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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. 

## A2.3 Computing APU Emissions with EDMS/AEDT 

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. 

