions to the NFF problem. Data and information
is often lacking and would require a great deal of commitment, effort and expense to
generate. There may even be an unwillingness to confront the problem from below for
fear of alerting management to poor practices. Job protection can also be an issue.

Time pressures on maintenance operations. When there is great pressure to return
the equipment to service quickly, time for diagnosis is critical and might just not be
possible. Consequently we see an overwhelming pressure on maintenance staff which
then often results in some speculative maintenance as this is the quickest way to return
the equipment to service. What happens is that instead of diagnosis to determine which
of three components is at fault, all three are changed. This means one out of the three
should have the fault found further down the repair chain, but the other two should
each generate a NFF occurrence. Whilst changing the three components was the
quickest solution, it has now caused expense and effort throughout the support chain.

Inadequate training and lack of training equipment. Technician training has to be
sufficient to cope with difficult diagnosis tasks and there has to be adequate training
equipment and facilities to support such training otherwise faults will not be diagnosed
successfully. Maintenance personnel also have to be given time to build up experience,
particularly on new equipment, otherwise the wrong processes or tests may be done
with little chance of finding the true cause or fault.

Communication, information exchange and lack of historical data. Components
need to be tracked by serial number so that there is historical evidence to pinpoint
rogue units. All those involved also need to share knowledge and experience of NFF,
which means designers, producers, maintenance providers and users, as there will be a
wealth of information that can help reduce systematic faults across fleets. Sharing
information and historical data though is always easier said than done and may require
some investment.
Procedures and rules. In many organisations such as the military there will be
procedures and rules that deal with NFF, or alternatively, either cause some of the NFF
incidents, or exacerbate and perpetuate their occurrence. The ability to have the STAC
procedure previously described is an example of a procedure that deals with the
occurrences for fail-safe designs and has been shown to reduce the subsequent cost of
NFF. On the other hand military rules and procedures may be such that it is too difficult
for rules to be changed purely for some fleets and not for others, as it would require a
whole raft of new rules and procedures with the attendant safety provisions in order to
ensure it is only applied to the authorised fleets; in such a large organisation with so many
6
diverse fleets, this has so far proved impossible to adopt in the military. Similarly there
has been no real incentive in the past to monitor rogue units because the overhaul and
repair costs were covered in-house and thus largely hidden. Indeed more repair work often
justified the need to keep the service as an organic capability rather than contract it out to
a third party. Times have changed with much of this support activity now being outsourced to industry who has a much greater incentive to drive out waste and increase
profits. Other considerations loosely under the heading of procedures and rules are:

Supply chain effect. NFF can have a huge effect on the supply chain. When a fault
occurs frequently it may generate the replacement of the same item, yet the fault keeps
re-occurring usually because the cause is intermittent in a completely different
component. The supply chain sees large numbers of this item being used so demands
more to keep up with demand; because there are then more items in the supply chain,
technicians believe it must be the unreliable candidate to change as the first choice and
so it becomes self-perpetuating. This is known as the supply chain effect or phantom
supply chain.

Discrepancies and errors in test routines. Errors in test routines and procedures
may not be obvious but actually will keep causing NFFs until the procedure or routine
is corrected. Similarly some tests or procedures may not be as comprehensive as they
need to be to diagnose some faults properly so result in a NFF.

Inaccurate reporting. Faults must be clearly and unambiguously reported so that
maintenance personnel have the best chance of diagnosing the cause. Without a clear
understanding the diagnosis may follow a completely spurious path leading to a NFF.
Technical inefficiencies. Causes from technical inefficiencies can be anything from the
lack of test equipment, poorly designed test equipment or processes, incorrect diagnostic
routines for new and novel faults not previously experienced before.

BIT/BITE. The pass/fail criteria for BIT/BITE must be correctly set at the right level
otherwise false alarms will be generated if set too low, or faults will not be correctly
isolated if set too high.

Incorrect repairs. Again faults usually caused by intermittency might not be able to
be diagnosed but during investigation a fault is found in the system but which actually
had nothing to do with the original fault. Nevertheless it is repaired but the original
fault still persists and should therefore the original job should be classed as NFF.

Operating environment. Without the relevant information on the environment it may
be a fruitless search for the reported fault and the result will be a NFF. Furthermore, a
representative operating environment, with the correct operating stresses being
properly replicated, may be impossible to provide during diagnosis.

