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State-of-the-art of 'Lean' in the aviation maintenance, repair, and overhaul industry



The increasing need for maintenance, repair, and overhaul (MRO) organizations to meet customers’ demands in quality and reduced lead times is key to its survival within the aviation industry. Furthermore, with the unpredictability in the global market and difficulties with forecasting characteristic of the MRO industry there is an increased need for the re-evaluation of the operation models of organizations within this sector. However, severe economic turmoil and ever-increasing global competition introduce the opportunity for the adoption of a resilient, tried, and tested business operation model such as ‘Lean’. In order to understand this concept, its long-term viability, and its application within the aerospace MRO sector fully, this paper presents the state-of-the-art in terms of the adoption of Lean within the MRO industry by carrying out a systematic review of the literature. This paper establishes the common perception of Lean by the MRO industry and the measurable progress that has been made on the subject. Some issues and challenges are also highlighted including the misconceptions that arise from the direct transference of the perception of Lean from other industrial sectors into the aerospace MRO industry. The ‘enablers and inhibitors’ of Lean within the aviation industry are also discussed. This paper exposes the scarcity of the literature and the general lagging behind of the industry to the adoption of the Lean paradigm and thus highlights areas where further research is required.
State-of-the-art of ‘Lean’ in the Aviation Maintenance Repair
Overhaul Industry (MRO)
P. Ay e ni1 , 2, *, T. Ba ines2, H. Li g htfoo t 2, P. Ba l l 2
1Hawker Pacific Aerospace, Hayes, UB3 1HP, UK
2Department of Manufacturing, Cranfield University, Cranfield, UK
The increasing need for Maintenance Repair Overhaul organisations (MROs) to meet
customers’ demands in quality and reduced lead times is key to its survival within the Aviation
industry. Furthermore, with the unpredictability in the global market and difficulties with
forecasting characteristic of the MRO industry there is an increased need for the re-evaluation
of the operation models of organisations within this sector. However, severe economic turmoil
and ever increasing global competition introduces the opportunity for the adoption of a resilient,
tried and tested business operation model such as ‘Lean’. In order to fully understand this
concept, its long-term viability and its application within the aerospace MRO sector, this paper
presents the state-of-the-art in terms of the adoption of Lean within the MRO industry by
carrying out a systematic review of literature. This paper establishes the common perception of
Lean by the MRO industry and the measurable progress that has been made on the subject.
Some issues and challenges are also highlighted including the misconceptions that arise from
the direct transference of the perception of Lean from other industrial sectors into the aerospace
MRO industry. Also discussed are the ‘enablers and inhibitors’ of Lean within the aviation
industry. This paper exposes the scarcity on literature and the general lagging behind of the
industry to the adoption of the Lean paradigm and thus highlights areas where further research
is required.
Keywords: Lean, Maintenance Repair Overhaul, Service, Outsourcing.
MRO Maintenance Repair Overhaul
OEM Original Equipment Manufacturer
BAMP Bundled Asset Management Programme
ICS Integrated Customer Support
HPA Hawker Pacific Aerospace
TAT Turn Around Time
LCC Low Cost Carrier
1. Introduction
Competition within the aviation industry is fierce [1]. Since 1992, the United States has signed
more than 50 bilateral Open Skies Agreements (OSAs) with the main objective of promoting an
international aviation system based on competition among airlines with minimum Government
regulation. The Government's motivation to support these OSAs is the desire to facilitate the
expansion of air-transport opportunities, making it possible for airlines to offer the travelling and
shipping public a variety of service options at the lowest prices [2]. The positive effect of this
agreement is not only reflected in the passenger population rise and financial gains but this
liberation also lends towards increased international competition within the aviation sector.
However, fluctuations in the global market resulting in difficulties with forecasting and an
increased pressure for reduced inventories, is placing a critical focus across all industrial arms
of the aviation industry (military and civil). Significant proportions of this pressure is been
cascaded into its service arms Maintenance Repair and Overhaul (MRO) sector [3]. With
fewer airline startups and increased exposure to global competition, the competition is fierce.
In dealing with these pressures, new strides in the application of Lean manufacturing principles
are achieving surprising new gains and innovative solutions for MROs [4]. Literature review
shows that there seems to be a strong emphasis on adopting Lean techniques within
manufacturing operations [5]. Kilpatrick [6] explained that Lean manufacturing facilities
increased capacity, quality, and productivity while simultaneously reducing inventory and order
lead time(s). Indeed, there is little doubt that the correct application of Lean principles in the
service sector represents an opportunity for improvements in competitiveness [7]. This paper
aims to provide an insight into the state-of-the-art of Lean within the aviation MRO industry.
Consistent with literature review methods, the initial approach to the study contained in this
paper involved the identification of relevant databases prior to any search that was carried out.
These search operations first employed the use of an array and combination of keywords and
phrases closely associated with the research subject (e.g. Lean, aviation, maintenance, MRO).
The results were then reviewed and the shortlisted publications were then critically assessed
and evaluated to present a set of key findings based on their consistency in literature.
Conversely, some key issues were also raised in areas where the results from literature review
were inconclusive or contradicting. By establishing these findings and issues, this paper
provides a state-of-the-art review of Lean within the aviation MRO industry and thus provides a
platform for more detailed research to improve the understanding of Lean thinking within the
aviation industrial sector.
This paper is structured as follows: First, the industrial context and the scope of this study are
further explained. Then the research methods including the selection process for the material
upon which this study is based on is explained. The paper then presents the analysis of the
literature in the form of key findings. Finally, the results of this analysis are discussed and
summarised with some conclusions drawn.
2. The Aviation MRO Industry: Industrial Context
To be able to establish the application of Lean in an industrial context within the aviation MRO
industry some questions naturally come to mind: ‘What is an MRO’? What are the
characteristics or the functions of an MRO? Are there any classifications or groups within the
MRO industry? What challenge(s) does the MRO industry face? Seeking answers to these
questions will help to set the stage upon which the state-of-the-art of Lean can be established.
1. Illustration of a Typical ‘Maintenance Repair Overhaul’ Organisation
Aircraft maintenance checks are carried out periodically after specified time or usage. These
checks are categorised into A, B, C, and D checks with the light checks referred to as A and B
checks and the heavy maintenance checks regarded as C and D checks. The aviation MRO
industry is primarily responsible for the retaining or restoring of aircraft parts in or to a state in
which they can perform their required design function(s). This includes the combination of all
technical and corresponding administrative, managerial, supervisory and oversight activities.
Inclusive of the described periodic checks, MRO-type activities are principally the servicing,
repair, modification, overhaul, inspection and determination of condition of the aircraft [8]. The
main role of the aviation MRO sector can thus be summarised as the arm of the aviation
industry that is essentially responsible for the provision of a fully serviceable aircraft when
required by the operator at affordable and reasonable cost with optimum quality. An example of
a typical MRO organisation is ‘Hawker Pacific Aerospace’ (HPA). With two facilities in the UK
and America, HPA specialises in the repair and overhaul of Landing Gears (aircraft/helicopters),
Hydro-mechanical components, Wheels, Brakes and Braking systems, Flap Tracks and
Carriages, Flight Controls, Constant Speed Drives, Integrated Drive Generators and even the
distribution and sales of new and overhauled aerospace spares.
2. Classification of MRO Organisations
Organisations within the aviation MRO industry can be classified using various criteria. For the
purpose of this study, MRO organisations will be classified based on the nature or type of the
function they perform and on their organisational structure. However, there is a growing new
trend of OEMs offering MRO-type services which will also be briefly discussed.
1. Classification of the MRO industry based on ‘type-function’
The MRO-type functions can be broadly classified into the following: Heavy Maintenance
Overhaul/Major Modifications; Engine Overhaul; Retro-fits and Conversion; Component
Overhaul; Line Maintenance and Avionics. Due to the nature and type of overhaul required,
MRO firms are usually specialised and specific in the type of overhaul they perform. The
specialist roles by which MRO organisations can be classified are briefly described below and
are illustrated in Table .
Heavy Maintenance Visit: This usually involves the disassembly of major components of
the aircraft for detailed inspection and repairs.
Engine Overhaul: This ranges from routine service checks to the complete repair of the
engines. It is potentially the largest sector within this industry.
Component Overhaul: This usually involves the overhaul of all other parts not
categorised under the heavy maintenance category. These range from Landing Gear to
Fuselage overhauls.
Line Maintenance: This function involves the routine maintenance of the aircraft. MRO
organisations within this category are responsible for the frequent inspection of the
aircraft to ensure its safe in-service use. MRO organisations within this category can
also carry out minor repairs as advised/required by OEM periodic publications [9].
