ENRI Int. Workshop on ATM/CNS. Tokyo, Japan. (EIWAC 2010)[EN­025] "Analyzing airlines potential cost savings when reducing
delays in international air traffic"(EIWAC 2010)
Michael Kreuz
AT-OneLilienthalplatz 7
Braunschweig, Germany
michael.kreuz@dlr.de

Abstract: Delays in international air traffic have garnered great attention over the past few years. Passengers, airports aswell as airlines are hit by the impacts of delays and suffer from their financial burden. In order to cut costs and keep competitiveness in the global market, strategies of managing delays are of prime importance for aircraft operators. Especially intimes of consolidations or airlines merger attempts, evaluating the performance and optimizing operations are the keys tosuccess in the global aviation market.
This paper focuses on airlines most important cost drivers being influenced by changes in delay. It does not deal with any
passenger or national economy related costs arising if flight operations are delayed. Actual delay statistics of Europe’s leading hub airports offer the basis for the calculation of the potential benefit that may arise if delays could be reduced marginally. Depending on the airport and accordingly its aircraft mix, movements per year and further characteristics, intervals ofpotential savings can be assessed respectively.
Keywords: benefit, marginal delay costs, ground / airborne delay

Nomenclature
APU

Auxiliary Power UnitIOC

ASMGCS

Advanced Surface Movement
Guidance and Control System

LCC

Low Cost Carrier

LH

Lufthansa

LHR

London Heathrow Airport

MTOM

Maximum Take-Off Mass

MUC

Munich Airport

SES

Single European Sky

ATM

Air Traffic Management

AZ

Alitalia

BA

British Airways

CDG

Paris Charles de Gaulle

CDM

Collaborative Decision Making

DOC

Direct Operating Costs

EC

European Commission

FAA

Federal Aviation Administration

FCO

Rome Fiumicino

ICAO

International
Organization

Civil

Aviation

363

Indirect Operating Costs

TOC

Total Operating Costs

US DOT

US Department of Transportation

M. Kreuz
no chance to cope with that growth without significant
initiatives such as the Single European Sky (SES) concept.
It aims to reduce airspace fragmentation and thus to overcome current capacity issues as well as to improve airtransportation's overall sustainability.

1. Introduction
Focusing on the airlines perspective this paper starts withan overview of recent delay situation. Various causes andconsequences of delays are analyzed and presented inchapter 2.

The impacts of delays shall be mentioned briefly for theareas of airlines, passengers and third parties in the following.

The definition of the respective flight phases in which
delays occur is inevitable when calculating airlines marginal delay costs. Therefore, a short overview about typical airline’s cost structure is given in chapter 3 and significant operative costs are chosen to evaluate the amount ofadditional costs to airlines in case of ground or airborne
delay (chapter 4).

2. Delay Situation in Europe

Notwithstanding the purpose of a journey (business or
holiday trip) delays are an inconvenience to the majorityof passengers. Increasing inconvenience among customers
can be decisive for declining image values of airlines andmay have negative effects on their market share. Furthermore, opportunity costs arise even for passengers in caseof delays. Since the loss of use, e.g. by a missed businessmeeting, differ from the loss of use by late start into holidays, opportunity costs need to be monetarily judged differently depending on the purpose of journey. Independently of this, efficiency decreases with every delay minutesince resources are not used optimally.

The Department of Transportation (DOT) defines a flightas “delayed” if it departs more than 15 minutes after its
scheduled departure time. This 15-minute window is also
used to define arriving flights as delayed. If a flight is cancelled it has no effect on an airline’s delay rate [19].

Following figure 2 gives an overview about the economic
effects of air traffic delay. The x-axis is the quantity demanded/offered and the y-axis the price of the goods. As
already mentioned, this figure shows the total delay costs
to airlines as well as other parties such as passengers or
the environment.

The calculation of the potential cost savings when reducing delays is done for selected leading European hub airports such as London Heathrow (LHR), Munich (MUC) or
Rome Fiumicino (FCO) and will be presented in chapter 5.

As shown in this figure, the equilibrium represented by QE
and PE is the market equilibrium based on demand andsupply. Any prices below or above this equilibrium will
not hold on the market due to economic reasons.

Using this definition, about 22 % of all commercial flights
in Europe in 2007 could be described as delayed whichequals an annual 0.4 percentage increase.
The following Figure 1 gives an overview of the development of departure delay in Europe from 2004 to 2007.

