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1998 Fuel Use and Emissions for Danish IFR Flights

4. New CORINAIR aircraft emission inventory

Several types of information must be available in order to set up the new CORINAIR aircraft emission inventory system. Consistent data should be obtained for all flights in terms of origin and destination airports, aircraft type etc. In parallel airport code translations must be obtained and a classification of aircraft types must be made. Finally fuel use and emission data must be provided to support the calculation procedure.

4.1 Aircraft categories and flight data

In general all flights can be denominated as Instrumental Flight Rules (IFR) flights, Visual Flight Rules (VFR) flights or military flights. IFR flights are guided by radar and ground control during the whole flight. Aircraft flying VFR are almost solely small gasoline-fuelled aircraft operating in altitudes with visual ground contact. The latter aircraft have only a very small share of the total fuel and emissions from aviation activities. Military flights are restricted by nature, which makes it difficult to obtain flight information on a satisfactory level.

4.1.1 ICAO aircraft classification

A systematic way to classify all single aircraft into major categories is to consider aircraft type, number of engines and engine principle. Such an overall categorisation of all aircraft is done by ICAO (1998). In this report aircraft type designators, Wake Turbulence Category (WTC) and aircraft type descriptions (overall type, number of engines and engine principle) are listed for all aircraft manufacturers and aircraft models present in today’s fleet, and larger than micro or ultra light types.

The aircraft designators are used for Air Traffic Service (ATS) and consist of no more than four characters usually derived from the manufacturers model number or model name, or from a common military type number. The WTC falls into three different Maximum Take Off Weight (MTOW) classes. A description of aircraft types consist of three characters namely the overall aircraft type, the number of engines and engine principle, respectively.

Table 4.1
ICAO WTC and aircraft types

The above-described ICAO codes was provided by the Danish Civil Aviation Administration (CAA-DK) in electronic files to the present project. In total ICAO have 1731 aircraft type designators. In some cases more than one aircraft manufacturer or aircraft model use the same designator code; in total there are 2861 unique combinations of manufacturer, model and type designator.

Table 4.2
A sample of aircraft classified according to the ICAO system

4.1.2 ICAO airport and country code notation

CAA-DK also provided the entire world’s ICAO country and airport code notations in an electronic data file. A hardcopy version of the codes is printed in ICAO (1999). The first and second letter indicates the routing area and the state (or territory) respectively, of which the airport is situated. The telecommunication centre of which the airport is connected is referred to in the third letter, while the fourth letter is assigned as desired.

Table 4.3
A selection of Danish airports with country and airport codes

4.1.3 EUROCONTROL IFR flight data

From the European Organisation for the Safety of Air Navigation (EUROCONTROL) log files were received with information on all IFR flights from Denmark in 1998. Even though Greenland and the Faroe Islands are a part of the Kingdom of Denmark they are not members of EUROCONTROL and therefore data are only provided for a limited number of flights leaving these two geographical areas. Those are flights going through EUROCONTROL area, and effectively this means flights bound for European countries such as Denmark, Norway and Scotland. According to the same definition internal flights in Greenland and the Faroes are excluded together with flights for Canada and Iceland. For consistency reasons all flights from Greenland and the Faroes are excluded from the present inventory.

Every flight was recorded by date and time of departure, origin and destination airport code, type designator, aircraft call sign and airline company name. Also the great circle distance between origin and destination airports was stated.The great circle distance is measured as the length of a natural curve between the origin and destination airports with no mileage compensation for actual flight profiles or the actual route followed. In many cases the great circle routing assumption is too idealistic. Stacking often occurs at airports - especially during peak hours – and flying must some times avoid restricted areas, e.g. areas with military activity.

A subsequent count on the number of flights and also a data query on specific aircraft types revealed 205.098 IFR flights represented by 223 different type designators. For reasons of consistency flights from Greenland and the Faroes to Denmark (1432) and other international flights (65) were excluded. Some flights were excluded from the inventory due to lack of fuel use and emission data; namely all piston engined flights (3846), military aircraft (330) and helicopter operations (133). Omitted were also flights with no indication of great circle distance, i.e. with same origin and destination airport code stated. Many of these flights (1652) were actually piston engined flights or flights of a military character.

Table 4.4
EUROCONTROL data for some flights in 1998

The EUROCONTROL origin and destination airport codes and aircraft type designators use ICAO nomenclature and can be used as entries in the airport and country code translation tables described in paragraph 4.1 and 4.2. This coupling of data enables all flights to be grouped into domestic and international flights and in turn facilitates further fuel use and emission calculations.

