Department of Science and Technology Institutionen för teknik och naturvetenskap
Capacity Constraints for Air
Traffic Flow Development
Rebecca Petersen
Capacity Constraints for Air
Traffic Flow Development
Examensarbete utfört i Logistik
vid Tekniska högskolan vid
Linköpings universitet
Rebecca Petersen
Handledare Alan Kinene
Examinator Tobias Andersson Granberg
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SAMMANFATTNING
Efterfrågan på flygtrafik ökar i snabbare takt än vad kapaciteten gör. Prognoser visar att efterfrågan kommer att fortsätta att växa även i framtiden och så även problemet med kapacitetsbrist. Om kapaciteten inte kan matcha efterfrågan av flygtrafik resulterar det i trängsel och förseningar. Det finns många faktorer som begränsar kapaciteten både på airside och landside. Begränsningsfaktorer vid en flygplats kan till exempel vara rullbanans kapacitet, bullerrestriktioner och miljön omkring flygplatsen. Även aktörer såsom flygbolag, marktjänstbolag, ICAO och IATA både påverkar samt påverkas av den tillgängliga kapaciteten.
Vid planering och öppnande av nya flygplatser eller vid förändring av flygplatsers placering och/eller storlek måste kravet på kapacitet samt den befintliga kapaciteten undersökas. Tidigare studier om kapacitetsbegränsande faktorer inom flygtrafik, har studerat olika begränsande faktorer, men det saknas en helhetsbild. En sammanställning av flygtrafikbegränsningar skulle därför vara ett värdefullt verktyg när kapacitetsbehovet ändras.
Rapporten syftar till att identifiera nyckelfaktorer för flygtrafikbegränsningar och se hur de påverkar flygtrafiken.
Rapporten analyserar och rankar olika begränsningsfaktorer i förhållande till betydelsen som tidigare forskning har gett de olika faktorerna. Som komplement till litteraturgranskningen intervjuades professionella flygplatsplanerare.
Resultatet från litteraturgranskningen samt intervjuerna visade att den största begränsningsfaktorn för flygtrafikkapacitet är rullbanan. Rullbanan var också den faktor som mest påverkades av samt påverkade andra kapacitetsbegränsande faktorer. Tidigare litteratur ansåg att wake vortex var den näst största begränsningen, medan intervjudeltagarna ansåg att stands var näst viktigast.
Sammanfattningsvis visade rapporten att rullbanan är den viktigaste begränsningsfaktorn för flygkapacitet. Rapporten visade också att olika begränsningsfaktorer är nära kopplade till varandra. För att få en övergripande förståelse av flygtrafikkapaciteten måste man veta vilka de kapacitetsbegränsande faktorerna är, men också förstå samspelet emellan dem.
ABSTRACT
In aviation, the demand for air traffic grows at a higher rate than the capacity. As the demand is predicted to continue to grow also in the future, so is the problem of capacity shortage. If the capacity cannot match the demand, it will result in congestion and delay. There are numerous factors that limit the capacity both on airside and landside, for example the runway capacity, noise restrictions, the environment surrounding the airport etc. Actors such as airlines, ground service companies, ICAO and IATA also affect and are affected by the available capacity. When planning opening of new airports or in case of changes in the location and size of the airports, the requirement for, as well as the currently available capacity must be examined. Previous studies regarding key limiting factors to air traffic capacity, address different constraints, but lack a comprehensive view. A compilation of air traffic constraints would therefore be a valuable tool in airport planning when capacity demand changes. The aim of this thesis was to identify key limiting factors and see how they affect air traffic. This thesis analyses the importance of different limiting factors in respect to the level of significance to which previous research has acknowledged the different constraints. To compliment the literature review, professionals in airport planning were interviewed.
The result from the literature review as well as the interviews showed that the major limiting factor to air traffic capacity is the runway. The runway was also the factor that was affecting as well was affected by other limiting factors. Previous literature considered wake vortex to be the second most important constraint whereas the interviewees considered stands to be the runner up limiting factor.
In conclusion, this thesis showed that the runway is the most important limiting factor to air traffic capacity. The thesis also showed that different limiting factors are closely linked to each other. For an overall understanding of air traffic capacity constraints and how these constraints affect air traffic flow, it is essential to understand the interaction between the limiting factors. Key words: Air traffic, limiting factors, capacity.
