The Effect of Service Quality and Sustainability Practices on Brand Equity: The Case of Korean Air Passengers

Abstract

A company’s brand equity is built through sustainable development. Sustainability practices are increasingly being adopted by a wide range of organizations, with the aviation industry being particularly prominent. This trend can play a key role in enhancing brand equity within the Korean aviation sector. Specifically, the focus is on whether sustainability practices contribute positively to brand value within the aviation industry. The primary objective is to examine how service quality and sustainability practices influence airline brand equity through mediating factors. While previous research has predominantly explored airline service quality, this study aims to analyze the influence of sustainability practices on brand equity, particularly targeting Korean Air, amid the increasing interest in sustainability research within the airline industry. Additionally, a survey was conducted on 379 Korean Air passengers, and structural equation modeling (SEM) was employed for analysis. The results indicate a strong positive correlation among service quality, sustainability practices, and brand equity, suggesting heightened passenger interest in airline sustainability practices, along with service quality. Hence, this theoretical investigation signifies a potential positive impact on the Korean aviation industry.

1. Introduction

In recent times, the airline industry has encountered considerable turbulence, facing challenges such as fierce competition from strategic alliances, heightened security measures, escalating fuel and labor costs, and technological advancements. Additionally, the industry has been profoundly affected by events such as the COVID-19 pandemic, which struck in the early 2020s, causing widespread disruption throughout the aviation market. This pandemic inflicted direct impacts on both airlines and airports as it spread, disrupting economic activity and leading to substantial losses in revenue and seating capacity. Consequently, the industry has faced significant amounts of time in recovering from this crisis [1,2,3]. Within this intensely competitive environment, airlines must gain a deeper understanding of their customers’ needs, expectations, and priorities to thrive. So, the service quality within the aviation sector has become increasingly vital for achieving and sustaining a competitive edge through customer satisfaction in the past decades. However, the mere effect of service quality represents only the initial step in setting an organization apart from its rivals. For airlines aiming to expand into international markets, obtaining comparable data on customer perceptions and their impact on satisfaction is crucial. In response to these challenges, airlines continuously develop strategies to compete effectively and gain an edge in the face of changing environments [1]. Furthermore, consumers are becoming more conscious of the environmental and social impact of their decisions and expect companies to take proactive steps in addressing climate change and social development rather than reacting afterward. As highlighted by other researchers [4], they expect companies to proactively address climate change and social development rather than reacting retrospectively, considering it beneficial for companies amidst the growing preference for environmental responsibility and social concern. In particular, companies in service industries, such as air transportation organizations, can leverage environmental claims in their business communications due to the intangible nature of services, positioning themselves favorably in the market [5]. This increasing environmental and social consciousness is evident in the air travel market, where passengers are becoming more aware of the environmental and social ramifications of air transport and are demanding more eco-friendly and socially responsible airline services [5,6]. Given the significant environmental impact of air transport, developing genuinely green airline products poses considerable challenges. Nevertheless, there is growing support within the air transport industry to initiate more sustainability practices in aviation [7]. However, to the best of the authors’ knowledge, there is a scarcity of studies conducted in the airline sector that have investigated the relationship between service quality, sustainability practices, and brand equity in Korean aviation. To address this gap and deepen our understanding of the significance of sustainability practices and their association with the brand equity of domestic airlines among contemporary individuals, our research prioritizes an investigation centered on Korean Air, a prominent player in South Korea’s airline sector. This study aims to achieve two key objectives: (1) Does the implementation of sustainability practices positively affect airline passenger’s perceptions? and (2) Does the integration of service quality and sustainability practices positively contribute to the enhancement of brand equity? Thus, our study represents the initial theoretical exploration of service quality and sustainability practices within South Korea’s domestic airline industry.

The objective of this study is to examine the relationships between service quality, sustainability practices, customer satisfaction, brand attachment, and brand equity through empirical analysis. The primary focus is on understanding the impact of sustainability practices, in conjunction with service quality, on providing airlines with a sustainable competitive advantage. This study is expected to underscore the significant implications and importance of enhancing brand equity and achieving brand competitiveness for Korean airlines, particularly Korean Air, by integrating service quality and sustainability practices. Additionally, it aims to highlight the significance of broadly disseminating the brand value effects of airlines, while also emphasizing the ongoing relevance of environmentally friendly and social policies in shaping relationships between airline passengers and stakeholders.

The paper’s structure is organized as follows: Section 2 presents a literature review by exploring service quality, sustainability practices, customer satisfaction, brand attachment, and brand equity. Section 3 outlines the methodology, detailing data analysis and collection procedures. Section 4 presents the results, including confirmatory factor analysis (CFA), goodness-of-fit analysis, path analysis, and hypothesis testing. Section 5 provides a discussion of the overall summary of this research. Finally, Section 6 offers conclusions and implications.

2. Theoretical Background

Recently, many studies related to sustainability practices such as CSR and ESG have played a vital role in determining a corporation’s sustainable development [8,9]. Accordingly, corporations are keenly aware of the need to implement sustainability practices both externally and internally, recognizing its importance in enhancing their brand’s value and promoting sustainable growth.