4.2 Representative aircraft and groupings

Fuel use and emission data is not readily available for each of the 223 different aircraft type designators in this project. A grouping has to be made into a smaller number of aircraft types representing the whole aircraft fleet and for which fuel use and emission data exist. In the present chapter the representative aircraft types are listed with their WTC and a description of overall aircraft type, number of engines, engine principle and approximate MTOW. These parameters are used as guidelines to append a representative aircraft type to each of the aircraft types present in the Danish inventory.

4.2.1 Representative aircraft

CORINAIR use 24 representative aircraft for jets and turbo-props. Their respective fuel use and emissions come from different simulation models with underlying assumptions that among others vary with respect to the choice of Take off Weight (TOW) in the actual simulation procedure. Instead the MTOW’s have been found in Frawley (1999). In many situations the representative aircraft type comprises several models with varying MTOW’s (and seating capacities) and due to this the indicated weight numbers must be regarded only as approximate values.

Table 4.5
Representative aircraft and size characterisations

4.2.2 Fuel use and emission data

In the new version fuel use and emission factors have been changed to more representative numbers for representative aircraft during LTO and cruise. In most cases the aircraft are generic. This means that the worldwide population of engines fitted to the aircraft in question is considered calculating the fuel use and emission factors. The factors for LTO are based upon ICAO LTO times-in-modes (see paragraph 4.2). For cruise the biggest improvement is the shift from rough fuel-based emission data to factors given per distance flown.

The new CORINAIR data can be found on http://www.eu.int.aegb/. They have been gathered mainly by harmonising existing data from the ANCAT/EC2 global aircraft emission inventory (ANCAT/EC2, 1998) and the European 4th framework project MEET (Methodologies to Estimate the Emissions from Transport), see MEET (1999). Data for small jets and turbo-props have been provided by FFA (2000).

In appendix 1 all fuel use and emission numbers are listed. The LTO figures are also displayed in graphs together with their emission indices (EI) in g per kg fuel burned. The engines used in the simulations are displayed in appendix 2. For the Dash8 400 and S2000 aircraft types no CO emission data were available. Instead the CO emission indices for F50 were used and emission numbers subsequently calculated as emission indices times fuel use for the two aircraft.

Since the simulated data derive from different models it is important to emphasise that inter-aircraft comparisons should be made with care for some aircraft. Also due to model boundary conditions the uncertainties on cruise fuel use and emissions are greater for the shortest distances. Therefore no attempts have been made in this report to analyse in more details the difference in background data for cruise emissions between representative aircraft.

Table 4.6
Data sources for fuel use and emissions

Apart from the airframe design fuel use and emissions heavily depend on the TOW, the engines installed and their corresponding emission indices are measured during the four modes of the LTO-cycle.

4.3 Grouping of aircraft

When fuel use and emission data are provided for representative aircraft types, all aircraft types present in the Danish inventory must be sufficiently grouped prior to the actual calculation procedure. In this study two parameters have determined the performance of the grouping procedure namely the aircraft engine principle and the aircraft size.

At first the actual aircraft engine principle is determined. A distinguishment is made between jets and turbo-propelled aircraft. Secondly a representative aircraft type with similar size is appended to the aircraft in question. The approximate MTOW number found in Frawley (1999) for each aircraft type supports this point of the grouping procedure. All aircraft and their representative types are listed in appendix 3.

The allocation of representative to actual aircraft types could be more detailed. In situations where large differences between actual and representative aircraft sizes exist, the fuel use and emissions for representative aircraft could be scaled with the actual/representative aircraft MTOW ratio. Or if more similar sized representative aircraft were available: Let the aircraft model date of entering into service decide the choice of representative aircraft. In this way the inventory would also reflect the modernity of the aircraft fleet.

Mainly two reasons explain why the suggestions for further refinement of the aircraft grouping has not been implemented in this study. In some cases the efforts do not bear comparison with the obtained improvements. As stated elsewhere in this report the actual TOW for an aircraft in many cases differ from the indicated MTOW. Furthermore it should be possible for other inventory makers to build a similar aircraft fuel use and emission inventory from a reasonable level of experience.

4.4 Fuel use and emission results

In the following the procedure for calculating LTO and cruise fuel use and emissions will be explained. Separate results will be listed for Denmark, Greenland and the Faroe islands and will be further divided into domestic and international figures.