PREFACE
The thesis is an independent part related to the SAILAS project. The thesis work deals with issues relevant to the SAILAS project's initial phase. The thesis may be relevant for the continued work in SAILAS project. SAILAS aims to produce a macro model that can be used to analyse the effects of changes in the Swedish airport system. In the current situation there are models available that analyse individual effects, but there are no overall general models for use in macro analysis. The thesis constitutes the final examination for the bachelor degree from the Air Transport and Logistics program at the University of Linköping, campus Norrköping. The thesis work is conducted at ITN under the supervision of Alan Kinene, PhD student, and examiner Tobias Andersson Granberg.Norrköping, March 2018 Rebecca Petersen
ACKNOWLEDGEMENT
I would like to thank the Department of Science and Technology (ITN), at Linköping University for giving me the opportunity to perform my thesis work at ITN. I would like to sincerely thank my supervisor, Alan Kinene, at Linköping University for his valuable feedback, good advice and continuous support throughout the thesis work. I would also like to express my gratitude the professionals at Swedavia Airports Master planning and Swedavia airport planning for participating in the interviews. Finally, I would like to thank my examiner Tobias Andersson Granberg, for giving me the idea to the thesis and for his valuable comments that has contributed to improve the report. Norrköping, March 2018 Rebecca PetersenTable of content
GLOSSARY viii 1. INTRODUCTION 1 1.1 Background 1 1.2 Problem formulation 3 1.3 Aim 4 1.4 Research questions 4 1.5 Delimitation 4 1.6 Outline 4 2. METHODOLOGY 5 3. THEORETICAL FRAMEWORK 9 3.1 Logistics 9 3.2 Transport and aviation 9 3.2.1 Movements 10 3.2.2 Airside 10 3.2.3 Landside 10 3.2.4 Airspace and Terminal Airspace 10 4. LITERATURE REVIEW 11 4.1 Introduction to the literature review 11 4.2 Runway 14 4.3 Taxiway 16 4.4 Wake vortex 18 4.5 Apron 18 4.6 Ground handling/turn‐around 19 4.7 Airspace 20 4.8 ATC 21 4.9 Aircraft fleet mix in the air traffic flow 22 4.10 Environment 22 4.10.1 Emissions 23 4.10.2 Noise 23 4.11 Weather 24 4.12 Terminal facilities 25 4.12.1 Gate 26 4.12.2 Check‐in desks/baggage drop 27 4.12.3 Baggage handling 28 4.12.4 Security screening 29 5. INTERVIEWS 31 5.1 Interviewees 31 5.2 Interview answers 31 6. RESULTS 33 7. DISCUSSION 38 8. CONCLUSION 42 REFERENCES 43TABLE OF FIGURES
Figure 1. Prognosis of domestic and international passengers departing from
Swedish airports from 2016 – 2023.
2
Figure 2. Chart of how different divisions and components in aviation are
connected to each other by previous research.
6
Figure 3. Various types of runway configurations. 15
Figure 4. Types of exit taxiways. Right‐angle exit taxiway with an intersection angle between 45°–90° is shown in (A) and 90° in (B). Rapid exit taxiway with an intersection angle between 25°–30° is shown in (C).
17
Figure 5. Showing the ground‐handling activities. 20
TABLE OF TABLES
Table 1. The representation of the ranking tool used for the literature review. 7Table 2. Forecast of airport congestion and capacity demand for five large
European airports. © European Union, 1995‐20171. 12 Table 3 Hours per day that demand exceed capacity. © European Union, 1995‐ 20171. 13 Table 4. Interrelations between different limiting factors to air traffic capacity. 34
Table 5. Ranking table of the different limiting factors extracted from the
literature reviewed.
35
GLOSSARY
Airside: The area beyond passport and customs control of an airport, open for airport staff and passengers with valid boarding cards.2
Airspace sector: Geographic volumes of airspace, i.e. airspace divided into air traffic control sectors.3 ATC: Air Traffic Control ATM: Air Traffic Management. Congestion: When demand exceeds the capacity congestion occurs. Delay: Delay occurs when demand exceeds the capacity for terminal airspace or runway approach paths.4
En route: The part of the flight from the end of the take‐off and initial climb phase to the commencement of the approach and landing phase (Eurocontrol definition).5
Eurocontrol: An intergovernmental organisation with 41 member states, of which all of the EU states are included. The organisation work for the safety of air navigation and for promoting enhanced cooperation between Member States.6
FAA: The Federal Aviation Administration that regulates civil aviation. It is a part of the United States Department of Transportation.
Fleet or Aircraft fleet: A group of aircraft of the same or varying type that belonging to one operator/airline.
Flow and traffic flow: The quantity passing a given area during a given timeframe.
Ground handling: The service provided to an airplane while (parked) on the ground.
IATA: The International Air Transport Association, the trade association for the world’s airlines. They support areas of aviation activity and help with the formulating of industry policy regarding critical aviation issues.7
ICAO: The International Civil Aviation Organization, a UN specialized agency assigned to manage the administration and governance of the Convention on International Civil Aviation.8
Landside: Landside extends from the curbside of the terminal to passport and customs control.2
LFV: Civil Aviation Administration (Luftfartsverket). Provides air traffic management and air navigation services.9
Movements: A movement is either a take‐off or a landing of an aircraft. Number of movements that can be preformed during a specific unit of time determines the runway/airport capacity.10
SKL: The Swedish municipalities and county councils (Sveriges Kommuner och Landsting) an employer and interest organization for Sweden's municipalities, counties and regions.11
Slot‐time: The timeslot allocated for a certain flight to arrive and depart from the airport.
Stands: Aircraft parking positions at the airport.
State: A state is a nation or territory whit a politically organized community and its own government. There are currently 195 independent states in the world, the UN's 193 member states, the Vatican and Taiwan.12
Swedavia Airports: A state‐owned company. They own, operate and develop the national basic supply of airports.13
Turn‐around: An aircraft’s turn‐around, or turn‐around time, is the time it takes from the airplane’s arrival at the airports till it’s departure.14
1. INTRODUCTION
The demand for air traffic is growing, and this growth is predicted to continue in the future. Yet the air traffic capacity is not growing at the same rate, and there are numerous factors that limit the current capacity and its ability to grow.15,16
There are several challenges regarding the practical implementation of new traffic flows, for example, new air traffic flows must be adapted to existing flows, and realized with regard to airspace design and airport capacity. These
challenges apply not only to air traffic, but also to other types of traffic such as road traffic, which can for example experience increased travel time as one of the affects.
