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1998 Fuel Use and Emissions for Danish IFR Flights

Summary

Like other transport modes aviation has many environmental effects such as noise, odour, land use and air pollution. The airports have land use requirements and furthermore restrict the land use of the surrounding areas. As regards air pollution two environmental effects attract special attention: Global warming and ozone depletion. Travel by air has increased substantially during the latest years and is expected to rise by 5% per year for the next 20 years. Air pollutants emitted at cruise flying levels are more harmful than emissions from sources at the Earth’s surface, and in addition most fuel use and emissions occur in this flying phase.

In order to bring down emissions according to national targets and international agreements and to monitor the state of the environment, Denmark is obliged to make annual air emission estimates for all sectors including aviation. For this purpose Denmark participates in the extensive European air emission inventory programme CORINAIR (COoRdination of Information on AIR emissions). The inventory system includes calculation methodologies for most sub-sectors and software for storage and further data processing.

The objective of this project is 1) to make operational the procedure for calculating aircraft emissions according to the new CORINAIR guidelines, 2) on the basis of this to recommend changes in national emission estimations and 3) to develop a tool for assessing fuel use and emissions for individual flights. The project objectives will be met by establishing an emission inventory for IFR (Instrumental Flight Rules) jet and turbo-prop flights from Danish airports in 1998. Emission estimations will not be made for helicopter operations, military flights and piston-engined aircraft movements. The new CORINAIR LTO and cruise data can also be used to make time series estimates of fuel use and emissions since new aircraft/engine combinations only have a slow speed of penetration in the aviation sector.

At first the report summarises the environmental impacts from aviation on global warming and ozone depletion, on the basis of the special report "Aviation and the Global Atmosphere" by the Intergovernmental Panel on Climate Changes (IPCC, 1999). This is followed by a short description of relevant international air pollution conventions and CORINAIR. Then the current CORINAIR methodology is explained, followed by a description of the new model version in terms of input, calculation principle and the computed results. Database queries are made to compare results with the current CORINAIR methodology, findings from international aircraft emission inventories, the Danish TEMA2000 model and sectorial shares for Danish transportation.

International conventions and CORINAIR

Emissions from aircraft are calculated in four sub-categories: Domestic and international LTO (Landing and Take Off) and cruise (>3000 ft). A LTO-cycle covers all flying activities below 3000 ft during descent and landing, taxiing, take off and climb out. The results are reported to the United Nations Framework Convention on Climate Changes (UNFCCC) and the United Nations Economic Commission for Europe Convention on Long-Range Transboundary Air Pollutants (UNECE CLRTAP), according to their respective classification procedures.

CORINAIR (COoRdination of Information on AIR emissions) serves the specific UNFCCC and UNECE reporting needs and is used by many countries to make national estimates. For aviation emissions three different and newly revised methods are offered with increasing levels of complexity. The new detailed methodology is used in the present study to make national CORINAIR calculations operational, while on the other hand the previous version is currently in use for official Danish emission reporting.

CORINAIR aircraft emission calculation methodologies

In the current version initial information must be provided on the number of domestic and international LTOs per aircraft type and their respective LTO timings. The most detailed data are available for Copenhagen Airport, while other Danish airports only submit their statistics for domestic and international LTOs in total numbers for large and small aircraft. From LTO times-in-modes the fuel use and emission factors are computed. These factors are used in combination with the number of LTOs per aircraft type to estimate the total LTO energy use and emissions.

Separately for domestic and international flights the cruise energy use is estimated as the difference between the total fuel use from aviation fuel sale statistics and the corresponding LTO fuel use totals. Finally the domestic and international cruise emissions are calculated as fuel related cruise emission factors multiplied with the fuel use. Due to scarce data on cruise fuel use and emission factors, results are not broken down further on aircraft types.