Poor system design. Some designs will not lend themselves to easy testing and
diagnosis and so may make NFFs inevitable.
7
Workforce behaviour.
This cause of NFF also impinges on the cultural aspects previously mentioned but not
from an organisation’s point of view; rather it is more about the individual’s attitudes and
behaviour. For instance maintenance personnel often get into bad habits and not
necessarily deliberately. They accept short-cuts or accepted divergence from procedures in
what is known in the aviation world as “Norms.” Very often managers have even tacitly
approved such divergences. This tacit approval then becomes the norm but can exacerbate
the number of NFF instances or hide the true path to successful diagnosis.

Communication. At the individual level, maintenance personnel may not appreciate
the importance of good communication and the sharing of experience and knowledge.
Poor communication can in itself cause NFF by sending the next shift off on a wild
goose chase or merely not sharing information about a commonly experienced
problem.

Resistance to change. Individuals are often reluctant to change what they believe is
well tried practice and procedures.

Poor Maintenance practice. Technicians may have got into bad habits but no-one
recognises them as poor maintenance practice. Simple disregarding of procedures,
perhaps due technician over-confidence and arrogance, may cause NFFs.
It can be seen from the above that all these issues will produce an increase in cost and
certainly a waste of effort and resources. It is also clear that NFF problems will certainly
impact badly on maintenance effectiveness and through-life engineering services.
5.
Cost of NFF throughout the support chain: It is still difficult however, to assess
overall costs for the NFF problem. Companies seem reluctant to declare what the costs
are, perhaps fearing the worst without the means to solve the problem. It may be the
issues are further down the support chain and possibly therefore not under their control.
There are various points at which the costs are going to appear: the user, the next level
repair organisation which might be quite close to the user, or the original equipment
manufacturer (OEM) or Maintenance Repair Organisation (MRO) both of which are
usually also remote from the user. At the user, no fault might be found despite a great deal
of diagnostic effort but no component is replaced and no actual solution therefore
established. All the tests prove satisfactory so the equipment is declared serviceable but
designated NFF. Nevertheless, the fault recurs during the next mission or very soon
afterwards, so further diagnosis is now required. Also at the equipment the wrong
diagnosis or investigation might get underway for a number of reasons resulting in the
wrong solution being applied; work has been done so it is expected the fault has been
fixed but it again recurs on the next mission. In this case the first fault is not usually
classed NFF but should be! Finally, very often in desperation, a component is
speculatively replaced in the hope that it will fix the fault, but at least something has been
changed! Unfortunately the removed component is now classified faulty but at the next or
subsequent level of repair, it will be classified NFF.
8
At the subsequent level of repair therefore there could be many wasted man-hours spent
looking for faults that are not there because the items had been removed ‘on spec’;
similarly man-hours may be spent looking for intermittent faults that cannot be replicated
because the environmental conditions cannot be applied as part of the bench test. Finally
all the same technical inefficiencies previously described will cause unproductive effort.
But the effects and cost will not just be felt at the repair sites and there will be costs and
effort expended throughout the supply and support chain. More items will need to be
provisioned into stock to cope because of the numbers of items undergoing diagnosis that
are in fact NFF but which are consuming time and effort and hence cost. The supply chain
effect causes more items to be in supply chain and thus additional inventory cost..
Diagnostic Success: Whilst the costs are difficult to establish, there has been better
information available in recent years on diagnostic success, particularly with respect to
avionics. Based on some research done by Copernicus Technology Ltd.[5], the diagnostic
success rate for avionics tends to divide into diagnostic success, diagnostic failure
resulting in speculative replacement and diagnostic failure of the functional tests.
Diagnostic Failure Speculative Replacement
Diagnostic
Success
Diagnostic Failure Functional Test Only
Figure 1: Diagnostic Success Rates for Avionics System Repairs
Fig 1 shows that considering all faults, both hard and intermittent faults, that diagnostic
success is comparatively low in avionics, perhaps only 40%. Diagnostic Failures account
for more than 50% of occurrences. The ‘Functional Test Only’ number is the case where
the technician cannot positively identify the fault, but by establishing there isn’t a fault by
doing the functional test, the equipment can be declared serviceable again. The other
diagnostic failure group covers all the remaining reasons previously identified.
6.
Mitigation of NFF: Having tried to establish something about the costs, we must