Avionics: MRO organisations in this category specialise mainly in the overhaul of the
aircraft avionics and associated components. Avionics are typically the various electronic
components and systems developed under various types of disciplines (both military and
commercial) into a cohesive working master system that would increase the overall
efficiency of the aircraft.
Retro-fits and Conversions: This sector is responsible for the major and minor design
retro-fits and the conversion of passenger aircrafts to freighter aircrafts.
Although all of the described functions are different in operation, there are huge similarities (in
principle) in the manner in which these services and operations are carried out. However, an
understanding of the different types of MRO organisation will facilitate a better understanding in
the adoption of Lean within the MRO industry.
Sector Examples
Heavy Maintenance Visits
AAR Corporation (Global, HQ Illinois, USA); SR Technics (Global HQ
Switzerland, Zurich); ST Aerospace (Global, HQ Singapore); GE (HQ
Engine Overhaul Lufthansa Technique (Hamburg, Germany); Rolls Royce (HQ UK).
Component Overhaul Hawker Pacific Aerospace (UK/USA); APPH (UK); Ameco (China)
Line Maintenance Scandinavian Aircraft Maintenance (Norway); SIA Engineering
Avionics Honeywell (Global); Selex Galileo Global (Italy/UK)
Major Modification/Retro-fits/
Aeronautical Engineers (USA); Airbus (Dresden, Germany), Haeco
(Honk Kong, China)
Table : MRO-type Functions and Logistics
2.2.2. Classification of the MRO Industry based on Organisational Structure
Using the organisational structure as the criteria for classification, MRO organisations can be
broadly grouped into two independent/third-party MRO organisations and airline
operated/owned MRO organisations [8], 10-11]. The MRO industry has evolved over the years
from when the majority of MRO activities were purely carried out by airline operated/owned
MRO organisation [8]. In some cases, approval was given by the OEM to carry out these MRO
type operations for components still under a valid warranty. The eventual parts and labour cost
of any such repair or overhaul was then invoiced to the OEM [12]. However, following
deregulation in the US in 1978, many airlines just entering the industry did not have existing
MRO facilities or spare parts inventory(ies) to support their fleet [13]. The growth of these new
low cost carriers encouraged the entry of independent MRO providers who offered relatively
low-cost services ranging from line maintenance to inventory control. In an effort to cut costs,
several of the established airlines, such as British Airways and American Airlines, began
outsourcing more of their MRO activities to independent MRO organisations. This allowed
managers to leverage resources and capabilities by concentrating on core competencies that
create value for the airlines’ customers, with non-value added activities being outsourced [8].
Establishing an airline MRO process is considered to be capital intensive which smaller and
newer airline carriers may not be able to commit to. Low fare carriers with traditionally
streamlined business models have avoided strategies adopted by major airlines of investing in
large maintenance stations, but instead, have opted to outsource most MRO-type operations
(especially heavy duty maintenance) to independent/third party MRO providers [10-11, 13-14].
In contrast, bigger airline operators prefer to retain a presence in this field [8]. The advantage of
this choice is that Legacy carriers can compensate for the varying passenger volumes by
offering MRO type services to other airlines [15].
An example of an independent/third-party MRO organisation is AAR Corporation. AAR is the
second largest independent provider of MRO services in North America and its operations range
from aircraft and engine support to engineering, logistics and precision fabrication capabilities.
AAR provides both stand-alone services and customised, integrated solutions offered through
unique combinations of diverse products and services. Conversely, Lufthansa has over the
years boosted its maintenance arm (Lufthansa Technik) and has seen a steady growth in its
MRO capabilities. Similarly, the joint venture between Air France Industries and KLM
Engineering & Maintenance has also experienced tremendous growth with regards to its MRO
capabilities hence retaining as much of the maintenance functions for its fleet in-house as
expected of a typical airline operated/owned MRO organisation.
2.2.3. Introduction of ‘Servitized’ (OEM) business models
Nowadays, there is a growing trend for OEMs to adopt ‘servitized’ business models and thus
offer an array of support packages directly to the customer. Servitization is traditionally
described as the shift by manufacturers from selling the product alone with a few essential
services to using services as a basis for competitive strategy [16]. With more value generated
with increased interaction with the customer (Wise and Baumgartner, 1999), OEMs are offering
packages that extend beyond the warranty of purchased products to include a complete service
package that deals with the maintenance, servicing and spare-part replacement over a fixed
time period. These support packages range from Bundled Asset Management Programmes
(BAMP) to Integrated Customer Support (ICS) [11]. An example of such support or service
offering includes ‘TotalCare’ offered by Rolls Royce [18] and ‘GoldCare’ offered by Boeing [19].
These packages essentially integrate engineering and planning services at a predictable and
competitive cost with enhanced economies of scale. With packages such as these, OEMs are
beginning to take up major stakes in the maintenance budget of airlines thus adding to the
paradigm shift in the way maintenance is been viewed within the aviation industry. This also
supports the proposition that more interest is not only given to how the maintenance service is
carried out but who carries this out.
Although this trend of asset management and asset management engineering are only an
emerging concept in the aviation industry, it is more prevalent within the aviation manufacturing
community (OEM) than the traditional MRO organisation. However, there is a general trend of
MROs owning assets that are used to support airline operators whilst their product is being
overhauled. This suggests that typical MRO operations extend beyond what happens in the
factory to the direct interaction with the customer also extending the scope of the application of
Lean. Furthermore, due to the nature of these asset management programmes, OEMs have
restructured their capabilities and MRO requirements resulting in a business operation that is
slightly different from the traditional MRO organisation. This new context albeit still within the
MRO sector, presents another opportunity for the application of Lean philosophy. However, this
new context was beyond the scope of this paper.
With the growing popularity of these support packages where OEMs are offering MRO-type
services, the study into the adoption of Lean can be extended beyond the typical MRO facility to
also include its adoption in MRO-type operations within the aviation industry. However, the study
presented in this paper was focused on the adoption of Lean within typical aviation MRO
3. Challenges to MRO Business Operations
Over the years, the nature of the challenges faced by the MRO industry has changed
dramatically. The initial challenge for the MRO industry was purely production goals’. These
goals were driven primarily by the concentration on core competences. Almeida [13]
demonstrated how airline-operated MRO organisations tended to be ‘most competitive’ within
the early years of product manufacture because of their substantial inventory and geographic
presence, which gave them the ability to serve customers around the clock. However, in the
later stages of the life cycle of parts the economies of scale, obtaining licenses from OEMs to
maintain and repair specific systems and specialising in state-of-the-art inventory control
measures to reduce costs, favours independent MRO organisations. Although the life cycle of
the product(s) to a large extent dictated who was most likely to carry out the maintenance
operation(s), based on their core competence, the main challenge however, was purely focused
on production goals.
The overall challenge for the MRO industry is now very different. The ever changing market
forces now require that apart from the initial ‘production’ goals, MRO organisations need to
increase the margin between stock and value by considering every possible resource to
maximise operational efficiency and minimise effort i.e. optimise and streamline business
operation [20]. This means that the aviation MRO industry has to manage effectively how it
minimises overall maintenance costs, reduces aircraft turn-around times (TAT) and establishes
return on experience in the form of accurate job standards. MRO organisations also find that
they have to contend with wildly varying asset types and configurations more than ever before.
Maximising the facility capacity and ensuring compliance with the customer’s maintenance
program is another major issue within the MRO aviation industry [21].
There are consequently many initiatives to improve enterprise-wide productivity as increasing
productivity has a universal appeal to any manufacturer faced with increasingly intense global
competition [22]. Detailed study into the Lean paradigm led Womack et al. [23] to argue the
position that Lean principles are applicable to any industry, a proposition that was supported by
Haque [5].
The argument for the adoption of Lean is usually made considering the remarkable commercial
performance of Toyota. It is important to point out that the success and discovery of Lean
principles within the Japanese automotive industry was during a severe economic climate [22]
similar to the current 2008/2009 global economic meltdown. At the end of 2003, Toyota
published profits of 8.3 billion US dollar; greater than the combined profits of General Motors,
Chrysler and Ford establishing Toyota as one of the top three car sellers in the USA [24].
According to company figures, Toyota in 2007, sold 2.348 million units in the US (the world’s
largest car market) with General Motors selling a total of 2.26 million.