4.4.1 Calculation procedure

To calculate the LTO fuel use and emissions the following equation is used for each flight:'

(2)

Where E_i is the fuel use or emission contribution from each of the five LTO-modes: Approach/landing, taxi in, taxi out, take off and climb out listed in appendix 1 for all representative aircraft. Appendix 1 gives figures for 13 mins in the taxi in and out modes, while more appropriate time intervals are 5.5 mins in Copenhagen Airport and 2.5 mins in other airports present in the Danish inventory. The fuel use and emission numbers are automatically downscaled in the calculation procedure according to this rationale.

In order to estimate the cruise fuel use and emissions for each flight two equations are used. If x_i and x_max denominate the separate distances and the maximum distance, respectively for which fuel use and emissions are known, and y denominates the great circle distance for the individual flight in nautical miles, then the fuel use or emission E (y) becomes:

xi<y<xi+1, i = 0,1,2….max (3)

If the flight distance y exceeds x_max the equation for calculating fuel use and emissions is:

y>xmax (4)

In appendix 1 the fuel use and emissions for separate distances and all representative aircraft are listed.

The grand totals for fuel use and emissions are computed by adding all the fuel uses and emissions estimated for each flight in (2) for LTO, and (3) or (4) for cruise.

4.4.2 Fuel use and emissions for LTO

Table 4.7 and 4.8 list the total fuel use, emissions and derived emission indices for Danish domestic LTOs per representative aircraft and for LTO modal splits, respectively. The same LTO figures are shown in table 4.9 and 4.10 for flights bound for Greenland and the Faroe islands.

Table 4.7
Danish domestic LTO fuel use and emissions for representative aircraft

Table 4.8
Danish domestic LTO mode fuel use and emission totals

Table 4.9
LTO fuel use ansd emissions for flights bound for Greenland and the Faroe Islands

Table 4.10
LTO mode fuel use and emissions totals for flights bound for Greenland and the Faroe Islands

The aircraft in North-Atlantic service between Denmark and Greenland in particular are larger sized than the aircraft flying Danish domestic trips. This is reflected in more fuel use in relative numbers, and on average a bigger EINO_x and smaller EIVOC and EICO’s. In this way the B767 has a great impact on the total result. This particular aircraft consumes one-third of the total fuel used by North-Atlantic flights, and has relatively large EINO_x and small EIVOC and EICO’s.

Also results for the total fuel use, emissions and derived emission indices for Danish international LTOs per representative aircraft and for LTO modal splits are given in the tables 4.11 and 4.12, respectively.

The total EINO_x number is almost the same for Danish domestic and international LTOs, while international EIVOC and EICO show an increase of about 40 and 20%, respectively. The larger EIVOC for international LTOs is mainly because of the more frequent use of F28 and due to a smaller relative importance of the F50, for which VOC measured is below detection limit. For EICO more F28 LTOs and the use of A320 in international traffic also cause the increase. Moreover the relative importance of fuel used for LTOs by MD82 (with fairly low EICOs) in international traffic is minor compared to the fuel use weightings of domestic LTOs.

Table 4.11
Danish international LTO fuel use and emissions for representative aircraft

Table 4.12
Danish international LTO mode fuel use and emission totals

4.4.3 Fuel use and emissions for cruise

Table 4.13 Look here!
Danish domestic cruise fuel use and emissions

Table 4.14
Cruise fuel use and emissions for flights between Denmark and Faroe islands

Table 4.15
Cruise fuel use and emissions for flights between Denmark and Greenland

Table 4.16  Look here!
Danish international cruise fuel use and emissions

4.4.4 Result summary

Danish international flights stand for almost two third of all flights and have even larger shares of fuel use and emissions; in total between 80 and almost 90%. This is explained by the presence of larger sized aircraft in service and longer flying distances. For LTO the international shares are close to 80% - due to larger aircraft and more flights – and for cruise around 90% because of larger aircraft and more and longer flights. Although fuel use and emissions are only between 1 and 2% in total numbers North Atlantic flights between Denmark and Greenland/Faroes reveal the same trend by shares as for Danish international flights.

Table 4.17  Look here!
Summary of fuel use and emissions

Almost one third of all flights are Danish domestic flights. Opposed to international flights they have more moderate fuel use and emission shares compared to flight numbers. The reason is the use of smaller aircraft and shorter trips.

