Transportation Research Part E

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1 Transportation Research Part E 46 (2010) Contents lists available at ScienceDirect Transportation Research Part E journal homepage: Structuring critical success factors of airline safety management system using a hybrid model Yueh-Ling Hsu a, *, Wen-Chin Li b,1, Kuang-Wei Chen a,2 a Department of Air Transportation, Kainan University, No. 1, Kainan Rd., Luzhu, Taoyuan County 338, Taiwan, ROC b Psychology Department, National Defense University, No. 70, Section 2, Central North N. Rd., Beitou District, Taipei City 112, Taiwan, ROC article info abstract Keywords: Airline Safety Management System Decision Making Trial Evaluation Laboratory Grey Relational Analysis Analytic Network Process With the global trend of legal requirement for a performance-based Safety Management System (SMS), to develop and implement an SMS to deliver services has become the most important goal within the airline industry. Yet there found some discrepancies concerning the use and the manner that SMS was being explained and taught. Therefore, this research aims to develop a quantitative evaluation model, which identifies the key components of airline SMS and considers the interaction between key components. To explore the core value of SMS, an extensive review regarding SMS components are firstly conducted and summarized from major aviation organizations and authorities, and then Grey Relational Analysis is used to group and select key components. After the critical components are derived, Decision Making Trial Evaluation Laboratory and Analytic Network Process are employed to analyze and map out all kinds of interactions among critical components and dimensions systematically. An empirical study is presented to illustrate the application of the proposed methods. From the results of the combined approaches, Organization is the most important dimension in SMS, which begins with Policies that convey to all staff the top managers vision on safety. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Improving air safety has always been the top priority for the airline industry, and having an acceptable air safety record is important to an airline s success (Liou et al., 2008). Yet with global aviation activity forecast continuing to rise, and the probability that this will bring with it an attendant increase in the accident rate, there is concern that traditionally reactive methods for reducing risks to an acceptable level may not be sufficient. In recent years, the systemic origins of many aircraft accidents have led to heightened interest in the way in which organizations identify and manage risks, and to the development of safety management system (SMS); the approach for understanding and managing safety is evolving (Hsu, 2004). In order to reinforce the conviction that safety management is a managerial and systemic business process, as of 23 November 2006, International Civil Aviation Organization (ICAO) has demanded Contracting States to establish a safety program for the acceptance and oversight of safety service providers SMS. SMS requirements are already a standard for air traffic services and airports, and the requirements will become standard for airlines on 1 January 2009 (Maurino, 2007). Therefore, to design, develop, and implement an SMS that complies with ICAO requirements and applies a system safety approach to deliver services has therefore become the most important goal within the airline industry. * Corresponding author. Tel.: x6128; fax: addresses: [email protected] (Y.-L. Hsu), [email protected] (W.-C. Li), m @ms.knu.edu.tw (K.-W. Chen). 1 Tel.: Tel.: /$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi: /j.tre

2 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) However, while many states and organizations have been involved in the implementation of safety management systems over the years, there found some discrepancies concerning the key terms, concepts and hypothesis they appropriate. Discrepancies were also apparent in the use of various terms as well as in the manner that SMS was being explained and taught (Galotti et al., 2006). As such, ICAO initiated an effort to publish a Safety Management Manual (Doc 9859-AN/460) in 2006 that aims to provide States with guidance material on safety management (ICAO, 2006). Although a more clear and common perception of SMS have been outlined in the comprehensive guidance document by ICAO, there still exist various definitions in different aviation authorities regarding components which comprising an SMS. In addition, little emphasis has been given to defining what constitutes an effective SMS and the relations among the factors in an SMS (Santos-Reyes and Beard, 2002; Liou et al., 2008; Hsu, 2008). To further clarify these issues, this research aims to develop an analytical framework for defining the key components of an SMS and their interaction. The common SMS components from major aviation organizations and authorities, including ICAO, United Kingdom Civil Aviation Authority (UKCAA), Transport Canada, US Federal Aviation Administration (FAA), and Australia Civil Aviation Safety Authority (CASA) are summarized first, and Grey Relational Analysis (GRA) is used to group and select the key components. After the critical components are derived, Decision Making Trial Evaluation Laboratory (DEMATEL) and Analytic Network Process (ANP) are then introduced to map put the complex relationship and analyze all kinds of interactions among critical components and dimensions systematically so that a quantitative measurement model can be constructed. By the empirical study, the application of the proposed methods is presented to illustrate the results. 2. Airline safety management system 2.1. Definition and characteristics of SMS A study of systems for the management of safety (System Safety) or Safety Management System raised consideration of the three constituent parts management, safety and systems. The System Safety discipline emerged on the engineering and management since 1962 in the US with the dawning of the space transportation era. System safety principles emphasize the rigorous development of effective safety risk mitigation strategies based on comprehensive and thorough risk assessment and its management is a long-term, comprehensive approach that assures that systems and techniques have safety designed in from the outset (McIntyre, 2002). According to Roland and Moriarty (1990), system safety is the application of special technical and managerial skills to the systematic, forward-looking identification and control of hazards throughout the life cycle of a project, program, or activity. Yet in the air transport industry, more researchers tend to use Safety Management System in order to emphasize the systemic management aspects. The term system conveys the notion of an integrated set of processes aimed at managing safety that crosses intra-departmental boundaries (Galotti et al., 2006). Profit (1995) states, A safety management system is no more than a systematic and explicit approach to managing safety just as a quality management system is a systematic and explicit approach to improving the quality of a product to meet the customer s requirement. Edwards (1999) also puts it A Safety Management System is defined as a systematic and explicit approach to managing risk, and is largely a loss control management system. ICAO Safety Management Manual (Doc 9859-AN/460) defines Safety Management System as a systematic approach to managing safety, including the necessary organizational structures, accountabilities, policies and procedures. As such, there exists three main characteristics of SMS, they are: (1) Systematic: safety management activities are in accordance with a pre-determined plan, and applied in a consistent manner throughout the organization; (2) Proactive: emphasizing prevention, through hazards identification and risk control and mitigation measures, before events that affect safety occur; and (3) Explicit: all safety management activities are documented, visible and performed independently from other management activities (ICAO, 2006; Hsu, 2008) Components of an SMS in the air transport industry In academic research, Profit (1995) suggests that in an organization, the policies, principles, accountabilities, directives and procedures constitute an SMS. Edwards (1999) and Overall (1999) describes the prerequisites (elements) of an SMS that should include a comprehensive corporate approach to managing safety, effective organization for delivering safety and robust systems for assuring safety. Liou et al. (2008) use fuzzy DEMATEL in visualizing the structural relations and identifying eleven factors in airline SMS and conclude that strategy and policy play the most important role in an effective SMS. Hsu (2008) applies a safety survey in an airline s Flight Operations Division to assess the effectiveness of proactive safety management within the airline SMS, and suggests that the proactive safety mechanism is a factor-structure concept, which consists of five factors. This result confirms the effects that management s efforts can have on instilling a culture where safety is an operational value in an SMS. Taking a systemic approach will help ensure that the factors necessary for building an effective system. The findings from academic research are summarized in Table 1. As for the empirical industry, various aviation organizations and authorities have made efforts in promoting SMS and making airline SMS become an official requirement in the near future. Extracted from major aviation organizations and

3 224 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) Table 1 Components of an SMS in the air transport industry (academic research). Author SMS components Research method Profit (1995) 1. Policies, 2. Principles, 3. Accountabilities, 4. Directives and procedures Qualitative research Edwards (1999) 1. Comprehensive corporate approach to managing safety, Qualitative research 2. Effective organization for delivering safety, 3. Robust systems for assuring safety. Overall (1999) 1. Comprehensive corporate approach to managing safety, Qualitative research 2. Effective organization for delivering safety, 3. Robust systems for assuring safety. Liou et al. (2008) (for airline) Fuzzy DEMATEL (survey) 1. Communication, 2. Documentation, 3. Equipments, 4. Incident investigation and analysis, 5. Safety policy, 6. Rules and regulations, 7. Safety committee, 8. Safety culture, 9. Safety Risk Management, 10.Training and competency, 11. Work practice. Hsu (2008) (for flight operations division in airline) 1. Crew safety compliance & participation, 2. Operational system, 3.Communication, 4. Managerial decision, 5. Management leadership & commitment. Factor analysis (survey) authorities in the world, such as ICAO, UKCAA, Transport Canada, FAA and CASA, followings are the components/elements comprising an SMS or the steps to achieve an SMS (see Table 2) ICAO Published in 2006, Safety Management Manual (Doc 9859-AN/460) aims to assist ICAO Contracting States in fulfilling the requirements of Annexes 6, 11 and 14 with respect to the implementation of SMS by operators and service providers. In the guidance manual, ICAO offers ten steps for integrating the various elements into a coherent SMS as starting and operating an effective process for safety management can be a daunting task. These steps may be addressed gradually, which would allow the organization to adapt to, and become acquainted with, the requirements and results of each step before proceeding United Kingdom civil aviation authority (UKCAA) The United Kingdom National Air Traffic Services (NATS) began the introduction of formal SMS in 1991, largely because of the increasing attention on safety matters and airspace capacity from outside groups, including the public, the media and Parliament (Profit, 1995). In early 1999, the UK Civil Aviation Authority s Safety Regulation Group (SRG) published an introductory document regarding SMSs Safety Management Systems Operating Standards Division Guidelines, version 1.6. The discussion that followed publication of the SRG document demonstrated the need for additional material to assist both the newcomer and the more experienced with the practicalities of SMS implementation. Therefore in 2002, SRG published Civil Aviation Publication (CAP) 712 Safety Management Systems for Commercial Air Transport Operations (UKCAA, 2002). In this guidebook, a SMS is an explicit element of the corporate management responsibility which sets out a company s safety policy and defines how it intends to manage safety as an integral part of its overall business, and an SMS can be compared with a financial management system as a method of systematically managing a vital business function. Three key elements within an SMS are outlined in the guidebook Transport Canada Since early 2000s, Canada s Commercial and Business Aviation Branch and the Aircraft Maintenance and Manufacturing Branch have promulgated amendments to the Canadian Aviation Regulations (CAR) requiring the establishment of SMS in certain types of operations. The guidance material Safety Management Systems for flight operations and aircraft maintenance organization (TP13881 E) was published in 2002 to provide clarification regarding the intent and application of the proposed regulatory requirements (Transport Canada, 2002). It is designed as a practical guide for the development and implementation of a safety management system within flight and maintenance operations. Key components are divided into six categories in TP13881E. Besides, a Safety Management System Assessment Guide (TP E) has also been published in 2005 to give Transport Canada a tool for systematically evaluating the effectiveness of Safety Management Systems (SMS) in civil aviation approved organizations Federal aviation administration (FAA) In 2006, FAA published AC to introduce the concept of SMS to aviation service providers (for example, airlines, air taxi operators, corporate flight departments, and pilot schools) and to provide guidance for SMS development by aviation service providers. FAA emphasizes that this AC is not mandatory and does not constitute a regulation. Development and implementation of an SMS is voluntary. It is suggested that SMS standards constitute followings five elements: General Organization of the SMS Standard, Policy, Safety Risk Management, Safety assurance and Safety Promotion (FAA, 2006).

