Optimising flight connection times in airline bank structure through Simulated Annealing and Tabu Search algorithms

In hub and spoke airline networks, flight arrivals and departures generally have a bank structure to increase connections among spoke cities through a hub airport in order to provide cheaper service for higher volumes of air traffic. In this study, we introduce the airline bank optimisation problem with a novel mathematical model for improving flight connection times. The mathematical model aims to minimise the total connection times for transfer passengers and generates flight schedules regarding slot capacities in the hub airports. Since the problem is a combinatorial optimisation problem NP-hard and computational complexity increases rapidly for real-world problems, we employ the simulated annealing and the tabu search algorithms to achieve better solutions in a reasonable time. We generate sub-problems using real-world data and investigate the effectiveness of the algorithms. Finally, we present the results of a real case study of a Turkish airline company which has a hub airport connecting the flights between Middle Eastern and European cities.     

Airline network structure and the gravity model

In this paper, we determine characteristics of the cost-minimizing airline network under economies of density. Airline demand is asymmetric and governed by the gravity model. Airline networks are restricted to those where each spoke city is assigned to a single hub and where hub cities are fully interconnected. The cost-minimizing network is a mixture of a point-to-point and a single hub network. Multi-hub networks where passengers change planes at more than one airport are found to be suboptimal.     

New potential hubs in the South-Atlantic market. A problem of location

Hub-and-spoke networks have become very popular in the airline industry. In this paper we study the potential hub candidates in the South-Atlantic market if a future process of liberalization creates a common air market area between South America and Europe. The analysis is based on the principal operating strategies that airlines consider when they choose their network configuration: central location in the market, local traffic at the hub cities and airport facilities. Traffic levels, great circle distances between the airports and other variables are used to analyze possible differences among airports. Other implications concerning the agents involved like gains in frequencies, time penalties and burden of capacity are also explored. Results of the analysis are used to extract some policy considerations and to stimulate discussion by government officials, air industry analysts and academics, about the necessity of the introduction of more liberalized measures in emergent markets.     

Embedding economies of scale concepts for hub network design

We explore the idea of endogenous hub location on a network. In contrast to much of the literature, we propose that hub networks may emerge naturally out of a set of assumptions and conditions borrowed from equilibrium traffic assignment. To this end, we focus on applying a nonlinear cost function that rewards economies of scale on all network links. A model is presented and implemented in a GIS environment using both a 100-node intercity matrix and several synthesized interaction matrices. We compare solutions for different assumptions about network costs, and visualize the results. We find that under discounted conditions, network flow is re-routed to take advantage of the cost savings for amalgamation and that several cities emerge as centers through which large amounts of flow pass. Larger cities such as Los Angeles, New York and Chicago serve gateway functions. We also find that smaller cities such as Oklahoma City, Pittsburgh, Indianapolis, and Knoxville serve major gateway functions because of their locational advantages. Our paper should be of interest to the planner of a surface transportation system, or those interested in nodal concepts such as gateways and transport geography. Results are discussed in light of hub and spoke networks and suggestions are made for future research.     

The impact of airport capacity constraints on future growth in the US air transportation system

This paper simulates airline strategic decision making and its impact on passenger demand, flight delays and aircraft emissions. Passenger flows, aircraft operations, flight delays and aircraft emissions are simulated for 22 airports in the US, under three airport capacity scenarios. The simulation results indicate that most system-wide implications for operations and environmental impact seem to be manageable, but local impacts at congested hub airports may be significant. The response of the air transportation system to avoid airports with high delays could significantly impact passenger demand and air traffic for these and directly dependent airports. The simulations also suggest that frequency competition effects could maintain flight frequencies at high levels, preventing a significant shift toward larger aircraft, which would otherwise reduce the impact of the capacity constraints.     

