CO2 emissions associated with hubbing activities in air transport: an international comparison

Hubbing is an important operational practice in air transport. Many studies have been conducted to examine the benefits and impacts of hubbing from an economic perspective. However, its impact on CO₂ emissions, especially across different air spaces, is not well understood. This paper explores the impact of hubbing activities in air transport from an environmental perspective. With a detailed methodology and data from the Greek and Hong Kong/Sanya flight information regions (FIRs), three levels of CO₂ emissions are estimated: airport-based, airspace-based and flight-based. After contrasting the CO₂ emission efficiencies of Athens International Airport (AIA) and the Hong Kong International Airport (HKIA), aircraft type and flight distance are examined to explain their emission efficiency differences. It is found that HKIA is associated with poorer CO₂ emission efficiency at the airport and airspace levels because of the larger aircraft and longer flight distance. However, when CO₂ emission efficiency at the flight level is considered, HKIA, with a higher passenger load factor, performs better. Major international hub airports should implement additional environmental measures to minimize the impact of hubbing activities on CO₂ emissions at the airport and airspace levels.     

The cost of abatement options to reduce carbon emissions from Australian international flights

In 2012, a total of 13.1 million tonnes of carbon dioxide were emitted by 14 airlines while transporting 72 per cent of international passengers into and out of Australia in 2012. With passenger and cargo traffic growing at between five to six per cent annually from 2013 to 2033, acquiring more fuel efficient aircraft to both renew the existing fleet and to service growth has the greatest potential in reducing emissions over the next 20 years. Our analysis shows that implementing carbon dioxide emissions abatement options such as installing light weight seats, iPad electronic flight bags, winglets, washing aircraft engines and reducing the number of engines used during taxiing, all offer net financial savings when considered over 20 years. Acquiring new fuel efficient aircraft has the biggest impact on emissions reduction. Low interest loans and longer loan repayment periods may incentivise airlines to acquire more fuel efficient aircraft to service traffic growth but other complimentary incentives and penalties are required to influence airlines to replace their current fleet with more fuel efficient aircraft.     

Investigations on the distribution of air transport traffic and CO2 emissions within the European Union

This study analyses the structure of air traffic and its distribution among the different countries in the European Union, as well as traffic with an origin or destination in non-EU countries. Data sources are Eurostat statistics and actual flight information from EUROCONTROL. Relevant variables such as the number of flights, passengers or cargo tonnes and production indicators (RPKs) are used together with fuel consumption and CO₂ emissions data. The segmentation of air traffic in terms of distance permits an assessment of air transport competition with surface transport modes.The results show a clear concentration of traffic in the five larger countries (France, Germany, Italy, Spain and UK), in terms of RPKs. In terms of distance the segment between 500 and 1000 km in the EU, has more flights, passengers, RTKs and CO₂ emissions than larger distances. On the environmental side, the distribution of CO₂ emissions within the EU Member States is presented, together with fuel efficiency parameters. In general, a direct relationship between RPKs and CO₂ emissions is observed for all countries and all distance bands. Consideration is given to the uptake of alternative fuels. Segmenting CO₂ emissions per distance band and aircraft type reveals which flights contribute the most the overall EU CO₂ emissions. Finally, projections for future CO₂ emissions are estimated, according to three different air traffic growth and biofuel introduction scenarios.     

Analysis of the recent evolution of commercial air traffic CO2 emissions and fleet utilization in the six largest national markets of the European Union

This paper presents the results of a study performed to analyze the evolution of commercial air traffic and CO₂ emissions in the European Union, from 2010 to 2013. Data sources are the European Commission's Eurostat Air Transport Statistics (Eurostat) and EUROCONTROL flight plans database. The changes in the fuel efficiency are analyzed and the potential reasons for those changes investigated. The evolution in the airline fleet composition during the last decade is presented as one of the reasons for the improvement in fuel efficiency, measured in burnt fuel per total Revenue Tonne Kilometre (RTK), as well as the different parameters depending on the airline business model (network carriers, low cost companies, etc.) and the aircraft type.Results show a slight reduction in the traffic, both for passengers and cargo (about −0.8%), and a more important reduction in CO₂ emissions (−4.3%), thanks to an improvement in the fuel efficiency parameter (−3.5%) for the three years period. There has been a relevant change in the fleet composition in the last ten years, with the replacement of older models for more efficient ones, and a shift to larger aircraft, particularly in the regional segment. Traffic has decreased in shorter distances (internal EU traffic), but increased in more efficient long range flights (extra-EU traffic), resulting also in an improvement of the efficiency parameter as average aircraft size and stage length increases.     