4 Table 2 SMS components/steps to achieve SMS. ICAO UK CAA Transport Canada FAA Australia CASA Doc9859 SMM (2006) UK CAP712 (2002) TP 1388IE (2002) OEP Version 1.0 (2007) AC (0) (2005) Steps: 1. Planning Review Safety assessment Performance indication and safety targets Safety strategy The plan 2. Senior managements Commitment to safety Safety policy Safety objectives 3. Organization Safety manager Organizational structure and statement of responsibilities and accountabilities Safety committee Training and competence 4. Hazard identification 5. Risk Management 6. Investigation capability 7. Safety analysis capability 8. Safety Promotion and training 9. Safety management Documentation and Information management 10. Safety oversight and Performance monitoring Safety oversight Safety performance monitoring 1. A comprehensive corporate approach to safety Published safety accountabilities Safety manager Positive safety culture Documentation of business policies and practices Independent safety oversight process Regularly reviewed safety plans Formal safety review processes 2. An Effective organization for delivering safety Arrangements for selection, recruitment, development and training Safety awareness training for management and staff Defined standards and auditing of asset purchases and contracted services Monitoring performance of safety significant equipment, systems or services Recording and monitoring safety standards Hazard analysis and risk assessment tools Change management Arrangements for staff to communicate significant safety concerns Emergency response planning 3. Systems to achieve safety oversight Arrangements for the analysis of flight data Written safety event/issue reports Conducting a safety audit review Conducting internal safety incident investigations and implementing remedial actions Effective use of safety data for performance analysis Arrangements for ongoing Safety Promotion Periodic review of the safety management system Line manager s monitoring 1. Safety management plan Safety policy Non-punitive safety reporting policy Roles, responsibilities and employee involvement Communication Safety planning, objective and goals Performance measurement Management review 2. Documentation Identification and maintenance of applicable regulations SMS documentation Records management 3. Safety oversight Reactive processes Proactive processes Investigation and analysis Risk Management 4. Training Training, awareness and competence 5. Quality assurance Operational quality assurance 6. Emergency preparedness Emergency preparedness and response 1. Safety policy Policy statement Organizational structure Procedures 2. Safety Risk Management Hazard identification Risk assurance Risk mitigation tracking 3. Safety assurance Internal audits External audits Corrective action 4. Safety Promotion Culture Training Communication 1. Safety policy and objectives 2. Organizational and staff responsibilities 3. Establishment and monitoring of levels of safety 4. Internal safety reviews 5. Internal reporting and management of safety concerns and incidents 6. Hazard identification/assessment/ control and mitigation 7. Interfaces 8. Change management SMS components (from Australia CASA 2008) 1. Safety policy, objectives, and planning 2. Safety Risk Management 3. Safety assurance and change management 4. Safety Promotion and training Y.-L. Hsu et al. / Transportation Research Part E 46 (2010)

5 226 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) In 2007, FAA presented an Operational Evolution Partnership (OEP) which is its plan/implementation mechanism for next generation (FAA, 2007b). OEP Version 1 provides a framework that is already being used to focus future work within the agency. It presents the key concepts and provides a strategic timeline for when transformational changes can be made. The OEP is organized around three key transformational areas: airport development, air traffic operations, and aircraft and operator requirements. The content of OEP Version 1.0 is presented in 10 Solution Sets. In the solution set - Increase Safety, Security and Environmental Performance, which involves activities relating directly to safety, the Next Generation Air Transportation (NextGen) system ensures safety through use of an integrated SMS approach for identifying and managing potential problems in a system, organization, or operation. Specifically, this method includes procedures, practices and policies for the management of safety. According to the solution set in OEP Version 1.0, there are four pillars or components that comprise an SMS: 1. Safety policy, 2. Safety Risk Management (SRM), 3. Safety assurance, and 4. Safety Promotion. In 2007, FAA has released AC 150/ Introduction to Safety Management Systems (SMS) for Airport Operators to introduce the concept of a SMS for airport operators (FAA, 2007a) Australia civil aviation safety authority (CASA) In view of the importance of SMS, Australia Civil Aviation Safety Authority (CASA) released a draft AC in 2002 as the guidance to assist in the establishment of course criteria for the training of safety managers as required by CASR to enable the Safety Manager to implement and maintain the Safety Management System. In 2005, an AC (0) was released in an attempt to provide general principles and practical guidance to illustrate compliance with the requirements for an SMS. Eight elements were proposed in an SMS (CASA, 2005). Recently CASA also published a guidance material named SMS An Aviation Business Guide and Safety Management & the CEO, which described more specifically that there are four key elements in an SMS (CASA, 2008). To sum up, combined the results of academic (Table 1) with empirical findings (Table 2), Table 3 shows the identical or similar components and their definitions from various studies and aviation authorities and organizations. In total there contains six dimensions together with 25 components in an SMS. 3. A hybrid model As a