The new CORINAIR version use fuel use and emission data per distance flown for 24 different civil jets and turbo-props. For the large jets generic aircraft – with worldwide weightings of engine population fitted – are used. Their fuel use and emission figures are mainly harmonised data from the European ANCAT/EC2 and MEET projects, while the Swedish FFA has provided additional data for small jets and turbo-props. For LTO International Civil Aviation Organization (ICAO) times-in-modes are used in most cases to simulate the fuel use and emissions; yet in this study shorter airport taxi times are used for Danish airports to account for local airport characteristics. The cruise fuel use and emissions are simulated by using realistic flight profiles.

Aircraft categories and flight data

ICAO classify all single aircraft according to aircraft designator code, aircraft type, number of engines and engine principle. Airports are also provided with four-letter codes describing their situation regarding i.e. routing area and state. In the present project this information was obtained from the Danish Civil Aviation Administration (CAA-DK).

EUROCONTROL (European Organization for the Safety of Air Navigation) provided data on IFR flights. Recordings for each flight were the origin and destination airport codes and type designators. Also the great circle distance between origin and destination airports was stated. The great circle distance is the length of a natural arc between airports without mileage compensation for actual flight profiles or the actual route followed. Some flights were excluded from the inventory due to lack of fuel use and emission data; namely all piston engined flights, military aircraft and helicopter operations. 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 were actually of a military character.

Representative aircraft and groupings

In 1998 145 different aircraft types carried out all civil jet and turbo-prop flying. These aircraft types were grouped into 24 representative aircraft types. A first distinction was made between jets and turbo-props. The second step was to let the aircraft Maximum Take Off Weight (MTOW, from aircraft directories) determine the choice of representative aircraft type. The CORINAIR databank (see www.eea.int/aegb/) contains data for fuel use and emissions for the representative aircraft. Data is available for each LTO-phase and as a sum for LTO. For cruise data is available for separate mission distances in nautical miles (1 nm = 1.852 km).

Fuel use and emissions calculation

For each flight fuel use and emissions are computed separately for LTO and cruise. LTO results are calculated as the sum of the contributions from five modes; approach/landing, taxi in, taxi out, take off and climb out. Cruise results are found by interpolating or extrapolating the fuel use and emissions for standard flying distances by using the great circle distance for each flight. The airport codes in each flight record make it possible to sum up the results as desired according to origin and destination airport and countries.

New results

In 1998 Danish international flights make up almost two thirds of all flights and 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. Almost one third of all flights are Danish domestic flights. As opposed to international flights they have more moderate fuel use and emission shares compared with flight numbers. The reason is the use of smaller aircraft and shorter trips.

Although fuel use and emissions are only between 1 and 2% in total numbers North Atlantic flights between Denmark and Greenland/Faroe Islands reveal the same trend by shares as for Danish international flights.

The present study’s aviation fuel use and emissions in 1998 Look here!

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 ideal cruise levels are between 6 and 8 km.

The new methodology only calculates 80% of all fuel sold in Danish airports for civil aviation purposes. Although helicopter operations are excluded from the inventory, 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 statistics such as the use of jet petrol for non-aviation purposes, military flying or fuel tankering. Influencing factors on the city-pair estimations are stacking at airports, model simulation uncertainties during the cruise flying phase, the omittance of flights with same origin and destination airports, inaccurate LTO times-in-modes or unrepresentative groupings for some of the aircraft into representative types.

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.

The average emission indices (EI) in g of emission per kg fuel burned and derived from all flights are: EINO_x: 13.0, EIVOC: 0.7 and EICO: 2.7.

Current CORINAIR Results

The official Danish aircraft emission estimates for the year 1998 is calculated with the current version of the detailed CORINAIR methodology. The emission figures are reported to the UNECE and UNFCCC conventions.

Comparisons with current CORINAIR results

For fuel use and emissions the most equal results are obtained for international LTOs in Copenhagen airport. This is also the part of the current model where precise details are given regarding different aircraft types and LTO modal timings. For LTO the weakest part of the current methodology regards all domestic flying and international flying from the provincial airports. In these inventory categories the current estimates are based on fuel use and emission data for the F50, and this data scarcity is reflected in the result deviations.

Danish 1998 aviation fuel use and emissions from the current CORINAIR method Look here!

