COMPARING THE ENVIRONMENTAL IMPACT FROM USING LARGE AND SMALL PASSENGER AIRCRAFT ON SHORT HAUL ROUTES

Transcription

1 COMPARING THE ENVIRONMENTAL IMPACT FROM USING LARGE AND SMALL PASSENGER AIRCRAFT ON SHORT HAUL ROUTES Moshe Givoni Transport Studies Unit Oxford University Centre for the Environment Piet Rietveld Department of Spatial Economics, Free University Working paper N 1033 June 2008 Transport Studies Unit Oxford University Centre for the Environment

2 Comparing the environmental impact from using large and small passenger aircraft on short haul routes Moshe Givoni * Transport Studies Unit, Oxford University Centre for the Environment South Parks Road, Oxford, OX1 3QY, UK Tel: +44 (0) Piet Rietveld Department of Spatial Economics, Free University De Boelelaan 1105, 1081 HV, Amsterdam, The Netherlands Phone: ; Fax: Abstract One of the main outcomes of open skies policies is the importance of service frequency in the competition between airlines. To keep load factors high while offering high frequency service, airlines tend to reduce the size of the aircraft used. On short haul routes this phenomenon is even more apparent, especially on routes between hub airports, even though these routes and airports are often congested. This choice of service frequency and aircraft size must have important environmental consequences that this paper aims to evaluate and quantify. The analysis considers local air pollution (LAP), climate change and noise impacts and aims to evaluate whether the competitive environment which drives airlines to offer high frequency service carries an environmental penalty. The analysis showed that increasing aircraft size and adjusting the service frequency to offer similar seating capacity will increase LAP but decrease climate change impact and noise pollution. When LAP and climate change impacts are monetized and aggregated the analysis showed that environmental benefits will result from increasing aircraft size. But these benefits, in monetary terms were found to be relatively small and sensitive to the assumptions made. The conclusion is that to make better use of available runway capacity and to reduce the environmental impact from aircraft operation, especially at large airports, the development of a large (wide body) aircraft designed for short haul operation is recommended. 1. Airlines choice of aircraft size In the summer of 2006 airlines operating between the London airports and Amsterdam Schiphol (371 km great circle distance) have been offering 55 daily oneway services, using aircraft with an average seating capacity of 125. Between Heathrow and Schiphol alone, there were 26 daily one-way services, and these were offered by an aircraft fleet with an average capacity of 143 seats. If airlines have utilised a fleet of wide-body aircraft instead of narrow-body aircraft a much lower frequency of service would have been required to offer similar seating capacity. This could have freed scarce runway and air space capacities and could have reduced congestion at these airports. At the other side of the world, Japanese airlines operating between Tokyo and Sapporo, also a short haul route in airlines terms (820 km great circle distance), offered 51 daily one-way services but utilising a fleet of aircraft with an average capacity of 395 seats. Most of these services were provided by a high seating capacity version of the Boeing 747. * Corresponding author. moshe.givoni@ouce.ox.ac.uk,

