Prioritization of aircraft maintenance unit strategies using fuzzy Analytic Network Process: A case study

In this paper, a new methodology for prioritizing strategies using an integrated approach of fuzzy Multiple Criteria Decision Making (MCDM) is proposed. A case study in an aircraft maintenance unit showed that the “Financial” criterion and the sub-criterion of “Competitiveness and Improving Customer Satisfaction” (with weights of 0.3108 and 0.84, respectively) were the most critical ones. Due to the internal relations between the criteria and sub-criteria in the fuzzy MCDM and the opinions of the experts of the aircraft maintenance unit, the weights of the main criteria obtained were closer to the actual conditions.     

An optimization approach to aircraft dispatching strategy with maintenance cost – A case study

This paper presents an optimization approach to identify aircraft dispatching strategy at a flight training school. The strategy adopted by the school was to dispatch the aircraft which is closest to its scheduled maintenance. This strategy was examined and compared with other potential dispatching strategies. The paper presents a mixed integer linear programming model to identify the strategy that minimizes the total cost of scheduled maintenance. The analysis shows that the optimization approach can save 2%–5% on annual maintenance cost compared with other strategies. The model can equally be applied to rental cars or trucking companies.     

Aircraft line maintenance scheduling and optimisation

With the advent of new technologies and more modern aircraft, many of the maintenance jobs traditionally scheduled for periodic block checks can now be performed in the ‘‘line maintenance” environment, i.e., during layovers between scheduled flights of an aircraft. This flexibility can be exploited to reduce maintenance costs and improve fleet utilisation of an airline. In this paper we introduce and study the Line Maintenance Scheduling Problem (LMSP). The LMSP assigns jobs to available maintenance opportunities, defined by aircraft routes, and sets the starting time for each job. Its objective is to minimise the deviation from this schedule with respect to given due dates for each task, without exceeding resource capacity at the airports at any moment. We formulate the LMSP as a mixed integer programming problem, and describe and compare two solution approaches for this problem: an integrated exact solution algorithm, which solves job assignment and timetabling simultaneously, and a sequential, heuristic approach. We tested our algorithms on a set of instances inspired on data provided by an industry partner. Our experiments show the applicability of both approaches on realistic settings: the exact approach was able to find the optimal solution for all instances, in less than 10 min on average. Our analysis also shows with an example that line maintenance can be more efficient when capacity is spatially spread, even if the total capacity is reduced.     

Aircraft noise exposure and resident's stress and hypertension: A public health perspective for airport environmental management

Noise management regulations and policies at commercial airports are reviewed. A cross-sectional study of environmental noise and community health based, on the SF-36, was conducted in residential neighborhoods near Sydney Airport with high exposure to aircraft noise and in a matched control suburb unaffected by aircraft noise. Noise measurements were analysed and a novel noise metric formulated based on background environmental noise levels. After controlling for confounders, subjects who have been chronically exposed to high aircraft noise level are more likely to report stress and hypertension compared with those not exposed to aircraft noise. Policy implications and further research are described.     

Aviation insurance and the implementation of the small aircraft transportation system

Aviation insurance is a unique field from a business, legal, and regulatory standpoint. Issues such as risk management, contracts, and liability raise particular challenges within this highly specialized market. The implementation of the small aircraft transportation system (SATS), as envisioned by NASA and its industry and academic partners entails a thorough analysis of aviation insurance to determine whether the current market structure could support this major policy initiative. In this paper, we investigate the impact of the current legal, regulatory, and market environments on the implementation and development of SATS. The primary goal is to determine what obstacles these conditions would raise vis-à-vis SATS’ implementation. We also seek to identify strategies, alternatives, and regulatory policies that would help achieve a successful transition to a modern, efficient, and fully developed market for small aircraft transportation services.     

Next generation single-aisle aircraft – Requirements and technological solutions

In recent years, aircraft manufacturers have concentrated on developing new long-haul widebody aircraft, such as Airbus’s A380 and A350XWB and Boeing’s 787 and 747-8. The next challenge for manufacturers and suppliers is the development of new short- and medium-range single-aisle aircraft. This paper outlines how the challenges and quantified goals as developed by the Advisory Council for Aeronautics Research in its Strategic Research Agenda would influence and contribute to the improvement of the next generation of civil transport aircraft. It continues with a discussion on possible aircraft requirements from the viewpoint of an aircraft operator. Subsequently, the most important technological elements available for the next generation single-aisle aircraft are briefly characterised. Using the Council’s objectives for CO₂ emissions and noise, as an example it can be shown that a decoupling of air traffic growth and emissions/noise can be achieved.     