An important part of Sweden's political transport goal is a safe and efficient air
traffic that caters to the public’s transportation needs and the accessibility by satisfying demand17,18. Prior to opening new, closing or relocating airports and
flight routes, analysis (of how the present traffic flow as well as the availability of required capacity will be affected) has to be performed. Furthermore, there are many different parties involved in aviation, all of which influence and contribute to the constraints of the air traffic flow capacity. Parties that may be significantly affected by a change in airport location are e.g. airlines, residential areas, municipals, and environmental organizations.
1.1 Background
There are many constraints that limit the air traffic capacity at airports. Such restrictions include; the number of runways available at an airport, runway width and length, the direction of the runways relative to each other, noise restrictions, airspace capacity, the airport's location and its surrounding environment and buildings.
Various parties/actors which also affect and are affected by the available capacity include airlines, ground handling companies, ICAO8 and IATA7 among
others.
In Sweden, domestic flights have seen a stagnation since the 1990s and the demand is predicted to remain at current levels in the future. When it comes to international flights, from and to Sweden, there has been a steady growth over the years. This growth is predicted to continuously increase.15 That means that
the demand for international air traffic in Sweden is growing, the same can be said for air traffic as a whole. Figure 1 is showing a prognosis of domestic and international passengers predicted to depart from Swedish airports from 2016 – 2023 based on forecast data for Swedish air traffic by the Swedish Transport Agency (Transportstyrelsen).19,15,16
Figure 1. Prognosis of domestic and international passengers departing from Swedish airports from 2016 – 2023.
The demand for good connectivity grows as travel for both business and leisure increases. Locating airports only in the metropolitan areas is not sufficient, especially not in a country like Sweden where main international airports are located in the two largest cities, Stockholm and Gothenburg. These cities are situated in the southern part and cater to a third of the country’s population. To meet the demand for good connectivity, opening of new airports and/or routes are occasionally done through transport policies even though they may not be commercially viable18. When referring to either airport or airspace capacity, it can mean several things. Airport System Development20, refers to capacity as ‘the overall ability of an airport to accommodate demand for service’. A commonly used definition of capacity is the number of aircraft movements an airport can handle per unit of time as well as rules and regulations, for example noise and environmental restrictions21,22. Furthermore the airport capacity, movements per unit of time, consists of several factors. These factors include air traffic controller capacity, ground handling capacity, runway capacity and more. In this thesis, the capacity is defined as mentioned above, which can be concluded as the overall ability to transport passengers from one airport to another. The definition of capacity can vary depending on what and how it is being measured. Capacity can be measured in many different ways. For example; by number of flights, number of aircraft on the runway, number of parking spots, etc. Brooker and Majumdar, state in their studies that the best way to measure 0 4 000 000 8 000 000 12 000 000 16 000 000 20 000 000 24 000 000 2016 2017 2018 2019 2020 2021 2022 2023 Domestic International N u mb er o f de p ar ti n g p asse n ge rs Year
based on air traffic complexity such as the dynamic density model, trajectory‐ based complexity models or identifying complexity factors98. The method for measuring the capacity is often determined by the reason for measuring. To be able to compare the different constraints and their degree of limitation to the capacity, a unified metric for measuring capacity needs to be formulated. The flow of departing or arriving passengers is not often evenly spread over the day or season, hence resulting in peak hours/seasons where the flow is far higher than in other periods. Peak hours can occur for instance when several busloads of departing tourists arrives at a small airport at the same time. Peak season can be the summertime at airports that primarily cater to vacation destinations, which are less utilized during winter months. During peak hours or seasons the demand to capacity ratio increases and it is crucial for the airports to handle these fluctuations to avoid congestion and delays in several parts of the airport20. If the demand is higher than the ability to fulfil it, i.e. if an airport has a lower capacity compared to its demand, congestion would lead into delays especially if the traffic flow is not well managed.21 1.2 Problem formulation
The thesis examines limiting factors of air transport capacity, as well as the different actors that influence these limitations in case of changes in the location and size of the airports. As mentioned above, the restrictions may for example be the number of runways at an airport, runway width and length, as well as the runway orientation, noise restrictions, airspace capacity, and the airport's location (surrounding environment and buildings). Relevant actors include airlines, ground handling companies, ICAO8, IATA7, among others. In case an
airport is opened, closed, relocated or expanded, not only should the need for transportation be examined, but also the currently available capacity on the operational airports and other modes of transport. As airports are a part of a system of airports, they are dependant and affected by the capacity on other airports.