This research seeks to explore the relationship between service quality, sustainability practices, and brand equity of Korean Air from the perspective of airline users. Additionally, this study analyzes the effect of service quality and sustainability practices on enhancing the airline’s brand equity through mediating variables such as brand attachment and customer satisfaction.

2.1. Service Quality

The significance of superior service quality has risen, as demonstrated by [8,10,11]. Service quality is defined as the customer’s overall level of service expectations of the service [12,13]. Numerous studies have investigated the effects of service quality on consumer behaviors, such as customer satisfaction, loyalty, and behavioral intentions, as well as on firm performance, in various service industries [9,14,15,16] and found it to have a positive impact [14]. Thus, it is deemed critical for enhancing service competitiveness [17]. Research on different airlines, including Thai, Ugandan, and Turkish low-cost carriers, has identified multiple factors influencing customer satisfaction with service quality [15,18,19,20]. Furthermore, the correlation between service quality and customer satisfaction is well-documented [12,21], implying that airlines can bolster their competitive edge by prioritizing and enhancing service quality.

In the aviation sector, service quality is acknowledged as pivotal for enhancing attractiveness and competitiveness, complementing factors like satisfaction and image, particularly within the airport industry [22,23]. This linkage stems from the belief that satisfaction is closely intertwined with service quality, influencing the overall airport or place experience [24,25].

In the contemporary industry, service quality plays a pivotal role in enabling companies to swiftly adapt to evolving customer needs, ensuring business sustainability. Research underscores the significant influence of service quality on customer satisfaction [26,27]. Organizations embracing service quality have witnessed improvements in both customer satisfaction and overall sustainability [28,29,30], fostering an environment conducive to customer engagement. Consequently, entities retaining satisfied customers tend to achieve greater success, profitability, and sustainability. Additionally, studies highlight the pervasive influence of sustainable management across diverse industries, with service quality significantly impacting sustainability practices within educational institutions [31,32]. In this vein, the relationship between sustainability practices and service quality has been explored in existing literature [33].

Despite abundant prior research, there exists a dearth of understanding regarding the comprehensive framework of service quality within sustainability contexts [34,35]. Prior studies have predominantly focused on defining service quality and examining its components, often overlooking broader implications [36]. Thus, there is an increasing imperative to explore the nexus between service quality, passengers’ perceptions of sustainable initiatives, and its potential impact on brand equity, particularly in the airline industry. Some scholars argue that in highly competitive environments, service quality can yield favorable outcomes [37,38], especially considering airlines’ substantial investments in understanding passenger needs [38,39,40]. However, few studies have investigated how service quality and sustainability practices jointly contribute to enhancing both brand competitiveness and sustainable competitive advantages, particularly concerning airlines in Korea. Hence, this paper aims to address this gap, providing insights into the pivotal role of service quality in shaping customer satisfaction and sustainability practices.

The following hypotheses are presented.

Hypothesis 1 (H1).

Service quality has a positive effect on sustainability practices.

Hypothesis 2 (H2).

Service quality has a positive effect on customer satisfaction.

2.2. Sustainability Practices

Research on environmental issues within air transport has surged in recent years, with a primary focus on employing policy instruments and technological advancements to mitigate aviation’s adverse environmental effects [41]. Basically, the term sustainability practices is a collective term for sustainable initiatives associated with green management and corporate social responsibility [42]. Notably, studies have highlighted that consumers who perceive environmental issues as significant are more inclined to patronize eco-friendly products and services [42,43,44,45]. Additionally, other researchers have highlighted the widespread influence of sustainability practices within educational institutions across different industries, with a particularly positive impact on consumer and student perceptions [31]. The impact of integrating sustainability practices into firms’ operations aims to transition working processes toward sustainability, reduce carbon emissions, and enhance air quality [46,47]. Some scholars argue that such sustainability practices not only improve customer trust and satisfaction but also contribute to enhancing the quality of social life and counteracting environmental degradation [48]. Additionally, socio-cultural sustainability, encompassing aspects like social equity, safety, and human health, plays a vital role in sustainability practices [49,50]. Moreover, the implementation of governance activities, including corporate governance and risk management, significantly impacts the airline industry’s operations [51,52]. Scholars have assessed the potential effects of these activities on the interaction between customers and airlines [53]. The literature reflects a growing interest among scholars in exploring various sustainability practices within the aviation industry.

Several researchers have empirically demonstrated that consumers’ perceptions of sustainability practices are closely associated with their green behaviors [42,54]. However, the impact of sustainability practices on brand attachment has received relatively less attention in scholarly research. Building on prior literature, environmentally conscious consumers are adept at recognizing eco-friendly brands and forming consistent and loyal relationships with them [55]. Brand attachment, akin to attachment between a person and a specific object, evolves through long-term relationships between consumers and brands [43,56]. Additionally, scholars have contended that consumers’ positive perceptions of a firm’s sustainability practices reinforce brand attachment [43]. Thus, it stands to reason that sustainable environmental practices positively influence brand attachment [55,57]. Furthermore, sustainability practices yield favorable outcomes when consumers prioritize environmental concerns, fostering a positive inclination toward environmentally conscious brands [58]. Research indicates that integrating sustainability practices into operations enhances cost-effectiveness and boosts brand equity [59]. However, despite these findings, there remains a notable dearth of studies investigating the relationship between sustainability practices and brand equity, although some scholars in brand asset management have acknowledged the potential of incorporating environmental considerations to enhance competitive advantage [44,60].