Moreover F50 is found somewhat small to be fully representative, since much flying is made with the larger jets MD80 and B737, thus influencing the total fuel consumption. In particular the fuel use is underestimated in the current model for international LTOs in provincial airports. Here the new methodology with a detailed fleet mix computes almost 50% more fuel.

Comparisons with international aircraft emission inventories

On a global level three important aircraft emission inventories have been made for the year 1992. All inventories make use of air traffic movement data, aircraft/engine combinations in operation and calculate fuel use and emissions for city-pairs using corresponding great circle distances.

Emission indices from the present study and other inventories

The EINO_x found in the present study are slightly below ANCAT/EC2 figures. This is mostly due to the inclusion of turbo-props and differences in fleet mix for jet aircraft, since emission data for jets mainly come from the ANCAT/EC2 inventory. The aircraft in the Danish CORINAIR inventory tend to be relatively small and flights are mainly short and medium distances. NASA findings for scheduled and charter flights underpin the above explanation. Beyond jets NASA includes also turbo-propelled aircraft and computes almost the same EINO_x as the present study. For VOC and CO the differences in emission indices lie mainly in the simulation methods developed by NASA, DLR, FFA and Psia-consult (4th framework research project MEET). The two latter institutes have provided CORINAIR with emission data for CO and VOC.

Comparisons with other results for domestic flights

In the Danish model TEMA2000 fuel use and emissions for Danish city-pairs and different aircraft types are simulated with the emission model ATEMIS based on real world flight profiles for specific aircraft and installed engines. It is recommended to use the TEMA2000 numbers if fuel use and emissions are evaluated for those domestic trips flown with the aircraft comprised in TEMA2000. For domestic emission inventories the CORINAIR data should be used primarily because of data consistency and because CORINAIR contains data for small jets and turbo-props not present in TEMA2000

Conclusions

This study has shown the feasibility of the new CORINAIR methodology for making city-pair aircraft emission inventories. Consistent data for individual flights and general classifications of aircraft types and airports exist together with fuel use and emission data for representative aircraft types. In this way EUROCONTROL provides information for individual IFR flights which correspond to essential data from CAA-DK on ICAO aircraft designators and airport codes. Fuel use and emission figures for representative aircraft are available from the CORINAIR databank. All data can be combined to build up the inventory system. In order to make the final grouping of aircraft into representative aircraft additional aircraft descriptions can be obtained from aircraft directories.

Much time is needed to build an aircraft emission inventory following the new detailed CORINAIR guidelines. Even though it would be less time consuming to make an inventory update each year, the working time required will exceed the time typically available for inventories - not least considering the requirements for emission estimates in other CORINAIR sectors. Therefore it is recommended to maintain the current methodology for national emission reporting. Instead of a shift to the new model version, one should make an update of the current model’s background data for fuel use and emissions.

Real improvement of the current version for LTOs - except for international LTOs in Copenhagen Airport – could be achieved by applying new LTO fuel use and emission factors derived from the new methodology as aggregated figures. For cruise it is recommended to break down the fuel use used by flights from Copenhagen Airport and other Danish airports according to their LTO fuel use estimates. This should be done separately for domestic and international traffic. Also the cruise emission indices should be updated. Both for domestic and international flights these can be derived from the new methodology results. The new CORINAIR LTO and cruise data can also be used to make time series estimates of fuel use and emissions since new aircraft/engine combinations only have a slow speed of penetration in the aviation sector.

This study’s findings clarify the need to further scrutinise for which purposes the aviation fuel is used in Danish Airports. A way to do this is to examine the most detailed data on aviation fuel delivered to the airports. Also the airport authorities on aviation fuel suppliance should be asked and their information should be verified by analysing other data available. Even though the fuel sale statistics have been improved after the finalisation of the present project the present study’s result could be valuable in a crosscheck examination of statistical data versus model estimates.

A double check on the fuel use from the CORINAIR databank with experiences from real world operation of aircraft during LTO and cruise flying conditions would also add to more precise fuel balances in future aircraft emission inventories. To make these comparisons information must be obtained from the airline companies on fuel use figures for the aircraft most frequently operating from Danish airports.

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