Airframe manufacturers: Which has the better view of the future?

For the development of Airbus’ A380 and Boeing's B787 it seems that these manufacturers have differing views of future airline networks. This paper assesses from published sources the likely preferences of leisure and business passengers for different airline network approaches and also assesses airline strategies through the economic cycle. The manufacturers seem to have substitutable aircraft types. Both leisure and business travellers are increasingly price elastic and growth in both markets means both aircraft type will be successful aircraft meeting differing needs. However, airline market-share strategies are likely to undermine the success of hub by-pass or hub-to-hub focus strategies throughout the cycle.     

Efficient aircraft spare parts inventory management under demand uncertainty

In airline industries, the aircraft maintenance cost takes up about 13% of the total operating cost. It can be reduced by a good planning. Spare parts inventories exist to serve the maintenance planning. Compared with commonly used reorder point system (ROP) and forecasting methods which only consider historical data, this paper presents two non-linear programming models which predict impending demands based on installed parts failure distribution. The optimal order time and order quantity can be found by minimizing total cost. The first basic mathematical model assumes shortage period starts from mean time to failure (MTTF). An iteration method and GAMS are used to solve this model. The second improved mathematical model takes into account accurate shortage time. Due to its complexity, only GAMS is applied in solution methodology. Both models can be proved effective in cost reduction through revised numerical examples and their results. Comparisons of the two models are also discussed.     

A qualitative study on the exploration of challenges to the implementation of the Safety Management System in aircraft maintenance organizations in Turkey

Safety management has recently started using a paradigm that ‘sees the world as it is’ rather than ‘prescribing how it should be’. The Safety Management System (SMS), a product of this paradigm shift, has fairly new and different characteristics. These changes are expected to pose a number of challenges to the successful implementation of the SMS. This qualitative research study sets out to explore challenges to the implementation of the SMS in aircraft maintenance organizations in Turkey, with reference to the perceptions of Quality Management Systems (QMSs) and SMS experts working at these maintenance organizations.Qualitative data was collected from thirty participants through an open-ended questionnaire. Both inductive and deductive methods were used for the data analysis. The results suggest that the SMS entails a cultural transformation and is likely to bring about certain challenges because of its new and different characteristics. It is concluded that significant challenges may derive from a poor positive safety culture. Top management support and the practices of the civil aviation authority also have the potential to pose challenges. Other challenges are expected to result from SMS training and the need for the integration of stakeholder SMSs.The research results are expected to improve the success of the SMS and hence safety in aircraft maintenance. The results may also encourage the regulatory authorities to take measures to improve the success of the SMS in the launch of State Safety Programs (SSPs).     

End-of-life aircraft treatment in the context of sustainable development,lean management,and global business

Dealing with retired aircraft taking into account the environmental, social, and economic impacts is emerging as an air transportation problem for the near future. The players involved in the problem wish to solve this challenge in a systematic way to benefit from the value extracted from the core activities of the end-of-life (EoL) aircraft treatment, decrease the environmental impacts, and at the same time maximize the social value. This paper proposes a holistic approach to EoL aircraft treatment considering lean management, sustainable development, and the global business environment. An integrated optimization framework is proposed to support decision-making at both the strategic and managerial levels. The flexibility of the framework makes it possible to compare different business models, dismantling strategies, and network structures that impact the efficiency, stability, and leanness of the recovery network. A solution methodology based on the joint application of fuzzy interactive approach and genetic algorithm is introduced. The application perspective and guidelines for pilot study are also provided. To the best of our knowledge, this is the first time that recovery of EoL aircraft is considered based on three aspects of sustainability, lean, and global business. Therefore, this study provides many promising perspectives in this context to enrich the literature of EoL aircraft as a new aviation industry challenge and opportunity.     

Global air travel: toward concentration or dispersal?