turn attention to mitigation and solutions. There has been a great deal of research over the
years but solutions and mitigations are certainly not universal even within some
Companies let alone within industries or across different industries. There is consequently
much still to do and hence the need for the consolidated 3 year research effort now being
undertaken at the newly formed EPSRC Centre for Innovative Manufacturing in Throughlife Engineering Services. Some of this effort is being directed at the design and
production stages where there is a need to create more fault-tolerant systems which
perhaps incorporate inbuilt redundancy. There is a requirement for some thorough
9
research effort into intermittency, its causes and solutions. Understanding intermittent
faults will rely on the ability to describe the various interactions accurately and how
mechanical, software and electronic elements all have to interact together. Modelling of
intermittent faults will be required but will need to include probabilities of fault detection.
A thorough understanding of individual systems will be required in order to provide fault
models and models that deal with false BIT alarms and the root causes of BIT deficiency.
In some industries and individual companies, adopting better HUMS and prognostics
would ensure that important operational parameters were monitored at all times to identify
adverse and out of limits variations. These technologies would help to change from a
policy of reactive maintenance to a predictive policy which would concentrate on
providing vital information on the root causes of faults which is not provided with
traditional BIT/BITE. Other technology improvements such as the use of RFID
technology can be adopted to track units within the supply chain and to monitor the
complete service history of items while they are in the supply chain and is certainly not a
new development [6]. Such technology solutions will go some way to mitigating NFF but
what is needed is a comprehensive approach dealing with organisational, procedural and
behavioural issues as well as all the technical issues.
7.
Current Research Effort: Research at the EPSRC Centre for Innovative
Manufacturing in Through-life Engineering Services has a three year project which started
in November 2011 and which seeks to address the problem of NFF and make some
progress with solutions. It has the following ambitious, but we believe, realistic
objectives:
•
•
•
•
•
Identify procedural, process and behavioural issues that need to be changed,
learning from best practice in each industry.
Develop an in-situ health monitoring approach at the board level to detect,
characterize and locate NFF intermittent failures and deliver a fault localisation
mechanism and demonstrator at the board and sub-system level.
Devise strategies, methodologies and system design rules to mitigate the
intermittent NFF failure mechanisms and to demonstrate their effectiveness in
reducing the likelihood of NFF occurrences.
Develop a multi-disciplinary approach at the System level for the effective analysis
of the root causes of NFF in order to assist design activity across domains.
Develop a handbook and a system design evaluation standard with procedures that
will reduce the problem of NFF.
Conclusion
This initial research in the EPSRC has confirmed that there is still a serious issue with
NFF and shows that there is still much to do in some organisations to change the culture
and behaviours if we are to avoid the huge costs that occur. One early conclusion is that
we should start that culture change by describing the issue as a Fault Not Found (FNF)
which has a more positive behavioural sense, rather than NFF which suggests an attitude
of resignation that there was probably no fault there anyway. FNF suggests that we must
still do something to solve a problem and there is an acceptance that something must be
done. Whilst this research project has only just started, it will continue for nearly three
10
more years and if all the objectives are met will certainly achieve a huge step forward with
this perennial problem
References
[1]. Cockram, J., Huby, G. (2009), “No Fault Found (NFF) occurrences and intermittent
faults: improving availability of aerospace platforms/systems by refining maintenance
practices, systems of work and testing regimes to effectively identify their root causes”,
CEAS European Air and Space Conference,26th-29th October, Manchester, UK
[2].
ARINC Report 672 (2008), “Guidelines for the reduction of No Fault Found
(NFF)”, Avionics Maintenance Conference, Aeronautical Radio Inc.
[3]
Söderholm, P. (2007),” A system view of the No Fault Found (NFF)
phenomenon”, Reliability & System Safety, Vol 92, No 1, pp. 1-14
[4]
Burchell, B., (2007), “Untangling No Fault Found”, Aviation Week, 9th Feb
[5]
Huby, G., Cockram, J. (2010), “The system integrity approach to reducing the cost
impact of ‘NO Fault Found’ and intermittent faults”, RAeS Airworthiness and
Maintenance Conference, 16th Sept, Cranfield University, UK
[6] Narsing, A. (2005), “RFID and supply chain management: An assessment of its
economic, technical and productive viability in global operations”, The Journal of Applied
Business Research, Vol 21, No 2, pp. 75-80
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