In case of delays (regardless of the actual causes) externalcosts are imposed on the air traffic system. To the traveler
additional costs in the form of schedule change as well as
opportunity costs are entailed.

85%

Punctuality rate

80%

75%

70%

65%
2004

2005

2006

National and European flights

Intercontinental flights

2007

Figure 1 Development of punctuality rate in Europe from 2004 to 2007
Source: [21]Decreasing punctuality figures of both national/European
and intercontinental flights might be the consequence ofsteady growth in international air transport. As airspace
and infrastructure on the ground (runways, aprons, taxiways, gates and terminals) are limited, there seems to be

Figure 2 Economic effects of air traffic delay
Source: According to [25]364

ENRI Int. Workshop on ATM/CNS. Tokyo, Japan. (EIWAC 2010)
To the airline additional costs in the form of higher fuel orcabin crew wages are imposed. Theses costs are shown by
the connection between A and B (line C).

DOCs largely depend on the flight operations and represent the largest proportion of airlines operating expenses[2].
Most important cost items contributing to direct operating
expenses are:Consequently a new supply curve can be set by parallel
shift of the old supply curve. As a result a new equilibrium
Q2P2 has been defined.
The effects on airlines as well as consumers can be described as follows:
As Q2P2 > QEPE consumers suffer from higher ticket prices
and airlines from lower fares that can be obtained on themarket. In detail, additional costs to airlines are equal to
the rectangle P3BCPE plus the triangle BEC. Costs to consumers can be defined as the rectangle PECAP2 plus thetriangle CEA.



Fuel Costs



Flight and Cabin Crew Allowances

Maintenance Costs

In contrast to US Department of Transportation (US DOT)[24] or International Civil Aviation Organization (ICAO)[16] categorization, landing fees can also be considered as
direct operating costs because flights can not be operated
without starting or landing at an airport [7].

Thus total delay costs on airlines and consumers are equal
to the rectangle P3BAP2 plus the triangle BEA. These welfare decreasing effects exceed by far the “positive” effects
of ground delays that passengers are encouraged to consume more goods when filling the time gap to boarding
which lead to higher sales in the non-aviation business[12].

4. Calculations
There are different methods for assigning airlines delay
costs. In this paper the cost items which already havebeen mentioned in chapter 3 are taken into account. Further operating or non-operating cost elements are not discussed as their amount is either not influenced by the (un)-punctuality level (i.e. marketing expenses) or negligible(changes in the amount of route/airport charges due todelays) [6].

Further considerations, such as any analogies to taxes thatare imposed on the air traffic market and the question if
delay costs are “lost” or if there is any return to the governmental authorities, are no matter to be discussed in thispaper.

Due to the fact that delay costs vary (amongst others) according to the equipment used, different aircraft types aredefined to estimate additional expenses.

3. Airline Cost Classification

Therefore a B737-500 is selected as a typical representative for medium jets and a B747-400 for heavy jets1.

A common approach to airline cost classification can beachieved by using functional categories such as operating
and non-operating costs [14]. Non-operating costs are
fixed with output and account more than 50 % of total
airlines costs (respective amount of non-operating costs
depends i.e. on airlines expenditures or assets).

4.1 Fuel Costs
Fuel costs of airlines mainly depend on fuel consumption
and fuel prices on the market. Since aviation fuel (Jet A-1)
is closely linked to oil prices, the impact of climbing oil
prices in past years needs to be considered when calculating fuel costs. Between 2001 and 2008 oil price rose morethan 330 % and reached a peak of more than $ 120 per
barrel in 2008. In order to keep the values up to date thefollowing calculation is based on an average oil price of$ 60 per barrel in the year 2009.

Focus in this paper is laid on operating costs because nonoperating costs are not directly related to airline’s air services (and therefore, independent of changes in delaylevel), but to any financial activities.
Total operating costs (TOC) can be furthermore subdivided into direct operating (DOC) and indirect operating
costs (IOC). IOCs are rather passenger-related (i.e. passenger services, catering) and contain sales-dependent
costs such as expenses for e.g. promotion [13].

