APPENDIX C$_{ }$ 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.  Fuel Usage (gallons)  = (463.4 pounds per hour x 1 hour per 3600 seconds x 2 seconds x number of  engines in the ICAO Engine Exhaust Emissions Databank / 6.84 pounds per gallon) + (829 pounds per  hour x 1 hour per 3600 seconds) x 40 seconds x number of engines in the ICAO Engine Exhaust  Emissions Databank / 6.84 pounds per gallon)  Equation C-4. Aircraft Engine Startup Jet A Fuel Usage  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.  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  C.2.2 Auxiliary Power Units  Equation C-5. CO$_{2e }$Emission Calculation for Turbine Aircraft during Startup (Jet A)  65$_{ }$ CO$_{2 }$(metric tons)  =  Fuel Usage (gallons) x 21.098 pounds CO$_{2 }$per gallon x short ton per 2,000 pound  x 0.907185 metric ton per short ton  CH$_{4 }$(metric tons)  =  Fuel Usage (gallons) x 0.000595 pounds CH$_{4 }$per gallon x short ton per 2,000  pound x 0.907185 metric ton per short ton  N$_{2}$O (metric tons)  =  Fuel Usage (gallons) x 0.000683 pounds N$_{2}$O per gallon x short ton per 2,000  pound x 0.907185 metric ton per short ton  CO$_{2e }$(in metric tons) = CO$_{2 }$+ CH$_{4 }$x 34 + N$_{2}$O x 298 