Contrary to popular perception, many characteristics of Lean techniques were first recorded at
the Ford production plants in the 1920s as documented by Henry Ford himself in his booksMy
life and work’ [25] andToday and tomorrow’ [26]. Ford demonstrated the need to focus on the
activities that are of service to the customer and wherever possible reduce the waste of material
time and motion. However, the term ‘Lean’ itself was popularised by Womack and Jones [27]
after careful consideration of the Toyota production operation. This study was sponsored by the
International Motor Vehicle Program (IMVP) as part of a worldwide auto manufacturing
benchmarking study. In 1996, Womack and Jones published the book The machine that
changed the world’ [27]. This book helped to demystify the Japanese auto manufacturing
techniques initially referred to as the Toyota Production System (TPS) showing its
manufacturing superiority.
It is however important to point out that modern references to Lean thinking have variations in
content and perspective [28]. The disparity ranges from the Japanese industries that tend to
focus on Lean ‘philosophy’ and ‘culture’ compared with their western counterparts who tend to
put more emphasis on the ‘tools and techniques’ of Lean. The disparity in the perspective of
Lean into these two divides has led to discussions of which one is more accurate.
Baines et al. [7] suggested that the philosophical approach is multidimensional’ in the sense
that it involves the entire organisation in every function and encompasses a wide variety of
management practices including just-in-time (JIT), quality systems, work teams, cellular
manufacturing, supplier management etc. in an integrated system’. Based on this definition, he
concluded that it is no co-incidence that the Japanese companies who approach Lean
implementation in this manner record greater successes than their western counterparts.
Literature study also shows that the benefits of Lean cannot be realised simply by adopting a
few tools and techniques. Intriguingly, most western manufacturers are focusing their Lean
initiatives on operations with few attempts to adopt Lean as a culture. Whatever the perspective,
neither of the positions is more correct than the other, since Lean exists at all levels both
practical and theoretical [29]. The aim of Lean however, is to reduce all forms of waste (‘muda’)
as identified by Ohno [30] in order to improve productivity and enhance overall customer value.
With this is mind, this paper will be careful in distinguishing between both perspectives Lean
thinking’ and ‘Lean principles’ in areas where their understanding and intent is crucial. However,
in areas where their intent and understanding is not crucial and to reflect popular usage, this
paper will refer to both perspectives simply as ‘Lean’.
The express approval and success record of Lean in the automotive industry has signalled other
industrial sectors to awaken to the immense benefits that this philosophy has to offer [31].
Within the aviation industry for example, some MRO firms have been able to cut TAT
dramatically by employing tools that relate to Lean principles. The most important factors in an
airline's selection of an MRO supplier are typically quality, TAT and price, in that order. However,
special circumstances can shift customer priorities which could mean that the priority changes.
For example, an airline could have a situation where there are temporarily more aircrafts than
needed to deliver its schedule thus giving TAT lower priority. But for a fleet sized right for its
network, a short TAT is key to minimising total maintenance costs. The progress in reducing TAT
should prove to be a strong competitive advantage [32].
Conversely, in an environment where quality and safety standards are tightly regulated, there is
the concern as to whether all the principles of Lean philosophy are viable in this context. Since
the main objective of the MRO industry is to restore the aircraft back to a state where it can
safely perform its design functions, a process which can be loosely referred to as ‘re-
manufacturing’, there is the assumption that all of the principles of Lean can be implemented
within this context. However, there is not enough proof in current literature to confirm this
assumption. Hence, the study described in this paper is targeted to investigate the extent of the
adoption of Lean principles and its philosophy within the aviation industry particularly within the
MRO sector.
3. Research Programme
4. Aim, Scope and Research Questions
The aim of the research presented in this paper has been to identify and review available
literature on the subject of Lean within the aviation MRO industry and thereby establish the
state-of-the-art in this field. However, with the adoption and application of Lean within the MRO
sector still in its formative years, the scope of this study was broadened to the application of
Lean within ‘maintenance’ and ‘service-based’ environments. Discretion was then employed in
making sure that the literature review that contributed to the success of this study was closely
related to the aerospace/aviation MRO industry.
The research questions that served as the framework of this study were:
How is Lean interpreted within the aviation MRO industry?
To what extent has Lean been adopted within the aviation industry?
What strategies have been employed in the adoption and sustenance of Lean?
What are the inhibitors and enablers to the adoption of Lean?
What are the strengths and weakness of existing literature?
With the understanding that the above questions may not result in major key findings or that
there may not be specific sufficient literature to make decisive conclusions; they serve as the
guide for the purpose of this study. All observations and notable points are briefly summarised in
the following text.
5. Search Strategy
The approach to the search strategy started by first identifying the relevant data sources, the
timeframe to be considered and the keywords. Initially, a broad selection of databases was
identified covering journals, conference proceedings, theses, books, and articles from trade
journals examples of which include EBSCOhost, Scropous (Elsevier), ABI/Inform (Proquest),
Compendex, Inspec, and Emerald. Through these databases, a host of relevant sources of
information were discovered such as the ‘European Journal for Operational Research’, ‘Journal
of Engineering Design’, ‘International Journal of Automotive Technology’, ‘Journal of Education
for Business’, ‘International Journal of Productivity and Performance’, ‘International Journal of
Operation and Management’, ‘Journal of Engineering Manufacture’, ‘Journal of Quality in
Maintenance Engineering’, ‘Journal of International Economics’.
In order to restrict the search to more recent publications, the timeframe for this study was
chosen initially to include only literature published in the last decade (1999-2009). However,
this time restriction was relaxed as the research progressed firstly by widening the timeframe
beyond the last decade to the early nineties and then by evaluating earlier publications cited in
Identifying relevant literature then required the use of an array of keywords which were carefully
combined to obtain a host of articles and publications. Keywords like ‘Lean’, ‘Maintenance
Repair’, ‘Maintenance and Overhaul’, ‘Case Study’, ‘Toyota’, ‘Aviation’, ‘Supply Chain’,
‘Outsourcing’ ‘Aerospace’ and ‘Airline’ were used and combined to identify a number of search
strings as shown in Table . Some wildcards were also employed to increase the number of
articles found such as ‘Aero*’, ‘Manufact*’ and ‘Maintenance Repair Op*’. The intention of these
wildcards was to capture articles with spelling variances published in either ‘UK’ or ‘American’
style English and to capture articles with similar inference and conclusions but with different
titles. For completeness, an Internet search was also conducted using similar techniques and
processes as alluded to the library databases. Duplicate records identified by the various search
strings were then eliminated. Abstracts of the remaining records were then reviewed as the final
criteria in selecting the articles that would be relevant to the scope of this research. A brief
review of MRO organisations with Lean implementation programmes (or similar incentives) was
also carried out. Although the review carried out was peripheral in nature in that most of the
publications were from internal magazines, a total of 6 companies were shortlisted as shown in
Table for the purpose of this research.
Search String Keywords Total Publications*
S1 Lean + Maintenance 166
S2 Lean + Maintenance + Repair 127
S3 Lean + Maintenance + Overhaul 97
S4 Lean + Maintenance + Repair + Overhaul 36
S5 Lean + MRO 91
S6 Lean + Maintenance + Repair + Operation 39
S7 Lean + Maint* 194
S8 Lean + Aero* 174
S9 Lean + Aviation 126
S10 Lean + Repair + Operation 43
Table : Literature keyword search results
Organisation Method of Research
Website Publications
Lufthansa Technik
British Airways
Exide Battery (Kansas)
Messier Dowty
Table : Identified MRO organisations with Lean Implementation Process
6. Results and Analysis
With the generic nature of this subject a huge amount of publications associated with Lean was
initially identified. Out of all of the publications found, Error: Reference source not found shows
a sample of the articles that were shortlisted for further review. The first criterion used in the
selection of these articles was based on their relevance to Lean (tools, techniques and
philosophy) in establishing a conceptual understanding of subject. An example of such an article
is “Learning to Evolve; a review of contemporary Lean thinking” by Hines et al [28]. The second
criterion used was the article’s relevance to the aviation MRO industry. This led to a fewer
number of relevant articles, as for example Mathaisel [21] - A lean architecture for transforming
the aerospace maintenance, repair and overhaul (MRO) enterprise”.
Following a review and cross-referencing of the publications that were retrieved, it was
established at the time of the search that 60 articles were suitable for the scope of this research
which satisfied the timeframe and relevance. The review of these documents involved a brief
summary of each of the publications against the initial research questions. An outline of the
main topics covered by each publication was then compiled including the emerging themes
observed. A critical review of all the publications was then carried out in order to capture and
represent the consistency and variance in literature which are presented as key findings in the
content of this paper.
The findings presented in this paper were tested by academia and practitioners to ascertain the
authors’ interpretations of the publications and the accuracy of the terminology used. On this
basis, the following key findings were developed.