3 On most routes airlines choice of aircraft is relatively limited, partly due to the bundling of size and range in aircraft development (Wei and Hansen, 2003). On long haul routes the choice will be limited to the wide-body (large) aircraft, those with a high range. On many short haul routes demand will not be enough to support large capacity aircraft, nor high frequency service. It is on the short haul high density routes, such as the London-Amsterdam or Tokyo-Sapporo, where airlines have a real choice. An analysis of short-haul routes around the world revealed that the London- Amsterdam route is the general rule while the Tokyo-Sapporo route is the exception Givoni and Rietveld (2007). In general, airlines opt for high frequency and small aircraft rather than lower frequency and larger aircraft when demand is relatively high on short haul routes. An empirical examination of airlines choice of aircraft size in airports and (short-haul) routes around the world found that the main explanation for the choice of high frequency and small aircraft is the importance of service frequency in airlines competition. To keep frequency high while striving to maintain high load factor, airlines must reduce aircraft size. Other contributing factors are the route density, distance and whether the airport is a hub (Givoni and Rietveld, 2007). The choice of aircraft size and service frequency by airlines must have environmental implications which this paper aims to investigate. The analysis considers local air pollution (LAP), climate change and noise impacts. The aim is to evaluate whether the competitive environment which drives airlines to offer high frequency service carries an environmental penalty. Over the next 20 years, European air traffic is forecast to continue growing. According to Airbus (2007), Intra-Western Europe traffic will grow on average by 3.8% each year in the next 20 years, bringing the revenue passenger km (RPK) from over 400 billion in 2007 to about 1000 billion in To this a 6.6% annual growth in RPK is forecast for Central Europe Western Europe traffic (RPK in 2026 over 200 billion) and 3.5% growth in Domestic European traffic (just under 200 billion RPK in 2026). What pattern of service frequency and aircraft size airlines will adopt to transport this demand has important implications for airport planning and for aircraft operation impact on the environment. The focus of the paper is on the environmental perspective, other issues, like customers benefits from a high level of service, are put aside and are not dealt with at this stage. The remainder of the paper is arranged as follows. In section 2 the aircraft chosen for the analysis and data issues are described. Section 3, 4 and 5 describe the analysis for LAP, climate change and noise respectively. In Section 6 the results are applied to case study routes and in Section 7 conclusions are drawn. The complexity of evaluating aircraft operation impact on the environment requires the methodology and data used to be clearly detailed, therefore large parts of the paper are devoted to this. 2. The choice of aircraft for analysis Aircraft size (measured in seats per service) can be divided into two groups: the single-aisle aircraft (also termed narrow-body aircraft and referred to here as small ) and the twin-aisle aircraft (also termed wide-body aircraft and referred to here as large ). To compare the environmental impact from the operation of small and large

4 aircraft representative model was selected for each group. The Airbus A (henceforth A320) is selected as a typical narrow-body (small) aircraft and the Boeing B (henceforth B747) as a typical wide-body (large) aircraft. These aircraft are amongst the most used aircraft in the world. In May 1999, the A320 accounted for 4.4% and 5.5% of the global aircraft departures and the distance flown by scheduled civil aircraft respectively. In that period, the B747 accounted for only 1.4% of the global aircraft departures but for 8.1% of the global distance flown by scheduled civil aircraft (Sutkus et al., 2001). The main characteristics of these aircraft are summarised in Table 1. The aircraft entered service about the same time and therefore represent similar level of technological development with respect to engines (the chosen engines are considered to be the basic version for these models), aerodynamic design and weight. In addition to the A320 and the B747, two additional aircraft are considered, the narrow-body Airbus A (entered service on May 1996, typical capacity of 124 seats, 2 CFM56-5B5 engines) and the wide-body Airbus A (entered service on January 1994, typical high density 2-class capacity of 335 seats, 2 CF6-80E1A2 engines). Table 1: Main characteristics of the Airbus A320 and the Boeing B747 aircraft Aircraft A320 B747 Manufacturer Airbus Boeing Model Entered service November 1988 February 1989 Maximum Take-Off Weight (MTOW) 77,000 kg 396,890 kg Engine model (no. of engines) CFM56-5A1 (2) CF6-80C2B1F (4) Engine thrust kn kn Seating capacity 150 (2-class) 164 (1-class) Source: aircraft manufacturers 416 (3-class) 524 (2-class) 568 (B D, 3-class) Despite advances in methods to evaluate transport operation impact on the environment, many scientific uncertainties remain, especially with regard to air transport operation impact on the environment. In this analysis these issues are of less concern since the focus is on the differences between different aircraft and less on the actual level of impact and there is no reason to assume a bias in current understandings towards a specific type of aircraft. In addition, very often the analysis of environmental impact is limited by data availability. Also this is not a major limitation in the current analysis since emission data for the certification of different aircraft engines are provided on the ICAO engine exhaust data bank 1. One major limitation with respect to the data does hold. The bundling of size and range in aircraft development means that large aircraft are normally deployed on longdistance routes only 2 and therefore the available data is based on the assumption that large aircraft are operating on long-haul routes and therefore carry on take-off the amount of fuel needed for that. This limitation is, for example, apparent in the 1 Hosted on the UK CAA web site ( 2 The average range for the worlds B747 fleet is 5,632 km compared to 1243km for the A320 - Sutkus et al. (2001).

