Capacity Constraints for Air Traffic Flow Development Rebecca Petersen

LiU-ITN-TEK-G--18/001--SE

2018-03-14

Department of Science and Technology Institutionen för teknik och naturvetenskap Linköping University Linköpings universitet nedewS ,gnipökrroN 47 106-ES 47 ,gnipökrroN nedewS 106 47 gnipökrroN LiU-ITN-TEK-G--18/001--SE

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

Norrköping 2018-03-14 Upphovsrätt

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Rebecca Petersen 2018–03–14 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.

Nyckelord: Flygtrafik, begränsande faktorer, kapacitet

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Rebecca Petersen 2018–03–14 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.

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Rebecca Petersen 2018–03–14 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

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Rebecca Petersen 2018–03–14 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 Petersen

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Rebecca Petersen 2018–03–14 Table 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 43

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Rebecca Petersen 2018–03–14 TABLE OF FIGURES

Figure 1. Prognosis of domestic and international passengers departing from 2 Swedish airports from 2016 – 2023.

Figure 2. Chart of how different divisions and components in aviation are 6 connected to each other by previous research.

Figure 3. Various types of runway configurations. 15

Figure 4. Types of exit taxiways. Right‐angle exit taxiway with an intersection 17 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).

Figure 5. Showing the ground‐handling activities. 20

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TABLE OF TABLES

Table 1. The representation of the ranking tool used for the literature review. 7

Table 2. Forecast of airport congestion and capacity demand for five large 12 European airports. © European Union, 1995‐20171.

Table 3 Hours per day that demand exceed capacity. © European Union, 1995‐ 13 20171.

Table 4. Interrelations between different limiting factors to air traffic capacity. 34

Table 5. Ranking table of the different limiting factors extracted from the 35 literature reviewed.

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Rebecca Petersen 2018–03–14 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

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Rebecca Petersen 2018–03–14 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

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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

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Rebecca Petersen 2018–03–14

24 000 000

20 000 000

16 000 000 Domestic 12 000 000 International

8 000 000

Number of departing passengers 4 000 000

0 2016 2017 2018 2019 2020 2021 2022 2023

Year

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 airspace capacity is trough air traffic controller workload.3,23 There are several methods to measure air traffic controller workload, for example measurements

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Rebecca Petersen 2018–03–14 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.

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Rebecca Petersen 2018–03–14 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.

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Rebecca Petersen 2018–03–14 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.

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Rebecca Petersen 2018–03–14

Airside' Landside'

' Air(ield' Airspace' Terminal' Terminal' '

Environ8 Ground8' Baggage'' Check8in'desks/ 'Baggage'' Security'' ment' Runways' Taxiways' handling' Gates' handling' baggage'drop' handling' check'

Wake' vortex'

Terminal'' airspace' Weather' Wake'vortex' ATC'

Environ8' Noise' ment' Obstacles' Weather'

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.

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Rebecca Petersen 2018–03–14 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 Ranking

(primary/secondary)

Author X, 2017, ref.A Database Z Primary Major

Factor x

Author Y, 2017, RefB Database Q Secondary Minor

Factor y

Factor z

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Rebecca Petersen 2018–03–14 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 actually being applied.

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Rebecca Petersen 2018–03–14 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.

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Rebecca Petersen 2018–03–14 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.

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Rebecca Petersen 2018–03–14 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;

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.

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

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Rebecca Petersen 2018–03–14 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

Demand exceeds Demand exceeds Demand exceeds Assumed 10% increase in Düsseldorf capacity most or capacity most or capacity most or capacity in 2015 but no all day all day all day further increase

New runway (2011) and Demand exceeds Sufficient Demand exceeds terminal (2015) allow Frankfurt capacity most or capacity most or capacity during increases from 83 to 126 all day all day part of day movements/hour

Assumes no new runway Demand exceeds Demand exceeds Demand exceeds London but increase of 2‐3 capacity most or capacity most or capacity most or Gatwick movements/hour on all day all day all day current runway

Assumes no third runway, Demand exceeds Demand exceeds Demand exceeds London or mixed mode, or capacity most or capacity most or capacity most or Heathrow relaxation of annual all day all day all day movement cap.

Demand exceeds Demand exceeds Demand exceeds Assumes no amendment to Milan Linate capacity most or capacity most or capacity most or Bersani Decree all day all day all day

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.

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Rebecca Petersen 2018–03–14 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;

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Rebecca Petersen 2018–03–14 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 runways that are used for both take‐off and landing increases the capacity compared to if the runway runs in a segregated mode47.

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Rebecca Petersen 2018–03–14 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.

Intersecting Parallel runways runways

Open‐V 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

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Rebecca Petersen 2018–03–14 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 ordinary taxiways, rapid exit taxiways require a long constant curvature radius, often between 25 and 45 degrees, when intersecting the runway. They also have

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Rebecca Petersen 2018–03–14 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.

Right-angle exit taxiways Rapid exit taxiway

Taxiway exit

Taxiway exit Straight distance

A. Runway C. Runway

Taxiway exit

B. Runway

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

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Rebecca Petersen 2018–03–14 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.

4.5 Apron

The area where the aircraft is parked during boarding or disembarking of passengers or loading/unloading of cargo is called the apron. When parked on

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Rebecca Petersen 2018–03–14 the apron, maintenance, servicing and refuelling are performed. During these activities also other vehicles such as baggage trucks, fuel trucks, apron buses etc. operate on the apron.

Although apron capacity is affected by very similar factors to those affecting the runway system according to Mirkovic et al 201477, it still does not get the same attention in research. Just like taxiways, apron capacity constrains are usually locally specific, and therefore it is hard to make any general models or conclusions54, 77. The survey by the U.S. Congress, Office of Technology Assessment in 19842 showed that the apron were a major limiting factor. In contrast, the authors also writes that aprons can be a constraint, though not a major one, to airside throughput, which reflects Mirkovic et al 201477 opinion that apron capacity constraints not are a general problem but a local occurrence, appearing only under certain conditions i.e. specific times of the day, some airports, etc.

Factors that are affecting apron capacity are for example design and layout, operational planning and layout of apron configuration and demand characteristics77. Aprons can have a predetermined number of stands (i.e. parking positions for a certain aircraft size) or a flexible area that facilitates various combinations of aircraft of various sizes. This gives a physical limitation of the stands due to aircraft type and/or stand size compatibility as not all planes can be parked at all positions which could constraint the capacity.