In grand totals the fuel use computed with the new methodology only amounts to 80% of the jet fuel sold in Danish airports for civil aviation purposes. Since international flights use almost 97% of all Danish jet fuel according to fuel sale statistics, variations between fuel sale figures and computed numbers are quite similar to the differences that appears for this sector.

Although helicopter operations are excluded by the new methodology, the smaller calculated fuel use amount and the large domestic fuel use deviation must primarily be explained by other factors. Many parameters have a potential effect on the precision of the fuel balance. These are the use of jet petrol for non-aviation purposes or military flying, fuel tankering and inaccurate domestic/international energy statistics. Factors which can affect the actual city-pair estimations are stacking at airports, the omittance of flights with the same origin and destination airports, model simulation uncertainties during the cruise flying phase, inaccurate LTO-modal timings or unrepresentative groupings for some of the aircraft into representative types.

Table 4.18
Fuel use and emission shares

By the end of the present project period the domestic fuel sale figure was only half of the present inventory’s computed fuel consumption. This difference is due to inaccurate domestic/international energy statistics where the amount of fuel sold for international aviation becomes accordingly bigger. After the finalisation of the present project the fuel sale statistics have been revised jointly by the DEA and the Ministry of Transport and the domestic fuel sale figure is now almost equal to the computed fuel consumption in the present inventory.

In figure 4.1 the North Atlantic flights are classified as international air traffic. The international cruise emissions of NO_x and CO₂ amount to around 80% of the Danish aviation totals. Moreover, most of them are injected directly to the atmosphere by jet aircraft and at flying altitudes between 9 and 11 km. In these altitude bands the NO_x emissions have the most harmful effects. Flying with turbo-props and the short distanced Danish domestic trips have less importance to the greenhouse effect. This is due to their limited share of total fuel burned and their typical flight profiles. The latter trips are flown at maximum altitudes between 5 and 7 km and for turbo-prop flying in general the ideel cruise levels are between 6 and 8 km.

Figure 4.1
Danish aviation emission shares

The domestic VOC and CO totals are very dominated by the high emissions during the LTO taxi-phase, see table 4.8. For both domestic and international flights the LTO emission shares of VOC and CO become 37 and 41%, respectively. Danish taxi-time intervals are around 11 mins in Copenhagen Airport (table 3.1) and five mins in the provincial airports. Both taxi-time durations are significantly lower than the 26 mins taxi-time in the ICAO LTO cycle. This emphasises the importance of using realistic LTO timings; if the ICAO standard LTO timings were used the VOC and CO emission factors would be overestimated, thus leading to even higher LTO emission percentages of air traffic emission totals.

4.4.5 Fuel use and emissions for typical flights

A survey of most frequent aircraft used - by representative aircraft type – is made for typical flights leaving Copenhagen Airport. Small and medium sized aircraft like F50, B737 and MD82 carries out Inter-European flights. Long distance flights to e.g. America and Asia are flown with large aircraft such as B767 and A340.

Table 4.19 Look here!
Some international flights from Copenhagen Airport

4.4.6 Fuel use and CO₂ emissions for different trips and transport modes

To assess the fuel use and CO₂ emissions for transport modal shifts relevant data are obtained for one domestic trip and two European trips. Due to scarce data on occupancy rates for international travels a 100% occupancy rate is assumed for the four different transport modes in the scenario (private car: 5 persons). Moreover the emission components of NO_x, CO, VOC and SO₂ are omitted from the present exercise, mainly due to lack of consistent emission data from power plants outside Denmark producing electricity.

The TEMA2000 model is used to calculate the results for the domestic trip between Copenhagen and Aalborg (Trafikministeriet, 2000). The model has incorporated realistic transport route choices, vehicle types and driving conditions. For aviation TEMA2000 is evaluated in more details in paragraph 5.3. More specifically the private car data is valid for an engine size between 1.4 and 2.0 l. and data for a long distance tourist bus represent this transport category. It is also assumed that both vehicle types comply with the EURO II emission technology.

Table 4.20
Modal shift variations in fuel use and CO₂ emissions per seat for three trips

Other data sources are used to find the results for the two international trips. For private cars and buses data are taken as background data from the COPERT III model (Ntziachristos et al., 1999) using trip speeds of 110 and 90 km/h, respectively. The same private car and bus types are used as for the domestic trip. A query on the present study’s database has provided data for the trips flown with the MD82 aircraft type.