1365Classification of aircraft to the wake turbulence categories according to [15]

M. Kreuz
Fuel burn data provided by [6] offers a reliable basis todetermine different fuel consumption according to thedifferent flight phases (APU, stationary ground, taxi, enroute and approach) and different aircraft equipment used
(B737 and B747). Fuel costs per minute for both aircraft
considered are given by the following Figure 3.

First of all the EU regulation No 1899\2006 (see above)
has been applied. Furthermore a total number of 347 seatsin a three-class configuration represents the basis for calculation. This number complies with the average numberof seats of airlines looked at (e.g. German Lufthansa,
United Airlines et al). In order to provide a higher service
level in business and first class, more crew members thanrequired on law are assumed. The number of seats as wellas the number of crew members (including one seniorflight attendant for medium haul flights and two seniorflight attendants for long haul flights) corresponds withmost both European and US network carrier seating plans
and therefore offer a valid basis for the following examinations. Apart from the size of crew per aircraft, wages forboth cabin crew and flight crew members are anotherpoint of interest. According to own examinations salaries
increase by the size of the equipment used. Therefore,
higher marginal flight crew costs are taken into accountfor a B747 than for a B737. For both aircraft types a flightcrew of one pilot in command and one first officer is assumed. In order to provide reliable results, values used inthis part were both derived by detailed examination doneby [22] and own examinations of payment mechanisms ofGerman airlines.

Figure 3 Fuel costs per minute

Airlines may benefit from cost-savings achieved by synergies established in alliances and fuel hedging practices.
Especially hedging activities are carried out by most European network airlines in order to achieve advantages ininvestment opportunities [18, 4].

Finally total marginal crew costs (flight crew and cabincrew) of approx. $ 10 per minute for B737 and approx.
$ 20 per minute for B747 for ground and airborne delays
can be derived. Reasons for this deviation can be seen in
the already mentioned different crew size as well as seniority-based payments.

4.2 Flight and Cabin Crew Allowances
Marginal crew cost contribution to airlines allowances isanother important factor that needs to be examined. Payment mechanisms depend on a wide range on parameters
beginning with the base country, economical development,social security contributions or any types of operations [7].
Most important cost drivers are the different payment
mechanisms, size of aircraft flown and legal restrictions
concerning number and composition of cabin crew andlabor time. The regulation (EC) No 1899\2006 of theEuropean Parliament defines the minimum number ofcabin crew as follows [10]2:

4.3 Maintenance Costs
Maintenance costs basically depend on the following cost
components:“An operator shall ensure that the minimum of cabin crewis the greater of one cabin crew member for every 50, or
fraction of 50, passenger seats installed on the same deckof the aeroplane […]”

Labor



Materials



Third Party

Burden[18] analyzed that total direct costs reach up to 60-70 % ofmaintenance costs. Consequently 30-40 % can be allocated to the burden costs. Representing the fixed costs,
these cost elements do not vary respectively to the delaylevel. In order to determine airlines´ marginal delay costs,
fixed costs can be excluded from the following calculation
method.

As mentioned in this regulatory framework the amount ofaircraft seats is decisive for the minimum allowed numberof cabin crew members. Estimating marginal crew costs
the following assumptions are made in this paper:2

The following calculation method basically focuses onthese parameters:

Equivalent regulations are given by Federal Aviation Administration (FAA) for the United States of America [11]366Block hours per yearVariable cost elements of maintenance costs

ENRI Int. Workshop on ATM/CNS. Tokyo, Japan. (EIWAC 2010)
At first focus is laid on the operating hours per year. Dueto the fact that the amount of block hours depends on theairlines aircraft mix, in-depth analysis were arranged toobtain reliable information. It is assumed that every aircraft is available 365 days a year. Aircraft groundings due
to economic crises or aircraft losses as a result of accidents
are not taken into account. As this paper tends to determine the benefit from reducing delay depending on thespecific flight phase in which it occurs, “operating minutes” implying total flight, gate and taxi minutes of anaircraft per year need to be defined. According to own
data (see the following chapter 5), it can be assessed thatwide bodies (here: Boeing B747) are airborne for about
13.4 hours per day. Relating to a whole year the percentage is about 56 % of total operating minutes. Remaining
44 % can be allocated to gate (approx. 29 %) and taxi
(approx. 15 %) depending on specific airline procedures,
airport layouts or aircraft operations.

at leading European airports only 1,73 takeoffs and landings per day are performed by long range aircraft whereas
typical mid-range aircraft have 4,2 takeoffs and landings
per day in average. The following Figure 4 gives an overview about the calculated marginal costs for the relevant
flight phases.