The geography of airline passenger movement through the major cities of the world has changed between 1990 and 2000. The change has been at the expense of the very large global cities and major hubs in favour of a group of next largest cities. It has been detected by comparing the shares of total passenger movement through cities in two separate ways, and by exploring changes in the connectivity between cities over a similar time period. The new pattern reflects the use of new aircraft technology, changes in the location of demand for air travel associated with a broadening in the global linkages between cities, new regulatory arrangements and airline corporate strategies. The implications are that the pressures for airport planning will be felt in a new set of cities, although because the share of passenger traffic through the very large global cities is still high they will remain a major focus for airport planning and management action in the immediate future.     

Resilience of passenger boarding strategies to priority fares offered by airlines

Increased efficiency of airplane boarding via the jetway is achieved by sequencing passengers at the airport terminal. Various strategies have been developed and implemented at airports. However, even the best strategy can be distorted by the airlines priority fare. Priority passengers board in a random order which destroy the desired boarding sequence. This causes the aircraft aisle to be blocked in different locations. The article analyses the sensitivity of most common boarding strategies to the number of priority passengers. The article gives an example for Airbus A320 with single aisle cabin, configured in 30 rows of 6 seats each. To investigate this issue an original simulation model was developed, which allows to estimate the impact of the number of passengers with priority on the implementation of selected boarding strategies. The results obtained are astonishing. Such distortions have a negative impact on some strategies, while for some strategies better results are obtained. This discrete event based simulation model allows the process manager to choose the appropriate strategy or to abandon the jetway and use the airport stairs to avoid or reduce delaying the aircraft.     

Aircraft and passenger recovery during an aircraft’s unexpected unavailability

Airlines design their initial schedules under the assumption that all resources will be available on time and flights will operate as planned. However, some disruptions occur due to mechanical failures and unexpected delays of maintenance, making the aircraft unavailable for a certain period of time. These deviations from the initial plan result in high operational costs in addition to the serious inconveniences experienced by passengers. In order to handle aircraft and passenger recovery problems simultaneously, we work on integrated networks at which aircraft routings and passenger itineraries are superimposed. Consequently, we could calculate the actual profit and cancellation cost by evaluating each passenger itinerary while considering the seat capacity limitations. In our computational results, we use a daily schedule of a major U.S. airline and clearly demonstrate that there is an optimal trade-off between operating and passenger-related costs.     

基于不同故障类型的不完全预防维护模型

通过引入受维修次数、预防维护费用共同制约的改善因子,全面考虑Type I和Type II两种不同的故障类型,建立不完全维护模型,求解相应系统装备的维修策略。模型以维修期内的最小单位时间维护成本率为目标,在不同可靠度的条件下,求得最佳的预防维修时间间隔及最佳的预防维修次数,分析了成本率曲线和时间间隔对不同参数的敏感度,并且对各种参数对系统最佳维修次数的影响进行讨论。     

Aircraft selection by applying AHP and TOPSIS in interval type-2 fuzzy sets

The selection of the appropriate aircraft can bring competitive advantages to airlines, however, there are a number of factors which introduce a degree of uncertainty to the selection process. By removing this uncertainty, airlines can increase their chances of achieving their long-term goals. New Multi-Criteria Decision Making (MCDM) methods provide decision-makers with a satisfactory solution for choosing suitable aircraft. Therefore, we focused on the multi-dimensional evaluation and selection of the most suitable commercial aircraft alternatives by using new MCDM method. This article provides decision support to airline planners on the selection of commercial aircraft under uncertainty. In the study, unlike other studies in the literature on aircraft selection, the model presented here uses an Interval Type-2 Fuzzy Analytical Hierarch Process (IT2FAHP) and Interval Type-2 Fuzzy Technique for Order Preference by Similarity to an Ideal Solution (IT2FTOPSIS) hybrid methods. The proposed model for aircraft selection allows commercial airlines to evaluate the aircraft in terms of specific criteria: economic performance, technical performance, and environmental impact, and, as a result, it helps decision makers select appropriate aircraft in an uncertain environment. In addition to use by commercial airlines, the methods in the study can also be applied to the selection of training aircraft, cargo aircraft and military aircraft. Our findings show that the Airbus A321neo is the most suitable commercial aircraft in terms of technical aspects, economic aspects and environmental aspects for airlines.     