In order to examine the available capacity and how it can be increased, it is necessary to know its limiting factors. For example, capacity can be increased if the factor that limits the capacity the most is rectified. However, if the capacity restrictions cannot be rectified, capacity needs to be acquired by other means, for example by opening new or expanding existing airports24,25. An example is
Bromma Airport that is expanding to meet the increased demand for airport service. To increase the capacity from 2,5 million to 3 million passengers a new arrival lounge was opened in 201725,26. Bromma airport expects 200 000 more passengers arriving 2017 compared to 2016.25 Arlanda airport is also expanding by building a new runway, a new terminal and pier to increase the capacity. The expansion further includes an airport city, Airport city Stockholm, and increased road and railway connections to and from the airport. The expansion of Arlanda airport is expected to be ready by 2040.
1.3 Aim The aim of the thesis is to identify the key factors that limit air traffic capacity and how these factors affect air traffic. 1.4 Research questions The research questions that are considered relevant and which form the basis of the thesis report are • What are the key factors limiting the capacity of air traffic? • How do these capacity constraints affect air traffic flow? These research questions have been chosen because they are considered to fulfil the aim of the thesis work.
The focus of the discussion is on factors that limit the capacity of air traffic on airside, airspace and landside and on how the different limiting factors are linked to each other. 1.5 Delimitation The scope of this paper is limited to addressing the factors that limit capacity development on airside, airspace and landside. Factors limiting capacity on curbside are not addressed. 1.6 Outline
The rest of the thesis report is structured as follows; first the methods are presented in Section 2 followed by the theoretical framework in section 3.
In section 4, the thesis main part is presented, the literature review, which focuses on airside, i.e. area beyond passport and customs control of an airport, and limiting factors to the airside capacity. A table in which the different limiting factors are ranked based on the literature that is examined is also presented. In section 5, the interview summery is presented followed by analysis of the findings in section 6. The discussion is presented in section 7 and lastly in section 8, the conclusions are presented.
2. METHODOLOGY
The main method used was literature review and it was supplemented, supported and validated with data gathered through interviews. Previous studies regarding capacity constraints and key limiting factors in air traffic, address different constraints, but lack a comprehensive view. This brings a need for a literature review, as presented in this thesis, compiling the limiting factors of air traffic capacity and how they affect air traffic flow. This thesis therefore gathered and analysed literature from previous studies and examined the importance of the different limiting factors in respect to the level of significance to which previous research has acknowledged the different constraints. Interviews were used to compliment and bring further clarity and strength to the analysis. A complete compilation of air traffic constraints could be a valuable tool in airport planning when capacity demand changes. In this thesis, literature review and semi‐structured interviews, which form the research methodology, are qualitative methods. In qualitative research, validity and reliability means that the tools, processes, and data used are adequate and the results replicable.27 According to Flick29, suitable criteria for validity and
reliability in qualitative research are transferability, credibility, dependability and conformability28. By using different sources of data i.e. literature review and
interviews, the credibility is increased. By methodically documenting data and analysis procedures, the dependability will increase as will the conformability by discussing possible bias. Transferability will be achieved by a thorough description of research context details making the findings applicable in other contexts.28, 29
The literature review was conducted by a critical description, and compilation of the research that had been done in the relevant research area. Findings about the topic in previous research was evaluated and compared Their differences and similarities were identified to form a basis for future research.30
It was possible to use literature review since there exists previously conducted studies about problems and limitations of air traffic capacity. Furthermore, different study areas in aviation were recognized to be linked to each other as shown in Figure 2. By combining the present study with the above mentioned findings, new insight into relations between the different research areas could be achieved.
Figure 2. Chart of different divisions and components in aviation.
The method used for the literature review was integrative methodology. The integrative study design allowed analysis and extraction of relevant data from several sources to get a new and comprehensive view of the different limiting factors in air traffic flow. The method was suitable because the literature used in this thesis was from different types of sources, mainly qualitative but to a minor extent, semi‐quantitative31, 32. To increase rigour of the review and avoid bias,
the steps in the review work had to be clear and stringently documented according to the chosen procedure.31 The problem of identifying key limiting
factors to air traffic capacity was well defined. In addition, the different inclusion and exclusion criteria were also well defined.
The inclusion criteria for the examined literature were sources that were peer reviewed and published in scientific journals or by reliable institutions in the field of aviation (for example ICAO, Eurocontrol and Swedavia). The literature examined also should concern air traffic capacity constraints.
Table 1 presents the instrument used to rank of the limiting factors according to
the degree of capacity limitation that the literature state them to have.
The main database search was Unisearch through the LIU library, which covers most of the LIU resources as well as Google search to include literature by other media like web pages. Keywords used are “air traffic capacity constraints”, “air traffic capacity limitations”, "airport capacity limitations", and "airspace constraints". Only studies that had a degree corresponding to major or minor attached to the capacity limitation were included. Literature not meeting the inclusion criteria was excluded. Airside' Air(ield' Runways' Wake' vortex'
Taxiways' handling'Ground8'
Environ8 ment' ' Terminal' ' Terminal'' airspace'
Noise' Environ8'ment' Obstacles' Weather'
Weather' Wake'vortex' ATC'
Airspace'
Gates' handling'Baggage''
Landside' Terminal' Security'' check' Check8in'desks/ baggage'drop' 'Baggage'' handling'
Ranking of the different limiting factors extracted from the literature search was performed to reflect which factors that were considered to be most important by the research community in the field. The factors were ranked major, medium and minor. Synonyms to major in the literature were; key factor, critical factor, crucial factor, main, critical, increasingly prominent and primary. Synonyms to minor were restrictive factor.