Figure 4 Marginal maintenance costs per minuteIn the next step, specific “load minutes” are calculated.
They offer an overview about how the most importantaircraft components (airframe and engines) are exposed on
the ground and in the air. Due to difficult mechanicalloads in the particular flight phases, weighting factors (“0”,“0.5”,”1”) are set to underline the difference in additional
delay costs when a delay occurs on the ground or in the air.

5. Evaluating the benefit for airlines
In this chapter focus will be laid on analyzing the potential
benefit of airlines by reducing delays. Therefore an approach of the procedures and the underlying database will
be given in the following chapter 5.1.

According to this approach aircraft engines are assumed to
be exposed only during taxi and in-flight. Numbers “1”and “0.5” represent the degree of exposure, e.g. full technical load is represented by “1”, while standing at the gate
is assumed to have no effect (“0”).

In the subsequent chapter 5.2 the results will be presented
and discussed.

Apart from the block hours, delay dependent maintenancecosts are the second important parameter that needs to be
calculated. As already mentioned, variable delay costs arecalculated by subtracting fixed cost components from total
annual maintenance costs. According to [23] delay dependent maintenance costs can be assigned as follows:

5.1 Explanation of the procedure and the database
As already mentioned in the introduction, the European
hub airports London Heathrow, Munich and Rome Fiumicino have been selected for the following calculations.
Figure 5 offers an overview about the key parameters ofthese airports.

65 % can be allocated for maintaining the airframe and
35 % for the engines. Monetary weighting factors are set
in order to calculate the different additional delay costs(analog to flight phase dependent weighting).
On basis of this method, marginal maintenance costs ofabout $ 8 per minute can be calculated for a B747. Costs
for both taxiing to/from runway (approx. $ 2.46) andstanding at the gate (approx. $ 1.04) are certainly lower.
In case of the medium aircraft type Boeing B737 temporary weighting factors are changed due to different aircraft
turnings compared to long range jets. Mid-range jets likethe B737 usually have more takeoffs/landings per day andspend more time on the ground than long range jets consequently. According to own analyses of airlines operating

Figure 5 Key parameters for calculation

367

M. Kreuz
The total number of departures in 2009 is given to distinguish the different dimensions among the hubs. According
to [9] London Heathrow was ranked number two (behind
Paris Charles de Gaulle (CDG)) in Europe with approx.
233.000 departures in 2009. Munich and Rome werelisted number six und seven.

out any differentiation in heavy, medium or light jets, unrealistic unit costs per minute would have to be adopted.
Counting the number of arrivals and departures, the total
average number of movements per day at one specificairport can be assigned.
Furthermore the percentage of LCC at the selected hub
airports has to be determined as LCC implement several
strategies in order to cut costs [7].

Rows two and three of Figure 5 offer up-to-date flight data.
These were gained from the FlightStats platform which
delivers worldwide flight on-time performance information [6].

The percentage of LCC as well as the ratio of the leading
carrier of the total movements is shown in the following
Figure 7.

The period of data collection extended over several
months from the beginning of May to mid-August 2010.

It can be witnessed that the percentage of LCC at London
Heathrow is negligible whilst almost 20 % LCC at Romeis an uncommon high value for hub airports. In general
network carriers are largely attached to hub airports
whereas secondary/regional airports are more attractive to
LCC due to idle capacities and lower airport charges [1,20].

The unprecedented Eyjafjallajökull 3 ash crisis (most severe from 15th to 22nd April 2010) was not taken into account as regular flight operations should be considered.
Most relevant data attained are for example:
Equipment_ actual

Number of departures _actual

Number of arrivals _actualOperating airline/codeshare partners

The need of these data can be explained by describing theprocedure of the calculation method which is showngraphically in the following Figure 6.

Figure 7 Ratio of LCC to network carrier

In consequence delay costs per minute are considerably
lower than those of network airlines4. Thus a differently
minted cost reduction potential can be suggested depending on this mentioned proportion.
In case of in-depth analysis, as done in chapter 4, in addition with explicit actual equipment data, more adequate
results could be achieved. As there are too many different
aircraft types at hub airports explicit analysis of marginal
delay costs can not be carried out for every one.
Figure 6 Explanation of the procedureThus the two aircraft types looked at in chapter 4 are assumed to be representative aircraft for the respective wakevortex category.