Moreover, it is imperative to assess whether airlines are implementing effective measures to address environmental and social issues under sustainability practices. Therefore, there is a pressing need for further examination of sustainability practices within the Korean airline industry to enhance our understanding of how airlines are embracing sustainability initiatives.

The following hypotheses were derived:

Hypothesis 3 (H3).

Sustainability practices have a positive effect on customer satisfaction.

Hypothesis 4 (H4).

Sustainability practices have a positive effect on brand equity.

Hypothesis 5 (H5).

Sustainability practices have a positive effect on brand attachment.

2.3. Customer Satisfaction

Today, airline companies face a multitude of challenges, including managing fluctuating demand, reducing costs, and meeting quality standards [17,61,62]. Moreover, the intense competition within the airline industry has underscored the significance of customers’ perceptions of service quality. In past decades, numerous studies have illustrated the correlation between airlines’ service quality, positive word-of-mouth, and revenue and their impacts on customer satisfaction and loyalty [61]. Basically, customer satisfaction can be defined as a comprehensive sense that refers to expected satisfaction from goods and services provided by a company [63,64]. It holds a pivotal role in a successful business strategy [65]. In the past, various studies have explored the association between consumer satisfaction and brand loyalty, revealing that heightened consumer satisfaction correlates with increased attitudinal brand loyalty [65,66]. Customer satisfaction results from service evaluations and has been examined across diverse contexts using various assessment methodologies [22].

Like in other industries, passenger satisfaction holds paramount importance in both airport and airline service quality, closely intertwined with passengers’ perceptions of service quality and the servicescape [22,67]. In particular, airlines recognize the significance of studying air traveler satisfaction and identifying key service quality indicators [68]. In previous research, some authors have investigated the relationship between consumer satisfaction and brand equity [65]. Other literature suggests that consumer satisfaction with a brand can evolve into brand attachment [69].

Similarly, other researchers have stated the significant and positive influence of customer satisfaction on brand equity [70]. Furthermore, Hsu identified customer satisfaction as a pivotal factor in the industry, positively affecting brand equity [71]. According to Ghorbanzadeh and Rahehagh [72], customer satisfaction with a product or service lays the foundation for brand attachment, consequently enhancing the brand’s value to meet consumer expectations and needs. Despite extensive studies on brand equity, brand loyalty, and consumer satisfaction, only a few have recently explored the relationship between brand equity and consumer satisfaction in the airline industry.

Therefore, this research aims to explore how an airline can leverage customer satisfaction to enhance brand equity and create a brand that resonates with consumers.

This discussion offers the following hypothesis.

Hypothesis 6 (H6).

Customer satisfaction has a positive effect on brand equity.

Hypothesis 7 (H7).

Customer satisfaction has a positive effect on brand attachment.

2.4. Brand Attachment

Prior research has characterized brand attachment as an emotional construct, often described in terms of affective states such as connection, passion, and affection [73]. Some authors described brand attachment as the standard of bonding relationship that connects the brand with an individual in a company [74,75]. Thus, when consumers develop a strong attachment to an airline brand, factors such as brand-self connection and brand prominence can significantly influence their decision-making processes.

Brand attachment is viewed as a close emotional bond that connects consumers with a specific brand [76,77]. Park et al. [78] argue that brand attachment is consistently associated with positive consumer cognitions and emotions toward the brand [76,79]. Furthermore, consumers’ brand engagement positively influences brand attachment, which in turn leads to positive brand evaluations, behavioral commitment, brand love, and brand equity [80,81,82]. According to Kang et al. [83], positive experiences lead to favorable affective responses, such as satisfaction, which contribute to consumers’ emotional connection with the brand. Satisfactory experiences also play a crucial role in maintaining consumers’ emotional consistency toward a brand [84]. The positive relationship between consumer experience and brand attachment has been highlighted in recent studies [85]. Yen et al. [75] proposed that consumers with a high level of brand attachment are more likely to sustain a relationship with the brand. Various studies have explored the link between brand attachment and brand equity. In the context of education, Fleury-Bahi et al. observed a strong association between individuals’ satisfaction and their attachment [86]. Jahn, Gaus, and Kiessling [87] emphasized that brand attachment is a relationship-based concept reflecting an emotion-laden bond between an individual and a brand. Mikulincer and Collins suggested that individuals with strong attachment to an object tend to have more prominent memories associated with it. Previous literature has shown that customers form attachments to various entities, including communities, travel agencies, and tours [75]. Additionally, consumers highly attached to a brand often exhibit protective behavior toward it, even in the face of unexpected incidents or mishaps [88]. Therefore, businesses in the airline industry must enhance their brand equity in customers’ perception through continuous interactions, given the significance of brand attachment.

This discussion offers the following hypothesis.

Hypothesis 8 (H8).

Brand attachment has a positive effect on business equity.