generalized quantitative evaluation model, which identifies the critical components and considers the interaction between components of an SMS, is lacking, here we try to address these issues by using a hybrid model combining Grey Table 3 Components of an SMS and their definitions. Dimension Component Definition Organization Safety policy A formal and written statement Safety objective and goals Safety objectives and goals are practical and achievable, and they are regularly reviewed Organizational structure, responsibilities and Designed to support SMS (Safety Manager + Safety Committee) accountabilities Management commitment Senior management is involved in and committed to the SMS Performance measurement/baseline Performance standards are established, i.e. indicator Documentation Identification and maintenance of applicable regulations Regulations, standards and exemptions are periodically reviewed to ensure that information is available. Documentation describing system component The completeness of SMS manual Records management The organization has a records system to generation and retention of all records to support operational requirement. Information management Collection and management of safety information and the distribution of that information to involved staff. Risk Management Investigation capability Incident/accident investigation process Hazard identification An occurrence reporting system is in effect. Supervisors will not be penalized for normal errors. Safety analysis capability Safety data tracking, trend analysis Risk assessment Matrix evaluation of risk Recommending actions based on safety metrics Suggestions according to trend analysis and assessment Quality assurance Safety performance monitoring Periodically review performance and performance index Audits Making sure SOPs are followed, like self-audit, IOSA, etc. Change management A process to evaluate the effectiveness of corrective actions. Safety Promotion Training Educating staff awareness and competence Safety culture Non-punitive reporting Safety lessons learned To share their experience implements about SMS. Communication To dissemination safety information, like spoken word, written word, videos, display, website, conference Proactive process LOSA, TEM, HF studies Emergency response Emergency response plan The organization has a process to distribute the ERP procedures and to communicate the control to all personnel. Risk Management capability When accidents occur, they can be controlled Emergency proactive action Making sure staff are familiar with the process

6 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) Relational Analysis, DEMATEL and ANP approaches so that the structural relations among the SMS elements will be clarified Grey relational analysis (GRA) GRA is a method to analyze the relational grade for discrete sequences. The GRA is based on the level of similarity and variability among all factors to establish their relation, which suggests how to make prediction and decision, and generate reports that make suggestions for the factor selection. Unlike the traditional statistics analysis handling the relation between variables, this approach requires less data and can analyze many factors that can overcome the disadvantages of statistics method. According to Wu (2007), a procedure for the GRA consists of the following steps: 1. Generate reference data series x 0. x 0 ¼ðd 01 ; d 02 ;...; d 0m Þ ð1þ where m is the number of respondents. In general, the x 0 reference data series consists of m values representing the most favored responses. 2. Generate comparison data series x i. x i ¼ðd i1 ; d i2 ;...; d im Þ ð2þ where i = 1,..., k. k is the number of scale items. So there will be k comparison data series and each comparison data series contains m values. 3. Compute the difference data series D i. D i ¼ðjd 01 d i1 j; jd 02 d i2 j;...; jd 0m d im jþ ð3þ 4. Find the global maximum value D max and minimum value D min in the difference data series. D max ¼ maxðmax D i Þ 8i D min ¼ minðmin D i Þ ð4þ 8i 5. Transform each data point in each difference data series to grey relational coefficient. Let c i (j) represents the grey relational coefficient of the jth data point in the ith difference data series, then c i ðjþ ¼ D min þ nd max D i ðjþþnd max ð5þ where D i (j) is the jth value in D i difference data series. n is a value between 0 and 1. The coefficient n is used to compensate the effect of D max should D max be an extreme value in the data series. In general the value of n can be set to Compute grey relational grade for each difference data series. Let C i represent the grey relational grade for the ith scale item and assume that data points in the series are of the same weights 1, then C i ¼ 1 m X m n¼1 c i ðnþ ð6þ The magnitude of C i reflects the overall degree of standardized deviance of the ith original data series from the reference data series. In general, a scale item with a high value of C indicates that the respondents, as a whole, have a high degree of favored consensus on the particular item. 7. Sort C values into either descending or ascending order to facilitate the managerial interpretation of the results Decision making trial evaluation laboratory (DEMATEL) The DEMATEL method is an effective procedure for analyzing structure and relationships between components of a system or a number of available alternatives. DEMATEL can be priorities the alternatives based on the type of relationships and severity of influences of them on another. Alternatives having more effect to another are assumed to have higher priority and called dispatcher and those receiving more influence from another are assumed to have lower priority and called Receiver (Seyed-Hosseini et al., 2006). According to Tzeng et al. (2007) and Wu and Lee (2007), the method can be summarized as following steps:

7 228 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) Calculate the initial average matrix by scores. Respondents are asked to indicate the direct effect they believe each element i exerts on each element j of others, as indicated by a ij, using an integer scale ranging from 0, 1, 2, 3, and 4, represented from 0 as no influence to 4 as very high influence. 2. The initial direct-relation matrix Z is a n n matrix obtained by pair-wise comparisons in terms of influences and directions between criteria, in which z ij is denoted as the degree to which the criterion i affects the criterion j, i.e., Z =[z ij ] nn. 3. The normalized direct-relation matrix X, i.e., X =[x ij ] nn and 0 6 x ij 6 1 can be obtained through Eqs. (7) and (8), in which all principal diagonal elements are equal to zero. X ¼ s Z s ¼ max 16i6n 1 P n j¼1 Z ; i; j ¼ 1; 2;...; n: ð8þ ij 4. The total-relation matrix T can be acquired by using formula 9, in which the I is denoted as the identity matrix. T ¼ Xð1 XÞ 1 5. The sum of rows and the sum of columns are separately denoted as D and R within the total-relation matrix T through Eqs. (10) (12): T ¼ t ij ; i; j ¼ 1; 2;...; n; ð10þ D ¼ Xn R ¼ Xn t ij j¼1 t ij i¼1 where D and R denote the sum of rows and the sum of columns respectively. 6. A causal diagram can be acquired by mapping the dataset of (D + R, D R), where the horizontal axis (D + R) is made by adding D R, and the vertical axis (D R) is made by subtracting D from R. ð7þ ð9þ ð11þ ð12þ 3.3. Analytic network process (ANP) Since the ANP/AHP was proposed by Saaty (1996), it has been widely used to deal with the dependence and the feedback decision making. According to Liou et al. (2007) and Yu and Tzeng (2006), followings are the steps to conduct ANP approach. The initial step of the ANP is to compare the criteria in the entire system to form a supermatrix through pair-wise comparisons by asking How much importance does one criterion have compared to another criterion, with respect to our interests or preferences? The relative importance is determined using a scale of 1 9 representing equal importance to extreme importance (Huang et al., 2005). The general form of the supermatrix can be described as follows: ð13þ

8 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) where C m denotes the mth cluster, e mn denotes the nth element in mth cluster, and W ij is the principal eigenvector of the influence of the elements compared in the jth cluster to the ith cluster. In addition, if the jth cluster has no influence to the ith cluster, then W ij =0. Therefore, the form of the supermatrix depends much on the variety of the structure. Here, two simple cases, which both have three clusters, are used to display how to form the supermatrix based on the structures. The supermatrix can be formed as the following matrix: ð14þ where W 21 is a matrix that represents the weights of cluster 2 in respect to cluster 1, matrix W 31 is the weights of cluster 3 with respect to cluster 1, matrix W 33 is denoted as the inner dependence and feedback within cluster 3. After forming the supermatrix, the weighted supermatrix is derived by transforming all columns sum to unity exactly. This step is much similar to the concept of Markov chain for ensuring the sum of these probabilities of all states equals to 1. Next, we raise the weighted supermatrix to limiting powers such as Eq. (15) to get the global priority vector or called weights. lim W k k!1 ð15þ In addition, if the supermatrix has the effect of cyclicity, the limiting supermatrix is not the only one. There are two or more limiting supermatrices in this situation, and the Cesaro sum would be calculated to get the priority. The Cesaro sum is formulated as lim k!1 1 X N N W k j j¼1 ð16þ to calculate the average effect of the limiting supermatrix (i.e. the average priority weights) where W j denotes the jth limiting supermatrix. Otherwise, the supermatrix would be raised to large powers to get the priority weights (Yu and Tzeng, 2006). 4. Empirical study As of 1 January 2009, development and implementation of an SMS will become mandatory for Taiwanese carriers. To introduce Safety Management System for airlines, Taiwan CAA has therefore published AC A titled SMS Safety Management System in Revised from FAA AC120-92(see Section 2.2.4), Taiwan CAA s AC A describes SMS elements similar to FAA. However, the complexities in developing an SMS have led to difficulties for airlines in implementation (Liou et al., 2008). As such, by applying the hybrid approaches presented above, this section presents an empirical study of how to develop the analytical framework for defining the critical components as well as investigate the structural relations among critical components. As SMS components have been extracted from the extensive literature review (see Table 3), a survey with structured questionnaires including importance and impact measurement, was then conducted to ask the aviation experts from Taiwan CAA, Aviation Safety Council (ASC) and safety professionals in six Taiwanese airlines. A total 28 safety experts were selected to distribute the survey during December 2007, including 19 from airlines, and 9 from ASC and CAA; all of them have been working in the aviation industry over 15 years Selection of critical SMS components using GRA In the first part of the survey, these 28 safety experts were asked to assess the importance rating from 1 to 5 (1 as not important, 5 as extremely important) to the dimensions and components (elements). Since the 25 SMS components seem too complicated to be analyzed, GRA is used here to derive the relationships between components and safety experts, and make suggestions for the critical SMS components selection. Let the value of each elements of x 0, the reference pattern, be 1, which stands for the best case for the elements in the normalized correlation matrix. By setting the distinguished coefficients n as 0.5, the Grey relation coefficients were derived using Eq. (5). Finally, the grades of Grey relation were derived using Eq. (6). Table 4 shows the Grey relation grade and the ranking of each component. According to Hwang and Tai (2008) and Tzeng and Hu (1996), the threshold value of grey relation grade is usually set as 0.75 in order to select the critical criteria. Therefore, 0.75 is used as the value to the threshold of grey relation grade in this research. By this approach, following 13 components are selected, they are Organizational structure, Accountability and responsibility, Recommending actions based on safety evaluation, Training awareness and competence, Safety policy, Safety analysis capability, Management commitment, Hazard identification, Risk assessment, Safety culture, Safety objective and goals, Performance measurement/baseline, Identification and maintenance of applicable regulations, and Communication.