5 EMEP/Corinair emission inventory guidebook (EEA, 2005) where fuel consumption and emission rates during the landing and take-off cycle remain the same when the assumed range is changed. To a large extent, therefore, the analysis here compares small aircraft flying short haul and large aircraft flying short haul but with fuel (and engine thrust at take-off) as if they were flying long haul. Attempts to overcome this limitation are described below. The size of aircraft depends not only on the model used but also on the seating configurations adopted by each airline. Usually two seating configurations are considered. For short haul flights these are 1-class (high density) and 2-class (standard) configurations and for long haul these are 2-class (high-density) and 3- class (standard) configurations. On hub-to-hub routes, the focus of this paper, lowcost carriers do not usually operate and the standard 2-class configuration is most common. If airlines will use large aircraft on short-haul routes there will probably not be demand for first-class reclining seats and therefore the 2-class configuration is assumed. The Japanese domestic market is an exception in this respect. On this market large aircraft are commonly deployed on short haul routes and in a very high seating capacity (this practice is also evident in other Far Eastern markets). The B D variant (D for Domestic, henceforth B747D) was developed by Boeing (mainly) for the Japanese domestic market, and its typical seating capacity is 568 seats 3. Other than the higher seating capacity, it is similar to the basic B , including similar engines. 3. Local Air Pollution (LAP) Aircraft are considered to impact LAP only when operating inside the Landing Take- Off (LTO) cycle. This cycle consists of four stages: take off, climb (up to 3,000ft), approach (from 3,000ft to landing) and idle (when the aircraft is taxiing or standing on the ground with engines on). It is within this part of the flight that aircraft emission standards are measured. The 3000ft (approximately 915m) boundary is the standard set by the ICAO for the average height of the mixing zone, the layer of the earth atmosphere where chemical reactions of pollutants can ultimately affect ground level pollutant concentrations (EPA, 1999a). The ICAO also set a standard profile for the LTO cycle with engine power settings and time for each stage, which is the basis for aircraft emission measurement and engine certification. The ICAO engine exhaust data bank is used for the analysis below. The data refer to engine performance: 100% power is assumed for take-off, 85%, 30% and 7% for the climb, approach and idle stages. Therefore, the route flown and the aircraft weight at take-off are not accounted for, a limitation mentioned above. SO 2 emission and Particulate Matter (PM) emission are major contributors to LAP (EPA, 1999b), but they are (still) not part of the engine certification process. Emission of these pollutants is directly related to fuel consumption and therefore can be incorporated in the analysis. The emission factors assumed are 0.8 grams SO 2 emission per kg of fuel consumed (Sutkus et al., 2001) and 0.2 grams per kg of fuel consumed for PM emission (Dings et al., 2003). 3 Its maximum seating capacity is considered to be 660 seats.