Considering the fleet mix, it is essential to look at thewake vortex category as well as the proportion of Low
Cost Carrier (LCC) (e.g. Ryanair, EasyJet) to network
carriers (German Lufthansa, All Nippon Airways). With-

3

Costs determined for B737 are assumed to be realistic
average costs for typical medium jets. Costs for B747 are

4

Eyjafjallajökull is one of the smaller glaciers of Iceland, which
covers a volcano that has erupted twice in April 2010.

368

The specific practices how to cut costs are no matter to be discussed in this paper.

ENRI Int. Workshop on ATM/CNS. Tokyo, Japan. (EIWAC 2010)
taken as the upper limit for heavy jets5. This procedure canbe justified by extensive analysis of marginal delay costsof different aircraft types done by [6]. This work showsthat the fuel consumption, which is the most importantcomponent of operating costs of a B737, is comparable tothe one of other medium jets such as A319/A320. As theamount of seats is also similar, comparable marginal crew
costs in case of delays can be assumed6.
Apart from these parameters it is necessary for the following consideration to define an “interval” in which the“average delay reduction per movement” due to current or
future measures can be expected. This procedure offers
considerably more meaningful values than the definitionof one concrete number since this is aggravated by thevariety of factors influencing punctuality in air traffic. [3]has shown that every taxi process can be lowered by optimized ground guidance control (A-SMGCS) by 24 seconds on average. Besides examinations dealing with theprinciple of Collaborative Decision Making (CDM) (see[8]) prove that additional ground time of an aircraft can be
reduced by a value up to approx. 60 seconds by implementation of this system.

Figure 8 Estimation of potential benefit

Depending on the reduction of the average delay, benefits
up to almost 20 Million Euros per year can be estimatedfor London Heathrow 7 . Values for Munich and Rome
Fiumicino are considerably lower in comparison withthose of London. One decisive reason is surely the lower
number of movements as well as the strongly divergent
fleet mix.
Despite a slightly higher percentage of heavy jets in Rome
Fiumicino, the estimated benefit is lower than in Munich.
This can be explained with the lower quota of LCC(~ 5.9 % vs. ~ 19.6 %) and the lower number of total
movements.

These scientific examinations offer a valid basis for thedefinition of the interval above. Therefore values ofapprox. 24 seconds as well as 60 seconds are considered
as lower and upper temporary barrier for the potential cost
reduction. It is assured by this procedure that the given
interval of the potential delay reduction is based on a realistic and furthermore scientifically verifiable basis.

If further operating and non-operating costs such as passenger costs, capacity-induced schedule delay or indirect
economic impacts were taken into account, the potential
cost reduction could be increased even further.

6. Conclusion and Outlook
This paper aimed to analyze the cost structure of airlines
in order to determine additional operating costs in case ofdelays in the air traffic system. On the basis of information
gained by scientific sources as well as own examinations
changes in operating costs are estimated.

5.2 Results
Based on the values given in Figure 5 and considering theprocedure pictured in Figure 6, the following benefit canbe estimated (see Figure 8).
The highlighted area represents the interval with the temporary boundaries mentioned above.

5

Marginal delay costs for the new A380 are not considered inthis paper.

6

According to German Lufthansa’s seat map there is a differenceof 21 seats comparing B737-500 and A319 and a difference of
5 seats comparing B737-300 and A319 respectively [17].

Having selected three main European hub airports, an interval of potential cost reduction could be evaluated on
basis of airport-specific data such fleet mix, percentage of
LCC vs. network carrier and total number of movements.
This paper therefore may function as a kind of impulse tosensitize ATM-Stakeholders to the amount of potential
cost reduction. Such considerations are of great importance, especially in times of economic recession and increasing consolidation trends in air traffic market since
airlines make large effort to cut costs in order to remaincompetitive in the global market.

7369

The benefit estimated in this paper is based on the definition of
the values explained in chapter 4.3.

