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main engines, provide electrical power to aircraft electronics, and to power the onboa rd air conditioning (heating and cooling) systems. 

Again, the computation and data inputs of APU fuel usage for computing GHGs is similar to that uses for computing APU criteria pollutants (see Appendix A2 , Auxiliary Power Units Emissions Inventory for Criteria Pollutant ). As discussed, EDMS/AEDT contains a database of aircraft and APU assignments as well as fuel flow rates (typically ranging from 50 to 860 pounds per hour) for the designated APU. However, EDMS/AEDT does not report this fuel usage. 

Therefore, APU fuel usage should be estimated based on the APU assignment, the fuel flow rate, the operating time, the number of operations, and fuel density. APU operating times (arrival plus departure) typically range from 7 to 26 minutes depending on gate infrastructure and airport operations. Table C-2 ( APU Fuel Usage Rates ) presents the APU fuel flow rates for the 38 units within EDMS/AEDT. 

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