Moreover, aprons with a predetermined configuration are less flexible and can have a further limited capacity from changes in the fleet mix.77,78 It could be costly to change the apron mix so that it accommodates the new aircraft mix. Additionally, domestic and international flights must in many airports be kept separate due to passport control, customs, etc. which further can limit the capacity if the apron are restricted to certain types of flights.77

4.6 Ground handling/turn‐around

For a quick and smooth turn‐around of an aircraft, good and efficient ground handling is required. Ground handling entails facilities for handling the aircraft on the ground, such as readying the aircraft for the next flight. This includes activities such as loading/unloading baggage, boarding and disembarking passengers, cleaning the cabin, toilet servicing, catering, filling up the potable water supply, disposal of waste water, aircraft maintenance, refuelling and de‐ icing the aircraft as well as push‐back of the aircraft before take‐off (Figure 5).

Ground handling is labour‐intensive and when it’s not managed properly it will result in longer turnaround times for the aircraft and delays which affects the capacity.79,80,81 This means that the number of flights each aircraft can make during a given time decreases. The delay caused by insufficient ground handling may also lead to the flight missing its slot‐time for take‐off. As can be seen, the ripple effect can be great and the airports capacity lowered.82 Furthermore,

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Rebecca Petersen 2018–03–14 every minute an aircraft sits on the ground costs. This means that a slow turnaround is costly for the airline which in the long run affects the capacity82,81.

Ground handling is an important topic were the literature proposes different strategies to improve ground handling management83‐86. Kabongo, et al even considers inefficient ground handling as a main cause of delay. The model presented by Kabongo, et al deals with the problem of organizing ground handling management. As several different ground handling operations are performed it would be beneficial if they were organized under a unified framework to increase efficiency which could lead to reduced turnaround time.84 Norin et al showed that by optimizing the de‐icing scheduling both waiting time and delays were reduced. The simulation, using ARENA, was applied to Stockholm Arlanda airport but is relevant also to other airports.85 Many actors and processes are involved in the turnaround process forming a complex network of operations that should be performed smoothly and within shortest possible time. Optimized scheduling of the different turnaround operations is therefore essential to avoid delays. Norin presents in her thesis a conceptual model for the turnaround process that could be used to study airport performance.85

Luggage( unload/load(

Cleaning(

Towing(truck(

Fueling( Portable(water/( waste(water(

Catering( Passenger(bridge(

Boarding(and(disembarking(passengers(

Figure 5. Showing the ground‐handling activities.

4.7 Airspace

Airspace is the air in which the aircraft operate. The part of airspace that is above a nation is coming under its jurisdiction. Airspace is divided into sectors, so called flight information regions, FIRs, that service their regions airspace87. The flight paths to and from an airport are affected by the surrounding

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Rebecca Petersen 2018–03–14 environment, such as natural obstacles and built features. If several airports are located with a close proximity, the airports share the same airspace. Interdependence of approach and departure paths, and the individual operations of one airport can interfere with those of the other. This can lead to situations where the airports must hold take‐offs and landings until the shared airspace is cleared, thus limiting the capacity.88 Approach and departure paths trough the airspace has, as mentioned, a great impact on the runway utilisation and therefore affect the capacity2.

Airspace capacity is dependent on the position and spacing of the aircraft operating in airspace. Between all aircraft there must be a safety margin, which increases when, for example there is bad whether. These safety margins increase the time each aircraft use a specific portion of airspace or runway and limit the capacity and traffic flow throughput.2 The survey by the U.S. Congress, Office of Technology Assessment in 1984 showed that airspace were a major limiting factor to capacity2 as did Majumdar et al49. It is interesting that the survey showed that not only the large busy hub airports found airspace to be a significant constraint, but also a majority of the smaller airports in the study2. As air traffic demand is growing, the airspace is getting increasingly crowded, hence leading to airspace congestion, which affects capacity. As authors consider airspace to be a major key limiting factor to air traffic capacity, models to better utilize the available airspace resources for increased air traffic flow are examined89‐91.

4.8 ATC

Air Traffic Control (ATC) is performed by air traffic controllers. It is a service that directs and assists aircraft in airspace as well as on the ground to avoid collisions, adverse weather or other safety issues. Air traffic controllers also assure that the aircraft not operates in prohibited airspace. They expedite the air traffic flow to achieve efficiency of aircraft operations and controls that safe separation between the aircraft are maintained both at take‐offs/landings and en route92.

ATC and ATC workload is an important topic in aviation and has been and continues to be a well‐studied subject as it affects the operational capacity both of an airport and airspace23,93. Brooker defines workload as ‘the amount of work assigned to an individual for completion within a certain time’23. As air traffic rate continues to increase, so does the ATC workload and it is therefore considered to be a key limiting factor to air traffic capacity21, 94‐97. There is a limit to how many flights an air traffic controller can handle at the same time without compromising safety. When the demand for ATC services exceeds the capacity of what the air traffic controllers can manage, air traffic capacity is limited. Several studies has addressed this issue and has presented models to measure or predict the ATC workload to meet the capacity demand95,96,98. Since Air traffic controllers must ensure safety, they should also keep in mind that the ATC procedures can contribute to congestion and delays. As previously mentioned, the workload that ATC can handle with maintained safety is limited. Therefore,

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Rebecca Petersen 2018–03–14 new technology, innovations and improvements of the ATC system could increase air traffic capacity24. Soykan indicates in his thesis that runway operation scheduling is a major problem and that better mathematical models to support air traffic controllers in their scheduling of aircraft landings and take‐ offs and would benefit the capacity.99 Although, improved ATC systems are required to increase air traffic capacity, there is also a drawback of more technically complicated systems as the amount of equipment on the aircraft expands. Improved ATC technology also excludes VFR (Visual Flight Rules) flights as, the part of airspace that is controlled by ATC expands.24 Additional capacity constraints to the ATC workload are the procedures, rules and regulations used to control airspace20.

4.9 Aircraft fleet mix in the air traffic flow

The mix of aircraft types using an airport or the airspace affects the capacity20. Depending on the aircraft types and weight classes in the air traffic flow, en route as well as when landing or taking off, different minimum spacing is needed as different aircraft types generate different wake vortexes. Heavier aircraft generate a larger wake turbulence trail, which demands a longer distance to the following aircraft.

Generally, when aircraft approaches the runway, a “first come – first served” policy is used. This means that the aircraft first in queue get served first. Depending on the size of the waiting and approaching aircraft lined up for landing, the spacing between them vary due to the separation requirements, which, with regard to capacity, can be optimal or suboptimal100. De Neufville and Odoni propose that an optimal aircraft mix could decrease the separation distance and thereby increase the capacity54. Also the U.S. Congress, Office of Technology Assessment 198221 considers aircraft fleet mix and performance to be a major capacity constraint as it affects runway usage and capacity due to the different wake turbulence trail of aircraft of different weight classes.