Size versus efficiency: a case study of US commercial airports

The paper presents a productivity analysis using data envelopment analysis (DEA) of 45 US commercial airports selected from the top 15 large, medium, and small hub airports. Financial and operational data, such as aircraft movements, number of airport gates, the annual number of enplaned passengers and runway capacity, is used. Initially, a DEA is deployed to analyze the efficiency and performance measures of airports within each group by comparing and cross-referencing them with each other. We then extend our analysis to identify those airports that are not efficient and are thus dominated by other airports that are more efficient.     

Measuring connectivity in the air freight industry

In this paper, we present an air transport connectivity model for air freight. For the purposes of this paper, connectivity is defined as all possible direct and indirect connections to or from an airport operated by wide-body aircraft, weighted for the quality of the connection in terms of transhipment and in-flight times. Using this model, we analyse the networks of seven European airports. Europe’s largest hub airports carry most air freight thanks to their extensive intercontinental passenger networks, while smaller airports with a strong focus on air freight carry large amounts of cargo on dedicated freighter aircraft. For air freight operations, the catchment area of an airport is much larger than it is for passenger services, as shipments are being trucked to their departure airport throughout all of mainland Europe. Since there are many airports sharing the same catchment area, potential competition for air freight is fierce. We found that well located regions between the four large European airports have access to large air freight networks, whilst regional air freight connectivity in northern and southern parts of Europe is substantially lower.     

A comparative efficiency analysis of Spanish and Turkish airports

AENA in Spain and DHMI in Turkey operate a large majority of the airports in their respective countries. These two airport operators share some similar characteristics, but also present many differences with respect to their management strategies. For instance, the Turkish DHMI introduced a Build-Operate-Transfer (BOT) model and concession agreements, which enables active private participation in airport management. In contrast, management and operation responsibilities at all airports in Spain –with a few exceptions-have remained with AENA. This paper utilizes a data envelopment analysis (DEA) to compare the relative efficiency of airports within AENA and DHMI for the years between 2009 and 2011. Based on the efficiency scores, it further identifies the sources of inefficiencies resulting from various management strategies and other external factors. The results indicate higher average efficiency levels at Spanish airports, but private involvement enhances efficiency at Turkish airports. The majority of the airports in Spain and Turkey operate under increasing returns to scale. Certain policy options, including a higher private involvement and improvement of the airport network by closing some inefficient airports, should be considered in order to increase the airport efficiency in both countries.     

Spatial and operational factors behind passenger yield of U.S. nonhub primary airports

Nonhub airports are an essential component in the National Plan of Integrated Airport Systems (NPIAS) of the United States in that they connect regional towns and small communities to the air transportation network. Understanding the interplay of operational and spatial factors in determining average passenger yield of nonhub airports provides airlines with valuable information for network planning and revenue management. This study examines factors contributing to the yield variation among nonhub airports in the U.S. Using ordinary least squares (OLS) based econometric models, this study captures the spatial dependence of passenger yield of nonhub airports, which tends to increase with a corresponding increase in distance to the nearest large hub airport. Nonhub airports surrounding large hub airports with higher passenger enplanements and higher average yields also have higher yields than other nonhub airports. In addition, this study finds the effect of Allegiant Airlines in lowering the average passenger yield of the nonhub airports served directly by the airline, which can be termed as ‘Allegiant Effect’. Findings of this study could provide valuable guidance for airlines to analyze network planning strategies and to identify future markets for growth and for policymakers when allocating resources to communities relying on these nonhub airports.     

An analysis of essential air service structure and performance

The US federal Essential Air Service program was established to subsidize air service to communities unable to retain commercial carriers after airline deregulation in 1978. In this paper, the subsidized service between program communities and commercial hub airports is investigated relative to several Essential Air Service planning objectives. Specifically, observed community hubbing activity is compared with that modeled to minimize hub access cost and maximize community accessibility within the commercial air transport system. Results highlight trends in system performance relative to these planning objectives and indicate that significant potential exists for enhancing the efficiency of the program in light of limited resources.     