Author Title Source
Baines et al, 2006. State-of-the-art in Lean Design Engineering: A literature
review on White collar lean.
Journal of Engineering Manufacture
(IMechE, Part B)
Haque, 2003 Lean Engineering in the aerospace industry Journal of Engineering Manufacture
Andrew et al, 2008 Self Maintenance works for repair firm Journal of Engineering and Technology
Al-Kaabi et al, 2007 An outsourcing decision model for airlines’ MRO activities. Journal of Quality in Maintenance
Mathaisel, 2005 A Lean architecture for transforming the aerospace
Maintenance Repair and overhaul enterprise.
Int. Journal of Productivity and
James-Moore and
Gibbons, 1997
Is Lean manufacturing universally relevant? An
investigative methodology.
International Journal of Operations &
Production Management
Alejandro and
Serebrisky, 2006
Competition regimes and air transport costs: The effects of
open skies agreements.
Journal of International Economics
George and George,
Lean Six Sigma for service: How to use Lean speed and six
sigma quality to improve services and transactions
McGraw-Hill Professional, New York
Table : Key publications identified
4. Generation of Key Findings and Issues
The analyses of the literature review carried out provided the basis for the following key findings
and issues.
7. The interpretation of Lean within the aviation MRO industry
There is a strong argument that the application of Lean principles alone to achieve the
organisation’s goal i.e. to improve the economic performance of the company and the
optimisation on the Return-On-Investment-Capital (ROIC) is mere wishful thinking [33]. This
argument is premised on the opinion that Lean principles alone cannot adequately bring a
company’s processes under statistical control nor can it define a sustaining infrastructure of its
implementation [33]. With this perception of Lean it is no surprise that many MRO firms are
implementing Lean principles in combination with other business strategies in a bid to achieve
the enterprise set goals. An example of such a combination is the ‘Lean’ and ‘Agile’ approach.
The integration of these two strategies as described by Andrew et al [3] is based on the
advantage that Agile processes when introduced into the organisation would help in dealing
with the issues of volatility in the market which makes forecasting difficult with irregular demand
patterns, characteristic of the MRO industry. Andrew et al [3] further explains that many
practitioners have attempted to integrate the two approaches by proposing what is referred to as
the ‘leagility’ and ‘agilean’ approach. This integrated approach was developed to create a Lean
yet highly responsive operational system beneficial to MRO organisations dealing with the
consequences of globalisation.
More recently, ‘Six Sigma has been regarded as a successful system capable of achieving
significant gains in business performance. Apart from the strength that it has in the focus on
quality and the ability to more adequately bring an enterprise process under statistical analysis,
many regard Six Sigma as a business strategy while others refer to it as a well structured and
highly effective methodology that achieves improvements in product and process variation
which in turn enhances operational performance [34]. Companies such as Motorola and
General Electric have implemented this approach (Lean principles and Six Sigma) to great
success and have based their Business-Process-Improvement (BPI) around the Six Sigma
concept and to good effect. Smith et al, [35] explains that Lean brings action and intuition to
quickly pick the low hanging fruit with kaizen events while Six Sigma uses statistical tools to
uncover root causes and provide metrics as mile markers and concludes that a combination of
both provides the tools to create ongoing business improvement.
The emergence and popularity of these hybrid Lean versions within the aviation industry has led
to the conclusion that:
Finding 1
Lean is widely interpreted as a viable tool within the aviation industry albeit not sufficient by itself
to realise all the goals set by the organisation.
8. The Focus of Lean
Mecham [36] stresses that although the principles of Lean implemented to great success in the
manufacturing world are similar to those of the maintenance industry, there still remains
scepticism about its focus. The cynicism conversely lies in the thought that the earlier exists in a
manufacturing environment and the later exists predominantly within a service environment
(albeit product-centric) and therefore it is not easy to directly transfer either’s perception in their
approach to Lean.
Furthermore, the introduction of Lean into the aviation MRO industry has led to the coining of
the term ‘Lean Maintenance’ to capture the application of Lean to the industry [35, 37]. Yile [37]
delineated the different phases and their corresponding focus in their interpretation of Lean
maintenance. The different expressions range from a focus on increasing up-time and reliability
to reducing operational cuts to the bare minimum. Other expressions of the focus of Lean
incorporated overlapping Lean tools in order to reduce waste. Although there is the indication
that MRO organisations are now beginning to see value creation potential in Lean application,
this however, is not prevalent within the industry [38]. Whatever the expression, the underlying
focus for the application of Lean currently is essentially, the reduction of waste [35].
Andrew et al [3] suggested that with OEMs employing Lean tools and techniques to build more
reliable equipment requiring less servicing and increased time-between-overhaul (TBO), the
need for customisable MRO work and cost pressures by airlines to have lower service costs and
less aircraft downtime is significantly increased. They suggested that more OEMs are opting for
the use of Lean tools and techniques in the pursuit of value creation’ as compared with the
MRO industry where Lean is presented as a tool for achieving the main aim of reduction’ of
With Baines et al [19] highlighting the danger of crossing and misinterpreting ideas put forward
by Lean especially when the paradigm between the principles, tools and techniques associated
with Lean have not been properly established, this has led to the conclusion that:
Finding 2
The focus of Lean within the aviation MRO industry is predominantly directed towards waste
reduction as opposed to the creation or the enhancement of value.
9. The extent of the adoption of Lean within the aviation MRO industry
Haque [5] argued that although the aerospace industry was initially reluctant to the adoption of
Lean, it is fully viable within the aerospace industry. Although Lean is gaining popularity within
the aerospace industry and can be implemented in small and large companies alike, there is still
a lack of sustainable methodology as well as proper application of supporting management tools
and technology. This may be attributed to the fact that Lean has only recently been seen by the
aerospace industry (particularly MROs) as a viable tool to improve the overall performance of
the company [21]. The paucity of literature on the subject of Lean within the MRO industry
serves as evidence of the industry’s initial reluctance to its adoption compared with other
industrial sectors.
Although the MRO business is vulnerable to both global and local market fluctuations, the
specialised nature of the industry requires that its general internal structure is defined and
conventional which is favourable for the adoption of Lean. The challenge however is that
although significant strides have been achieved in the adoption of Lean, the extent of its
adoption and the maturity across the whole MRO industry cannot be ascertained. Literature
suggests that quite a lot of companies have embarked on their Lean journeys since the late
1990s, however, the spread of its application is significantly smaller in comparison to other
industrial sectors especially the automotive industry [38-40]. This has led to the conclusion that:
Finding 3
There is strong emphasis on the adoption of Lean within the MRO industry, although the extent
of its adoption is difficult to ascertain.
10. Strategy for the implementation and adoption of Lean
Pettersen [29] after successfully confirming the validity of the Lean paradigm, stressed that the
overall goal of an organisation will be responsible for the way in which the concept is
approached. Although he identified that there are generally two different types of goals:
internally focused goals [24,41] and externally focused goals [42-43] he also stressed that the
formulation of goals is essential to the Lean implementation approach. The lack of a precise
definition and goal formulation will lead to difficulties in determining whether changes made in
an organisation are consistent with Lean principles or not and this will subsequently lead to
difficulties in measuring its effect and effectiveness [44].
Literature review reveals that different approaches have been adopted in Lean implementation
programmes within the aviation MRO industry which complements the findings by Pettersen
[29]. For example, Lufthansa Technik in its implementation journey has adopted a strategy
similar to the Kaizen Blitz approach [45] which has recorded great success in its formative
years. They have internally interpreted the Lean concept and developed a three phase
approach to its implementation: ‘Technical Systems’ (Lean tools and techniques), ‘Management
Infrastructure’ (monitoring and continuous improvement measures) and Attitudes and Abilities
(aligning the working culture and mentality with Lean philosophy i.e. paradigm shift) [46].
Mathaisel [21] postulated a ‘transformational’ approach to the adoption of Lean within the
aerospace MRO industry. After careful consideration of different approaches including the
design-build approach proposed by Pearce and Bennet [47], and the Kaizen Blitz approach
proposed by Laraia et al., [48], Mathaisel proposed the Lean Enterprise Architecture (LEA)
implementation programme. He described it as a structured sequence of activities for the
transformation of the MRO enterprise from a current state to a desired future Lean condition by
using phased system based on transformation life cycle”.
Conversely, Fedex have adopted a different implementation strategy by completely redesigning
its Los Angeles Airport facility in order to deal with the challenge of reducing cost and the need
to boost revenue. The focus at the facility was to use Lean principles to increase its capacity
using the same equipment and staff [49].
In many contexts, Lean success is often times regarded as the existence of a “Kaizen culture”.