Towards the optimisation of the schedule reliability of aircraft rotations

A cost minimisation model is developed to optimise the scheduling of aircraft rotation by balancing the use of schedule time, which is designed to control flight punctuality, and delay costs. A case study is conducted using schedule and punctuality data from a European airline. Optimisation shows that the operational performance of an aircraft rotation schedule is improved in terms of: schedule regularity, mean delays and expected delays of aircraft rotation. Although the total schedule time of the study rotation is increased by 5%, a system cost saving of some $9.3 million/1000 aircraft rotations is gained after schedule optimisation. Three schedule reliability surrogates—mean delay time of aircraft rotation, expected delay time of aircraft rotation and schedule regularity—are employed to evaluate the reliability of aircraft rotation schedules. It is found that the reliability and robustness of schedule implementation is significantly improved after optimisation.     

Identifying airline cost economies: An econometric analysis of the factors affecting aircraft operating costs

This paper provides the results of an econometric analysis of the influences of airline characteristics on the average operating costs per aircraft movement. The analysis combines a comprehensive selection of airline-output variables, airline-fleet variables, and airline-market variables. The results confirm the existence of economies of density, economies of load factor, economies of aircraft utilisation and economies of aircraft size. The paper does not provide evidence of economies of scale, economies of stage length or economies of fleet commonality. Furthermore, airlines that additionally operate full freighters, airlines that are members of a worldwide alliance and airlines that operate a multi-hub system face higher average operating costs per aircraft movement. Surprisingly, the regression results demonstrate that airlines that use newer aircraft have higher average operating costs per aircraft movement, suggesting that ownership costs (depreciation and leasing costs) of new aircraft outweigh the increasing maintenance costs of old aircraft. Finally, the results show that airlines that have a dominant position at their hubs or bases have higher operating costs per aircraft movement, implying that the absence of serious competitive pressure enables airlines to charge higher ticket prices and, with that, leads to a limited focus on cost savings.     

The risk in using financial reports in the study of airline business models

A review of published articles has shown that many researchers use financial reports as the main source of information in regard to airline business models. A study of accounting policies and other external information, however, has highlighted the differences in assumptions as to useful lives and the residual values of aircraft, which are the principal assets of airlines. While the considerable, unexplained differences in the accounting policies of enterprises with similar business models indicate there may be risk in using this data, the risk can be eliminated by making appropriate adjustments in the financial statements.     

A qualitative study of outsourced aeronautical maintenance: The case of Brazilian organizations

The outsourcing of aeronautical maintenance has been criticized for the quality of services offered. According to the literature, airlines have contracted repair stations to perform maintenance activities on their aircraft or parts when attempting to optimize resources (time, facilities, personnel, money). The attempt to reduce costs in maintenance activities and regulatory deficiencies can lead to maintenance management practices that could threaten equipment airworthiness. Therefore, the aim of this research was to evaluate whether outsourced aeronautical maintenance is aligned to common industrial maintenance management practices. To achieve this goal, qualitative exploratory research was conducted on Brazilian repair stations. For data collection, a questionnaire was developed based on seven factors related to aircraft maintenance. The data revealed that a mismatch exists between the best maintenance management practices and expected repair station performance.     

Management of airport congestion through slot allocation

The lack of airport slots (the time allocated for an aircraft to land or take off), particularly at airports which experience congestion, have reached unmanageable proportions in recent years. The International Civil Aviation Organization (ICAO) records that, by the end of 1997, there were 132 slot controlled international airports. The World of Civil Aviation, 1997–2000. ICAO Circular 273-AT/113, p. 12 (118 year round and 14 during peak seasons). Between 1989 and 1998 the reported number of commercial aircraft in service increased by about 60% from 11,253 to 18,139 aircraft. In 1998, 1463 jet aircraft were ordered, compared with 1309 in 1997, and 929 were delivered compared with 674 aircraft in 1997. In 1998, the total scheduled traffic carried by airlines of the 185 Contracting States of ICAO amounted to a total of about 1462 million passengers and about 26 million tonnes of freight. These figures¹ are reflective of the rapidly increasing frequency of aircraft movements at airports, calling for drastic management of airport capacity. To cope with the demand, airlines are forming strategic alliances with themselves by utilizing such commercial tools as franchising, leasing and interchange of aircraft. The management of airport capacity through slot allocation is a critical consideration for the world aviation community. This article analyses the problem and discusses various issues related thereto.