Mapping of the literature was performed to display, visually and theoretically (i.e. described in words), the importance of different limiting factors to air traffic capacity and the linking between them. As part of the mapping, in addition to the ranking matrix, a visual aid, a graph, was constructed to display the key limiting factors visually. Table 1 shows the layout of the instrument used to rank each factor according to the degree of capacity limitation that each paper states them to have.
Table 1. The representation of the ranking tool used for the literature review
Factor Paper/author Database Source Level
(primary/secondary)
Ranking
Author X, 2017, ref.A Database Z Primary Major
Factor x
Author Y, 2017, RefB Database Q Secondary Minor
Factor y Factor z
Interviews were used to complement the literature and hence cover the possible gap between research and practice.
Interviews are generally divided into three different types. These are unstructured, semi‐structured and structured.
When unstructured interviews are being used, no questions are prepared beforehand and the interview is conducted in an informal manner. Semi‐ structured interviews have the interview questions prepared before the start of the interview, and all respondents can answer all of the questions. However, additional questions/follow‐up questions can occur during the interview to clarify or expand certain questions. Structured interviews have a set of predetermined questions that all respondents answer in the same order and are often questions that can be answered with short replies33.
There are both advantages and disadvantages of the different interview methods hence they are suitable for different situations. In this project, semi‐structured interviews were performed as it allowed a framework, i.e. the interview questions, around the issue to get reasonably consistent interviews, while still providing the flexibility to explore new topics that arise during the interview. It also gave the respondent space to freely self‐develop their response.
The main focus lied with people in the field with core competence and a role within the relevant organization. Relevant interview persons were individuals working with air traffic planning, air traffic routing, planning and capacity for airports, as well as at the aviation regulatory department.
The questions were mainly determined by the literature review and were used to verify and supplement the findings of the literature review. The interviews connect the research part and the application part, i.e. what literature and what research as well as professionals in the field say. The interview questions were: 1. How is the capacity of an airport measured, i.e. the metrics for measuring capacity? 2. What factors, regarding airside and landside, limit the air traffic capacity the most? 3. Why do you think these factors are the most limiting? 4. How would you rank these factors (from minor to major) in regard to their significance for limiting air traffic capacity? The interviews were answered by e‐mail followed by telephone discussions. In the literature, several models as well as research on the topic is available. Therefore, interviewing professionals with core competencies in the field could provide a basis for comparison between what literature suggests and what is
3. THEORETICAL FRAMEWORK
Several relevant theories for the research questions raised are presented in the thesis framework. The thesis builds on previous research in relevant areas from which significant theories are extracted. Research is subjected to change due to new findings over time, while rules and regulations are more consistent. When studying how and which constraints affect air traffic capacity, regulations have to be considered and combined with the analysis of the literature review. The theoretical framework combines widely accepted facts, regulations, previous research as well as answers from the conducted interviews. Studies and projects for the opening, expanding and closing airports, both past and current, are relevant. For example, the planned expansion of Landvetter Airport including the surrounding area with new hotels and a new train connection demonstrate many relevant limitations and problems for different traffic flows13.
3.1 Logistics
Logistics as a concept basically means to plan and manage the flow of both information and goods 34. Logistics from an airport perspective means to enable
safe, efficient, comfortable and cost effective transport services.
Airports, airlines, ground‐handling companies, among others, are the providers of transport service at the airport. This means that there are several different actors, all with their own objective working together under a tight schedule, to make the flow of information, travellers and goods, optimal. Thus, the need for logistics is crucial. The capacity limiting factors restrict the traffic flow and thereby the ability of actors to provide their service.
3.2 Transport and aviation
Countries have laws and regulations that control air traffic and air travel. In Sweden, as in the rest of the EU, it is the Standardised European Rules of the Air (SERA) that governs. Additionally to SERA, there are often additional national rules and regulations.35 In Sweden these are the aviation act and aviation
regulation36.
Both SERA and the national rules restrict air traffic by the rules and procedures they enforce. For example noise restrictions and minimum separation limit the number of aircraft at a given airport. Therefore the rules and regulations have an effect on the capacity and causes capacity constraints.
To get a full understanding of the text in the literature review, some terms need to be defined. Presented below are the definitions that have been used in this thesis. Further expressions are presented in the glossary at the beginning of the report.
3.2.1 Movements
A movement is either a take‐off or a landing of an aircraft. Number of movements that can be performed during a specific unit of time determines the runway/airport capacity10.
3.2.2 Airside
Airside is the area beyond passport and customs control of an airport, open for airport staff and passengers with valid boarding cards. The components of airside are simply the area where aircraft operate. It includes runways, taxiways, the aprons and gate areas. Airside usually also include terminal area airspace2. At airside, the passengers board the aircraft and the aircraft are serviced before take‐off2. Terminal area airspace is customary a part of the airside. This since the approach and departure paths greatly affects the runway utilization2. 3.2.3 Landside
Landside consists of the area accommodating the ground transportation. This may include roadways and car parking areas that help airport users access the airport2.
Landside extends from the curbside of the terminal to passport and customs control2.