9 230 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) Table 4 The grades of Grey relation with respect to SMS components (n = 0.5). Components Dimension Grade Ranking Organizational structure, accountability and responsibility O Recommending actions based on safety evaluation RM Training awareness and competence SP Safety policy O Safety analysis capability RM Management commitment O Hazard identification RM Risk assessment RM Safety culture SP Safety objective and goals O Performance measurement/baseline O Identification and maintenance of applicable regulations D Communication SP Risk Management capability ER Emergency proactive action ER Proactive program SP Emergency response plan ER Documentation describing system component D Safety lessons learned SP Investigation capability RM Records management D Information management D Performance monitoring QA Audits QA Change management QA O Organization, RM Risk Management, SP safety Promotion, D documentation, ER emergency response, QA quality assurance Mapping out the structured relation of SMS dimension using DEMATEL By using GRA, SMS components are deducted from 25 to 13 items, which can be categorized into four dimensions and coded as Table 5. In an attempt to investigate the structural relations among the four dimensions, DEMATEL is employed to measure the causal impact of each dimension in SMS. As these safety experts were asked to indicate the degree of influence that they believe each dimension has on every other dimension, firstly the direct relation/influence matrix D is introduced, as shown in Fig. 1. After that, the direct/influence matrix D is normalized, based upon Eq. (7) and after normalization, the direct/indirect matrix T is shown in Fig. 2. Using Eqs. Table 5 Critical components and dimensions in an SMS. Dimension D 1 Organization D 2 Documentation D 3 Risk Management D 4 Safety Promotion Component C 1 safety policy C 2 safety objective and goals C 3 organizational structure, accountability and responsibility C 4 management commitment C 5 performance measurement/baseline C 6 identification and maintenance of applicable regulations C 7 hazard identification C 8 safety analysis capability C 9 risk assessment C 10 recommending actions based on safety evaluation C 11 training awareness and competence C 12 safety culture C 13 communication Fig. 1. The direct relation/impact matrix D. As these safety experts were asked to indicate the degree of influence that they believe each dimension has on every other dimension, firstly the direct relation/influence matrix D is introduced.

10 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) Fig. 2. The direct relation/impact matrix T. The direct/indirect matrix T is matrix D after normalization. (11) and (12), the influences given and received for each dimension are shown in Table 6 with (r i + c i ) presenting the effect dimension i contributes to the system, and (r i c i ) shows the net effect that dimension i has on the system. The impact-direction map of the total relationship is therefore plotted (see Fig. 3). Based on matrix T, the impact-relation map (IRM) can be drawn. However, there is a need to simplify the web of casual relationships in T by setting different threshold values to filter insignificant ones. For this reason, a discussion had been made with survey respondents, and the consensus was reached on a threshold value of 2.83, which deemed as the most appropriate value to acquire a suitable relationship. When the value is above 2.83, the relationship is not obvious and an IRM will be too sparse to draw. The value under 2.83 gains too many factors which result in complex relationships in the whole system. As such, the IRM for critical dimensions of SMS is illustrated in Fig. 4. The looped arc signifies the inner dependences. The result shows these four dimensions are related to each other, which will be applied in the following ANP analysis Weighting SMS components by ANP After selecting the critical components and mapping out the relationship structure among dimensions in an SMS, the ANP method is applied to obtain component weights. As airline business is highly regulated and the completion of an airline SMS will be determined and audited by its aviation authority and safety inspectors, this part of research therefore mainly focuses on the investigation of SMS criteria weights from the viewpoint of CAA. Accordingly, an ANP expert survey was conducted and distributed to 15 safety inspectors in Taiwan CAA during February/March surveys were collected and 10 were valid, which makes the effective response rate as 67%. Within the survey, the experts were asked to respond to a series of questions, such as For the Safety polices of airlines, how much more important is Hazard identification to Safety analysis capability? These pair-wise comparisons are based on Table 6 Total effects and net effects for each dimension. Code Dimension r i c i r i + c i r i c i D 1 Organization D 2 Documentation D 3 Risk Management D 4 Safety Promotion Fig. 3. The impact-direction map. r i + c i (impact level) presenting the effect dimension i contributes to the system, and r i c i (relation level) shows the net effect that dimension i has on the system.