The emission reduction potentials of First Generation Electric Aircraft (FGEA) in Finland

Under the looming climate crisis, aviation needs to find new solutions to cut its greenhouse gas emissions. One pathway towards zero emissions is the use of electric aircraft. While current battery technology will not allow for medium and long-haul flights at full capacity, on short-haul routes First Generation Electric Aircraft (FGEA) could play a significant role in the near future. Current FGEA under development could carry 9–19 passengers on distances of 400–1046 km by 2025. This study focuses on the emissions reduction potentials of FGEA in Finland. It compares the carbon dioxide equivalent (CO₂-eq) emissions and real travel times (RTT) from door-to-door of FGEA on 47 routes with existing aircraft, train and car transport modes, as well as with proposed high-speed rail (HSR) and electric vehicle implementation. The study found that replacing all existing aircraft with FGEA can clearly be recommended as it would result in a reduction of CO₂-eq emissions and RTT. Existing cars should only be replaced by FGEA on routes beyond 170 km. The replacement of existing trains by FGEA under the current energy mix is not recommended. However, once electricity could be provided from renewable energy sources exclusively, it would become feasible to replace existing trains on distances beyond 170 km and HSR beyond 400 km with FGEA.     

Cost savings from trajectory deviations in the European air space

Air transport deregulation has lead to an increase of air traffic, together with a reduction of air fares. Air fare reduction has narrowed operational margins of airlines, bringing financial and employment instability. This has brought airlines to pay increasing attention to flying costs reduction. Two important components of flying costs airlines can try to cut modifying the planned flight are en route charges and operational costs. We rely on Demand Data Repository (DDR2) data to calculate deviations from planned flight trajectories to analyse the extent to what airlines try to cut operational costs making shorter flights than planned if possible, and cut en route charges providing a planned flight with lower en route charges than the planned flight. Our findings show that there is no generalised strategy among airlines to reduce en-route charges asking for deviations of the planned route. On the other hand, airlines are achieving savings of operational costs regularly. Higher savings per nautical mile are obtained in night flights, with longer planned distance and operated by low cost carriers.     

The effect of flight distance on fuel mileage and CO2 per passenger kilometer

In this study, the effect of distance on fuel mileage (fuel burn per nautical mile) and CO₂ intensity, based on a large amount of actual flight data, is discussed for narrow-body commercial aircraft performing domestic flights for flight distances of between ～200 and ～800 NM, in Turkey. For twenty-nine domestic routes, the average CO₂ intensity is calculated to be 88 gr/pa-km, with an 80% load factor, ranging from between 112 gr/pa-km (207 gr/pa-NM) for the shortest route and 78 gr/pa-km (145 gr/pa-NM) for the longest route. An overall runway-to-runway analysis reveals that the average flight fuel consumption increases by 5.1 kg for each additional nautical mile. The discussion is extended to cover wind effect, through westbound and eastbound flights, on fuel consumption. The average fuel mileage of the eastbound flights, above 30 kft, is found to be 11.2% lower than those for the westbound flights. A sensitivity analysis is also carried out to reveal the effects of three main flight performance parameters, namely, cruise altitude, cruise speed and aircraft mass on the cruise CO₂ intensity.     

Grounded aircraft: An airfield operations perspective of the challenges of resuming flights post COVID

The global COVID pandemic, national lockdowns and unprecedented decline in passenger demand worldwide has led to airlines cancelling services, furloughing staff, applying for financial support and placing aircraft into temporary storage. However, with finite space available, and up to two-thirds of the world's total passenger fleet grounded for an indeterminate period of time, airlines have been forced to park their aircraft in unusual places, sometimes at airports they do not normally serve and in volumes never normally experienced. The aim of this paper is to investigate the extent of grounded aircraft at UK airports and explore the challenges, from an airfield operations perspective, of resuming flights post-COVID.     

