## 1 Introduction  
As has occurred in many other business sectors, the airline industry has grown considerably as a consequence of the arrival of the internet, which has allowed multiple new opportunities, from online ticket purchase to real-time information updates for customers about flights or company functioning. The position of airlines in the virtual world of the internet is considered a key point to attract new customers and keep them faithful. Twitter accounts, Facebook pages, or YouTube channels, just to mention a few, are online media used for this purpose.  
We can find in the literature many works assessing the efficiency of airlines [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]. Analysis of the efficiency of the airline industry has traditionally been carried out from an economic perspective, mainly using micro-and/or macro-economic estimates to assess the viability of a company, its business plan, its fleet optimization, or its route planning, just to mention a few [2; 7; 10; 11; 12; 13; 14]. Some authors focus on specific economic variables such as the cost or passenger revenue [2; 15; 16], while others analyze efficiency by taking into account other airline features, such as fleet or aircraft departures [17; 18], and some even include variables such as network size [1; 16] or aircraft manufacturers [19].  
The maximum efficiency an institution can attain is determined by the heterogeneity of its [1; 2; 3; 4; 5; 6; 7; 8; 9; 10] resources and the capabilities of its management [20]. Resource-based theory [21; 22; 23] has been widely adopted as the reference point for research into efficient production management within institutions as it can help explain why some firms consistently outperform others. Actually, only a few approaches include some other more heterogeneous aspects of study when considering how to evaluate the efficiency of an airline [1; 24]. However, the emergence of new features able to describe the functioning and the position of an airline in the market--such as its relative presence on the internet or its development with regard to other companies--have brought about new opportunities to compare its behavior in the airline business. Designing new models to utilize those non-economic parameters in order to study efficiency has become an interesting topic to address. This paper attempts to add into the equation some important features not often included into the efficiency analysis of airlines, namely social media indicators or network analysis measures.  
We propose a novel approach that addresses the aforementioned issues by using data envelopment analysis (DEA) techniques along with several variables relevant to the efficiency of an airline, such as business management factors, the position of the company in terms of network analysis, and social media indicators. We aim to compare how including the two latter factors in the analysis of efficiency may produce different results from relying on traditional economic variables. To the best of our knowledge, this is the first paper on this topic and should help to build a more holistic view of the airline industry.  
The paper is organized as follows. In the next section, we motivate our work by reviewing some related work in the literature. In Section 3, we present the methodology we use to study efficiency throughout the paper. Section 4 sets out the data collected related to the European airlines we study. We present the results obtained in Section 5. Finally, we discuss the results, draw some conclusions, and sketch some future avenues for research in Section 6.