3.2.4 Airspace and Terminal Airspace
Airspace is a region of the atmosphere available for aircraft to fly in and terminal airspace is the airspace that surrounds an airport and has air traffic services provided37. The design of the terminal area airspace must consider ground
constraints, obstacles and built terrain as well as noise restrictions38.
Furthermore, an airspace sector is a geographic volume of airspace, i.e. airspace divided into air traffic control sectors3,39.
4. LITERATURE REVIEW
This chapter reviews the literature regarding air traffic and airport capacity limiting factors. In the literary review, the different limiting factors were discussed as well as ranked from minor to major, based on the degree of capacity limitation that each paper stated them to have. The amount of research performed on the different limiting factors with regard to capacity can also indicate the significance of the different constraints.
The literature review is organized in subsections starting with an introduction to air traffic capacity and capacity constraints in subsection 4.1. In the following subsections, 4.2 – 4.12 discuss the different limiting factors and how they affect air traffic capacity. Ranking of the limiting factors based on the reviewed literature is also stated and discussed. The connection between the different factors and how they affect each other are discussed and presented in Table 4. Furthermore, the different levels of attention received by different limiting factors in the literature, are discussed and presented.
4.1 Introduction to the literature review
In the book Airport and Air Traffic Control System the U.S. Congress, Office of Technology Assessment writes about the capacity of an airport in terms of “airside” and “landside” capacity21.
They define capacity as;
They also suggest that the capacity is not a single number, but rather is dependent on many different factors both on landside and airside.
The landside capacity is dependent on the amount of passengers an airport terminal can accommodate, for example size and number of lounges and the capability of the baggage‐handling equipment. One further important part of an airport’s landside capacity is the ground access. This means sufficient transit connections, roadways, and passenger parking spaces.21
The curbside is the area that links the ground transports with terminal building and the airside. If this area does not function well there will be unbalance, which can affect the capacity. Delayed activities and departures/arrivals can severely infringe the airports capacity. However, curbside limitations are not addressed in this thesis.
In a memo from the European commission several limitations to capacity are mentioned1. Among these are insufficient ground handling and noise
restrictions . They also address that the demand of air traffic is increasing, and will continue to do so, nearly double the air traffic in Europe by the year 2030. As
The number of air operations, landings and takeoffs, that the airport and the supporting air traffic control (ATC) system can accommodate in a unit of time, such as an hour.
it stands today, five large European airports, Düsseldorf, Frankfurt, London Gatwick, London Heathrow and Milan Linate (Table 2), have already reached their maximum capacity, and by 2030 nineteen more will be at their capacity limit1. Table 2 shows only a sample of five European airports, but it is clear that
there is a problem with lacking capacity and that problem will escalate during the coming years. Table 2. Forecast of airport congestion and capacity demand for five large European airports. c.f. European Union, 1995‐20171. Airport 2010 2017 2025 Capacity assumptions Düsseldorf Demand exceeds capacity most or all day Demand exceeds capacity most or all day Demand exceeds capacity most or all day Assumed 10% increase in capacity in 2015 but no further increase Frankfurt Demand exceeds capacity most or all day Sufficient capacity most or all day Demand exceeds capacity during part of day New runway (2011) and terminal (2015) allow increases from 83 to 126 movements/hour London Gatwick Demand exceeds capacity most or all day Demand exceeds capacity most or all day Demand exceeds capacity most or all day Assumes no new runway but increase of 2‐3 movements/hour on current runway London Heathrow Demand exceeds capacity most or all day Demand exceeds capacity most or all day Demand exceeds capacity most or all day Assumes no third runway, or mixed mode, or relaxation of annual movement cap. Milan Linate Demand exceeds capacity most or all day Demand exceeds capacity most or all day Demand exceeds capacity most or all day Assumes no amendment to Bersani Decree
The memo from the European commission in 20111 shows that six of eight sample airports will have an increased number of hours per day where the demand exceeds the capacity (Table 3). For example London Gatwick have today (2017) 14 hours per day were demand exceeds capacity and the number of hours will increase to 17 in 2025, showing the necessity for measures to increase capacity.
Table 3. Hours per day that demand exceed capacity. Airport 2010 2012 2017 2025 Dublin 1 3 0 0 London Gatwick 14 14 14 17 London Heathrow 15* 15* 15* 15* Madrid Barajas 6 12 6 12 Paris CDG 8 11 12 15 Palma de Mallorca 2 2 2 3 Rome Flumicino 5 6 6 9 Vienna 5 5 9 5
Note: Covers daytime period (16‐18 hours depending on airport). * Very limited capacity available in some off‐peak hours, but cannot be allocated due to annual movement cap – in effect airport is full all day, year‐round. c.f. European Union, 1995-20171.
Congestion and the resulting delay are not uniformly distributed among the airport system. In fact, 4% of all airports handle 50% of the entire air traffic, thus a rather disproportionate distribution40. The congestion and delay are
concentrated to a few airports, while the rest operate under their available capacity20. Therefore, it is possible to increase the capacity by a more balanced
usage of airports in the region21.
The European commission states that 70% of the delays are due to capacity limitations on the ground at airports and not in the air. Although there is on‐ going work to improve ATM performance, delay and congestion problems cannot be handled successfully if the performance of airports on the ground is not improved.