4.10 Environment

The environmental impact of airports and air traffic can be seen as major and includes several aspects such as emissions, in form of greenhouse gases, amongst them CO2, and noise. There are therefore several air traffic rules and regulations put in place, both nationally and internationally. These rules and regulations can vary between countries but ICAO recently took a decision to introduce a global market‐based instrument, Annex 16 of the Convention on International Civil Aviation, which apply to ICAO’s 191 member states101,102. The global instrument means that, from the year 2020, airlines have to buy emission credits for emissions that exceed the set level. The economic constraint for airlines having to buy emission credits could be considerable, which could limit the capacity.

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Rebecca Petersen 2018–03–14 4.10.1 Emissions

Until 2020 CO2 emissions are allowed to grow. The set level corresponds to emissions in 2020. This will contribute to emission reductions in sectors other than in the international air travel, so that the international air travel will have a so‐called carbon‐neutral growth after 2020103. This will further limit the operations and add to the already existing environmental constraints. The economic constraint can be significant for airlines if having to buy emission credits to maintain capacity.

Aircraft emissions affect the environment both en‐route and during ground operations104. Emissions from aircraft include carbon monoxide (CO), nitric oxides (NOx), carbon dioxide (CO2), hydrocarbons (HC), black carbon (BC), and sulphur dioxide (SO2). Despite environmentally better engines and other technical improvements, it is not expected to be sufficient to prevent future growth of emissions as air traffic continues to increase, thus affecting capacity. The European aviation environmental report 2016105 express that it is unlikely that the production of sustainable aviation alternative fuels will be sufficient to meet the regulated 2020 emissions level, which will limit air traffic capacity105. There are extensive research regarding aircraft emissions, however to our knowledge it is not ranked with respect to air traffic capacity and is therefore not presented in the metric.

4.10.2 Noise

A problem with air traffic is that it causes noise. The impact of noise is greatest during landing and take‐off when the aircraft flies at low altitude. This can affect the capacity of the runways as they may not be able to operate at their full potential due to noise restrictions21,106,2. If the noise‐affected areas are mostly for industrial, or similar use, there is often less of a problem. If instead the area around the airport is occupied by hospitals, schools and residential areas, problems can arise as well as further restrictions on how much noise can be emitted.21

IATA states that night‐time operating restrictions decrease capacity as well as gives suboptimal use of an airports capacity. It also limits the flexibility for delayed traffic to operate and limits the connectivity for travellers.107

Basner et al108 as well as other authors2, 21, 54, 109, 110, mean that aircraft noise is a major limiting factor to air traffic and airport capacity as it annoys in communities in close vicinity of airports. Noise can also be a major constraint to expansion or building of new airports due to residential areas in the vicinity2,110. However, noise is not only annoying, but also has biological effects such as increased risk for cardiovascular disease and sleep disruption108,111. Although aircraft has become less noisy, the noise annoyance from aviation is still increasing. Increased air traffic is one explanation, but non‐acoustical factors should also be considered The non‐acoustical factors are all factors other then the noise level itself, i.e. the psychological perception of the noise109. These can

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Rebecca Petersen 2018–03–14 include personal characteristics like age, gender, noise sensitivity, as well as social and residential factors.112

There are different procedures to reduce the noise, such as making approaches over less noise sensitive areas or use of a specific preferred runway.21 ICAO's strategy, Balanced Approach to Aircraft Noise Management, pose additional restrictions, including operating restrictions against using the noisiest aircraft. The restrictions could apply to either specific aircraft types or restrict landing and take off to certain times of the day, usually daytime. Prohibiting aircraft with a high noise level to use a specific runway or flight route can also be applied. By relating the take‐off charge to aircraft noise level, airlines are encouraged to use less noisy aircraft, i.e. noisier aircraft, higher charge. ICAOS strategy also means that by identifying areas that in the future are expected to be exposed to noise levels exceeding the target values, these areas can be avoided as residential areas. Another strategy is to insulate housing to reduce noise113.

ICAO’s more stringent requirements regarding noise from jet‐ and propeller driven aircraft apply from December 31, 2017 for heavier aircraft (a maximum take‐off weight of 55 000 kg and up) and from December 31, 2020 for other aircraft with a maximum take‐off weight below 55 000 kg to be type‐certified. Conducted analyses have shown that increased stringency means that approximately one million fewer people in the world are exposed to an 24‐hour average noise level of 55 dBA or higher in 2036 compared to 2020, despite the fact that air traffic is increasing113.

As can be expected, many of these regulations and procedures limit the capacity. For example, if only a specific preferred runway can be used it can cause congestion and delay, which in turn affects other parts of the airport and air traffic system like gate and slot‐time allocation, apron and stand capacity, taxiway utilization and ATC workload. If a specific runway only can be used certain times of the day the runway utilization is suboptimal. Not being able to use all aircraft types to the same extent as previous or even having to change the aircraft fleet, which is very costly, can affect capacity. Higher charges for aircraft operations put additional pressure on airlines' finances, which can lead cutbacks such as reducing the number of flights to certain destinations or lay off flight crew, which affects the capacity.

4.11 Weather

As mentioned above wake vortex is affected by weather, foremost wind, but adverse weather conditions affect air traffic and airport capacity in several different areas. De Neufville et al54 and several authors as Kicinger et al114, Halili et al115, Dillingham116, the U.S. Congress, Office of Technology Assessment21, Barbaresco et al117, Klein et al118 and the U.S. Congress, Office of Technology Assessment88 considers bad weather, as precipitation, heavy rain‐ or snowfall , icing, wind and poor visibility, to be major constraints that affects runway utilization and aircraft operations.

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Rebecca Petersen 2018–03–14 Precipitation and icing can constrain runway capacity due to time consuming deicing procedures and can reduce aircraft braking capability, whereas low cloud ceiling can reduce runway capacity as only instrumental runways can be used (depending on the degree of visibility). Dependent runways that are parallel and closely spaced or crossing are particularly sensitive to wind and during extreme weather as snowstorms and thunderstorms airports may even have to close down temporarily.54,21,118

As previously mentioned, fog reduces the visibility. That in turn leads to delays and thereby limits the capacity. Robinson shows in a study conducted at Atlanta International Airport 1989 that fog results in extra taxi‐in delays leading to additional airborne delays. Thunder on the other hand mainly results in extra taxi‐out delays.119 According to Robinson timing is crucial when it comes to snowstorms. Snowstorms that appears during night or early morning prior to the take‐off of the morning flights, has far less impact on air traffic than if the storm hits later in the middle of the daily operations. Early in the morning the runways can be cleared without too much disturbance in contrast to clearing during mid‐day.119 Adverse weather not only limits the capacity directly, but it brings indirect effects on other flights and airports as a flight that deviates from the scheduled plan or even has to reroute to another airport affects factors as the scheduled time‐slots for the runway, ATC workload, gate allocation, apron capacity, taxiway utilization and baggage handling. It can also lead to long work shifts for the flight crew, and terminal as well as airspace crowding. However, there are also economic consequences due to bad weather conditions as every minute of delay cost, which in the long run limits airport capacity. Costs for crew overtime, passenger compensation and rebooking can be considerable.69, 119

In contrast to many other constraints, weather cannot be changed or rectified. Better weather forecasts would be a good tool in planning flight and airport operations as inaccurate weather forecasts can lead to inadequate costly decisions regarding both planning and costs, for instance cancellations and take‐ off/arrival delays. Currently, research is done to improve weather forecasts or to predict the impact of weather on capacity for different types forecasts by using or modifying various analysis models118, 120‐122.