2.5. Brand Equity

Brand equity has long been a focal point in brand management, with prior studies defining it as the differential consumer response [89,90]. In this study, brand equity is an additional marketing effect used to evaluate the value and symbolism of a particular brand. It affects the long-term development of a company [65,91]. This concept underscores the importance of brand equity as a source of competitive advantage, particularly in industries marked by intense competition. Indeed, research across various sectors has highlighted the significance of identifying the dimensions of brand equity, with organizations aiming to achieve sustainable competitive advantages by cultivating a strong brand image that enhances profitability, long-term cash flow, and premiums [92,93].

In the context of the airline industry, which operates within the service sector, there is a pressing need for airlines to adapt their strategies to measure brand equity in alignment with the nature of their business and customer focus. Scholars have stressed the importance of rethinking traditional strategies to secure a desirable brand position [94,95]. Additionally, research has demonstrated a positive association between brand equity and a company’s profitability, suggesting that sustainable development can be achieved in the long run by building a strong brand equity [96]. While scholars often delve into studies on brand equity, brand loyalty, and consumer satisfaction, only a few have recently focused on the interplay between brand equity, consumer satisfaction, and brand loyalty [65,97]. For example, other literature has suggested that when customers develop a strong attachment to a brand, brand equity is likely to be increased [98,99]. Brand equity has been found to be closely linked with customer satisfaction and brand loyalty [97,100].

In modern times, as consumers increasingly value environmentally sustainable products [101,102], and with the abundance of information available on the internet, they are becoming more aware of corporations’ environmental performance [103]. In response, companies must adapt their brand equity management to leverage the brand equity associated with green initiatives [101]. This trend of incorporating green initiatives into brand equity has garnered attention among researchers and practitioners. Moreover, research has shown that brand equity with green initiatives can positively influence consumers in various ways, including generating positive word-of-mouth, shaping brand attitudes, and influencing purchase intentions [102,104]. Building a robust brand is, therefore, crucial for airlines to navigate the complex challenges they face and ensure their survival in the future. However, despite some studies investigating the brand equity of airlines [92,95], there remains a lack of conclusive guidelines for managers due to the limited consideration of the direct impact of airline services on brand equity [105]. Therefore, it is essential to consider factors such as sustainability practices, which aim to enhance communication and pursue economic, social, and environmental sustainability, when examining the relationships between brand equity, customer satisfaction, and brand attachment. This study aims to explore the relationships between service quality, sustainability practices, and brand equity among air passengers, with a particular focus on the potential mediating effects of customer satisfaction, using a sample of Korean Air passengers. Through this investigation, the study seeks to contribute to a deeper understanding of the dynamics at play in shaping brand equity within the airline industry.

3. Methodology

This study examines the impact of service quality and sustainability practices on brand equity through customer satisfaction and brand attachment (see Figure 1). The research model, hypotheses, and survey questions were developed and tested with Korean Air passengers. To analyze the theoretical relationships and causal links among these constructs, customer satisfaction mediates the relationship between service quality, sustainability practices, brand attachment, and brand equity for Korean Air passengers.

The authors selected Korean Air for several reasons. Firstly, Korean Air is one of the most widely recognized full-service carriers in Korea, making it an apt example for studying airline brand equity due to its diverse passenger demographics. Secondly, Korean Air presents an opportune setting for exploring sustainability initiatives through its comprehensive sustainability report. Additionally, Korean Air has consistently promoted eco-friendly initiatives through various media channels, distinguishing itself from other airlines. This makes it an ideal context for examining the effects of sustainability practices on brand equity.

3.1. Data Collection and Sampling Procedure

To analyze the data and test the hypotheses, this study surveyed consumers who regularly flew with Korean Air and had a good understanding of environmental and social issues. Random sampling was utilized to gather primary data from loyal Korean Air passengers who had flown with the airline at least twice within the past year. These participants were well-versed in high-quality services and sustainable practices. To ensure the quality of the completed questionnaire and to communicate with the customer, the researcher used a Google Form survey and employed SPSS 25.0 and AMOS 23.0 for data analysis [106]. The questionnaire was composed of six sections: service quality, sustainable practices, satisfaction, brand attachment, and brand equity, with a total of 26 validated items. Additionally, a five-point Likert scale was used to record responses to 20 questions, except for demographic information. The current study has a sample size of 379, which adheres to the guideline of being five to ten times greater than the total number of items, following the rule of thumb [42,107].

To reduce the risk of a low response rate, we distributed the survey questionnaires widely. The questionnaire was originally in English, but to address language barriers and enhance comprehension, a pre-testing procedure was conducted. Furthermore, respondents had significant knowledge of environmental and social issues and were already aware of several environmental practices. The original questionnaire structure was in English, but we performed a pre-testing procedure to address language issues and make it more understandable. To ensure clarity, three university lecturers specializing in aviation management quickly and effectively revised the language. Moreover, to make necessary changes, researchers conducted a pilot test with two airline operators to improve the questionnaire’s comprehensibility. After reviewing the questionnaire, the pilot test did not find any language ambiguity. Lastly, the questionnaires were distributed in Korean, and professional translation services were employed to ensure cultural and linguistic equivalence.