6 Table 2: Fuel consumption and emission per seat during the LTO cycle Aircraft (seats) Fuel (kg) HC (g) CO (g) NOx (g) SO 2 (g) PM 2.5 (g) A (150) A (164) B (524) B D (568) A (124) A (335) Fuel consumption can be a good indication for environmental impact since in general the higher this is the higher is the level of emission. It is clear from Table 2 that the narrow-body aircraft outperforms the wide-body aircraft even when the latter are in high-seating configuration. More important, however, is the mix of gases emitted. The operation of the A320 results in less emission than the operation of the B747D (and therefore also the B747) across all the gases/pollutants, with the exception of HC emission. The newer and smaller A319 consumes more fuel per seat than the base aircraft, the A320, and therefore might be considered to contribute more to LAP, but it emits less HC and NOx, so a conclusion cannot be made. The A320 also outperforms the wide-body A330 across all the criteria measured, also when assuming a high-seating configuration of 360 seats for the A330 (such a configuration is not known to be used by any airline). The most common way to compare between emissions of different gases/pollutants is to evaluate the cost of damage they impose. Such estimates are provided by Dings et al. (2003) and were applied to the emission levels reported in Table 2. The cost of LAP from the operation of different aircraft is given in Table 3. Carbon Monoxide (CO) emissions from aircraft operation do not appear to result in substantial health effects and therefore a cost estimate for emission of this gas is not provided (Dings et al., 2003). The results show that the cost of LAP from aircraft operation during the LTO cycle depends very much on the volume of NOx emission. Emission of PM is the second most important contributor to LAP from aircraft operation around airports. The cost analysis shows that smaller aircraft outperforms the larger ones, even when the latter are in high seating capacity configuration. Although the operation of the smaller and newer A319 requires more fuel per seat for the LTO cycle, the fact that the A319 emits less NOx means its impact on LAP is smaller than that of the A320 (when it is in standard seating configuration). However, the cost of LAP from the operation of the A330 is higher than the cost from the bigger and older B747, due to lower emission of NOx from the latter. As noted, the data used do not account for the route distance and the different weight at take-off this will imply. Lower weight, especially at take-off implies lower engine thrust and lower emission. To try and account for this in the analysis two approaches are pursued. First, accounting only for the approach stage of the LTO cycle when comparing between aircraft. On the approach stage it can be assumed that an aircraft have used the fuel required to fly up to that point and therefore, in comparing between large and small aircraft, there is no penalty for large aircraft for flying further. The

7 A320 (150 seats) consumes 0.93 kg fuel per seat on the approach compared with 1.19 kg for the B747 (524 seats). On approach, the A320 emits almost half the NOx emission emitted from the B747 (7.45 gr/seat and gr/seat for the A320 (150 seats and the B747 (524 seats) respectively). Overall on the approach stage, the cost of LAP from the A320 (150 seats) is 45% lower the cost of LAP from the B747 (524 seats). This supports the conclusion reached above that the operation of narrow-body aircraft results in less LAP than the operation of wide-body aircraft. Table 3: The cost of LAP from aircraft operation during the LTO cycle (Euro/seat) Euro/kg * Aircraft (seats) HC NOx SO 2 PM 2.5 Total A (150) A (164) B (524) B D (568) A (124) A (335) * Data on the cost of emission are based on Dings et al. (2003). The second approach is to assume lower engine thrust at take-off for large aircraft. In a study for Heathrow airport (AEA Energy & Environment, 2007) it was noted that typically, for large jets, actual take-off thrust lies between 75% and 90% of maximum thrust and not the 85% to 100% assumed in the ICAO database. The AEA Energy & Environment (2007) report notes that the lower limit on engine thrust at take-off is between 75% and 80%. For take off thrust between 80% and 90% the report suggests to assume climb thrust of 78% and for take off thrust between 75% and 80% the report suggests to assume climb thrust of 70%. The report also states that linear interpolation between 100% and 85% thrust has good accuracy in this range (p. 6). To calculate emissions assuming different engine thrusts, interpolation or extrapolation from the engine emission standards given for engine thrusts of 100% and 85% were used. A sensitivity analysis shows that under some assumptions on engine thrusts at the take off and climb stages of the LTO cycle using large rather than small aircraft can result in lower LAP (Table 4). Yet, given that the maximum range of the A320 is above 5000 km (when fully loaded) we can assume that on most short haul flights a lower than 100% engine thrust is necessary at take off. In that case, the conclusion that the operation of A320 results in lower LAP than that from the operation of B747 still holds. Assuming large aircraft flying short haul will operate with lower engine thrusts than those assumed by ICAO for the standard LTO cycle, the differences between large and small aircraft almost diminish, to less than 10% difference in cost of LAP during the LTO cycle, mainly due to reduction in NOx emission 4. In the context of the analysis, the second approach (assuming lower engine thrust at take-off) seems better 4 NOx emissions depend on engine temperature which in turn depends on engine power - the higher the combustion temperature, i.e. the engine thrust, the higher are the resulting NOx emissions.