The difference between hub and non-hub airports – An airside capacity perspective

Airport airside capacity is limited by the runway system capacity or apron capacity, whichever is more constraining. Sometimes, taxiway system can also impose constraint to airside capacity, but in the case of fully developed taxiway systems (involving parallel taxiway, high speed exits, etc.) that is usually not an issue. To determine which airside element is more constraining it is not always as simple as comparing runway system and apron capacities directly one to another. It is important to understand and take into consideration their relationship. Runway-apron relationship depends on demand characteristics e.g. dominant market segments (e.g. scheduled, charter, low-cost, general aviation, cargo), and/or specific traffic patterns (hubbing or point-to-point services, seasonality in demand, etc.).The paper brings up the issue of available airside capacity under different traffic characteristics, faced by hubs vs. non-hub airports, and the necessity to understand runway-apron interdependency in order to properly identify the bottleneck on the airside. Referring to earlier findings related to apron capacity analysis, the paper summarizes various factors that affect apron capacity at non-hub and hub airports and uses them to define the runway-apron relationship, as well as its role in the process of analyzing airside capacity under various demand characteristics.The main finding is that functional relationship between the runway system and aprons is much stronger in the case of hub airports, and should be carefully considered when analyzing airside capacity. Besides runway capacity, few other variables that affect apron capacity at hub airports are discussed. Generic examples are used to support the discussion.     

Hub competition and travel times in the world-wide airport network

The aim of this work is to measure the competition between airport hubs based on an analysis of travel times in the world-wide airport network. By considering the minimum travel time required to connect each pair of airports, it is possible to create new measures of hub competition, separating the effects of hub position and temporal coordination. This analysis was carried out at the global level, considering all 232 airports with more than 3 million seats yearly offered in departure flights in 2008, and also in relevant geographic markets. The results show a high level of competition among the most important world airports, but the major airports of Europe have a geographical advantage in relation to world markets over the major American and Asian airports. We also show that airports located in different continents often compete for the same origin–destination markets. Geographical position appears to be the most important variable explaining hub performance. Secondary hubs show a higher degree of specialization towards specific markets.     

The determinants of aeronautical charges of U.S. airports: A spatial analysis

Using U.S. airport data from 2009 through 2016, this study examines the determinants of aeronautical charges of large and medium hub airports and accounts for the spatial dependence of neighboring airports in a spatial panel regression model. Our results show that U.S. airports' aeronautical charges are spatially dependent, and neighboring airport charges are positively correlated, implying that U.S. airports are in price competition with each other even though they are government-owned infrastructure. Additionally, we find evidence of airport cost recovery through non-aeronautical revenues. This may be indicative of the airport's cross-subsidizing aeronautical operations with non-aeronautical revenues. In addition, we found the airports that share revenues with airlines charge lower aeronautical fees than those that do not share revenues. We also found that more congested airports charge higher aeronautical fees.     

The impact of regional jets on air service at selected US airports and markets

Regional jets, normally defined as jet aircraft introduced since 1993 with less than 100 seats, have been thought to have significant impacts on air services at airports, for example, in improving service frequency, allowing airlines to exploit niche markets and to feed hubs. Previous studies have focused on regional jet deployment strategy and the overall situation and they suggest that deployment was generally to larger cities first and, in addition, to locations east of the Mississippi. It has also been suggested that smaller airports might lose service when regional jets replace turboprops and that carrier competition would increase, to the benefit of the consumer.This paper aims to throw more light on these issues from the individual airports' point of view. Data on changes in schedules from the Official Airline Guide (OAG) at a series of case study airports from 1994 to 2002 is used to examine, the impacts on new route development, market dynamics, carrier competition and concentration and deployment status. In particular, the impact on smaller airports is examined.It is concluded, subject to the usual caveats on sample size, that there is little evidence of a uniform impact on routes or airports. The aggregate picture often described by the industry and government is shown to be a combination of highly dissimilar cases. A spectrum of effects is identified across different types of airports and routes but some of the anticipated trends, such as hub bypassing, are not observed. Some airports reaped significant benefits in terms of improved frequency and services to new destinations, whilst others gained little.     