3.2. Measurement

Data collection occurred from 13 June 2023 to 15 December 2023, with a total of 379 respondents completing the questionnaire through random sampling. The initial section of the survey collected demographic information from participants, including gender, age, education level, occupation, travel purpose, and frequency, as outlined in

Table 1. Demographic features.

Category		Frequency	Percentage
Gender	Male	165	43.5%
	Female	214	56.5%
Age	Less than 20	1	0.3%
	21~30	52	13.7%
	31~40	110	29.0%
	41~50	92	24.3%
	51~60	92	24.3%
	Over 60	32	8.4%
Education level	High School (Graduated)	9	2.4%
	College (Graduated)	31	8.2%
	University (Graduated)	213	56.2%
	Masteral/Doctoral (Graduated)	126	33.2%
Occupation	Student	33	8.7%
	Practitioner/Researcher	71	18.7%
	Sales/Services	50	13.2%
	Office Worker	123	32.5%
	Governmental Official	9	2.4%
	Freelancer	18	4.7%
	House Wife	41	10.8%
	Others	34	9.0%
Purpose	Travel	300	79.2%
	Business/Work	52	13.7%
	VFR (Visiting For Relatives)	17	4.5%
	Study Abroad	5	1.3%
	Others	5	1.3%
Frequency	Less than 2 times	219	57.8%
	3~4 times	95	25.1%
	5~6 times	34	9.0%
	More than 7 times	31	8.2%

. To comprehensively assess the impact of service quality and sustainability practices, a Likert five-point scale ranging from strongly disagree (1) to strongly agree (5) was utilized to gauge individual opinions. The hypotheses established in this research are shown in

Table 2. Research hypotheses.

Hypothesis 1 (H1)	Service quality has a positive effect on sustainability practices	[31]
Hypothesis 2 (H2)	Service quality has a positive effect on customer satisfaction	[31]
Hypothesis 3 (H3)	Sustainability practices have a positive effect on customer satisfaction	[31]
Hypothesis 4 (H4)	Sustainability practices have a positive effect on brand equity	[42]
Hypothesis 5 (H5)	Sustainability practices have a positive effect on brand attachment	[42]
Hypothesis 6 (H6)	Customer satisfaction has a positive effect on brand attachment	[62]
Hypothesis 7 (H7)	Customer satisfaction has a positive effect on brand equity	[69]
Hypothesis 8 (H8)	Brand attachment has a positive effect on brand equity	[42]

, and

Table 3. Measurement items.

Construct	Item	Related Studies
Service quality	The airline has modern, clean, and comfortable in-flight facilities.	[40]
	The airline is making efforts to keep accurate flight times.	[40]
	The airline is working precisely to prevent baggage from being lost.	[40]
	The airline employees fully understand and actively help me with my request.	[12,14]
	The airline provides the number of flights and schedules that customers want.	[13]
Sustainability practices	The airline is committed to building partnerships with businesses and industries for sustainability.	[31]
	The airline is emphasizing the importance of sustainability through a variety of customer-centered support services.	[49]
	The airline is conducting a recycling campaign to protect the environment.	[42]
	The airline is making social contributions through social support activities.	[31,42]
Satisfaction	I am satisfied when I use the airline.	[14,31]
	The airline has always satisfied my expectations so far.	[15]
	I really enjoy using this airline.	[14,31]
	Using that airline is a smart choice.	[31]
Brand attachment	The airline is famous for delivering comfort and pleasure to its customers.	[75,77]
	The airline strives to provide the services that customers want most.	[75]
	When I think of the airline, I think of very pleasant experiences.	[77]
Brand equity	If I had to choose the most famous airline brand, it would be this airline.	[95]
	Even if the brand is as famous as the airline, I choose this airline.	[92]
	If the airline has the same price as another airline, I prefer this airline.	[95]

presents the items related to service quality, sustainability practices, customer satisfaction, brand attachment, and brand equity. Five indicators sourced from [40] were employed to gauge service quality, while an additional four items pertaining to sustainability practices were adapted from a prior study [31]. Moreover, satisfaction-related items were drawn from previous research [14,31]. Brand attachment was evaluated using a three-item scale [77]. Brand equity was quantified using a three-item scale sourced from [95]. Respondents provided evaluations of specific airline activities based on an extensive literature review, considering passenger environmental requirements, personal significance, and values.

4. Empirical Analysis

4.1. Validity of Constructs

This study examined the theoretical model and hypotheses based on the theoretical research examined. To validate the theoretical models, including the measured variables and structural model, the SEM is employed for empirical analysis [107]. The purpose of this study is to conduct a structural equation modeling (SEM) using confirmatory factor analysis (CFA) to verify all measured variables in the research model [108]. To assess the feasibility and reliability of the measurements, this model utilized SPSS 25 to conduct various analyses, including internal reliability (Cronbach’s alpha), descriptive statistics, and AMOS 23 for analyzing CFA, including model fit analysis, path analysis, convergent reliability, discriminant reliability, and hypothesis validation [109,110].