8 than comparing aircraft on the approach stage, and this approach suggests the differences between large and small aircraft are relatively small. Table 4: The cost of LAP from aircraft operation during the LTO cycle for different engine thrusts at take off (Euro/seat) Aircraft (seats) Engine Thrust (%) Take-off + Total for Take-off Climb climb LTO A (150) B (524) B D (568) The above analysis demonstrated that under current design and technology used to build large and small aircraft there is no environmental benefit from operating large (wide-body) aircraft on short-haul routes rather than operating small (narrow-body) aircraft. There is actually an environmental penalty from switching to large aircraft. When comparing the A320 (150 seats) with the B747 (524 seats) the benefits per seat amount to 19% lower fuel consumption during the LTO cycle, which translates to 27% lower LAP in monetary terms (mostly associated with lower NOx emission for the larger aircraft). This is based on ICAO LTO cycle standards, but the differences in reality are probably smaller (see Table 4). 4. Climate change To account for aircraft operation impact on climate change the whole flight must be accounted for, from engines-on to engines-off position. Thus, to fuel consumption and emission during the LTO cycle the rest of the flight must be added. This includes climb from 3000 ft (the LTO boundary) to cruise altitude, the cruise stage and the descent stage to 3000 ft where the approach stage of the LTO cycle begins. To measure aircraft operation impact on climate change the flight profile must be determined given the route distance. Eurocontrol Experimental Centre (2004) provides aircraft performance summary tables where fuel use for every flight level, for the climb, cruise and descent stages, is indicated for different aircraft. Using this, and assuming a cruise level of ft and a medium range route of 500 nm (927.5 km), fuel consumption is calculated. Under the above assumptions, climb from zero to cruise altitude will take minutes, cruise time will be 40.1 minutes and the descent to sea level minutes 5. The data provide fuel flow rates at cruise for three categories of mass (low, nominal and high) for each aircraft type, but not for different engine thrusts. For the large aircraft the low mass was assumed and for the small aircraft the nominal mass, to try and correct for the lighter weight of large aircraft flying short rather than long haul flight. 5 These data were obtained from Eurocontrol Experimental Centre by exchange.

9 Current aircraft engine certification procedures include emission standards for the LTO cycle only. Therefore, emissions outside the LTO cycle are not measured as part of the engine certification procedure and such data are not readily available. To overcome this, fuel consumption for the entire flight is calculated which serves as the basis for emission calculation using different emission indices. The indices available for this research do not distinguish between different types of aircraft making fuel consumption the only important basis to compare large and small aircraft. The results are presented in Table 5. Overall, based on fuel consumption, large aircraft appear to have lower impact on climate change, per seat, than the smaller aircraft. This conclusion is sensitive to the seat capacity assumed. For a flight distance of 500nm, the cruise stage is the most substantial in terms of fuel consumption (Table 5). In cruise stage, using the B747D rather than the A320 in 2-class configuration will result in over 10% reduction in fuel consumption per seat. The A330, in 2-class configuration, is more fuel efficient than the A320 and the A319 models. The descent from cruise stage has a relatively minor contribution to fuel consumption and the differences between aircraft are not large. More important is the climb stage, and its importance increases with decrease in the flight range 6. Per seat, overall the B747 and the A330 outperforms, in terms of fuel consumption, the smaller A320 and A319 when these are in 2-class configuration. Table 5: Fuel consumption during a 500nm (927.5 km) flight (kg/seat) Aircraft (seats) LTO Climb Descent Cruise Total A (150) A (164) B (524) B D (568) A (124) A (335) Note: climb is from 3000 ft (boundary of the LTO cycle) to cruise level, cruise is at ft and decent is from ft to 3,000 ft (start of LTO cycle). To calculate the impact on climate change the fuel consumed was converted to emissions and then to the cost of climate change. Aircraft operation impact on climate change is related mainly to CO 2, NOx and H 2 O emission. CO 2 and H 2 O emissions are directly related to fuel consumption and therefore can be estimated accurately. A ratio of 3.15kg per kg of fuel is used for CO 2 emission (Sutkus et al., 2001; Dings et al., 2003) and 1.237kg per kg of fuel is used for H 2 O (EEA, 2005). NOx emission is not directly related to fuel consumption but depends on combustion temperature which increases with engines power setting. Sutkus et al. (2001) provide emission indices for different aircraft/engine combination calculated as part of the scheduled civil aircraft emission inventories for For NOx emission two indices are given for each aircraft/engine combination, one for emission at 1-9 km and one for emission at 9-13 km, the former was used in this analysis. 6 As long as cruise level is set at ft mainly cruise time and fuel consumption during this stage will change as the range increases or decreases. In addition, changes in cruise time/range imply different fuel capacities at take off which will impact emission at this stage of the flight.