However, capacity limitations due to adverse weather conditions have different impact on airport operations with respect to other factors like air traffic demand, airport capacity, amongst other. For instance, fog during night at an airport with low transport demand, have small impact while other capacity limitations like high traffic demand can cause severe delays at an busy airport during daytime with perfect weather conditions.118

4.12 Terminal facilities

There are further factors that limit the capacity of an airport which might not be so obvious, such as the terminal capacity, passenger security‐check capacity, the amount of check‐in desks and baggage drop, as well as the “behind the scenes” activities such as baggage sorting.

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Rebecca Petersen 2018–03–14 The terminal is the transitional zone were passengers pass from landside to airside. The terminal provides and manages all processes and services that are needed to transfer the passengers and their luggage from landside to airside2.

The departure lounges on airside in the terminal, are basically waiting rooms for passengers waiting to board a flight. Several different factors have impact on passenger’s perception. Among the most important factors are the amount of seating, but also the availability of concessions and amenities close by, Wi‐Fi and power/USB outlets, as well as space for movement and circulation. The departure lounges needs to be sized and function for the amount of passengers during peak periods of time. By using shared or reversible lounges, that can be used by domestic or international passengers, the space can be more optimally used and space capacity shortage and excess can be avoided more easily even during peak and off‐peak periods.123

As seen in the case of Landvetter Airport, Gothenburg, the terminal is crowded during peak hours and several facilities are insufficient to handle the current and future demand. Hence, 1.9 billion SEK are invested in the extension of the airport. Additional to the terminal extension there will be an expanded arrival hall, more sorting pockets for departing luggage, a luggage hotel, expanded security check, as well as three more gates124, 125.

Furthermore, a railroad line between Mönlycke – Landvetter – Bollebygd is to be constructed for a better commute to the airport and faster access to the city centre of Gothenburg126.

4.12.1 Gate

The gate is the parking position for the aircraft during turnaround. It is also the link between the departure lounge and the aircraft that the passengers pass through when boarding or leaving the aircraft.

Holding aircraft at the gate with the engines off instead of letting them queue on the taxiway with the engines running, both reduces fuel burn as well as taxi time. Khadilkar and Balakrishnan acknowledged the benefits of avoiding taxiway queuing by controlling pushbacks and holding aircraft at the gate. Their optimizing simulation model showed both significantly reduced waiting time for gate assignation as well as reduced taxi out times and thereby also less fuel consumption as well as decreased congestion.127 Well‐performed gate management not only can increase air traffic capacity by avoiding congestion, it also contributes to environmental savings.

A significant problem in air traffic management is the task to assign available gates to arriving aircraft without delay, the so‐called gate assignment problem (GAP). Benlic et al128, refer to GAP as “one of the most important airport related problems”, a view also shared by Yu et al.66 GAP is a complex problem were operational efficiency as well as passenger convenience has to be meet. The assigned gate must be compatible with aircraft size, service requirements, origin

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Rebecca Petersen 2018–03–14 or destination due to safety regulation as well as the distance between runway and gate, and departure time as adjacent gates cannot have the same departure time. Regarding passengers, the walking distance should be minimized to increase passenger satisfaction.129 As the flights not always arrive or depart on time, the flight‐schedule and gate assignment must be dynamic.

A vast number of studies like Neuman et al130, Benlic et al128, Yu et al133,131, Guclu et al132, Bouras et al129 and Aktel et al133 have proposed different optimization models to reduce passenger dissatisfaction, delay and capacity limitations due to suboptimal gate assignment planning. Gate allocation problems affect runway and taxiway utilization and thereby causing delay. That in turn adversely affects the landing/take off capacity, thus limit the air traffic and airport capacity. Furthermore, delay due to GAP affects ground handling services, baggage handling, and towing time.130,132 GAP can also cause push‐back blocking, i.e. the aircraft at the gate ready to leave is blocked by another aircraft128. However the problem can also be reversed, delay caused by capacity limitations in other parts of the air traffic system disrupts the planned gate allocation and the gate assignment problem is a fact. As gate assignment is complex problem that affects as well as depends on many factors, gate assignment is a huge problem to manage.

4.12.2 Check‐in desks/baggage drop

Passenger’s first activity at the airport and at landside usually is the check‐in and baggage drop at the check‐in desks. Since this is one of the first activities that the passengers go trough during their travel, a delay here can easily affect other activities and delay flights.

Even though automated check‐in desks are available at many airports today, the manned check‐in desks are important with respect to personal service, security and baggage logistics134. The check‐in process has to be efficient with respect both to passenger satisfaction and operational costs. The capacity of the check‐in comprises of number and type of check‐in counters, as well as automated checking‐in machines available123. At peak hours conflicts between airlines for of check‐in desk availability can arise as well as long waiting time for passengers if the resources are insufficient134. As check‐in desks are space consuming, expansion in may not be possible due to terminal building size. Available space might also be more profitable if used for shopping areas. Effective planning of check‐in desk utilization is therefore crucial.135,136

Psaraki‐Kalouptsidi highlights resource problems in regional airports with seasonal demand. Large groups of tourists organized by tour operators arrive to the airports, which usually are fairly small, resulting in long queues for check‐in in a crowded area. As the passenger flow is very high during a few peak months, while being moderate during the remaining months, it is complicated to design terminal buildings that adequate for the year round demand.137,138

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Rebecca Petersen 2018–03–14 To reduce queuing for check‐in and baggage drop, self‐service baggage‐drop systems are introduced alongside automated check‐in kiosks in some airports84,139,81, 140. Although check‐in and baggage drop can be a capacity constraint, it has not been stated as to which degree.