Information on international trains as regards locomotive types, electricity consumption per seat km and distance driven in each country are supplied by Danish Railways (Næraa, 2000). The electricity use data are listed per seat for each of the countries: Denmark, Germany, Belgium, France and Spain and are basically derived from own data (also implemented in TEMA2000) and the European MEET-project (1999).

For the distance driven in Denmark CO₂ emission factors for electricity production are supplied by the Danish Energy Agency (Hansen, 2000). The international trip sections are simulated by combining data from the International Energy Agency (IEA, 1999c) and CO₂ emission factors for the combustion of fossil fuels in power plants. IEA provides information on the quantity of electricity produced per fossil fuel type in Germany, Belgium, France and Spain and subsequently a fuel conversion efficiency of 40% is used to estimate the quantity of fossil fuel used specifically for electricity production.

The private car has high fuel consumption and correspondingly high CO₂ emissions per seat compared to the figures for buses and trains. It is worthwhile to notice that if only two persons made the trips in a private car, the fuel consumption and CO₂ emissions for the international trips would be higher than the figures for the aircraft. The latter vehicle type is without question the least fuel-efficient means of transportation at full occupancy for all transport modes. Buses and trains have about similar numbers for energy use and CO₂ emissions. Trains are a little more energy efficient, but on the other hand have slightly higher CO₂ emissions.

From the numbers it is possible to make other fuel use and CO₂ scenarios by alternating the occupancy rates and varying the fuel use and CO₂ numbers accordingly. Two persons in a private car and an occupancy rate of 70% for buses, trains and aircraft give only slightly lower energy use and CO₂ emissions per person for international trips in a private car compared with the aircraft figures. With relatively low numbers buses and trains are still the most environmentally friendly modes of transport. Since the trip lengths for cars, buses and trains in particular are considerably longer than those flown by aircraft, the figures per person km turn out less environmentally friendly for the latter transportation type.

Table 4.21
Fuel use and CO₂ emissions per person and person km for two persons in a private car and an occupancy rate of 70% for buses, trains and aircraft

The impact on fuel use and emission performances if more modern DAC (Double Annular Combustion) engine types such as CFM56-7B20/2 and CFM56-7B26/2 (fitted to the new SAS B737-600 and -700 aircraft, - (Näs, 2000) are used in the entire SAS MD80 fleet was also analysed. This exercise only focuses on comparisons for approved ICAO LTO test figures since no cruise data are available for these two engine types.

Moreover it should be emphasised that ICAO LTO fuel flows and emissions for the different engines in some cases can be substantially different from observed values when the aircraft/engine combination is actually used in the airport vicinity. This is mainly due to differences in LTO times-in-modes, aircraft aerodynamic performance and the actual aircraft take off weight.

Three different engine types are used in the SAS MD80 fleet (Klee, 1999). These are JT8D-209, JT8D-217C and JT8D-219 with almost equal fuel flows and emission performances (see appendix 4) measured according to the approved ICAO test procedure. The engines are fitted to 1, 62 and 15 aircraft, respectively. From this distribution of engine types fuel flows, emission indices and total LTO figures are calculated for a generic engine.

Table 4.22
Generic engine for SAS MD80 aircraft fleet

A shift to CFM56-7B20/2 would improve the fuel efficiency with almost 30% - thus reducing the CO₂ emissions - and give less than half of the NO_x emission for a full LTO cycle. Take off and climb out has the highest NO_x emissions and for these two modes the largest emission reductions are achieved. Since the NO_x emissions decrease for all four LTO modes, lower NO_x emissions are expected also during cruise and as a consequence the impact on global warming will be smaller.

Reversibly the use of the CFM56-7B20/2 engine type would lead to an increase in VOC and CO emissions of over 40 and 200%, respectively. The main concern of the two latter emission components is their impact on the local airport air quality. On the other hand it is the overall experience that the contribution from aircraft is negligible compared to the emissions from road vehicles driven on the airport ground and in neighbouring streets.

Table 4.23
Ratio between CFM56-7B20/2 and SAS MD80 generic engine

Though the fuel efficiency is somewhat lower and the NO_x emission performance is not as good compared to the CFM56-7B26/2 engine type, in terms of global warming the environment would still benefit from a shift to the CFM56-7B26/2 in the SAS MD80 fleet. Almost the same increases in VOC and CO emissions are observed for the two new engine types compared with the generic engine for the SAS MD80 fleet.

Table 4.24
Ratio between CFM56-7B26/2 and SAS MD80 generic engine

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