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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. Aircraft reverse thrust typically is
applied for 15-20 seconds on landing.
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.)
D-6
D2.2 Data Sources
D2.2.1 Aircraft type and number of LTOs
Sources of site-specific aircraft fleet and activity data include published references, records of
aircraft and airport operators, and the Department of Transportation (DOT). Domestic carrier
aircraft fleet and activity data by airport and airline are reported to the FAA by certificated route
air carriers on FAA Form 41, Schedule T-3s: Airport Activity Statistics. FAA T-3 data are
available on data tape (Reference 64) or in FAA’s Airport Activity Statistics of Certificated
Route Air Carriers (Reference 53). The data also includes activity information for certificated
route air carrier operations at military air bases. Foreign carrier aircraft operations are available
from the DOT Bureau of Transportation Statistics. Conducting on-site activity monitoring and
contacting individual airports for data are alternative options for collecting domestic and foreign
data on aircraft type and operating frequency.
D2.2.2 Engine Type and Number
Site-specific engine data are not readily available, although it should be used if obtainable. If the
specific engine type is not known for an aircraft but the aircraft operator is known, an appropriate
surrogate engine can be chosen based on the operator’s national fleet. Domestic and foreign
airline fleet data that includes aircraft engine models are published in Bucher & Co.’s JP Airline-
Fleets International (Reference 2) and Jet Information Service’s World Jet Inventory (Reference
24). If the aircraft operator is not known, typical aircraft-engine combinations are provided in
EPA’s Procedure for Emission Inventory Preparation, Volume IV, Chapter 5. Finally, on-site
collection of engine type data is feasible but not recommended due to the difficulty in identifying
specific engine models.
D2.2.3 Engine Emission Indices and Engine 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 and in the ICAO Engine Exhaust Emissions Databank (Reference 27). Generally,
emission factors are listed in pounds of pollutant per 1000 pounds of fuel consumed and fuel
flow is listed in pounds per minute. Only EPA’s Procedures document provides particulate
emission factors, and data are available for only a few 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. Neither
source provides SOx emission factors. A SOx emission factor of 0.54 lb/1000 lb can be used for
most air carrier aircraft, which is based on a national average sulfur content of aviation fuels.
As mentioned above, reverse thrust mode is not included in EPA’s methodology. There also are
no specific reverse thrust emission factors available. Takeoff emission indices and fuel flow
should be used as inputs for calculating emissions from reverse thrust (as well as takeoff) mode.
D2.2.4 Time in Mode
There are six possible operating modes of aircraft standard LTO cycles: approach, taxi/idle-in,
taxi/idle-out, takeoff, climbout, and reverse thrust (if applicable). the time an aircraft operates in
each mode depends on a variety of factors and should be adjusted to represent local conditions
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