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1998 Fuel Use and Emissions for Danish IFR Flights

5. Comparisons

Four comparisons are made to evaluate the results from chapter 4 with other findings. First of all a comparison is made to the current CORINAIR methodology results. In this exercise the database for flights is slightly modified in order to make comparable model runs. Next the results from chapter 4 are compared with the findings from other aircraft emission inventories. Then fuel use and emissions for single flights are evaluated with results from the Danish TEMA2000-model. Finally the present study’s emission share for IFR flights are related to the total Danish transport emission budget.

5.1 Current CORINAIR results

Two modifications of the database for flights presented in chapter 4 have been made in order to evaluate the new model with the current version. First of all flights from Denmark bound for Greenland and the Faroe islands are regarded as international, in order to suit the official fuel sale statistics. Next a distinction is made between flights from Copenhagen airport and all other Danish airports to support the current model’s available fuel use and emission data. The flight database is listed in appendix 5.

To obtain new model results fuel use and emissions were computed with (2) and (3) as described in chapter 4 – also in terms of representative aircraft types.

Table 5.1
Danish aviation fuel use and emissions with new CORINAIR methodology

Table 5.2
Danish aviation fuel use and emissions with current CORINAIR methodology

The allocation of LTOs to the current version’s representative aircraft types is also viewed in appendix 5. The factors for fuel use and emissions are taken from table 3.4 and the calculation method is explained in chapter 3.

5.1.1 Total differences

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. Almost the same model difference occurs for NO_x, while the new methodology calculates 40% more CO and inversely only 36% of the old VOC emissions estimate. Since international flights use almost 97% of all Danish jet fuel according to fuel sale statistics, variations in total fuel use and emission figures between the two methods are almost the same as the differences that appears for this sector.

A very bad fuel use agreement is obtained for domestic air traffic alone; the new fuel estimate is almost twice as high as fuel sale numbers. New emission estimates for national flights are 177, 72 and 236% more for NO_x, CO and VOC, respectively.

The most likely reasons for fuel use deviations are discussed in paragraph 4.4.4.

Figure 5.1
Difference in percentage between new and current CORINAIR method

Table 5.3
Ratio between new and old CORINAIR fuel use and emissions estimates

5.1.2 Differences for LTO

Looking into the differences in LTO fuel use and emission estimates the most similar results are obtained for international LTOs in Copenhagen airport. This is also the part of the current model where precise details are given in terms of different aircraft types and LTO times-in-modes. For LTO the weakest part of the current methodology regards all domestic air traffic and international air traffic in the provincial airports. In these inventory categories the estimates are based on fuel use and emission information for only one aircraft (Fokker 50) and this data scarcity is reflected in the result deviations.

Appendix 4 displays the number of domestic and international flights from Copenhagen airport and other Danish airports. Apparently F50 is a little to small to be the fully representative choice of aircraft, 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 by the current model for international LTOs in provincial airports. Here the new methodology with a detailed fleet mix computes almost 50% more fuel.

Most comparable emission results for the three LTO classes appear for domestic LTO CO emissions, where the two model estimates are of similar size. The NO_x emissions are over 60% up to almost twice as high for the new methodology in the three sectors. For VOC the differences are even bigger; the new estimates are from twice to over four times the emission amount computed with the current methodology.

5.1.3 Differences for cruise

For cruise the fuel use is found in the current methodology as the difference between national fuel sale numbers and calculated fuel use for LTO. The subdivision in cruise fuel use for flights from Copenhagen Airport and provincial airports is made according to the total number of flights irrespective of aircraft type. For domestic flights the aircraft size distributions in Copenhagen Airport and other airports are in the same range, while the larger aircraft in general make international flights from Copenhagen Airport. The latter airport therefore tends to get a too small cruise fuel use amount. This is displayed in table 5.3. The ratios between old and new international cruise fuel use totals should be more or less the same for Copenhagen Airport and the other Danish airports but are remarkably different; the ratios are 0.77 and 0.48, respectively.

5.1.4 Recommendations

Much time is needed to build an aircraft emission inventory following the new CORINAIR guidelines as explained in chapter 4. Even though it would be less time consuming to make an inventory update each year, the working time required will exceed the amount of time typically available for inventories.

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. All data in current CORINAIR format derived from the new CORINAIR method are given in table 5.4.

To estimate the fuel use and emissions for international LTOs in Copenhagen Airport the current model version should still be used. The differences between the new and current results are small and the airport can provide flight data to support the needs of the current model. The flight data describe the fleet mix each year and are easy to implement in the model. With flight data from other airports provided by official Danish statistics and by making some model assumptions – as described in chapter 3 - it is straightforward to make a complete and consistent Danish inventory.

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 supply 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 landing, taxiing, take off, climb out 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.

Table 5.4
Fuel use and emission factors in current CORINAIR format derived from the new CORINAIR method

5.2 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 correspondent great circle distances. Short descriptions of the emission inventories are given in IPCC (1999).

NASA (Baughcum et al., 1996) makes separate inventories for scheduled jet and turbo-prop flights, charter flights, domestic air traffic movements in the Former Soviet Union and China, general aviation (piston-engined aircraft) and military flights. ANCAT/EC2 (1998) only includes jet aircraft in the inventory divided into civil and military flights. DLR (Schumann et al., 1997) use the ANCAT/EC2 database for civil aircraft movements.

Table 5.5
Emission indices from NASA, ANCAT/EC2, DLR and present study