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23 Using Method 2 would improve the Method 1 evaluation emissions method. Both fuel consumption and CO2 emis- by allowing emissions to be reported in a disaggregated form sions data are available, and the data are expected to be fur- (LTO and cruise). As a result, tracking of these emissions over ther separated into domestic and international categories. The time would be improved. stratification by the different modes (ground, above ground, above 3,000 ft, and total) is expected to enable airport opera- 3.1.3 Aircraft Method 3 tors and other parties to identify the effects of various actions on emissions on aircraft operations in these general geo- Unlike the other methods, Method 3 does not rely on the graphic areas. The fuel data can be used with appropriate use of fuel sales information to provide (encompass) cruise emissions factors (see Section 3.1.1) to calculate emissions of fuel use. Rather, Method 3 involves the use of sophisticated CH4 and N2O. methods/models to predict fuel usage for the entire flight as shown in Figure 3-3. Although some European methods/models exist, the pre- The AEDT/SAGE data are 100% consistent with mier U.S. model that should be used is the FAA's AEDT/ EDMS results for the LTO cycle (except for System for Assessing Aviation's Global Emissions (SAGE) startup emissions) and are also consistent with (FAAb 2005). AEDT/SAGE and other models that could be the EPA's national GHG inventory. used for this Method 3 require extensive information about the aircraft fleet, flight schedules, trajectories, and aircraft performance. Note that while preparing this report, concern Due to the model integration work under the FAA's AEDT was expressed with the accuracy of fuel sales data to reflect project, both AEDT/SAGE and AEDT/EDMS use common fuel consumed in a flight segment because some flights may computational components. Hence, the aircraft LTO fuel con- tanker fuel for use on later segments. At this time, it is not sumption (below 3,000 ft) computations from AEDT/SAGE possible to estimate how fuel sales may compare to the fuel are identical to those from AEDT/EDMS except for the start-up burn evaluation computed by AEDT/SAGE. Currently, AEDT/ emissions, which are currently only modeled in AEDT/EDMS SAGE is a research tool and is not available to the general and not in AEDT/SAGE. Also, since AEDT/SAGE inventories public. However, the FAA intends to make fuel burn and CO2 are currently used by the USEPA as part of the U.S. national data (totals for each airport) available in the following form GHG inventory development, the AEDT/SAGE airport data for each U.S. airport: promulgated as part of this method is fully consistent with the national inventory. Ground level (reflecting the previously defined taxi/idle Note the following information about backcasting and mode), forecasting. For airports that require either a backcast or fore- Above ground to below 3,000 ft (reflecting the takeoff, cast condition, it is likely that the FAA AEDT/SAGE dataset will climb-out, and approach modes), not include the data that the analysis may require. Thus, there Above 3,000 ft (reflecting cruise), and may be some inconsistencies between the existing inventory Total. (if reflecting the FAA's Method 3 or AEDT/SAGE data), and the use of Method 1 or Method 2 for backcast or forecast con- dition. This can be handled in one of two ways. First, airport The FAA AEDT/SAGE-based aircraft fuel burn and CO2 operators could note that the backcast and forecast condi- data are expected to be made available on an annual basis for tions are prepared with differing methods, reflecting the state each U.S. airport and, as such, could be the preferred aircraft of available data. Alternatively, an airport could prepare its existing inventory using Method 2 and compare the results to the FAA's Method 3 (AEDT/SAGE) dataset for the same year. AEDT/SAGE One difference in the results could be due to fuel tankering Airport Inventories (fuel transported on the aircraft that is being used for later flight segments). Another could just have to do with the pre- cision of the methods. The purpose of this comparison would be to identify any substantial variances in the fuel sales data Aircraft LTO GHG Aircraft Cruise relative to the Method 3 (AEDT/SAGE) calculation and use Emissions GHG Emissions that information to assist with adjusting the Method 2 back- cast and forecast analysis. Using a Method 2 approach for the Figure 3-3. Overview of Aircraft backcast and forecast, the results of the Method 2 data could Method 3. be adjusted in a manner reflecting the variance. It needs to be