11 232 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) Saaty s 9-point scale with a score of 1 indicating equal importance and 9 as the extreme importance of one component over another. According to the steps described in Section 3.3, an unweighted supermatrix can be generated (see Table 7). Then by calculating the limiting power of the weighted supermatrix, Eq. (15) is used until a steady-state condition is achieved (see Table 8). The weight of each component (criteria) and ranking are shown in Table 9. D 1 : Organization D 2 : Documentation D 3 : Risk management D 4 : Safety Promotion Fig. 4. Impact-relations map for SMS. Based on matrix T, the impact-relation map (IRM) can be drawn. To simplify the web of casual relationships in T, a threshold value is set as 2.83 to filter insignificant ones. The threshold value is the group decision of survey respondents. Table 7 The unweighted supermatrix. C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 C 9 C 10 C 11 C 12 C 13 C C C C C C C C C C C C C Table 8 The limiting supermatrix. C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 C 9 C 10 C 11 C 12 C 13 C C C C C C C C C C C C C

12 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) Table 9 The results of ANP. Dimension Component Weight Rank D 1 C 1 Safety policy D 4 C 12 Safety culture D 4 C 13 Communication D 4 C 11 Training awareness and competence D 2 C 6 Identification and maintenance of applicable regulations D 1 C 2 Safety objective and goals D 3 C 7 Hazard identification D 3 C 8 Safety analysis capability D 3 C 9 Risk assessment D 1 C 5 Performance measurement/baseline D 1 C 3 Organizational structure, accountability and responsibility D 3 C 10 Recommending actions based on safety evaluation D 1 C 4 Management commitment Discussions 5.1. The critical components and dimensions for a performance-based SMS In this decade, the definition of safety is now transformed from zero accident to reduce risk to an acceptable level (Hsu, 2004). The introduction of the concept of acceptable level of safety responds to the need to complement the prevailing approach to the management of safety based upon regulatory compliance, with a performance-based approach (ICAO, 2006). And performance-based approaches to the management of safety are best exemplified by the safety management system (Galotti et al., 2006). In other words, airlines as well as other service providers are asked to organize their safety activities following a pattern the system is called SMS so acceptable level of safety is able to set and achieve. To this end, there is a need to identify the critical components within an SMS so that the pattern of safety activities will become more solid and efficient for implementation and inspection. With the aid of proposed analytical methods, a number of important results are found from the empirical study in regard to airline SMS. First, within the SMS framework summarized from researchers and various aviation organizations, there found 13 critical components, including five items in Organization, one item in Documentation, four items in Risk Management, and three items in Safety Promotion. Compared Table 3 with Table 5, it shows that all five original items from Organization remain on the list of critical item, but none are from either Quality Assurance or Emergency Response. This result explains that the performance-based approach starting from Organization dimension. From the perspective of the relationship between authorities and airlines, critical SMS components Safety policy and Safety objectives/goals provide targets in terms of the safety performance that airline should achieve while conducting their core business functions, as a minimum acceptable to the oversight authority. It is also a reference against which the authority can measure safety performance. The concept of acceptable level of safety is expressed by safety Performance measurement/baseline, i.e. safety performance indicators and safety performance targets, and implemented through various safety requirements, under the Management commitment. Management authorities come from the Organizational structure, which accompanies accountability and responsibility. Meanwhile, the 13 critical items and 4 dimensions fully reflect the characteristic of an SMS systematic, proactive and explicit, as stated in Section 2.1. The Organization, Documentation, Risk Management and Safety Promotion dimensions contain essential components to systematically conduct and document safety management activities according to a pre-determined plan, as well as emphasize prevention through the identification of hazards, risk mitigation measures before the risk-bearing event occurs and adversely affects safety performance Causal relationship of SMS dimensions Fig. 3 presents the impact-direction map among SMS dimensions. As Organization has the highest positive r i + c i, (impact level), which suggests it is the largest net generator of effects and plays the most important roles in an SMS. Thus, Organization will affect other 3 dimensions much more than these 3 dimensions will affect Organization, which implies Organization (including policy, structure, commitment, etc.) should be a priority for implementation or improvement. Risk Management and Safety Promotion also have high r i + c i, but their r i c i (relation level) are negative, meaning these dimensions have a large effect on an SMS, yet also affected by the other dimensions. In other words, these two dimensions are Receiver and should be ranked lower in management priority. Combined the result of Fig. 3 with Fig. 4, Fig. 5 here demonstrates a more clear relationship among SMS dimensions. When a threshold value of 2.83 is set, Organization will affect Documentation, Risk Management and Safety Promotion. Risk Management and Safety Promotion will also have influence on Organization ; they also exert influence on each other. Documentation will affect Safety Promotion. All these four dimensions are inseparably related to each other.