4.12.3 Baggage handling

In the baggage handling system, the bags are transported from the check‐in on landside through a security screening and further on to the piers on airside were the bags are loaded on the aircraft140. The baggage handling system is often located under ground at airports, which means that it can be difficult and sometimes impossible, as well as expensive, to expand it. Insufficient space baggage handling system can result in challenging working conditions and high costs. The practical capacity is also often underestimated due to the uneven arrival of bags onto the baggage handling system. De Neufville and Odoni states that planners need to provide adequate space for baggage handling already at initial planning stage to provide for future capacity demand.54

As passenger satisfaction is very important in all aspects of commercial air traffic, it is interesting that only 5% of all complaints between 2009‐2012 are baggage‐related and of which only 0.3% are attributed to the baggage handling system81.

The baggage handling is usually not performed by the airport but by the airline or a handler appointed by the airline. As baggage handling is one link in the chain of operations for air transportation, airport management and airlines has a close collaboration.81

In the baggage handling system, security screening is an important component. There are guidelines published by the US Transportation Security Administration (TSA) how to perform the security screening in order to detect prohibited items in the bags. Firstly the bags are automatically screened. If cleared, the bags are passed on in the handling system. If the machine detects something that could pose a threat, the bag will get an alarm tag and then is passed to security level two, were TSA staff scans the bag. If not cleared, the bag will be opened and examined. The bags are subsequently stored until they are loaded on their designated flight.81

Ideal are if passengers arrive to the reclaim area at about the same time as their bags. Then the bags are removed from the conveyor carousel and the passengers move on. However, if the passengers are delayed or if there is a delay in the baggage handling, the reclaim area can get crowded or bags can pile up. Both are non‐desirable events.81

There are several studies regarding baggage handling planning and optimization of throughput141‐144. However, in the literature the effect of baggage handling on air traffic capacity is not stated.

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Rebecca Petersen 2018–03–14 4.12.4 Security screening

Security screening of both passengers and carryon luggage, are required before entering the departure lounge to maintain the in‐flight safety and especially for preventing potential terror attacks. The terror threat was accentuated after the September 11 attack in 2001 and new security policies, Regulation (EC) No 2320/2002, were adopted by the European Parliament and the Council. Regulation (EC) No 2320/2002 were later replaced by Regulation (EC) No 300/2008 in 2008.145,146 In the US the Aviation and Transportation Security Act (ATSA) were enacted by the US Congress in November 2001 and the Transportation Security Administration (TSA) were established. TSA implemented improvements to ensure aviation security.147

At the security screening the passengers put their carry‐on luggage as well as metal objects on a tray that is passed through an x‐ray machine to detect any prohibited items. While the carry‐on bags pass through x‐ray machine, the passengers pass through an enhanced walk‐through metal detector (WTMD). Metallic items carried by the passenger, interacts with a magnetic field that is detected by the WMTD. In active detection, the magnetic field is produced by the WMTD itself, while in passive detection the Earth’s magnetic field.148,149 In case a passenger trigger the metal detector alarm, a handheld metal detector (HHMD) is used for a second inspection and sometimes a pat down, i.e. a hand search by a security officer, is performed. To detect traces of explosives on passengers or bags explosives trace portals (ETP) or detectors (ETD) can be used. Some airports use whole‐body scanners instead of WTMD. There are two types of whole‐body scanners, backscatter x‐ray scanners and terahertz scanners. Both are serving the same purpose but are using different technologies as backscatter x‐ray scanners use very low dose of ionizing radiation and terahertz scanners use high‐frequency radio waves.81

The security screening checkpoint can be situated just inside the airport entrance, after the check‐in desks and baggage drop or by each gate. Inadequate security screening efficiency caused by undersized security check stations, staff shortages or insufficient logistics can slow or disrupt the passenger flow. This can cause delays and not the least passenger dissatisfaction123 Screening all passengers and luggage are both time consuming and costly150. However, as anyone could be a potential risk, a thorough screening is essential. As security has to be performed, models to optimize the screening procedure to decrease costs and passenger waiting time are developed149‐153.

The security screening of passengers and carry‐on luggage can be centralized or decentralized. At centralized security screening, there is one security checkpoint that the passengers and their carry‐on luggage must pass through before entering the departure lounges. At decentralized security screening, there are checkpoints at the gates and after passing through them the passengers are confined to the gate departure lounge. Both methods have advantages and disadvantages. Centralized security screening only needs staff and equipment at one location. Passengers can also enjoy restaurants and shopping while waiting for their flight to departure. However, surveillance of passengers is more difficult and departing and arriving passengers are mixed in the same area. Another

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Rebecca Petersen 2018–03–14 shortcoming of centralized screening is that staff entering the departure area has to be screened and all merchandize, food and drink has to be rigorously examined. Decentralized screening, on the other hand, are very secure but requires far more staff and equipment. The risk for passenger dissatisfaction is high due to long waiting time for scanning and to being confined to a lounge without amenities. It also allows potential terrorists to get close to the aircraft.81

A vast number of articles address the challenge of improving air transport security, yet being cost effective, capacity efficient and keeping up passenger satisfaction. However, the effect of congestion or slow throughput at security screening checkpoint on air transport capacity is rarely debated.

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Rebecca Petersen 2018–03–14 5. INTERVIEWS

The results of the conducted semi structured interviews, are summarized and presented in this chapter. The interviewee’s individual answers are not stated, nor the interviewee’s identity, only their professional title/position in the company is presented.

5.1 Interviewees

The interviewees are professionals at Swedavia. The state owned Swedish company Swedavia develops and operates Swedish airports nationwide. Swedavia run the commercial air traffic of ten airports of which they own eight.13

The Head of master planning and a consultant at Swedavia airport planning was interviewed. The division for airport master planning sets up long‐term plans for future development of the company’s airports. The consultants at Swedavia airport planning plan and develop new as well as existing airports.

5.2 Interview answers

The answers of the interviewees are summarized after each question respectively.

1. How is the capacity of an airport measured, i.e. the metrics for measuring capacity.

The interviewees defined the capacity at an airport by how many aircraft, passengers or luggage that could be handled within a certain time interval.

Capacity could be measured both for airside and landside. Airside capacity could be measured by for example, how many starts and/or landings the airport's runway/runways could handle. This capacity limit could be defined at hourly or at shorter intervals, such as at 15‐minute intervals. The interviewees considered it often to be possible to handle higher numbers for shorter periods of time than for an entire hour.

For aircraft stands, the capacity was measured as the number of stands an airport had. The stands were also dependent on aircraft size and the destination of the aircraft (domestic/Schengen/non‐Schengen).

