Choice of activity data

Since emissions from domestic aviation are reported separately from international aviation, it is necessary to disaggregate activity data between domestic and international components. For this purpose, the following definitions should be applied irrespective of the nationality of the carrier (Table 3.6.6). For consistency, it is good practice to use similar definitions of domestic and international activities for aviation and water-borne navigation. In some cases, the national energy statistics may not provide data consistent with this definition. It is good practice that countries separate the activity data consistent with this definition. In any case, a country must clearly define the methodologies and assumptions used.

Table 3.6.6

Criteria for defining international or domestic aviation (applies to individual legs of


Journey type between two airports



Departs and arrives in same country



Departs from one country and arrives in another



Based on past experience compiling aviation emissions inventories, difficulties have been identified regarding the international/domestic split, in particular obtaining the information on passenger and freight drop-off and pick up at stops in the same country that was required by the 1996IPCC Guidelines/GPG2000 (Summary report of ICAO/UNFCCC Expert Meeting April 2004). Most flight data are collected on the basis of individual flight segments (from one take-off to the next landing) and do not distinguish between different types of intermediate stops (as called for in GPG2000). Basing the distinction on flight segment data (origin/destination) is therefore simpler and is likely to reduce uncertainties. It is very unlikely that this change would make a significant change to the emission estimates.19 This does not change the way in which emissions from international flights are reported as a memo item and not included in national totals.

Improvements in technology and optimization of airline operating practices have significantly reduced the need for intermediate technical stops. An intermediate technical stop would also not change the definition of a flight as being domestic or international. For example if explicit data is available, countries may define as international flight segments that depart one country with a destination in another country and make an intermediate technical stop. A technical stop is solely for the purpose of refuelling or solving a technical difficulty and not for the purpose of passenger or cargo exchange.

If national energy statistics do not already provide data consistent with this definition, countries should then estimate the split between domestic and international fuel consumption according to the definition, using the approaches set out below.

Top-down data can be obtained from taxation authorities in cases where fuel sold for domestic use is subject to taxation, but that for international use is not taxed. Airports or fuel suppliers may have data on delivery of aviation kerosene and aviation gasoline to domestic and to international flights. In most countries tax and custom dues are levied on fuels for domestic consumption, and fuels for international consumption (bunkers) are free of such dues. In the absence of more direct sources of data, information about domestic taxes may be used to distinguish between domestic and international fuel consumption.

Bottom-up data can be obtained from surveys of airline companies for fuel used on domestic and international flights, or estimates from aircraft movement data and standard tables of fuel consumed or both. Fuel consumption factors for aircraft (fuel used per LTO and per nautical mile cruised) can be used for estimates and may be obtained from the airline companies.

Examples of sources for bottom-up data, including aircraft movement, are:

• Statistical offices or transport ministries as a part of national statistics;

• Airport records;

• ATC (Air Traffic Control) records, for example EUROCONTROL statistics;

It is good practice to clearly state the reasoning and justification if any country opts to use the GPG2000 definitions.

• Air carrier schedules published monthly by OAG which contains worldwide timetable passenger and freight aircraft movements as well as regular scheduled departures of charter operators. It does not contain ad-hoc charter aircraft movements;

Some of these sources do not cover all flights (e.g. charter flights may be excluded). On the other hand, airline timetable data may include duplicate flights due to codeshares between airlines or duplicate flight numbers. Methods have been developed to detect and remove these duplicates. (Baughcum et al., 1996; Sutkus et al, 2001).

The aircraft types listed in Table 3.6.9, LTO Emission Factors were defined based on the assumptions listed below. Aircraft were divided into four major groups to reflect and note the distinct data source for each group:

Large Commercial Aircraft: This includes aircraft that reflect the 2004 operating fleet and some aircraft types for back compatibility, identified by minor model. It was felt that this method would most accurately reflect operational fleet emissions. To minimize table size, some aircraft minor models were grouped when LTO emissions factors were similar. The Large Commercial Aircraft group LTO emissions factors data source is the ICAO Engine Exhaust Emissions Data Bank (ICAO, 2004a).

Regional Jets: This group includes aircraft that are representative of the 2004 operating Regional Jet (RJ) fleet. Representative RJ aircraft were selected based on providing an appropriate range of RJ aircraft with LTO emissions factors available. The RJ group LTO emissions factors data source is the ICAO Engine Exhaust Emissions Data Bank (ICAO, 2004a).

Low Thrust Jets: In some countries, aircraft in the low thrust category (engines with thrust below 26.7 kN) make up a non-trivial number of movements and therefore should be included in inventories. However, aircraft engines in this group are not required to satisfy ICAO engine emissions standards, thus LTO emissions factors data are not included in the ICAO Engine Exhaust Emissions Data Bank and difficult to provide. Therefore, there is one representative aircraft with typical emissions for aircraft in this group. The Low Thrust Jets group LTO emissions factors data source is the FAA's Emissions and Dispersion Modelling System (EDMS) (FAA 2004b).

Turboprops: This group includes aircraft that are representative of the 2004 Turboprop fleet, which can be represented by three typical aircraft size based on engine shaft horsepower. The Turboprop group LTO emissions factors data source is the Swedish Aeronautical Institute (FOI) LTO Emissions Database.

Similar data could be obtained from other sources (e.g. EEA, 2002). The equivalent data for turboprop and piston engine aircraft need to be obtained from other sources. The relationship between actual aircraft and representative aircraft are provided in the Table 3.6.3.

Aircraft Fleet data may be obtained from various sources. ICAO collects fleet data through two of its statistics sub-programmes: the fleet of commercial air carriers, reported by States for their commercial air carriers, and civil aircraft on register, reported by States for the civil aircraft on their register at 31 December (ICAO 2004b).

Some ICAO States do not participate in this data collection, in part because of the difficulty to split the fleet into commercial and non-commercial entities. Because of this, ICAO also makes use of other external sources. One of these sources is the International Register of Civil Aircraft, 2004, published by the Bureau Veritas (France), the CAA (UK) and ENAC (Italy) in cooperation with ICAO. This database contains the information from the civil aircraft registers of some 45 States (including the United States) covering over 450 000 aircraft.

In addition to the above, there are commercial databases of which ICAO also makes use. None of them cover the whole fleet as they have limitations in scope and aircraft size. Among these one can find the BACK Aviation Solutions Fleet Data (fixed wing aircraft over 30 seats), AirClaims CASE database (fixed wing jet and turboprop commercial aircraft), BUCHAir, publishers of the JP Airline Fleet (covers both fixed and rotary wing aircraft). Other companies such as AvSoft may also have relevant information. Further information may be obtained from these companies' websites.

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