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Where: 

463.4 pounds per hour and 2 seconds is fuel flow rate and duration, respectively, for the first phase of startup. 

829 pounds per hour and 40 seconds is fuel flow rate and duration, respectively, for the second phase of startup. 

Aircraft engine startup mode is divided into two fractions: (1) the raw fuel released prior to ignition, and (2) the products of incomplete combustion during the acceleration to idle power . The latter fraction contributes the most fuel usage. Equation C-4 ( Aircraft Engine Startup Jet A Fuel Usage ) presents the fuel usage calculations of Jet A from both fractions in gallons. During the first phase, 463.4 pounds per hour and 2 seconds is fuel flow rate and duration, respectively. During the second phase, 829 pounds per hour and 40 seconds is fuel flow rate and duration, respectively. The other input data is the number of engines. 

Once the engine startup fuel usage (in gallons) is determined, Table C-1 ( GHG Emission Factors for Aircraft Fuel ) and Equation C-5 ( CO$_{2e }$ Emission Calculation for Turbine Aircraft during Startup ) should be used to determine the CO$_{2}$, CH$_{4}$, and N$_{2}$O emissions, which should then be adjusted to account for GWP with a result of CO$_{2e }$(in metric tons). Equation C-5 ( CO$_{2e }$ Emission Calculation for Turbine Aircraft during Startup ) provides an example for Jet A. 

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## C.2.2 Auxiliary Power Units 

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The following section discusses the methodology for computing GHG emissions from aircraft APUs. APUs consist of small turbine engines used by many commercial jet aircraft to start the 