2. What factors, regarding airside and landside, limit the air traffic capacity the most?

The interviewees thought that it generally were features that either have or do not have capacity that were the most limiting. For example, the runway and stands, because either the runway has capacity for an aircraft to land/take off, or

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Rebecca Petersen 2018–03–14 it has not, or either there were enough stands or there were not. However, the runway was considered to be the very most limiting factor.

On landside in the terminal, the interviewees considered that it was terminal operations that set the limitations. These limitations could be on; the number of check‐in counters/machines, the number of security check points, the number of gates, the number of passport control counters (both arrivals and departures), the number of conveyor belts as well as available seating and circulation space for passengers. The interviewees also considered the baggage handling systems to be a factor that could limit the capacity. In the baggage handling system it was the x‐ray capacity, the ability to sort luggage, the number of sorting positions, etc. that could limit the capacity. Regarding other factors, such as the number of security check points, the interviewees considered that it was still possible to handle passengers even if demand was greater than capacity. If that was the case, there would be queues and people would have to wait which lead to decreased levels of service and passengers would be dissatisfied.

3. Why do you think these factors are the most limiting?

The interviewees considered the runway to be the most limiting because either the runway(s) had sufficient capacity or it had not.

It is also time‐consuming and very costly to build an additional runway. For example, when building a 4th runway at Arlanda airport, the time horizon is about 30‐years from today until it is operational. The long timeframe is too a large degree, due to the fact that amended environmental permits has to be applied for.

4. How would you rank these factors (from minor to major) in regard to their significance for limiting air traffic capacity?

None of the interviewees wanted to rank the factors that limited air traffic capacity the most or the least, because it depends on the situation. But as previously stated, the functions that either have or do not have capacity and that are most costly to expand, such as runway and stands, are limiting capacity the most.

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Rebecca Petersen 2018–03–14 6. RESULTS

In the literature review, relevant literature regarding air traffic capacity constraints has been examined and compiled to get an overall picture of the different limiting factors and how they affect capacity. The interconnection between the different limiting factors was also studied (Table 4).

When examining the current literature regarding air traffic capacity constraints, it was quite clear that the factor considered to limit air traffic capacity the most was the runway. The runway was mentioned as the key limiting factor not only in studies of the runway, but also in studies regarding other limiting factors, showing the impact of the runway as the major capacity constraint.

In the literature wake vortex as well as weather was also considered as a very important limiting factors. Other factors, such as taxiway and apron, were considered to limit capacity locally at some airports, for example at specific times of the day or under other certain conditions, but generally not. Noise and ATC are also significant limiting factors. Emissions, baggage handling, check‐in desks/baggage drop and security‐ check received the least attention in the literature.

Table 4 shows how the different limiting factors are possibly liked to each other as described in the literature review for the different limiting factors. However, there may be further interrelations between the limiting factors that has not been addressed the literature review and thus not in table 4. The table shows that most of the factors are affected by as well as affects several other factors. The factor that is affected by most by other factors is the runway followed by taxiway and gate. The factor that affects most other factors is weather. Table 4 can be read in two different ways, to see which factors that are affected by other factors as well as which factors that affects other factors. The factors that are affected are presented in the horizontal header row and the factors that affects are presented in the vertical header column. For example, airspace is affected by runway, air fleet mix, ATC, wake vortex, weather and emissions/noise. Airspace also affects runway, taxiway, apron and ATC.

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Rebecca Petersen 2018–03–14 Table 4. Interrelations between different limiting factors to air traffic capacity.

Is affected ! Airspace Runway Taxiway Apron Air fleet Ground Gate ATC Security- Check-in Terminal Baggage Wake Weather Emissions/ Land Buildings/ mix handling check /Baggage space handling vortex Noice obstacles Affects " drop Airspace

Runway

Taxiway

Apron

Air fleet mix

Ground handling

Gate

ATC

Security-check

Check-in/Baggage drop

Terminal space

Baggage handling

Wake vortex

Weather

Emissions/Noice

Land Buildings/obstacles

To complement the review, a ranking matrix was created based on literature in which the authors have ranked the different limiting factors. The ranking matrix shows the ranking of each factor in accordance to the degree of capacity limitation each paper states them to have (Table 5). In Table 5, the source level defines if the reference is a primary study, i.e. original work or a secondary source, i.e. a review article.

The ranking degree used in the table is major or minor. Words used in references to correspond to the degree “major” in the table are; key factor, critical factor, crucial factor, main, critical restrictive factors, increasingly prominent, most important, primary and major.

As the method used for the literature review is integrative methodology and not systematic, all relevant literature was not examined.

For the ranking matrix, only literature that ranks the key limiting factors to air traffic capacity addressed in this thesis was analysed. A vast number of articles in the literature addresses the same limiting factors, but does not attach a degree to the importance of different limiting factors.

Examination of literature that had ranked the different limiting factors corresponded to the result of the literature review. The ranking table shows that the factor that the research community considered to be the most prominent constraint to air traffic capacity is the runway, followed by wake vortex (Table 5). In contrast, environment/emissions, baggage handling, check‐in desks/baggage drop, security‐ check were not ranked in the literature examined (Table 5). Only two of the factors, taxiway and apron, were considered to limit the capacity to a minor extent (Table 5).

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Rebecca Petersen 2018–03–14 Table 5. Table presenting the different limiting factors and how they are ranked based on the literature.

Factor Reference Database Source Level Ranking

U.S. Congress, Office of Technology Unisearch Primary/ Major Assessment 1984, ref. 2 secondary Lau et al 2014, ref. 50 BASE Primary Major Barbaresco, F. et al 2011, ref. 51 IEEE Primary Major Barbaresco et al 2014, ref. 52 Inspec Primary Major Herrema et al 2015, ref. 53 Inspec Primary Major

Blumstein 1959, ref. 40 Business Primary Major Source Premier Runway Powell et al 2005, ref. 55 IEEE Primary Major Berster et al 2013, ref. 58 ScienceDirect Primary Major

de Neufville 2013, ref.54 LiUB Library Secondary Major Catalogue Mirković and Tošić 2017, ref. 67 Supplemental Primary Major Index Majumdar et al 2005, ref. 49 Scopus Primary Major Tether and Metcalfe 2003, ref. 56 EconLit Primary Major Narendra, 2016, ref. 57 Academic Primary Major Search Complete U.S. Congress, Office of Technology BASE Primary Major Assessment 1982, ref. 21

U.S. Congress, Office of Technology Unisearch Primary/ Major Assessment 1984, ref. 2 secondary Lau, 2014, ref. 50 BASE Primary Major Yu 2017, ref. 66 EBSCOhost Primary Major

Taxiway de Neufville 2013, ref. 54 LiUB Library Secondary Minor Catalogue Mirković et al 2016, ref 68 ScienceDirect Primary Minor