The collected data were analyzed using structural equation modeling (SEM) to test the hypotheses and validate the research model. By applying SEM, the aim was to visualize and verify the research model and to understand the relationships between the latent variables and observed variables [111,112]. Typically, a sample size of at least 200 is required for this method. Path analysis and the measurement model are evaluated to estimate the results. In this study, the confirmatory factor analysis (CFA) was used to measure the specified measurement model using empirical data [113,114]. Moreover, the specified measurement model must be assessed for reliability as well as validity. To confirm the characteristics of the measurement model, both convergent validity and discriminant validity must be evaluated. All latent variables should have high loadings, typically above 0.6 [115,116,117]. Conversely, an indicator should load highly on only one latent variable, and cross-loadings must be excluded or avoided.

Convergent validity was evaluated for all multi-item constructs, including service quality, sustainability practices, customer satisfaction, brand attachment, and brand equity, by examining the factor loadings and significance levels of each variable item. To assess convergent validity, we analyzed the factor loading and significance level of each variable item in its specific variable [118,119,120]. To ensure the internal consistency and reliability of our measurement model, we used a structural equation model (SEM) to test the theoretical model and hypotheses. The SEM validates the theoretical models, including the measured variables and structural models. This study performed a confirmatory factor analysis (CFA) to verify all measured variables in the research model [121]. The purpose was to examine the internal consistency and validity of the measurement model, as presented in

Table 4. Results of confirmatory factor analysis.

Latent Variable	Measurement Variable	SRC a	SMC	AVE	C.R b	C.R c	CA d
Service quality	SQ1	0.672	0.452	0.519	0.843	11.189	***
	SQ2	0.696	0.484			11.217	***
	SQ3	0.780	0.609			12.314	***
	SQ4	0.764	0.583			12.457	***
	SQ5	0.682	0.465			-	-
Sustainability practice	SP1	0.812	0.659	0.627	0.870	17.024	***
	SP2	0.817	0.667			17.142	***
	SP3	0.738	0.545			15.141	***
	SP4	0.797	0.636			-	-
Customer satisfaction	CS1	0.872	0.761	0.741	0.920	21.254	***
	CS2	0.864	0.747			20.942	***
	CS3	0.875	0.766			21.375	***
	CS4	0.831	0.690			-	-
Brand attachment	BA1	0.848	0.719	0.716	0.883	20.228	***
	BA2	0.854	0.73			20.471	***
	BA3	0.836	0.698			-	-
Brand equity	BE1	0.865	0.749	0.681	0.865	19.723	***
	BE2	0.768	0.590			16.852	***
	BE3	0.840	0.706			-	-

Note: *** p < 0.001; ^a SRC: Standardized Regression Weights; ^b Critical Ratio; ^c Composite Reliability; ^d Cronbach’s;

. The fit indices analysis confirmed the researcher’s model. Additionally, the study assessed the convergent validity and internal consistency using the squared multiple correlations (SMC) value and composite reliability (CR) value. The composite reliability of all variables exceeded the minimum threshold of 0.70. Additionally, the average variance extracted (AVE) of all variables was above 0.50, indicating the measurement model’s exceptional reliability [106,121]. Therefore, the measurement model components are within the acceptable level of goodness-of-fit for both the CFA and path analysis. The CFA results are shown in Table 4.

4.2. Fit Indices

The model’s fit, as evaluated with confirmatory factor analysis, was examined, and the findings are outlined in Table 4. Importantly, all indices exceeded the threshold of 0.9, which is satisfactory. (x² = 383.707, CMIN/DF = 2.760, GFI = 0.900, AGFI = 0.864, SRMR = 0.0432, RMSEA = 0.068, NFI = 0.928, TLI = 0.942, IFI = 0.953, CFI = 0.953). Accordingly, this summary of results showed that the CFA met the predefined acceptance levels for goodness-of-fit (

Table 5. Model fits by a goodness-of-fit analysis.

Division	Result		Good Fit	Acceptable Fit	Source
Absolute fit index	CMIN/DF	2.760	0 $\le {\mathrm{x}}^2/\mathrm{d}\mathrm{f}\le$ 2	$2\le {\mathrm{x}}^2/\mathrm{d}\mathrm{f}\le$ 3	[123]
	SRMR	0.0432	0 $\le \mathrm{S}\mathrm{R}\mathrm{M}\mathrm{R}\le 0.05$	$0.05\le \mathrm{S}\mathrm{R}\mathrm{M}\mathrm{R}\le 0.10$
	GFI	0.900	$0.95\le \mathrm{G}\mathrm{F}\mathrm{I}\le 1.00$	$0.90\le \mathrm{G}\mathrm{F}\mathrm{I}\le 0.95$
	AGFI	0.864	$0.90\le \mathrm{A}\mathrm{G}\mathrm{F}\mathrm{I}\le 1.00$	0 $.85\le \mathrm{A}\mathrm{G}\mathrm{F}\mathrm{I}\le 0.90$
	RMSEA	0.068	$0\le \mathrm{R}\mathrm{M}\mathrm{S}\mathrm{E}\mathrm{A}\le 0.05$	$0.05\le \mathrm{R}\mathrm{M}\mathrm{S}\mathrm{E}\mathrm{A}\le 0.08$
Incremental fit index	NFI	0.928	$0.95\le \mathrm{N}\mathrm{F}\mathrm{I}\le 1.00$	$0.90\le \mathrm{N}\mathrm{F}\mathrm{I}\le 0.95$
	CFI	0.953	$0.97\le \mathrm{C}\mathrm{F}\mathrm{I}\le 1.00$	$0.95\le \mathrm{C}\mathrm{F}\mathrm{I}\le 0.97$

Note: SRMR: Standardized RMSR; GFI: Goodness-of-fit statistic; AGFI: Adjusted goodness-of-fit statistics; RMSEA: Root mean square error of approximation; NFI: Non-normed fit index; CFI: Comparative fit index.