The other limiting factor mentioned is the noise restrictions. There are noise restrictions at most of the larger European airports. These restrictions are meant to protect people living near airports from the noise emitted from aircraft. The restrictions are part of a wider noise reduction strategy that consists of four principal elements: better planning of flight paths and ground use, reduction of number of evening and night flights and quieter aircraft. These restrictions may lead to a decrease of a the available capacity.1 When analysing the literature, it is clear that several limiting factors have great impact on the capacity. The impact of the limitations can also vary depending on type of airport, for instance large, medium or small hub as well as type of traffic;
long–, medium– or short haul. In a survey by the U.S. Congress, Office of Technology Assessment, limiting factors that caused capacity problems at 54 US airports of different size and type of traffic were examined. The survey from 1984 studied present capacity problems as well as expected capacity constraints 10 years later, i.e. 1994.2 The survey showed that the areas where most of the airports in the survey experienced limitations were airfield, airspace and environment (in respect to noise), whereas the most severe limiting factor was airfield (runway system, land etc.), followed by apron, airspace, taxiways, gates, terminal and noise. Gate and terminal problems were most common in large airports.
In large and medium hub airports, other important factors found, though not within the scope of this thesis, were on‐ and off airports roads, curbfront and car parking. Many of the limiting factors present in 1984 were expected to limit the capacity also in 1994.2 4.2 Runway Runways are a considerable capacity constraint. The runway system capacity is not only affected by the number of runways, but also runway length and the interaction between runways.21 Additional factors that affect the capacity and
need to be taken into consideration are; the predominant wind direction, ATM system performance, noise restrictions as well as obstacles and structures in close vicinity21, 41. These aspects, along with the runway layout (Figure 3), can
affect the flights approach and departure routes, which in turn can lead to limitations of the overall runway capacity.
Blumstein defines runway capacity as the hourly rate of aircraft landing or take‐ off operations that can be accommodated by a single or combination of runways.41,42.
Dependent runways, in contrast to independent runways, are restricted due to operations on runways in close vicinity. Parallel runways are common at large airports and the space between them as well as the type of operations used determines the limitations43. Simultaneous approach to parallel instrument
runways can be dependant or independent. In this context, dependent refers to when radar separation minima are prescribed between aircraft using adjacent instrument landing system in contrast to independent were radar separation minima not are prescribed. Regarding departures, runways are referred to as independent when aircraft simultaneously depart from parallel runways. Segregated operations are when aircraft simultaneously approach or depart on parallel runways, in opposite directions.44,45
Capacity can be increased by using an independent approach when running parallel runways or near‐parallel runways. When running parallel runways, safety is a big issue and operations have to be well managed.46 Newell stated that
Using intersecting runways is a common way to manage variable wind directions and crosswinds. Intersecting runways also provides shorter taxi‐ and approach‐ ways, which increase flight efficiency. However, safety is an issue when utilizing intersecting runways and strict regulations and procedures must be stated and followed.43, 48 Thus, intersecting runways is also a capacity limitation due to the required regulations when using such runways.
Figure 3. Various types of runway configurations.
Spacing requirement regulations for parallel or near‐parallel runways depend on type of runway and operation as well as if the runway is instrumental or non‐ instrumental. Non‐instrumental runways are runways where visual approach procedures are used, in contrast to instrumental runways where aircraft use instrument landing systems44,45. Non‐instrumental runways are more sensitive
to bad weather and darkness due to poor visibility. The specified distance between the runways centre lines depend on whether the runways are instrumental or non‐instrumental, if they are used simultaneously or segregated and if the aircraft are departing from or approaching the runway. The vertical separation between aircraft approaching the runway, and the distance between successive aircraft, on the same or adjacent instrument landing system localizer course are also specified.44,45 Spacing as well as runway length, width, and slope,
coupled with different weight limits for the runways are all also limiting factors in air traffic capacity44,45.
Runway capacity problems are not a new phenomenon. In 1959, Blumstein wrote about the runway capacity problem caused by the minimum separation spacing between landing aircraft. In several studies, the runway system is considered to be a major, and often the main limiting factor for air traffic capacity49. However, the runway limitation addressed in the literature is not only Intersecting runways Parallel runways Open‐V runways
due to the runway itself (for example too few runways, limited arrival and departure routes or too short runway length) but also due to other secondary factors like minimum aircraft separation time due to wake vortex, crosswinds or aircraft fleet mix etc.
Yu and Lau discuss in their study that runways and taxiways are major capacity constraints as many airports only have one or two runways for both landing and take off. Taxiways and runways are connected, thus optimal scheduling and routing for taxiways and runways are required to avoid delay and congestion. Wake turbulence and minimum aircraft separation time, which in turn depends on the aircraft fleet mix as well as safety regulations, are also contributing factors to the runway limitations therefor Yu and Lau present a model that simultaneously optimizes gate, taxi‐ and runway scheduling for both arriving and departing aircraft.50 Several other authors as Barbaresco et al51, Barbaresco
et al52, Herrema et al53, de Neufville et al54, Powell et al55 and Tether et al56 all
consider the runway as a major limiting factor with respect to wake vortex, minimum spacing between landing aircraft, wind, the number of runways and runway layout. This shows that different limiting factors are connected and affect each other. A case study of Delhi International Airport (DIAL) in India used a performance efficiency index model to examine airport throughput and the factors causing the most significant delays. The study showed that the major capacity constraints were runway and central infrastructure.57 The number of
available runways as well as direction and layout has been regarded as prominent constraints to capacity in the literature for several years. Gelhausen et al58 as well as De Neufville et al54 addressed this issue in their studies in 2013
and so did U.S. Congress, Office of Technology Assessment in 198221,which
showed that runway configuration was a significant constraint where further improvements were required.
