For a criteria pollutant emissions inventory, EDMS/AEDT uses static times in mode (TIM) for  ground-based aircraft movements (i.e. taxi times) but these times often do not capture airport- specific operating parameters such as ground delay, airfield configuration, ramp locations ,  variation in aircraft speed, and other important factors. So, users are allowed to modify taxi times  on a per-aircraft basis to account for these airport -specific operating conditions.  Appendix F  ( Data and Information Sources ) presents resources available to obtain actual taxi times,  simulated taxi times, and to apportion/estimate airfield delay.  GSE criteria pollutant emissions inventories using EDMS/AEDT capture two distinct sets of  utilization at an airport:  (i) GSE servicing gated aircraft on the  apron, and (ii) other  activities of the GSE population not tied to gate service operations. An example of a gate service  operation is a baggage tractor visiting an aircraft at the apron to drop off baggage; an example of  a population activity is a deicing truck driving back and forth to a deicing area during the deicing  season.  To compute GSE emissions, EDMS/AEDT applies emissions factors (in grams per horsepower  hour [g/hp-hr]) specific to the make/model, year of manufacture, approximate horsepower , and  fuel type of a given equipment to annual hours of operation for that equipment. These emissions  calculations are further adjusted using the observed horsepower of the equipment and equipment’s average percentage of full throttle (i.e., load factor). EDM S/AEDT offer “default”  values for many of these parameters and affords a user to override them to the extent information  on an airport’s GSE fleet is known.  For GSE population activities, users need only specify the make/model, model year, horsepower,  fuel type, and annual hours of operation for a given piece of equipment (or accept  EDMS’s  default information). This approach also applies to the gate service GSE. EDMS/AEDT computes annual hours of operation for gate service GSE by considering number of aircraft LTOs for which GSE service is provided and the total running time of the  GSE per LTO.  Calculation steps and input data necessary to compute GSE emissions in EDMS/AEDT further explained in  Appendix A3  ( Ground Support Equipment Emission Inventory for Criteria  Pollutants ).  When input to EDMS/AEDT, most large commercial and cargo aircraft are automatically  assigned a representative make and model of APU if agency/industry documentation indicates  that an APU is used on that aircraft.$^{$_{43}$, $_{44 }$}$Annual APU emissions are a function of the number of  LTOs performed by the equipped aircraft, the time the assigned APU operates per LTO, and the  emissions factors assigned to the APU. When assigning APU operating times per infrastructure considerations such as the availability of fixed  electrical ground power and pre- conditioned air, as well as meteorological conditions such as the annual temperature in the area,  43  FAA & EPA,  Technical Data to Support FAA’s Advisory Circular on Reducing Emissions from Commercial  Aviation,  September 29, 1995, http://www.epa.gov/oms/regs/nonroad/aviation/faa-ac.pdf.  44  EPA, Williams, Randall C., Honeywell Engines & Systems. Letter to Bryan Manning, September 29, 2000.  40$_{ }$ Auxiliary Power Units (APUs)  Ground Support Equipment (GSE)  Aviation Emissions and Air Quality Handbook 