) [122]. These findings highlight that there were no issues in fulfilling the predefined acceptance criteria for goodness-of-fit in the CFA (Table 5).

4.3. Discriminant Validity

Discriminant validity was assessed by comparing the correlation among the latent constructs with the square root of AVE [107]. The researcher used covariance-based structural equation modeling (CB-SEM) in conjunction with the analysis of moment structures (AMOS). To assess discriminant validity, the square root of the average variance extracted (AVE) was compared with inter-construct correlations, aligning with established criteria [107].

Table 6. Discriminant Validity.

Variable	A	B	C	D	E
Service quality	1
Sustainability practices	0.521	1
Customer satisfaction	0.634	0.558	1
Brand attachment	0.621	0.687	0.815	1
Brand equity	0.438	0.465	0.661	0.663	1

outlines the square root of AVE for service quality (SQ), sustainable practices (SP), customer satisfaction (CS), brand attachment (BA), and brand equity (BE), comparing the latent constructs. The discriminant validity was acceptable for all constructs, except for brand attachment to customer satisfaction, as their values were lower than the square root of AVE [120].

4.4. Hypothesis Test

To assess the path analysis from the research model with hypothesis testing, this study provides a summary of the path analysis based on the proposed research model.

As illustrated in

Table 7. Results of hypothesis testing.

Path		SRC a	C.R	p-Value	Decision
H1	Service quality → sustainability practices	0.728	10.360	***	Supported
H2	Service quality → customer satisfaction	0.572	7.652	***	Supported
H3	Sustainability practices → customer satisfaction	0.33	5.110	***	Supported
H4	Sustainability practices → brand equity	0.025	0.290	0.772	Rejected
H5	Sustainability practices → brand attachment	0.349	6.378	***	Supported
H6	Customer satisfaction → brand equity	0.418	3.355	***	Supported
H7	Customer satisfaction → brand attachment	0.645	11.050	**	Supported
H8	Brand attachment → brand equity	0.414	2.570	0.01 (**)	Supported

Note: *** p < 0.001; ** p < 0.01; ^a SRC: Standardized Regression Weights.

and Figure 2, service quality significantly impacts sustainability practices (SRC = 0.728, CR = 10.360, p < 0.001), while customer satisfaction exhibits a significant effect on brand equity (SRC = 0.418, CR = 3.355, p < 0.001), and brand attachment similarly influences brand equity (SRC = 0.414, CR = 2.570, p < 0.001). Notably, all variables considered demonstrate statistically significant effects on Korean Air’s brand equity. However, upon scrutinizing the path analysis, we identified that the most influential path is customer satisfaction on brand attachment, which manifests a statistically substantial level of influence on brand equity compared to other hypotheses tested. In practical terms, customer satisfaction and brand attachment are pivotal in enhancing brand equity, thereby exerting a robust positive impact on Korean Air’s overall performance.

5. Discussion

This study examined the connections between service quality, sustainability practices, customer satisfaction, brand attachment, and brand equity through empirical analysis. Initially, direct associations among these variables were explored, followed by an investigation into the mediating role of customer satisfaction between service quality, sustainability practices, and brand equity. The findings indicated a significant direct correlation between service quality and sustainability practices (H1) and between customer satisfaction and brand attachment (H7). Previous research has yielded mixed results regarding the relationship between service quality, brand equity, brand loyalty, and behavioral intention [9,14,15]. Some studies have reported significant positive correlations of sustainability practices in various industries, while others have highlighted a lack of focus on this relationship within the aviation industry. Thus, it is apparent that sustainability practices serve as a potent and positive determinant of brand equity, mediated by the influence of customer satisfaction and brand attachment. These results have significant academic and managerial implications. This study contributes theoretically to the literature on service quality, sustainability practices, and brand equity, particularly within the context of Korean airlines. By identifying brand attachment and customer satisfaction as crucial mediating variables of brand equity, the research enhances knowledge regarding customer experiences and perspectives (H6, H8) [31,42]. For example, integrating corporate social responsibility (CSR) or environmental, social, and governance (ESG) practices could enhance the long-term value of airlines and positively shape customer perceptions [123,124,125]. This suggests that consumers tend to respond more positively to green initiatives associated with sustainability practices through interest in satisfaction and attachment.