However, this point was discredited by Roper [50] on the assumption that there is no roadmap
for achieving this kaizen culture and without proper control; most organisations will run out of
time and patience before they discover this path to leanness. Maithaisel [21] also explained that
benchmarking oneself against best internal operations or against external direct competitors or
against best external functional operations or against other generic functions regardless of the
industry can be one measure of the value of one’s relative leanness.
Although these organisations have recorded significant progress and profits that can be linked
to their Lean implementation programmes employing several strategies, with everyone left to
their own devices on their Lean journey the effectiveness and correctness of many Lean
programmes will become questionable. This is because the numerous implementation
strategies suggest that the overriding objective(s) and moderating factor(s) that ensure the
successful implementation of Lean within MRO organisations is yet to be defined. This has led
the authors to conclude that:
Finding 4
Various implementation strategies have been employed in the adoption of Lean, however, the
moderating factors for its successful implementation remain unclear.
11. Inhibitors of Lean within the MRO industry
There is no doubt that the whole of the aerospace industry is now warming to the benefits and
opportunity that are proposed by Lean to eliminate ‘waste’ within its operations and the Lean
revolution is underway within the industry [40]. However, there are some contextual factors that
have inhibited the application and advancement of the Lean paradigm within the aviation
industry. With very little published information on the challenges of Lean within the MRO
industry, the following key inhibitors identified from literature review reflect the inhibitors of Lean
within the aviation industry as a whole.
4.5.1. Comprehensive understanding of Lean
Crute et al. [40] suggested that the lack of comprehensive understanding in the interpretation of
Lean served as an inhibitor to the early adoption of the Lean paradigm within the aviation
industry. They suggested that one of the earlier misconceptions that inhibited the transfer of
Lean from the automotive industry to the aviation industry was the challenge of adapting Lean
from an industry of high-volume capacity (automobile) to an industry of low-volume capacity
(aircraft). However, Womack et al [27] provide a detailed account of the introduction of Lean
principles within Pratt & Whitney thus validating the aerospace sector as a suitable environment
for the application and success of Lean. They also suggest that the aerospace industry may be
at an advantage over automotive in the application of Lean principles, on the basis that lower
volume capacity infers a closer association to the Lean ideal of single piece flow.
Another major misconception of Lean that inhibited the application and advancement of the
paradigm is the confusion that arose from the different Lean capabilities across countries, from
firm to firm but more so within firms. The differing interpretation of Lean led Crute et al. [40] into
a case study research with the conclusion that Lean capabilities are plant’ specific. The
uncertainty surrounding the interpretation and understanding of Lean contributed both to the
reluctance to its adoption and/or the success of many Lean implementation programmes within
the aviation industry. Pettersen [29] also came to the similar conclusion that the capabilities of
Lean have to be fully understood and appreciated before any successful implementation can be
Lean production requires a change in attitudes and behaviour not only of managers but also of
employees [51]. While the aerospace sector may have some advantages in implementing Lean,
the challenges of implementation are real and prove difficult for many firms. Karlsson and
Ahlstrom [52] suggest that traditional ways of thinking and practices are difficult to shed and
radical change would be difficult and require an immense amount of effort to overcome. The
introduction of Lean into an organisation will in most cases translate into the change of the
existing working culture to one where the employees themselves look for potential problems,
seek out and eliminate waste, and take responsibility for continuous improvement, quality
assurance and maintenance. Bamber and Dale [51] suggest that the lack of a concise
understanding of Lean by all employees will somewhat inhibit the advancement of Lean in
organisations where it has been adopted or increase the reluctance of other organisations to
adopt the philosophy. Consequently, it is important for researchers and practitioners to develop
a comprehensive understanding of the Lean paradigm in order to demystify the myths
surrounding Lean that have inhibited its adoption and successful implementation [53].
Finding 5a
The lack of comprehensive understanding on Lean and its capabilities is evident within the
aerospace industry thus hindering the successful adaptation of Lean to be plant specific.
4.5.2. Inaccurate Forecasting and Uncertainty in Operations within the MRO
It is also not uncommon for some of the technology in avionics and weapons systems to be
outdated much earlier than expected either because suppliers cease production of some of
these parts due to cutbacks in procurement (e.g. military) or in order to pursue higher-demand
and more profitable commercial opportunities [54]. Similar logic also applies to the issue of
difficult-to-find parts [53]. Due to the difficulty in accurately predicting these scenarios, decisions
have to be made by MRO organisations to hold some of these components in excess inventory
earlier on in the product's life cycle [55]. With excess inventories held by many MRO firms, there
seems to be a contradiction with the ideals of Lean as discussed by Ohno [30].
Also, with high labour rates forcing the majority of aviation MRO type logistics carried out in
Europe and North America to move to lower wage countries particularly to Asia, Eastern Europe
and Central America as a way of reducing cost, the associated supply chain process supporting
the MRO industry becomes more complicated [11]. To minimise the issues that come with
complex supply chains, the majority of MRO organisations tend to hold excess levels of
In other instances where excess inventory is not kept, the inherent variability of repair work
unlike repetitive manufacturing is impossible to precisely forecast until a full inspection is
accomplished. However, upon inspection of an unserviceable aircraft, the “unpredicted” or
“emergent” rework or damaged parts found will then have to be ordered on an expedited basis
[10]. The danger inherent is that these uncertainties result in delays which could disrupt the
original schedule and final delivery of the overhauled items. In order to overcome these
challenges, it is not unusual for MRO organisations to hold more than the required inventory
which again contradicts the ideals of Lean as explained by Ohno [30].
Finding 5b
The difficulty in accurate forecasting, typically characteristic of the aerospace MRO industry,
results in practices which contradict the ideals of Lean thus serving as an inhibitor to its
adoption and or its advancement.
12. Motivation for the adoption of Lean
Although there were and still are challenges in the interpretation of Lean within the aviation
industry, Womack and Jones [27] was able to establish that Lean is viable and suitable in this
industry. Whilst the drivers and motivators for the adoption of Lean within the aviation industry
have changed over the years, the main factor(s) that consistently enables its suitability and
successful implementation within the aviation MRO industry is concealed in increased business
pressures and globalisation.
The need for improving operational performance in the MRO industry is intensifying [4].
The increase in globalisation has clearly necessitated a complete rethink for some firms in terms
of how they can organise and reconfigure themselves [40]. These business pressures infer that
MRO organisations not only have to continually evaluate and cut TAT to be able to compete
within the global market but also to cut internal cost i.e. doing more with less and subsequently,
improve customer asset availability. MRO organisations are therefore searching for solutions to
dramatically improve performance and enhance their competitive advantage.
The true motivation and enablers of Lean within the aviation MRO industry are measured
against the perceived benefits they offer. These benefits are usually associated with the time,
productivity, efficiency, space, quality, people and cost savings. However, Shah and Ward [56]
suggest that most of the empirical studies focusing on the impact of Lean on operational
performance are constrained to one or two facets of Lean i.e. JIT or TQM. Notwithstanding, a
recent Lean Aerospace Initiative study by MIT [57], found that the introduction of Lean led to
approximately 10-71 percent improvement in labour hours; 11-50 percent improvement in cost;
27-100 percent improvement in productivity; 25-81 percent improvement in factory floor space
and 16-50 percent improvement in customer lead time. Other benefits included 31-98 percent
improvement in inventory or work in progress (WIP) and a scrap/rework/defects/inspection
improvement of about 20-80 percent. All of these benefits are indicative of the motivations for
the adoption of Lean in the Aviation MRO industry.
As a result of these factors a number of major players within aerospace are pursuing Lean
practices [40, 58]. It is no surprise that more and more MRO firms are turning to the same
philosophy that ensured the survival and growth of the Japanese automotive industry when
faced with similar challenges.
Finding 6
A major driver for the adoption of Lean is based on the assumption that MRO business
pressures are consistent with what Lean can deliver.
13. Critical Success Factor for the Implementation of Lean
The pressures’ forcing the MRO industry to turn to Lean’ as a saviour are tangible [20].
Andrew et al. [3] suggest that in order to successfully compete on a global scale, there should
be a clear and novel way by which MRO process strategy tackles the real issue of improving
operational facility performance and reduce variation in key-performance-indicator attainment
that achieves long-term economic sustainability. As already established by Karlsson and
Ahlstrom [52], a company does not achieve Lean product development simply by implementing
Lean techniques alone, instead, a successful move towards Lean requires approaching these
interrelated techniques in a coherent way. Successful Lean implementation will require the
involvement of everyone up and down the ranks in the company as seen from both literature
and case studies [7].