Integrated airline productivity performance evaluation with CO2 emissions and flight delays

This paper evaluates the airline productivity change by applying a modified global Malmquist productivity index (GMPI) model, incorporating both CO₂ emissions and flight delays. Statistical inference is also performed on the GMPI results using the bootstrapping method. Empirical research was conducted on 15 international airlines during 2011-2017. The obtained results showed that the productivity of all airlines had been fluctuating and experienced a slight increase over 2011–2017. Most of these 15 airlines made more progress in managing punctuality than CO₂ emissions. High punctuality policy may not be the best choice for all airlines when considering financial constraints, while airlines in more liberalized aviation markets are more likely to improve productivity by reducing flight delays. Efficiency change and technological change were the major driving factors for the growth of airline productivity. European and US airlines benefitted more from superior technology, while most Asian and Oceanian airlines still benefitted from the advantage of efficiency. Based on the findings, specific management advice was given.     

CNG2020 strategy and airline efficiency: A Network Epsilon-Based Measure with managerial disposability

In this paper, we analyze the impacts of CNG2020 strategy on the efficiency of 29 international airlines during 2021–2023. Predictions are made through neural networks based on the empirical data from 2008 to 2015. Following the principle of CNG2020 strategy, we calculate the emission limit for each airline. Then we propose a new model, Network Epsilon-Based Measure with managerial disposability, to discuss the difference in efficiency of the airlines when the CNG2020 strategy is considered. The main findings are: (1) For most of these 29 airlines, the CNG2020 strategy has little influence on their efficiency. (2) The efficiency has little variation under the following conditions: when the carbon price is 8 $/ton CO₂-eq, when the price is 14 $/ton CO₂-eq, and when the price is 20 $/ton CO₂-eq. (3) Scandinavian is identified as the benchmarking airline.     

Aviation and the environment in the context of the EU–US Open Skies agreement

We examine the impacts of the EU–US Open Skies agreement on the environment on emissions from the aviation sector. We use the Hamburg Tourism Model of domestic and international tourist numbers and flows, to estimate these impacts. The Open Aviation Area will result in increased competition between carriers and falls in the cost of transatlantic flights. This will not only have implications for the size and structure of the industry but also for climate policy. The paper assesses what effects the expected increases in passenger numbers will have on CO₂ emissions and tests whether this increase in travel will result in a corresponding rise in emissions. Simulations show that passenger numbers arriving from the US to the EU will increase by between 1% and 14% depending on the magnitude of the price reductions because of substitution between destinations, the percentage increase in global emissions is much smaller (max. 1%) than the increase in cross-Atlantic traffic.     

Airline fuel usage and carbon emissions: Determining factors

Using annual data on individual US airlines over the 1995–2015 period, this paper presents regression results relating an airline's total fuel usage to seven variables: the available ton miles of capacity (passengers plus freight and mail) provided by the airline; the average seat capacity of its aircraft, average stage length (flight distance); average load factor (measured by weight); the average vintage (construction year) of its aircraft; the percentage of the airline's flights that are delayed; and the average annual fuel price. The results show how fuel usage and carbon emissions depend on a small set of crucial variables. The estimated fuel-price effect allows the emissions impact of an optimal emissions charge to be computed, and the estimated delay effect shows the emissions impact of an industry-wide reduction in flight delays. The regression model is generated from a theoretical framework.     

Evaluating airline efficiency: An application of Virtual Frontier Network SBM

In this paper, airline efficiency is divided into three stages: Operations Stage, Services Stage and Sales Stage. The new three-stage strategic operating framework of airline efficiency is a modification of existing models. A new model, Virtual Frontier Network SBM, is proposed to evaluate the efficiency of 22 international airlines from 2008 to 2012. The results demonstrate the following: 1. The new model can apply to a new benchmarking airline such as Scandinavian Airlines. 2. Although passenger traffic, cargo traffic and revenue decreased from 2008 to 2009, most airlines’ overall efficiency increased in the period.     

The impact of terminal re-organisation on belly-hold freight operation chains at airports

While it is widely acknowledged that airport re-organisation from destination to dedicated airline group terminals makes passenger travel more seamless, more efficient and also more profitable for both airlines and airports, there is little known about the impacts of such change on freight and in particular belly-hold cargo chains. Our analysis includes data from all airports in Australia but focuses primarily on the proposed re-organisation of Sydney Kingsford Smith airport. This paper reveals a significant relationship between international freight volumes, terminal organisation and freighter operations. However, our interview results only confirm the volume/aircraft type relationship. The paper aims to contribute to the general discussion on the impact of passenger terminal organisation on belly-hold freight operations and more specifically to the consultation process around airport master planning.     