Additionally, the study revealed that sustainability practices have a less significant relationship with brand equity compared to other mediating variables. This may be attributed to consumers’ awareness of a company’s sustainable initiatives [126,127,128]. As a result, it is advisable for companies to refrain from engaging in greenwashing practices to improve brand equity [101,129]. Instead, this finding suggests alternative ways to emphasize the genuine green benefits of their services to consumers who support sustainable consumption, thereby enhancing brand equity [127,128]. The findings also supported the mediating hypotheses, suggesting that both brand attachment and customer satisfaction mediate the relationship between sustainability practices and brand equity. There is partial mediation between sustainability practices and brand equity through brand attachment and customer satisfaction [130,131,132,133]. Therefore, airline practitioners and operators should promote their sustainable initiatives more effectively, as the study revealed that customer satisfaction and brand attachment significantly impact brand equity. Moreover, the literature on sustainability practices identifies recyclable take-out containers, energy-saving lighting, and recycling waste as critical sustainability practices that significantly contribute to emotional brand attachment [59]. Additionally, brand attachment plays a vital role in fostering long-term relationships between consumers and companies, leading to higher brand equity [134,135].

Lastly, the study’s findings reveal that Hypothesis 4 is rejected, suggesting a comparatively lower emphasis on the association between sustainability practices and brand equity in contrast to other hypotheses. While there is limited research on brand equity in this context, consumers’ perceptions of a company’s sustainability efforts frequently influence their perception of green practices, indicating their level of engagement with sustainable activities. This underscores the significance of introducing sustainable management, not only to enhance the financial and non-financial value of a company but also to positively influence customer satisfaction among airline users, as well as aspects like brand attachment and brand interest.

6. Conclusions

During this period of rapid growth and economic development within the airline industry, there has been a notable rise in the significance of service quality, which has garnered increased attention from passengers. However, as environmental and social advancements gain importance among passengers, there is a growing emphasis on sustainability practices within the industry, reflecting emerging trends in business practices. Additionally, there is a growing emphasis on sustainable development within the industry, reflecting emerging trends of establishing a competitive advantage. This study aims to provide a comprehensive understanding of sustainability practices within the airline industry, recognizing it as a multifaceted process that spans various stages crucial for meeting passengers’ expectations. Previous research [31,37] has highlighted the intricate nature of service quality in airlines, emphasizing its importance across different aspects of the service delivery process. Importantly, the research underscores that sustainability practices are aligned with brand equity because they can positively influence passenger perceptions and contribute to the airline’s overall brand value. The study’s findings carry important implications for enhancing brand equity through the enhancement of sustainability practices within organizations operating in the Korean aviation industry to secure brand competitiveness and sustainable competitive advantage. Firstly, the research highlights the critical role of service quality, consistent with previous literature, as a fundamental factor positively impacting brand equity [136]. Moreover, it emphasizes how both service quality and sustainability practices foster sustainable business development and cultivate positive brand equity over the long term. Likewise, the implementation of corporate eco-friendly, reducing CO₂ emissions, SAFs, and social policies emerges as a pivotal approach for service-oriented companies to enhance customer satisfaction while simultaneously elevating brand value [137,138,139]. This comprehensive approach highlights not only the significance of sustainability practices in the Korea airline industry but also provides valuable guidance for developing theoretical frameworks that align with evolving passenger needs and expectations.

Thus, within these connections among service quality, sustainability practices, and brand equity, future studies can offer deeper insights into an airline’s sustainable development. Although this study contributes to an understanding of sustainability practices in relation to an airline’s brand equity, it is important to acknowledge its limitations. Firstly, the survey questionnaires were exclusively distributed to Korean passengers of Korean Air. To obtain a more comprehensive understanding, it would be beneficial to include survey participants from diverse nationalities, providing a broader perspective on airline passenger perceptions. Therefore, we recommend expanding the respondent pool to encompass a more diverse demographic. Secondly, many respondents were limited to one domestic airline, resulting in a lack of analysis of service quality and sustainability practices among other airlines. To address this limitation and enhance theoretical insight into the Korean airline industry, future research should consider conducting comparative analyses of various airlines. Furthermore, while the focus on theoretical research into sustainable management characteristics by Korean Air, the leading domestic full-service carrier, is noteworthy, it is crucial to ensure a comprehensive understanding of the role of airlines in sustainability practices. This can be achieved by including passenger groups who value service quality and sustainability practices. As the number of subjects in this group increases, attention can be directed toward enhancing the sustainable competitive advantage of airlines. Additionally, it is important to investigate and broaden the scope of other variables associated with brand equity, which can serve as proxies for assessing the brand value of airlines. While we acknowledge the narrow focus of our research, primarily centered around Korean Air as a representative airline of Korea, we are cognizant of its inherent limitations and intend to enrich our conclusions by expanding the research scope to include other airlines and airports in the future.

In conclusion, the insights gained from this study contribute to understanding the relationship between sustainability practices and brand equity within Korean Air. By deepening our comprehension of these influential factors, we can underscore the significance of sustainable development by integrating sustainability practices such as corporate social responsibility (CSR) and environmental, social, and governance (ESG) initiatives [137,138,139]. Therefore, the managerial implications of this study are multifaceted. This study can assist airline practitioners and operators in understanding brand equity and the efficacy of sustainability practices, enabling them to develop marketing strategies targeted at large aviation market segments, such as Korea’s flagship airline.