A spatial analysis of air transport access and the essential air service program in the United States

In the United States, the goal of essential air service (EAS) is to provide a minimum level of air transport service from smaller, often remote communities to the national network. While supporters of EAS tout the economic benefits of connecting rural and isolated communities, critics cite high costs, low use and antiquated eligibility requirements as factors which compromise the value of the program. In this paper, a comprehensive database of US airports is combined with network analysis techniques and a geographic information system to evaluate population access (at the census tract level) to EAS airports for 2006. Results suggest that redundant coverage of EAS market areas by alternative Federal Aviation Administration designated hub airports can contribute to EAS airport market leakage and that alternative definitions of EAS community eligibility have the potential to dramatically increase programmatic efficiency and reduce federal monies spent on EAS subsidies.     

What hurts the dominant airlines at hub airports?

This paper estimates a frequency equation to explain the determinants of network airline service levels at their hub airports. Drawing on European data for 2002–2013, we find that network airlines reduce frequencies when the share of low-cost airlines increases both on the route and at the hub airport. On the contrary, frequency choices of network airlines are not affected by competition from low-cost airlines operating in nearby secondary airports. We also find some evidence that mergers in Europe may result in a re-organization of the route structure in favor of the hubs of the larger airline.     

Global maritime networks: The case of Maersk

Two contrasting approaches to the provision of maritime services are frequently presented: one based on direct port to port services, the other characterised by a hub and spoke network. We demonstrate there is no contradiction between these two models, that in fact they are complementary. Integrating direct services with a hub structure is necessary for assuring a wider geographical coverage. The complementarity is explained by analysing the world’s largest container shipping line, Maersk, which over the last 30 years has created a global shipping network.     

The environmental implications of airlines' choice of aircraft size

One of the main outcomes of open skies policies is the importance of service frequency in the competition between airlines. To keep load factors high while offering high frequency service, airlines tend to reduce the size of the aircraft used. On short-haul routes this phenomenon is even more apparent, especially on routes between hub airports, even though these routes and airports are often congested. This choice of service frequency and aircraft size must have important environmental consequences that this paper aims to evaluate and quantify. The analysis considers local air pollution, climate change and noise impacts and aims to evaluate whether the competitive environment that drives airlines to offer high frequency service carries an environmental penalty. The analysis showed that increasing aircraft size and adjusting the service frequency to offer similar seating capacity will increase local pollution but decrease climate change impact and noise pollution. When local pollution and climate change impacts are monetized and aggregated the analysis showed that environmental benefits will result from increasing aircraft size. But these benefits, in monetary terms, were found to be relatively small and sensitive to the assumptions made.     

Statistical modelling of runway incursion occurences in the United States

Runway incursions are an important aviation safety concern; between 2002 and 2015 there were 16,785 runway incursions at United States airports ranging in size from small general aviation (GA) to large commercial airline hubs. When examining airports with the 50 highest incursion count over the past 5 years, the predominant categories were large hubs, which accounted for 21 airports and general aviation (GA) airports which accounted for 16 airports. In June 2015, the Federal Aviation Administration (FAA) announced the Runway Incursion Mitigation (RIM) program to identify airport risk factors that might contribute to a runway incursion and develop strategies to help airport stakeholders mitigate those risks. Different size airports serve different aircraft fleets, serve different operating volumes, and have different resources available (both funds and technologies) for incursion mitigation. Therefore, it is valuable to determine the correlating factors that affect incursions at different size airports. This paper uses econometrics based modelling techniques to identify statistically significant factors in data provided by the (FAA) public web sites on runway incursions. The model identified statistically significant variables that correlate with incursions, based on severity, for airports categories defined by the National Plan of Integrated Airport Systems (NPIAS).The model results indicate that operational incidents (OI) are more likely at large hub airports. In contrast, at GA/non-hub airports, pilot deviations (PD) were significant for less severe incursions (severity C and D). Only one variable, “number of years since 2002”, was found to be significant for all the three airport categories; this variable was correlated with severity A incursions and indicated a statistically significant reduction in severity A incursions, despite an overall 80% increase in incursions between 2002 and 2015.