Mirković and Tošić 2017,ref. 67 Supplemental Primary Minor Index U.S. Congress, Office of Technology Unisearch Primary/ Major/ Assessment 1984, ref. 2 secondary minor Apron Mirkovic and Tošić 2014, ref. 77 Academic Primary Minor Search Complete de Neufville 2013, ref. 54 LiUB Library Secondary Minor Catalogue

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Rebecca Petersen 2018–03–14

Barbaresco et al 2011, ref. 51 IEEE Primary Major

52 Barbaresco et al 2014, ref. Inspec Primary Major

Herrema et al 2015, ref. 53 Inspec Primary Major Gertz et al 2002, ref. 71 ScienceDirect Primary Major

Wake vortex U.S. Congress, Office of Technology BASE Primary Major Assessment 1982, ref. 21

Hahn and Schwarz 2007, ref. 70 British Library Primary Major Document Supply Centre Inside Serials & Conference Proceedings Van Dinther et al 2015, ref. 69 BASE Primary Major

Haverkamp and Neuwerth 2005, ScienceDirect Primary Major ref. 72

Janic 2008, ref. 73 ScienceDirect Primary Major

Barbaresco et al 2014, ref. 117 Inspec Primary Major

Air fleet mix De Neufville 2013, ref. 54 LiUB Library Secondary Major Catalogue U.S. Congress, Office of Technology BASE Primary Major Assessment 1982, ref. 21

Soykan 2016, ref. 99 BASE Primary Major

Eurocontrol 2003, ref. 94 Eurocontrol Primary Major

ATC Majumdar and Polak 2001, ref. 96 Science citation Primary Major index Lee and Prevot 2012, ref. 95 Scopus Primary Major

Hermes et al 2009, ref. 97 Inspec Primary Major

U.S. Congress, Office of Technology BASE Primary Major Assessment 1982, ref. 21

U.S. Congress, Office of Technology Unisearch Primary/ Major Assessment 1984, ref. 2 secondary

Chen and Yue 2014, ref. 89 ScienceDirect Primary Major Airspace Jiangjun et al 2012, ref. 90 Inspec Primary Major

Zhaoning et al 2014, ref. 91 Inspec Primary Major

Majumdar et al 2005, ref. 49 Scopus Primary Major

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Rebecca Petersen 2018–03–14

Ground handling Kabongo P.C., 2016, ref. 84 Scopus Primary Major

Barbaresco et al 2014, ref. 117 Inspec Primary Major

de Neufville 2013, ref. 54 LiUB Library Secondary Major Catalogue Halili et al 2008, ref. 115 Scopus Secondary Major

Kicinger et al 2011, ref. 114 Scopus Primary Major

Weather Dillingham 2005, ref. 116 Business Source Primary Major Premier Klein et al 2009, ref. 118 Scopus Primary Major

U.S. Congress, Office of Technology BASE Primary Major Assessment 1982, ref. 21

U.S. Congress, Office of Technology Unisearch Primary/ Major Assessment 1984, ref. 2 secondary U.S. Congress, Office of Technology BASE Primary Major Assessment 1982, ref. 21 Environment/ Basner et al 2017, ref.108 Scopus Secondary Major noise Suau‐Sanchez et al 2011, ref. 109 ScienceDirect Secondary Major

Niemeier 2014, ref. 110 EconLit Primary Major

de Neufville 2013, ref.54 LiUB Library Secondary Major Catalogue Environment/ None emissions Gate Yu et al 2017, ref. 66 EBSCOhost Primary Major

Benlic et al 2016, ref. 128 EBSCOhost Primary Major

Baggage None handling

Check‐in desks/ None Baggage drop

Security‐ check None

To supplement the literature review, interviews with airport planning and airport masterplan professionals were added. The interviews with the professionals showed that the factors considered to be the most limiting to air traffic capacity are runway and stands. Factors considered to be less limiting were factors where it still was possible to handle passengers even if demand was greater than capacity, for example the number of security check points.

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Rebecca Petersen 2018–03–14 7. DISCUSSION

The demand for air traffic have more than doubled in the last two decades and it is expected to continue to increase in the future15, 16, 19. This growth in demand is dependent on good connectivity. As more people work internationally as well as travel for leisure, fast and cheep air travelling with good connectivity is required. Safety is also important because threats to safety can negatively affect the demand. To cater to all these demands it is important identify possible bottlenecks or factors that limit the air traffic capacity and air traffic flow.

There are several different solutions, methods and measures that can be taken to reduce the effect of factors that limit capacity. To succeed it is essential to understand all the different factors and the level of effect at each airport. More importantly, one must understand how the different factors are connected and how they interact. This is even more important when planning new airports because there are various possibilities to make the most optimal solutions right from the start. For already existing airports it can be problematic to overcome factors that limit the capacity, because even if identified, it may not be possible to rectify the constraint. For example if the number of runways is constraining the capacity, it may not be possible to build another runway due to aspects such as increased noise nuisance to urban areas in close vicinity or it may not be possible to acquire new land to expand the airfield. This is also an example were the identified constraint is actually a secondary effect of other primary limiting factors, i.e. land, noise and urban areas.

There are a vast number of previous studies on the different factors that limit capacity. However, almost all studies examine a single factor and how that factor can be optimized for more efficient service provision at the airport. As shown in the literature review (Table 4), the problem is not that easy because most factors are inter‐related, implying that a solution to a single factor does not solve the capacity problem as intended.

Analysis of the literature showed that the runway is the factor considered by researchers as the most limiting to capacity in terms of air traffic capacity (Table 5). In some cases the it is the runway itself that is the constraint as being too short or to narrow or the number of runways are too few21, but in most cases it is other factors that affects and limits the runway capacity50‐56. Our study suggests that the runway was the factor that was most affected by other factors (Table 4). Therefore, this makes the runway the major factor that limits capacity. It is good to note that capacity limitations may be a result from other components of the aviation system. Thus, it is important to find bottlenecks and prevent them to affect other factors that can limit the capacity and air traffic flow. The professionals in airport planning that were interviewed also considered the runway to be the main limiting factor to air traffic capacity. This supported our analysis of the literature. Runway capacity can be improved through either expansion or construction of a new one. The problem with this solution as stated by the airport planning professionals, is that it is also very costly and it takes a very long time, often several decades, to plan, build and get a new runway operational.