All of these responsibilities will require strong leadership skills. Literature [59] suggests that
these responsibilities are driven by targets and deadlines. Therefore, the person(s) tasked with
these responsibilities should have proven engineering excellence, leadership skills to control the
programme and must be able to effectively interpret customer satisfaction into practical
engineering practices and vice-versa within the scope permitted by the Lean paradigm [5, 24].
Finding 7
Lean implementation success is reliant on the key project management strengths and skills of
the person(s) tasked with the responsibility of the whole project. Any successful Lean
implementation programme will require the complete involvement of all staff.
14. Strengths and Weakness of Existing Literature
Haque [5] highlights the relative lack of the application of Lean within the aerospace industry. It
therefore goes without saying that the extant literature on its application within the industry,
particularly the MRO sector, will be relatively small. This could be as a result of the relative
newness of the paradigm to the industry.
Furthermore, Crute et al. [40] came to the conclusion that the application of Lean is plant
specific; a standpoint that Pettersen and Liker [29, 60] also subscribed to. They also highlighted
the need for a comprehensive understanding of the paradigm before any successful
implementation can be achieved. Although the aerospace industry as a whole has woken up to
the possible benefits that could be reaped from Lean, many practitioners and company
managers are still sceptical about the results and are thus, still piloting different adaptations of
Lean. This scepticism and underlying lack of precise understanding and clarity on the subject
may also lead to the paucity of literature on the subject pertaining to the MRO sector.
Conversely, there currently seems to be an aggressive implementation of Lean (or its variants)
within the aviation MRO industry. This might have been exacerbated by the increased
globalisation and global financial crisis of 2008/2009. This suggests that with the amount of
attention given to Lean within the aviation industry, there will be a significant increase in the
amount of relevant literature on Lean within the aviation industry particularly within the MRO
sector in the near future.
Finding 8
There is a paucity of Literature on the adoption of Lean in the aerospace MRO industry.
5. Discussion
It is clear from literature that in order to mitigate the continuously increasing competition within
the aviation MRO industry, many organisations are turning to Lean philosophy especially
because of the benefits it is perceived to offer. This is premised on it success within the
automotive industry. However these perceived benefits have to be clearly understood in the
context of the environment where it is to be implemented.
Firstly, it has been established in literature that there is an increasing demand for reduced TAT
from airline operators. This demand is sometimes even considered as one of the order-winning
criteria especially when dealing with LCC who cannot afford the lengthy downtime associated
with aircraft maintenance. However, attention also has to be drawn to the fact that, in most
cases, only very limited information is known about the condition of the product before it is sent
for overhaul. This therefore presents a puzzling situation where the customer has been
guaranteed a delivery date for the overhauled product based on speculation about the condition
of the product and consequentially, the required MRO operations and the associated time is not
known. Although the ideals of Lean suggest its suitability within such an environment in that it is
supposed to remove wasteful operations in the overhaul process, the huge uncertainties
involved also point to the challenges that it must overcome for it to be considered as successful
within this industry.
The inclusion of OEM in the MRO market through asset management programmes
(servitization) introduces a new dimension to the competition. OEMs are able to install remote
monitoring programmes to the product that provide up-to-date information on the condition of
the product which enhances their competitive advantage. This also means that they know the
maintenance operations that are required before actual receipt of the product. This informs their
planning and supply functions, making it a more conventional environment for the
implementation of Lean. However, this is a relatively new but growing phenomenon within the
aviation industry and particular to certain sectors (engine). These genres of remote monitoring
programmes are capital intensive and a luxury that most traditional MRO organisations cannot
afford simply because of the huge investments and because the proprietary rights of the product
still remain with the OEM or the airline operator. Therefore, this major and peculiar challenge of
the industry presents a prospective area for further research especially with its interaction with
Furthermore, the context of its implementation also suggests that a thorough understanding of
the Lean philosophy has to be achieved in order to ensure its relevance, effectiveness and
sustainability within the industry. As identified in literature, there cannot be a direct transference
of Lean principles from one industry (automotive) to another (aviation). This is not indicative of
an inherent limitation of the Lean philosophy, but that the emphasis of its application in practice
may differ between industrial sectors albeit having similar goals. A significant amount of current
literature suggests that more clarity on the philosophy of Lean is still needed within the industry
especially considering current focus and interpretation of Lean.
There is a growing proposition that Lean focuses on the creation of value as opposed to the
elimination of waste. Although both motivations are closely linked, they could be misleading in
practice. The creation of value infers a greater threshold for inefficiency in the production system
as far as value is created whilst the focus of waste elimination holds a much lower tolerance for
inefficiencies in the production system. This is also indicative of the clarity that is required on the
adoption of Lean by the industry.
As pointed out in literature, all of these challenges present an exciting opportunity for Lean in
this industry with some companies already reporting successes directly linked to Lean
implementation. Although the extent of its application within the industry cannot currently be
ascertained; the robustness of the Lean philosophy will be judged by its performance in this
6. Concluding Remarks
This literature review as summarized in Table indicates that Lean is viable within the MRO
sector of the aviation/aerospace industry with significant benefits when applied to both
independent and airline operated/third party MRO organisations alike. However, the various
implementation strategies within the aviation MRO industry, and a distinct lack in the
comprehensive understanding of the factors that contribute to the long-term success of its
application, suggest that several Lean implementation programmes will become questionable
over time. A comprehensive understanding of the Lean concept will help in validating the
success of Lean as an independent tool in overcoming the challenges of the MRO industry.
It has also been established that the MRO industry is vulnerable to both external and internal
demands and fluctuations (e.g. passenger volume, difficulty in forecasting and sourcing parts
etc.), the interpretation of Lean has to be specific to the MRO industry and suited in a way that
minimises the consequences of all these variables.
Although Lean in its simplest form is primarily focused on the reduction of waste, the associated
support functions and the consequence of internal changes are yet to be established. This infers
that the strategy for the successful implementation of Lean which considers all of the supporting
functions is yet to be established.
There are also findings that expose the shortcomings of Lean. There is a general belief that
Lean alone is insufficient to achieve a company’s goals and thus has to be combined with other
tools such as Six Sigma etc. This belief might either be as a result of the lack of understanding
of the subject or an inherent fallibility of the paradigm itself. Whatever the case, the capabilities
of Lean still require clarity especially in its adaptation to the MRO industry.
Literature within this field (i.e. Lean within the MRO industry) remains scarce compared to other
industries where these principles have already been established over time. However, the surge
of companies welcoming the Lean idea suggests that this will encourage more academic
research providing better and accurate documentation of proven practices and methods for the
successful implementation and the growth of Lean within this sector. The newness of this
paradigm to the MRO industry means that many practitioners are still ‘experimenting’ with these
principles and there is scope for further research into the ideal lean framework for the aviation
MRO industry. This involves mapping out the most suitable implementation approach and
customised measuring metrics to benchmark the success of its implementation. This will also
involve developing a qualitative and quantitative system and/or methodology that sustains the
successful implementation of Lean. There clearly is scope for future research in this area.
Topic Key Finding/Issue
Interpretation of Lean Lean is widely interpreted as a viable tool within the aviation industry albeit not sufficient
by itself to realise all the goals set by the organisation.
The Focus of Lean The focus of Lean within the aviation MRO industry is predominantly directed towards
waste reduction as opposed to the creation or the enhancement of value.
Extent of the adoption of Lean There is strong emphasis on the adoption of Lean within the MRO industry, although the
extent of its adoption is yet to be ascertained.
Lean Implementation strategy Various implementation strategies have been employed in the adoption of Lean,
however, the moderating factors for its successful implementation strategy remains
Inhibitors of Lean The lack of comprehensive understanding on Lean and its capabilities is evident within
the aerospace industry thus hindering the successful adaptation of Lean to be plant
The difficulty in the accurate forecasting typically characteristic of the MRO industry
results in practices that contradict ideals of Lean thus serving inhibitors to its adoption
and or its advancement.
Enablers of Lean A major driver for the adoption of Lean is premised on the assumption that MRO
business pressures are consistent with what Lean can deliver.
Critical factor for successful
Lean Implementation
Lean implementation success is reliant on the key project management strengths and
skills of the person(s) tasked with the responsibility of the whole project. Any successful
Lean implementation programme will require the complete involvement of all staff.
Strengths and weakness of
Existing Literature
There is paucity of Literature on the adoption of Lean in the aerospace MRO industry.
Table : Summary of key findings and Issues
7. Acknowledgments
The authors would like to thank Jacob Lim, Jonathan Rumble and Sander Podgoric for their
support, advice and assistance during this course of this project. The authors also acknowledge
the support from Hawker Pacific Aerospace who is funding this research at Cranfield University.