4.3 Taxiway
As for runways, strict requirements and procedures also apply for taxiways. These include length, width, slope and separation between the centreline of adjacent taxiways, or between taxiways and runways as well as the distance to fixed objects. Taxiway intersection with the runway and the curvature of the taxiway is very important. The curvature radius of the taxiways depends on size of the aircraft that are operating on them, as the aircraft has to be able to turn, still having the outer wheel within the regulated distance from the edge of the taxiway.44,45
The placements of the turnoffs are important to maximizing capacity of the runway systems because taxiways can significantly affect runway capacity21. By
using rapid exit taxiways (also called high‐speed taxiways or high speed turn offs), the capacity can be increased. This is due to the fact that the aircraft can exit the runway at higher speed and thereby vacate the runway faster, thus making it possible for successive aircraft to land quicker. However, compared to
a long straight distance after the turn‐off curve enabling the exiting aircraft to slow down and come to a full stop before intersecting another taxiway (Figure
4).44,45
Taxiway layout is important for optimal runway use. During congestion for instance, taxiways not only can be used for taxi, but also for holding and sequencing departing aircraft21. How the taxiways are designed has a great effect
on the occupancy time of the aircraft on the runway. The placement and angle of the taxiways used for exiting the runway is vital for the runway occupancy time. If the taxiways are poorly placed incoming aircraft are forced to taxi off the runway at low speed. Hence limiting the runway capacity.2
As for runways, the weight bearing capacity of the taxiway has to be sufficient to carry weight of the aircraft using them. Gothenburg city airport is one example were the commercial airlines had to relocate to another airport (Landvetter airport), due to insufficient weight bearing capacity of the taxiways. The cost for repairing and reinforcement of the taxiways were considered too high, hence, relocation was a better alternative59‐64. Gothenburg city airport, now called it’s
former name, Säve airport, was bought by Serneke Fastighet AB in 2016 and is today used for non commercial flights such as rescue services and aero clubs59,65. Figure 4. Different types of exit taxiways. Note; Intersection angle 45°–90° (A), 90° (B) and 25°–30° (C). As previously mentioned, the survey by the U.S. Congress, Office of Technology Assessment in 19842, the study by Yu and Lau50 in 2014 and Yu et al in 201766,
showed that taxiways were major capacity constraints. In contrast, according to De Neufville and Odoni, 200254, Mirković and Tošić 201767 and Mirković et al
201768 taxiways are generally not a major capacity limiting factor although
Right-angle exit taxiways Rapid exit taxiway
A. Taxiway exit Runway B. Runway Taxiway exit Taxiway exit Runway Straight distance C.
taxiways locally can be bottlenecks. These capacity limitations can appear where the taxiway crosses active runways, at taxiway intersections or where taxiways with high‐speed exits.54, 67, 68 4.4 Wake vortex Wake vortex is the turbulence that is generated by an aircraft in flight. It occurs in the wake of an airplane passing through the air. The occurrence of wake vortex means that there needs to be a separation between the aircraft. This in turn leads to a lower capacity in both airspace and runways.21
Wake vortex is a major limiting factor to air traffic capacity affecting both airspace and runway capacity21, 53, 69‐73. It is affecting the airports landing
capacity even to a higher extent during peak air traffic capacity due to the spacing requirement between aircraft caused by wake turbulence56.
With respect to wake vortex, the capacity is further reduced by poor weather conditions and runway placement as strong wind causes the wake vortex to shift its position and thereby affecting other aircraft, even more so for parallel runways or runways that are closely situated2,16. For safety reasons minimum spacing distances between aircraft are established by ICAO74, dividing aircraft into three different weight classes. The ICAO wake vortex separation rules were re‐categorised by Eurocontrol in collaboration with the FAA as of further aircraft characteristics like wingspan and speed, were taken into consideration. The new categorisation resulted in six different classes, classes A – F. The new categorisation, called RECAT in the US and REACT‐EU in Europe, were implemented in the US at Memphis international airport in 2012 followed by some other airports and in Europe at Charles de Gaulle Airport in Paris in 2015. By using RECAT/REACT‐EU classification the minimum separation distance can be reduced and thus boosting capacity.75, 76
The wake turbulence trail varies depending on aircraft size. The heavier the aircraft, the stronger is the wake turbulence. A stronger turbulence trail needs a longer safety distance between the aircraft in airspace and during landing, thus decreasing the air traffic capacity. ICAO’s safety regulations are static and do not take parameters like atmospheric conditions or wind that affects the decay of wake turbulence into account. Hence, several authors propose that these regulations are limiting the capacity more than required69‐71. Different strategies
are suggested to measure, detect or decrease the effects of wake vortex by optimizing current models and operations or other technical and operational procedures53, 69‐71, 73.
