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sources, particularly aviation sources, such as aircraft as well as auxiliary power units (APUs), and ground support equipment (GSE) (see Appendices A2 ( Auxiliary Power Units Emissions Inventory for Criteria Pollutants ) and A3 ( Ground Support Equipment Emissions Inventory for Criteria Pollutants ) for more information on computing emissions from APUs and GSE). 

As discussed, aircraft emissions inventories prepared using EDMS/AEDT are mainly a function of the number of aircraft operations, fleet mix, TIM and aircraft engine operating features (i.e., fuel flow rates and emission factors). 

## A1.3.1 Aircraft Operations 

In this application, aircraft operational data are subdivided among four operational categories: 1) air carrier (including cargo), 2) air taxi/commuter, 3) GA, and 4) military. The types and number of aircraft within each of t hese aircraft categories can vary widely and are rather airport-specific. These operational data for most airports under current and historical conditions can be obtained from the referenced sources listed in Table A1-2 ( Aircraft Operational Input Data Sources ) or may be obtained from the airlines. 

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