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... D-checks are performed for typically one month ( Transport Studies Group 2008 ). In addition to the above checks, daily maintenance checks involve routine maintenance which includes inspection, minor repairs, and servicing ( Ayeni et al., 2011 ). Daily maintenance checks are performed at gate before first flight or at each stop when the aircraft is in transit. ...
... Scheduled maintenance is planned according to flight hours, flight cycles, and calendar period ( Hölzel and Gollnick, 2015 ). Unscheduled maintenance is initiated by technical failures, reported defects, and faults identified during inspection ( Ayeni et al., 2011 ). Flight hours (FH) refer to the actual number of hours flown by the aircraft over a specific period from the time it lifts the wheels from the ground during take-off to the time the wheels touch the ground during landing. ...
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The life cycle of an aircraft consists of design, production, operation and decommissioning phases. For an airline the main focus is on the maintenance process during the operation phase. This paper presents a case study of an airline facing a challenge of increasing maintenance cost. The objective is to understand factors that drive increase in cost. Maintenance cost, flight hours, flight cycles, dispatch reliability and pilot reports were analyzed to find out the maintenance cost drivers. The study identified that the aircraft which dominated the maintenance costs had the highest flight hours, and the lowest dispatch reliability in the fleet.
... There are many different lean strategies as in [24] and various maintenance performances measurement frameworks [15]. Although the "lean" management concept has its roots in the automotive industry, it has been successfully used in insurance and IT companies, health care, in public activities such as the civil service and education [16], aircraft maintenance and repair [3], and many industrial branches as described in [6]. ...
... The researches related to the application of lean philosophy in maintenance have been mainly based on findings that lean concept leads to the identification and elimination of activities that are harmful to the maintenance process and in same time increase the profit of the organizational systems [20]. The great application of the lean philosophy in maintenance is achieved in the airline branch [3]. Amir Mahmud Sahrabi et al. has shown the possibility of AHP method and Expert Choice as lean software tools that helps to decision makers to find out the possible cause of the failure and to determine activities to be undertaken in order to solve the problem, [19]. ...
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ZAstosowAnie nArZędZi sZcZupłego utrZymAniA ruchu do poprAwy efektywności obsługi systemów technicZnych specjAlnego prZeZnAcZeniA Today, executives from the system of maintenance of technical systems for special purposes (military combat vehicles), are trying to improve their organizational processes and create competitive advantage through increasing the quality of maintenance services (increase effectiveness), reducing the total cost (increase efficiency) and reduce the maintenance cycle-time. One of the possible ways for improvements in the maintenance system is the application of lean concept of maintenance, by usage of different tools as 5S, Layout, Visual systems, Kanban and new developed "Technical system maintenance" tool. In order to gain a better understanding of this concept, the paper presents a new developed maintenance model for the application of the lean concept in the real maintenance system. The results of empirical and experimental testing of the proposed model are analysed based on Analysed of methods and effects of improvements (IMEA), Benchmarking methods and multi-criteria, 22 analysis by using the statistical software application MINITAB. The special character of experimental testing are obtained regression equations that describe the changes of the duration of the maintenance cycle, depending on the applied lean tools. The obtained results show that the duration of maintenance cycle is reduced for about 23%, the improvement of maintenance effectiveness is around 14% and the efficiency is showing an upward trend. eksploatacyjnego. Jednym z możliwych sposobów udoskonalenia systemu utrzymania ruchu jest zastosowanie pojęcia szczupłego utrzymania ruchu z wykorzystaniem różnych narzędzi, takich jak 5S, Layout, Visual systems , kanban oraz nowo opracowanego narzędzia "Obsługi Ruchu Systemu Technicznego". Aby lepiej zrozumieć tę koncepcję, w artykule przedstawiono nowo opracowany model obsługi technicznej, który pozwala na zastosowanie koncepcji szczupłego utrzy-mania ruchu w rzeczywistym systemie obsługi. Wyniki empirycznych i eksperymentalnych badań proponowanego modelu anali-zowano na podstawie analizy metod i efektów doskonalenia IMEA, metod benchmarkingowych oraz analizy wielokryterialnej 22 przy użyciu oprogramowania statystycznego MINITAB. W badaniach eksperymentalnych otrzymano równania regresji, które opisują zmiany czasu trwania cyklu eksploatacyjnego w zależności od zastosowanych narzędzi. Uzyskane wyniki wskazują, że przy zastosowaniu proponowanej metody czas trwania cyklu eksploatacyjnego ulega skróceniu o około 23%, efektywność utrzymania ruchu wzrasta o około 14%, a wydajność wykazuje tendencję wzrostową. Słowa kluczowe: efektywność, wydajność, narzędzia szczupłego utrzymania ruchu, utrzymanie ruchu, goto-wość, system techniczny. EPLER I, SOKOLOVIĆ V, MILENKOV M, BUKVIĆ M. Application of lean tools for improved effectiveness in maintenance of technical systems for special purposes. Eksploatacja i Niezawodnosc-Maintenance and Reliability 2017; 19 (4): 616-625, http://dx.
... These types of systems employ extending and blending lean quality techniques to multiple phases of the transformation system to synthesize and a versatile quality system (Lyons & Ma'Aram, 2014). Furthermore, the research about the strategic adoption of lean in aviation maintenance repair and overall industry Ayeni has determined, Ball and Baines (2016) that the key decision areas highly influenced by the lean strategy are "planning and control" (waste reduction, cost reduction, customer satisfaction) and "process & technology" (Ayeni et al., 2011). ...
This research aims to account for the cost of quality through lean and agile operations strategies with empirical evidence from the Aviation industry in the UAE. The cost of quality improvement through lean and agile strategies was not researched enough in the aviation industry. This research will contribute with great knowledge in the aviation industry. The research design used a descriptive, explanatory, causal, and analytical method. A cluster sampling technique was used with a valid sample size of 251 respondents for analysis by multiple regression using ANOVA. Results indicated the significant relationship between lean and agile operations strategies on the cost of quality. There is a direct positive significant relationship between the cost of quality and SC strategies to get quality products cost-effectively. This research was limited to the lean and agile strategies and cost of quality analysis in the aviation industry in one city in the UAE. In contrast, it requires detailed research to explore other cities and assess the aviation industry's challenges while implementing lean and agile strategies. Cost elimination with high-quality production is fundamental for a successful business; lean and agile operations can reduce airline companies' costs and propose the criteria to adopt the strategic implementation efficiently.
... The demand for these services in the UK alone accounts for an estimated £15 billion turnover annually and with the rapid increase in the number of commercial flights year-on-year, the value is set to increase [1]. For MRO service providers, lean innovation is central to ensuring that the capability in meeting the increased demand is satisfied through transitioning from traditional inspection methods based on manual processes with limited data capture towards digitised, sensor-based, data-driven methodologies [2,3]. ...
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Sandwich panels consisting of two Carbon Fibre Reinforced Polymer (CFRP) outer skins and an aluminium honeycomb core are a common structure of surfaces on commercial aircraft due to the beneficial strength–weight ratio. Mechanical defects such as a crushed honeycomb core, dis-bonds and delaminations in the outer skins and in the core occur routinely under normal use and are repaired during aerospace Maintenance, Repair and Overhaul (MRO) processes. Current practices rely heavily on manual inspection where it is possible minor defects are not identified prior to primary repair and are only addressed after initial repairs intensify the defects due to thermal expansion during high temperature curing. This paper reports on the development and characterisation of a technique based on conductive thermography implemented using an array of single point temperature sensors mounted on one surface of the panel and the concomitant induced thermal profile generated by a thermal stimulus on the opposing surface to identify such defects. Defects are classified by analysing the differential conduction of thermal energy profiles across the surface of the panel. Results indicate that crushed core and impact damage are detectable using a stepped temperature profile of 80 ∘C The method is amenable to integration within the existing drying cycle stage and reduces the costs of executing the overall process in terms of time-to-repair and manual effort.
... Meeting customer demands in quality and reducing lead times in maintenance, repair and overhaul (MRO) of vehicular structures is critical for original equipment manufacturers (OEM) in automotive and aerospace industry [1]. With extensive application of bonded joints in structures used in vehicle design and manufacturing, service records attribute more than 50% of structural defects to adhesive bond failures [2]. ...
