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Explora: Environment
and Resource WTW emissions of road, rail, sea, and air transport

2.5.2. Air transport of a mission input file is shown in Table S3b. Variable taxi-

The methods available for estimating aircraft FC and out (triangular distribution T: 5, 30, and 10 min, defined
emissions include analysis of payload-range diagrams, 25-27 as T: min, max, and mode) and taxi-in (T: 5, 10, and
average flight emission estimates, 28-30 and detailed in-flight 6 min) phases were added in the simulation to construct
a complete operational profile that defined taxi time, true
emission models. 31-33 For this study, the Air Transport
Emission Model (ATEM) was used. ATEM uses an air speed, phase distance traveled, and average altitude.
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approach that strikes a balance between a complex and Relevant atmospheric conditions at different altitudes
detailed high-resolution FC and emissions simulation, and (temperature, density, and pressure) were obtained,
high-level average flight emission estimates. assuming (still air) International Standard Atmosphere
(ISA) conditions (Table S3c).
ATEM simulated aircraft tank-to-wing FC over a full
Two operational aircraft modes were modeled,
operational profile for both aircraft types and for engine reflecting two commonly used aircraft in Australia and
combinations with available input parameters. An example different engine options:
of an aircraft/engine input file is shown in Table S3a. FC
during the taxi-in and taxi-out modes was estimated • Mode 1: Fully-laden and maximum mass aircraft
for the varying taxi times using corresponding aircraft/ (i.e., maximum take-off weight, MTOW); 70 t for a
B737 and 78 t for an A320, which would include both
engine-specific FC rates. For the other non-cruise phases, passengers and cargo or, alternatively, just cargo, and
FC was estimated using the fuel fraction method, which where the mass of on-board fuel could be estimated
is expected to provide reasonably accurate and robust before the simulation
results. This approach assumes that a certain percentage • Mode 2: Variable payload (either passengers only or
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of aircraft mass was used as fuel from take-off (end of taxi-
out) to cruise conditions and that a certain percentage of cargo only), reflecting the plausible range in the load
factor, and where the mass of on-board fuel was not
aircraft mass was used as fuel from cruise conditions to known before the simulation and required model
landing (start of taxi-in).
iteration.
FC during the cruise mode was simulated in more The second mode required an iterative simulation, in
detail. In-flight cruise describes the portion of a flight which the initial (seed) fuel burn for the flight and extra
from the point where the aircraft has leveled off following fuel was repeatedly replaced with recomputed fuel burn
a climb to its initial cruising altitude until the point where until the simulation converged and the prediction error
it commences its descent. Under cruise conditions, the was negligible (<0.01%).
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aircraft mass is constantly decreasing due to fuel being The great circle distance (GCD) between Brisbane
consumed, and the effect of this reduction in mass on and Melbourne was estimated to be between 1,379 and
FC itself is significant, in contrast to other transport 1,382 km (https://www.airportdistancecalculator.com/
modes. This was simulated on a continuous basis using a brisbane-australia-to-melbourne-australia-flight-time.
total energy approach. 32,36 Assuming a constant air speed html). Actual flight distance is subject to a wide range of
and altitude under cruise conditions, the drag force on influences, such as air traffic control constraints, restricted
an aircraft is equal to the net thrust. FC could then be air space, and prevailing winds. The International Civil
estimated for each minute after considering the change in Aviation Organization (ICAO) allows for this by adding
aircraft mass.
100 km to the GCD for flights with GCD values between
The prediction of formulas and associated aircraft/ 550 and 5,500 km, which, in this case, added 7% to the
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engine parameters was obtained from various total flight distance (U: 1,479 and 1,482).
studies. 25,32,35-39 A full list of ATEM model inputs and model The impact of headwinds or tailwinds – defined as the
variables is presented in Table S4. The FC estimates for the ratio of air distance to ground distance – varies between 0.7
various flight modes were combined, and the result was and 1.6. In reality, this will depend on local wind fields,
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multiplied by 3.16 to convert it to CO -e emissions. 28 which, in turn, depend on time of year, hour of day, and so
2
A typical operational profile was constructed using forth. For this study, the potential impact of (vectorized)
information from the Eurocontrol aircraft performance headwind or tailwind during a flight was modeled as the
database, which describes relevant parameters for ten ratio of air distance to ground distance and was assumed
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flight phases from take-off to landing, including cruise to vary between 0.9 and 1.1 with a triangular distribution
and climb/descent to different flight levels. These include (T: 0.90, 1.10, and 1.00). After applying the corrections for
aircraft-specific parameters such as indicated air speed, GCD and wind speed, the total flight distance (in the air)
rate of climb, cruise speed, and rate of descent. An example varied between 1,334 and 1,628 km, with a mean value

Volume 1 Issue 1 (2024) 6 doi: 10.36922/eer.3471