Data Inputs  Description  Source  aircraft should be used.  Emission Factors  and Fuel Flow  Emission factors and fuel flow vary by  APU model. APU emission fact ors  generally are in pounds of polluta nt  per 1000 pounds of fuel consume d.  APU fuel flow typically is in pounds per minute of usage.  Potential sources of additional emission fuel flow data are APU engine manufacturers. Where  data are unavailable for a specific APU, data for an  alternative unit of the same or similar should be used. Otherwise default emission factors and fuel flows within FAA’s EDMS /AEDT can be used.  Operating Time  The APU operating time for the  aircraft  arrival/departure  must  be known to calculate emissions . This includes time the APU operates while  parked at a gate or parking sp ace,  during aircraft or APU maintenan ce, and  during  aircraft  taxi. APU  operating  time  varie s  by  arrival/departure,  aircraft,  operat or,  and airport.  Potential sources of site-specific APU operating time  data are individual aircraft operators at airports or in- the-field measurements.  If no information is available, EDMS /AEDT default  values of 13 minutes per arrival and 13 minutes per  departure can be used. If gate available, then a value of 3.5 minutes per arrival and  3.5 minutes per departure can be used.  Source: FAA,  Emissions and Dispersion Modeling System (EDMS) User’s Manual , [FAA-AEE-07-01 (Rev. 10 – 06/07/13)],  June 2013,  http://www.faa.gov/about/office_org/headquarters_offices/apl/research/models/edms_model/media/EDMS_5.1.4_User_Manual  .pdf.  EDMS/AEDT assigns a default APU based on aircraft/engine assignments and also includes  criteria pollutant emission factors corresponding to the horsepower for each unit. The user can  specify the number of minutes the APU will operate during both arrivals and departures.  EDMS’s/AEDT’s default values are 13 minutes for each operating cycle (i.e., during arrival and  departure), which represents the operating time without PCA/400 Hz.  As previously mentioned, in the absence of an APU a combination of 400 Hz electric power and  PCA can be supplied to the aircraft using a fixed system at each gate to allow for operation. Fixed systems usually generate little or no emissions at the airport and  therefore are  not included into EDMS/AEDT. Operating times of 3.5 minutes for each operating cycle (i.e.,  during arrival and departure) represents the operating time with PCA/400 Hz.  A2.3  Computing APU Emissions with EDMS/AEDT  APPENDIX A2$_{ }$ 12$_{ }$