Impact loads transferred to the bondline of adhesive joints can result in deterioration of the bond and significantly decrease the load carrying capacity. If the damage in the adhesive layer can be healed or reversed, such losses in structural behavior can be recovered. One such healing technique can be implemented in the use of thermoplastic ‘reversible adhesives (RA).’ RA are thermoplastics doped with conductive nanoparticles that can be rapidly heated/melted through exposure to electromagnetic radiations and can be used to heal/repair bonded joints. In this work, single lap joints (SLJ) were bonded using ABS (Acrylonitrile butadiene styrene) thermoplastic reinforced with ferromagnetic nanoparticles (FMNP). The joints were subjected to impact loads (10 J) to induce bondline damage followed by lap-shear tests to obtain damage-induced performance. Next, the impacted joints were subjected to electromagnetic (EM) exposure to introduce healing followed by lap-shear tests to obtain the healed performance. Results were compared with pristine, non-damaged lap-joints. To obtain the efficiency of EM-based healing, a parallel study was carried out to heal the impacted samples by heating in a convection oven. The loss in joint strength due to impact and its subsequent recovery due to healing was evaluated. Up to 92% of joint strength was regained through both oven and EM based healing whereas the processing time for EM based healing was 60 times faster than oven-based healing.
Maintenance plays an essential role in the progress of an organization. In order to achieve excellent performance, maintenance strategies must be linked to manufacturing strategies such as Lean. Based on the available data, this paper provides an understanding of the existing research related to the use of Lean and TRIZ within the maintenance process. In order to identify the need for further research in this area. The objective of this paper is then to answer the following question: How can Lean and TRIZ improve the maintenance process? To do this, we focus mainly on the analysis of previous work where TRIZ tools or Lean manufacturing methods have been used individually to improve the maintenance process. The results of previous studies were analyzed and then the main problems that were detected in the previous literature were identified.KeywordsLean manufacturingMaintenanceTRIZLean maintenanceProcess
This research aims to investigate increasing the amount of labor that adds value by removing wastes and decreasing incidental and non-value-adding tasks as much as possible. Waste is anything that is not essential to the survival of people, machines, and the environment. Materials required to increase the value of the product. When it comes to lean manufacturing, any step that does not increase the value of a product might be viewed as a waste. Analyzing lean waste concerns is a crucial first step in putting lean ideas into practice in various industries, including the liquid batteries industry. To better understand why various lean waste challenges are so significant in Babylon liquid batteries plants, this research will examine how lean adoption can boost productivity while eliminating waste. This research used a survey questionnaire approach to gather data from (BLBP) manufacturing professionals on 17 lean waste concerns. Because of research and conversations with academics as well as experts in the liquid batteries industry sector, we've come to this conclusion, the survey instrument for lean waste issues was created. We received replies on a Likert scale of 1 to 5, with 1 being “never” and 5 being “mostly”. In order to compare various kinds of lean waste, descriptive data analysis is used. When developing new constructs, exploratory factor and reliability analyses are used to help determine the Cronbach's alpha for each one. Finally, the research shows that to execute lean manufacturing and meet the needs of liquid batteries, lean waste issues must be eliminated.
The process of scheduling and planning refers to examining aircraft history based on when and where the aircraft should go for service checks. In this paper, the authors focused on line maintenance activities and examined the impact of unexpected factors (Missing tools and safety requirements) on such activities during the process through a Discrete Event Simulation (DES) model. The DES was used to determine the following: 1. The plan time of each maintenance task according to maintenance scheduling based on the X airline company in Libya; 2. A tasks and productivity evaluation which involved examining the number of tasks required to do per check according to the scheduling plan and planned tasks performed by technicians, and; 3. The total elapsed time involved by analysing the average time for each task according to maintenance schedule planning. The results show that, for all scenarios conducted, the DES model was operating at a high level, and in some scenarios, there was a breakdown in service tasks; a clear indication that the workload factor was high during check periods. However, the main finding in this study highlights how a number of different tasks or the breakdown of maintenance work packages were not being completed before the actual time that had been allocated for the general external condition A-check of the aircraft. This made it necessary to study the work package for each check separately and examine these work packages as they relate to DES which presents a potential solution to a more efficient planning approach. This feature enhances the applicability of the proposed method in real-life, and helps airlines cope with the dynamic environment of airline MRO.
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Purpose – To examine supply chain competences necessary to efficiently and/or effectively succeed in aftermarket support. Design/methodology/approach – Using the aerospace industry as a context, this paper provides a brief overview of aftermarket support practices and trends and discusses the broader implications for aftermarket supply chain managers. Findings – There are multiple approaches to aftermarket support. Which approach should be used depends on key variables including: technology, need for visibility and/or traceability, and need for collaborative product commerce. Research limitations/implications – This paper is a general review. Future research should examine resources necessary in individual industries, other forms of relationships, and the influence of new technologies. Practical implications – In many industries, there are significant opportunities for incremental profit in aftermarket support. Collaborative product commerce, alliances, a number of new technologies (e.g. web commerce), and security needs may play critical roles in determining whether or not a company's aftermarket support practices will be profitable. Firms without competences in these areas should seek help from trusted partners to fill competence gaps. Originality/value – This paper explores an often ignored but significant line of business – aftermarket support. Lessons demonstrated in this paper may be used in a number of industries that rely on aftermarket support for incremental profit.
Management literature has suggested that contextual factors may present strong inertial forces within organizations that inhibit implementations that appear technically rational [R.R. Nelson, S.G. Winter, An Evolutionary Theory of Economic Change, Harvard University Press, Cambridge, MA, 1982]. This paper examines the effects of three contextual factors, plant size, plant age and unionization status, on the likelihood of implementing 22 manufacturing practices that are key facets of lean production systems. Further, we postulate four “bundles” of inter‐related and internally consistent practices; these are just‐in‐time (JIT), total quality management (TQM), total preventive maintenance (TPM), and human resource management (HRM). We empirically validate our bundles and investigate their effects on operational performance. The study sample uses data from IndustryWeek’s Census of Manufacturers. The evidence provides strong support for the influence of plant size on lean implementation, whereas the influence of unionization and plant age is less pervasive than conventional wisdom suggests. The results also indicate that lean bundles contribute substantially to the operating performance of plants, and explain about 23% of the variation in operational performance after accounting for the effects of industry and contextual factors.
Six Sigma is primarily a methodology for improving the capability of business processes by using statistical methods to identify and decrease or eliminate process variation. Its objective is defect reduction and improvements in profits, employee morale and product quality. Developed by Motorola, Six Sigma is an extension of many existing quality tools and techniques, but with the addition of financial accountability. This resulted in process improvement gains at Motorola that increased productivity and profitability.
The NASA's Ames Research Center has started the development of small satellites that can be launched quickly. The small satellite mandate is part of a larger realignment of center priorities to support NASA's Constellation Program for space exploration. Ames will lead NASA's efforts to develop a thermal protection system (TPS) for the Crew Exploration Vehicle (CEV) and Crew Launch Vehicle (CLV). Its computers will be used to develop integrated systems for health monitoring and analysis for the CLV. Ames and the Johnson Space Center have developed room-size blowtorches that can heat air to temperature above the surface temperature of the Sun. These use 10-60 megawatt electrical arc jets equivalent of sending a lightning bolt through a long, narrow tube. The goal of the project is to validate and verify the fault detection software used in the design of CEV/CLV, and to create Computational Fluid Dynamics (CFD) analysis for risk assessment.
The companies that benefits from the `go downstream' theory are presented. Managing downstream businesses requires looking at new variables such as profit per installed unit, share of customer's total downstream-activity spending and total customer return over the product life cycle. Manufacturer's cannot afford to ignore the opportunities that lie downstream, if they do, the next decade will decade will be even bleaker than the last.
New strides in the application of lean manufacturing principles are achieving surprising new gains and innovative solutions for maintenance, repair and overhaul operations (MROs). Imagine an aircraft MRO that runs like clockwork. Technicians, inspectors, engineers, support vehicles and material handlers all roll out at preset times to carry out their work. The operations of each work area are synchronized and the flow of work is clear to each employee from start to finish. Systems are in place to alert management at regular intervals if flow breaks down and since stoppage triggers standard responses, a predetermined response occurs to get flow started again. Simultaneously, a team analyzes the problem and implements a solution to prevent it from reoccurring. Does this image sound like pure fantasy? It shouldn't because it depicts the implementation of lean manufacturing in MRO that has been utilized by a significant portion of the aviation industry to achieve outstanding results. Lean techniques can achieve sustainable improvement throughout production, repair and business processes leading to continuous growth in market share and profits. One example is the significantly improved turnaround time for airplane engine overhaul and repair recently achieved by Delta TechOps (See AM April 2007, page 16). Lean manufacturing principles also have sparked the development of more sophisticated, software-based, support tools for better managing the aviation parts supply chain.