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Evaporative related emissions are small due to the low vapor pressure of the fuel and quickconnect
refueling nozzles.
Procedures are set forth in EPA’s Procedures for Emission Inventory Preparation, Volume IV,
Chapter 5 for calculating military aircraft exhaust emission inventories of standard LTO
operations, which is the same detailed procedure used for commercial, general aviation, and air
taxi aircraft. Emissions are calculated for one complete LTO cycle of each aircraft type by
knowing the emission indices for the aircraft’s specific engines at each power setting or mode of
D-10
operation, as well as the time spent in each mode. The activity of aircraft for the inventory period
can then be applied to calculate their total emissions.
This EPA procedure addresses emissions from five operating modes of a standard LTO cycle:
approach, taxi/idle-in, taxi/idle-out, takeoff, and climbout. A sixth operating mode, reverse
thrust, often is included in a standard LTO cycle but is not included in EPA’s procedure. After
aircraft land, engine thrust reversal typically is used to slow the aircraft to taxi speed (otherwise
the aircraft is slowed using only the wheel brakes). Reverse thrust is now considered by EPA as
an official mode and should be included in calculation procedures as a sixth operating mode
when applicable. Since reverse thrust engine operating conditions are similar to takeoff, time
spent in reverse thrust should be combined with takeoff mode emission indices and fuel flow as a
means of accounting for reverse thrust mode emissions.
The emissions calculation methodology presented in EPA’s Procedure for Emission Inventory
Preparation estimates emissions for HC, CO, NOx, SO2, and PM-10. The NOx emission factors
provided in EPA’s procedures should be used to calculate a NOx emissions inventory that is used
to compare against NO2 emission standards. (When both nitric acid (NO) and NO2 are emitted,
they are referred to collectively as total oxides of nitrogen, or NOx.)
Not all aircraft operations follow the standard LTO cycle. The more detailed EPA procedures,
adjusted for the non-standard conditions, also can be used to calculate emissions from nonstandard
operations of military aircraft. Examples of non-standard operations include pilot
training, engine operation/testing, and the addition of an afterburn mode. In a training touch-andgo
operation, the taxi/idle mode is eliminated, the approach and climbout modes shortened, and a
“return flight” mode added (to allow the pilot to turn around and repeat the procedure). To
calculate the emissions from a touch-and-go, the taxi/idle mode should be eliminated from the
calculations. Rather than reducing the approach and climbout times and then adding additional
time for circling the airfield, the full approach and climbout times should be used (assuming this
will account for the additional flight time within the mixing zone).
D4.2 Data Sources
D4.2.1 Aircraft Type and Number of LTOs
For those operations that occur at military facilities, this data should be obtained from the base
operations sections. If the operation occurs at a civilian facility, this data should be obtained
from the individual airport.
D4.2.2 Engine Type and Number
A potential source of site-specific engine type and number data is the base operations section of
the air base where the operation occurred or the air base where the aircraft is stationed. If sitespecific
data is not available, default, typical aircraft-engine data is provided in the EPA’s
Procedures for Emission Inventory Preparation, Volume IV, Chapter 5 and the USAF’s The
Engine Handbook (Reference 44).
D4.2.3 Engine Emission Indices and Fuel Flow
Emission indices (i.e., emission factors) and average fuel consumption rates for aircraft engines
are listed by operating mode in EPA’s Procedures for Emission Inventory Preparation, Volume
IV, Chapter 5. Generally, emissions indices are listed by operating mode in pounds of pollutant
per 1000 pounds of fuel consumed and fuel flow is listed in pounds per minute. EPA’s
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Procedures document provides particulate emission factors, but data are available for only a
couple engines. A recent investigation of particulate emissions by EPA indicates that the
particulate emission factors can be used to calculate reasonable estimates of PM-10 emissions
from these engines. Until further data is available, PM-10 emission factors of engines for which
no data is available should be assumed to be zero. The EPA Office of Mobile Sources should be
contacted for additional guidance.
The Air Force is in the process of converting from JP-4 to JP-8 fuel. This conversion is expected
　
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