Spatial concentration and connectivity of international passenger traffic at Brazilian airports

This paper examines concentration and connectivity of international passenger airport traffic in Brazil. The analysis considers seat supply and scheduled flights from 1999 to 2012. The 2000–2005 period was marked by concentration and limited international flight links, which was followed by the movement to recover capacity and connectivity from 2005 to 2010. Brazil started to liberalize bilateral agreements in 2002, and eventually moved towards the “open skies” concept in 2010, facilitating the process of operational de-concentration and increasing seat supply. The Brazilian government's liberalisation policy through bilateral agreements did not spark off a significant turnaround for national airlines; rather, the revived traffic growth was led by foreign airlines. This movement brought significant changes in the composition of international passenger traffic in Brazil, although changing little in terms of concentration and connectivity. The real change was the dominance of foreign airlines and seat distribution by regions, with the Latin America and Caribbean region shrinking to less than half of the market.     

Airport classification based on cargo characteristics

Air cargo has received little attention in airport research. In this paper, 114 airports are grouped according to their cargo business characteristics. Applying a hierarchical cluster analysis, the paper uses absolute (cargo tonnage) and relative measures (share of cargo work load units, of freighter movements and of international cargo) to establish the reliance of different airport types and groupings on air cargo. Eight distinct clusters are identified which show clear differences in the characteristics of the sample with regard to cargo activities. Geographic patterns of these airports are also revealed. For example, North American and European airports are characterised by features unique to these regions. Airports that are highly dependent on air cargo tend to benefit from a central location within networks of cargo airlines, while other airports with high cargo volumes generate these as a result of significant belly-capacity of passenger operations. Understanding the heterogeneity of cargo airports is important for future benchmarking studies in this field.     

Will the EU-ETS instigate airline network reconfigurations?

Based on the proposal of the European Commission on including the aviation sector into the European Emission Trading Scheme, a route-based analysis is conducted simulating cost and demand implications for selected airlines. For a scenario of €20/tons CO₂, results indicate that the EU-ETS CO₂-based cost increases for the airlines are between €9 and €27 per route and therefore, as an individual factor, are not high enough to instigate major route reconfigurations among European airlines.     

The impact of environmental variables on the efficiency of Chinese and other non-Chinese airlines

This paper explores the impact of an international focus, the proportion of cargo traffic, and the level of salaries on the operational efficiency of Chinese airlines and other non-Chinese airlines. Data envelopment analysis (DEA) is employed to evaluate the operational efficiency and a bootstrapped truncated regression is applied to explore the impact of environmental variables on efficiency. The results show that an international focus has a negative impact, while the level of salaries has a positive impact. Also, we demonstrate that there is an inverted U-shaped relationship between efficiency and the proportion of cargo traffic.     

Limitations of DEA-based approach and alternative methods in the measurement and comparison of social efficiency across firms in different transport modes: An empirical study in Japan

This paper measures and compares social efficiency of railway firms and airlines in Japan’s domestic intercity travel market. Unlike other efficiency studies, our input and output measures are more comprehensive because we incorporate the life-cycle CO₂ emissions as an undesirable output and travelers’ time and government spending on air infrastructure as inputs. We use the nonparametric directional output distance function (DODF) together with the composite social efficiency index to analyze the yearly panel data of the three major railroads and two major airlines during 1999–2007. The results indicate that the railroads are more socially efficient than airlines. Furthermore, we discuss the inability of nonparametric DODF method for comparing the social efficiency of firms across modes.     

Measuring the productivity changes of Chinese airlines: The impact of the entries of non-state-owned carriers

The competitive environment of the Chinese airline industry has experienced rapid change since non-state-owned airlines entered the market in 2004. We focus on measuring the productivity changes in the Chinese airlines, especially state-owned ones after this change. The results show that non-state-owned airlines are performing better than state-owned airlines. The productivity changes of state-owned airlines are mainly driven by technical changes before or after the entries of non-state-owned airlines. They have little efficiency improvement. However, the productivity changes of private airlines are mainly due to efficiency improvement. The changes associated with international joint venture cargo carrier are due to its significant improvement in both the efficiency and technical changes.