M. Kreuz
agement”, DOC 4444 ATM/501, Fourteenth Edition,
2001

7. REFERENCES[1] Barbot, C., “Low-cost airlines, secondary airports,[16] International Civil Aviation Organization, “Outlook

and state aid: An economic assessment of the Ryanair–Charleroi Airport agreement”, Journal of Air
Transport Management, Volume 12, Issue 4, 2006

for Air Transport of the Year 2025”, Montreal, 2007[17] Lufthansa, German Airline, “Seat maps of short- and[2] Barnhart, C., Belobaba, P., Odoni, A., “The Global[18] Morrel, P., “Airline Finance”, Third Edition, Ashgate

medium-haul fleet”, www.lufthansa.com, 2010

Airline Industry”, John Wiley & Sons Ltd., 2009

Publishing Limited, 2007

[3] Busacker, T., “Steigerung der Flughafen-Kapazität[19] Mueller, E., Chatterji, G., “Analysis of aircraft arrival

durch Modellierung und Optimierung von FlughafenBoden-Rollverkehr - Ein Beitrag zu einem künftigen
Rollführungssystem (A-SMGCS)“, University ofTechnology, 2005

and departure delay characteristics”. In: AIAA Aircraft and Technology, Integration and Operations, Los
Angeles, 1-3 October 2002
[20] Neufville, R., Walker, W., Marchau, V., “Low-Cost[4] Chew, D., “Corporate Risk Management”, Journal ofApplied Corporate Finance, Columbia Business
School, 2008

Airports For Low-Cost Airlines – Flexible Design To
Manage The Risks“, Journal of Planning and Technology, 2007

[5] Conducive Technology Corp., “FlightStats – Fly[21] Reichmuth, J. et al, “Luftverkehrsbericht 2008 – Da-

Smarter”, www.flightstats.com, 2010

ten und Kommentierungen des deutschen und weltweiten Luftverkehrs, 2008

[6] Cook, A. et al, “Evaluating the true cost to airlines of

one minute airborne or ground delay”, Performance
Review Commission, EUROCONTROL - Preparedby the University of Westminster, 2004[22] University of Westminster, “Aircraft crewing – mar-

ginal delay costs”, Prepared by Transport Studies
Group for Innovative Actions of R&D in EUROCONTROL Programme CARE INO III, 2008

[7] Doganis, R., “Flying Off Course: The Economics ofInternational Airlines”, Third Edition, Taylor & Francis Ltd, 2002[23] University of Westminster, “Aircraft maintenance –marginal delay costs”, Prepared by Transport Studies
Group for Innovative Actions of R&D in EUROCONTROL Programme CARE INO III, 2008[8] EUROCONTROL, “Performance Review Report” –An Assessment of Air Traffic Management in Europe
during the Calendar Year 2008[24] US Department of Transportation, “Air Carrier Finan-cial Reports – Form 41 Financial Data”, Bureau ofTransportation Statistics, Washington, 2007

[9] EUROCONTROL, “CODA DIGEST – Delays to Air

Transport in Europe”, Central Office for Delay
Analysis 2010[25] Vasigh, B. et al, “Introduction to Air Transport Eco-nomics – From Theory to Applications”, Ashgate
Publishing Limited, 2008[10] EUOPEAN UNION, “Regulation of the European

Parliament and of the Council of 12 December 2006”,
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?
uri=OJ:L:2006:377:0001:0175:EN:pdf, 2006[11] Federal Aviation Administration, “FAA Code of Fed-

eral Regulations”, Title 14 Aeronautics and Space,http://ecfr.gpoaccess.gov/cgi/t/text/textidx?c=ecfr&tpl=/ecfrbrowse/Title14/14tab_02.tpl,
2008

COPYRIGHT
Copyright Statement[12] Guest, T., “A Matter of Time: Air Traffic delay in

The authors confirm that they, and/or their company or
institution, hold copyright of all original material includedin their paper. They also confirm they have obtained permission, from the copyright holder of any third party material included in their paper, to publish it as part of theirpaper. The authors grant full permission for the publication and distribution of their paper as part of the
EIWAC2010 proceedings or as individual off-prints from theproceeding

Europe”. In: EUROCONTROL – Trends in Air Traffic, Volume 2, 2007[13] Harris, F., “An Economic Model of US Airline Oper-

ating Expenses”, University of Maryland, 2005[14] Holloway, S., “Straight Level Practices – Practical

Airline Economics”, Third Edition, Ashgate Publishing Limited, 2008[15] International Civil Aviation Organization, “Proce-dures for Air Navigation Services – Air Traffic Man-

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