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Rebecca Petersen 2018–03–14 The second major capacity‐limiting factor to the runway in the literature review analysis was wake vortex (Table 5). The main difference between the two primary limiting factors is that while runway capacity is affected by a number of factors (Table 4), wake vortex is only affected by a few. However, the limiting factor itself is as important as the number of factors. This shows the complexity of the problem. As previously mentioned, wake vortex and runway capacity limitations are closely connected. The effect of wake turbulence is most limiting during landing due to the minimum spacing distance and thereby limiting the runway capacity21,74‐76. The minimum spacing regulations due to wake vortex also applies to capacity limitations in airspace21,57,70. The only factors addressed in this thesis that affect wake vortex are air fleet mix and weather. Different types of aircraft produce different wake vortex trails74‐76 and weather, as wind can move the position of the wake turbulence2, 16.

Weather is the one limiting factor that cannot be changed, making it very difficult to handle. While weather forecasts are fairly good nowadays, they are not completely reliable and the impact of adverse weather on air traffic capacity still is significant. The only way to decrease the constraint on capacity is to be flexible in other sectors of aviation such as ATC and reroute aircraft to other airports or, if possible, to fly around the bad weather. However, adverse weather often causes delay that affects capacity21, 57, 91, 117–122. Flights might have to be rerouted or rescheduled, which also affects allocations of gates and slot times etc. However, from a passenger’s point of view, actions such as information, food/beverages, hotel vouchers or other compensation are also important during delay. Passenger perception of a delay not only depends on the duration of the delay, but also how they are cared for. Passenger satisfaction is important in many aspects of commercial air traffic.

In the literature analysis, factors such as taxiway and apron were considered to be both major and minor constraints. This is because the limitations to capacity due to these factors are not considered a common problem, but occurs at some airports under certain conditions for instance during peak hours or seasons57, 70– 71, 80. However, for the airports whose capacity is limited by these factors, the effect can be significant. However, the airport planners that were interviewed considered the apron as the second most important limiting factor. Similar to the runway, the apron either has capacity or it has not as the number of stands on the apron is limited. Regarding the interaction with other limiting factors, the apron is a more isolated factor. The aprons are physically characterised by the number, type and layout of stands. These characteristics limit apron capacity and they are related to the air fleet mix. In a wider perspective, the ability of aprons to accommodate certain types of aircraft, affects gate and runway capacity. This makes the impact of apron constraints far greater.

Air traffic control is a vital component that handles aircraft in airspace as well as on the ground95. It is also a key limiting factor to capacity. The ATC workload increases with a steadily growing air traffic industry. The capacity will be constrained when the possible workload for the air traffic controllers is exceeded. ATC is also an important secondary factor to limitations as it affects several other limiting factors.

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Rebecca Petersen 2018–03–14 In the literature reviewed, the ranks at which the factors such as emissions, baggage handling, check‐in desks/baggage drop desks and security‐check limit capacity were stated. Still, these factors can be a potential source of congestion and delay. For example, congestion in security screening may delay boarding of passengers. Delayed boarding may in turn lead to missed slot‐times, causing congestion on the taxiway and holding area, as well as delayed take‐off. Under dimensioned capacity and space for functions such as security check and check‐ in desks/baggage drop desks can be a problem. It not only leads to passenger dissatisfaction, but it might not be possible to expand due to limited terminal space. The view of the airport planners is that even if there is some capacity constraint in functions such as baggage handling, check‐in desks/baggage drop desks or security‐check, the traffic can still be handled by the existing capacity. These constraints can reduce throughput in a given period, which can cause congestion and passenger dissatisfaction, while still managing the task.

Like for all of the society, the environmental issues in aviation are of concern and these concerns are likely to increase in years to come. The petroleum‐based fuels that are used in aviation, similar to other modes of transportation, produce greenhouse gases, which have a great impact on global warming. Fuel is a major cost for airlines but investments in more fuel‐effective engines as well a change to sustainable aviation biofuels is necessary to meet ICAO’s the regulations for the emissions level in 2020101. These investments are costly and the production of aviation biofuels are not expected to be sufficient to meet the 2020 emissions level regulations, which could limit air traffic capacity108. Other measures to reduce emissions also being beneficial for the environment has been proposed by Khadilkar et al127. By holding the aircraft at the gate, were the engine is turned off, until optimal time to start taxiing instead of waiting on the taxiway with the engines running, the environmental savings are significant.127 All measures contributing to a better environment are important.

Another huge environmental problem in aviation is noise. Noise is considered a major problem in several studies2,21,54,108–110. Restrictions against noise levels as well as other noise reducing actions as discussed in 4.9.2 can be a serious capacity constraint. As the impact of noise is greatest during landing and take‐off when the aircraft fly at low altitude, urban areas in proximity to airports are affected. However, the paradox of the problem is that people want the airports to be close to the cities with fast transfer to and from the airport, but on the same time, no one wants to live near an airport. The only way to decrease the problem is noise‐reducing procedures such as regulations against noise levels or restrictions against air traffic operations at certain times as well as better and faster connectivity to and from airports.

The importance of the different factors that limit the capacity can vary between different types and sizes of airports. Large international airports handle aircraft and passengers from all over the world. There are separate gates and passenger areas for domestic, international, Schengen and non‐Schengen flights. When passengers leave or transit between the areas passport‐ and security screening checkpoints has to be passed. The requirement for separate areas decreases the flexibility, for example if there are to few available gates or stands for international aircraft, domestic gates or stands cannot be used even if available,

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Rebecca Petersen 2018–03–14 which affects the capacity. Whereas small airports that only handles domestic flights can use any available gate or stand for similar sized aircraft.

At large international airports the traffic flow is very high especially during peak‐ hours, which requires high throughput. Key factors, such as runway or aprons, are therefore sensitive to changes in air traffic scheduling. Since the air traffic demand at smaller airports is generally low, the inability to accommodate larger sized aircraft can be a constraint.

Identification of the key capacity limiting factors and how they affect air traffic flow can be used as a tool in airport planning and to understand the nature of capacity constraints at existing airports.

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Rebecca Petersen 2018–03–14 8. CONCLUSION

Knowing the limitations is only one part of what needs to be examined at an expansion, new opening or closing of an airport, but a necessary one. To increase capacity several factors needs to be considered. This thesis analysed data from previous research and through interviews to for a comprehensive view of the limiting factors for air traffic capacity and how they affect air traffic flow.

The literature review as well as interviews with airport and master planning professionals showed that the runway is the most important limiting factor to air traffic capacity. Other key limiting factors are wake vortex, weather, noise, ATC and apron.

The limiting factors affect as well as is being affected by several different limiting factors. 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.

For future research, an interesting aspect to examine further is if and how the different factors that limit the capacity varies between different types of airports. For example, if and how the limitations differently affect an international airport compared to one that mostly handles domestic flights. Airport types may also differ depending on the airport’s location (urban or remote areas) and size.

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Rebecca Petersen 2018–03–14 REFERENCES

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