13 234 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) r - c (Relation level) Documentation (21.25,0.07) Organization (23.59,0.86) 0 Risk Management (23.45,-0.32) r + c (Impact level ) Safety Promotion (23.40,-0.61) Fig. 5. The causal relationship of dimensions. It demonstrates a more clear relationship among SMS dimensions. When a threshold value of 2.83 is set, Organization will affect Documentation, Risk Management and Safety Promotion. Risk Management and Safety Promotion will also have influence on Organization ; they also exert influence on each other. Documentation will affect Safety Promotion. All these four dimensions are inseparably related to each other Relative importance of critical components Table 9 shows the result of ANP. It is noted that the ANP survey were only distributed to safety inspectors in CAA, so the result mainly reflects the opinions from the regulatory authority in Taiwan. The findings of this part of research reveal that Safety policy has the highest weight of relative importance (12.2%), followed by Safety culture (10.4%), Communication (10.1%), Training (9.8%), Identification and Maintenance of applicable regulations (9.1%), Safety objective and goals (8.8%), Hazard identification (7.4%), Safety analysis capability (6.1%), Risk assessment (5.9%), Performance measurement (5.8%), Organizational structure, accountability and responsibility (5.6%), Recommending actions based on safety evaluation (4.8%) and Management commitment (3.9%). As these 13 components are all selected as critically important criteria, it is reasonable that the weight value for each component is relatively close to each other. From the viewpoint of aviation authority, Safety policy is situated on the first place, implying that SMS is beginning with policies that convey to all staff members the top management s emphasis on safety. Safety policy should be a written document, which outlines the methods and processes that organization will use to obtain desired safety outcomes, and management s commitment. As ANP results are evaluated by CAA inspectors, it also reflects that safety policy should be consistent with relevant State regulations. Three components of Safety Promotion dimension are situated on the second, third and fourth place, it implies that system safety must be infused into the management systems if it is to have the desired effect on safety outcomes. The procedures for Safety Promotion, along with policy requirements, provide for an organizational environment that supports a just safety culture. Also, as policy must be translated into procedures and processes to provide clear instruction, the component Identification and maintenance of applicable regulations, situated on the fifth place, is quite important. The development of weight for each component presents the priority that aviation authority deem as relatively important in an SMS. Not only it can be referred when CAA design SMS assessment criteria and/or undertake SMS oversight, but also can be provided to the airlines as the focused points to implement and improve their SMS. 6. Conclusions At a time when a performance-based SMS has gradually become a global trend and legal requirement in the airline industry, there found some discrepancies concerning the use of various terms and the manner that SMS was being explained and taught in different states. Therefore, this paper starts with an extensive literature review to investigate the airline SMS study in academia and legal requirements in the industry. Combined the results of academic with empirical findings, there found 6 dimensions and 25 identical or similar components and definitions from various studies and aviation authorities and organizations. Based on the finding, the major contribution of this paper lies in the development of comprehensive methodologies, which incorporate the practical and diversified issues for a performance-based SMS. The Grey Relational Analysis leads to

14 Y.-L. Hsu et al. / Transportation Research Part E 46 (2010) the result of identification of 13 critical components and 4 dimensions in an airline SMS. The DEMATEL approach enables us to visualize the causal relationships and the degree of influence among 4 dimensions, and the ANP technique demonstrates the interdependence among various criteria, and provides related importance as well as ranking of 13 critical components. The hybrid model consisting of above three approaches has rarely been applied in the context of airline safety management system. This research concludes with that compared to dimensions of Risk Management, Safety Promotion and Documentation, Organization is the most important dimension and has the largest effect on other dimensions in an airline SMS, which begins with Policies that convey top managers viewpoint and vision on safety. The proposed methodologies and research findings serve as guideline for both airline managers and inspectors in civil aviation authorities. While airlines can be provided with the knowledge to prioritize the resources to build and maintain their SMS, CAA inspectors can also refer to the results when conducting safety audits, and further use the weights to quantify SMS performance for each airline in the future. Acknowledgements This research is supported by the National Science Council of Taiwan, ROC, under Grant no. NSC P Y. The authors also would like to thank Professor Sveinn V. Gudmundsson, and anonymous referees for their valuable comments and advices to enhance the quality of paper. References Australia Civil Aviation Safety Authority (CASA), Guidance for preparing a safety management system (SMS), AC No.: (0). Australia Civil Aviation Safety Authority (CASA), Safety Management & the CEO, CASA. 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