10 To convert emissions to cost, estimates by Dings et al. (2003) were used. These estimates are based on the cost of CO 2 emission and the relative radiative forcing and quantity of NOx and H 2 O emission in respect to CO 2 emission. These estimates are based on the 1992 air traffic situation, as analysed by the IPCC (1999). The estimate for NOx emission refers to climate change impact only, and therefore there is no risk for double counting of damage when the impacts of LAP and climate change are later aggregated. The costs of climate change from the operation of different aircraft operating on a 500nm route are presented in Table 6. The operation of larger aircraft results in lower climate change impact per seat than the operation of small aircraft (in 2 class configuration). In operating large aircraft, there is no difference between the smaller (A330) and the larger (B747) aircraft when both are in the 2-class configuration, but substantial differences exist between the two small aircraft. The operation of smaller aircraft (A319) imposes a larger impact on climate change than the larger aircraft (A320), this can be attributed to the fact that the A319 is not a new aircraft (design) but a downscaled version of the A320 (Endres, 2001). Table 6: Cost of climate change from a 500nm flight (Euro/seat) Euro/tonne * Euro/kg * Euro/tonne * Aircraft (seats) CO 2 NOx H 2 0 Total A (150) A (164) B (524) B D (568) A (124) A (335) * Data on the cost of emission are based on Dings et al. (2003). It is questionable if in the above analysis water vapour emission should be included. On short-haul flights most of the emission will occur at relatively low altitudes where the concentration and impact of H 2 O are largely determined internally within the climate system and are not significantly affected by human sources (Archer, 1993) 7. Removing water vapour emission from the analysis would not change the results much and will not change the relative difference between aircraft, since this was measured as a fixed proportion of fuel consumption. Contrary to the LAP analysis, the climate change analysis suggests that increasing aircraft size is environmentally beneficial, from a climate change perspective. The benefits from increasing aircraft size are mainly attributed to reduction in CO 2 emission followed by reduction in NOx emission. There is also a reduction in H 2 O emission, but it is relatively small in cost terms. The analysis did not provide evidence 7 The IPCC (1999) notes that water vapour emissions in the troposphere (generally up to 12 km at mid latitudes), where most subsonic aircraft water vapour emissions are released, will be removed by precipitation within 1 to 2 weeks.

11 to suggest that technological development in aircraft design and engines resulted in a lower environmental impact for newer aircraft, at least with respect to climate change. 5. Noise emission The nonlinear characteristic of noise makes it hard to compare between aircraft of different capacities, as the noise level from a flight cannot be divided by seat capacity. Instead, the noise level from the operation of several flights can be estimated. To compare between aircraft of different capacities the noise level from transporting different volumes of passengers by different aircraft types was calculated. For each aircraft type, the fleet exposure level was calculated using the formula below, after determining the number of air transport movements (atms) required by each type of aircraft to transport a certain volume of passengers. The formula used was: L fleet cat = 10 log ncat 10 L ave /10 Where L fleet is the fleet noise exposure; n cat is the number of aircraft movements (including time-of-day weightings, which here is not accounted for) for an aircraft type (here, only one aircraft type is assumed in each calculation); and L ave is the average of the three noise certification levels for an aircraft type (Busink, 2001). Rewriting the above formula and assuming n flights of one aircraft type for each calculation yields: L fleet = L ave +10log (n). This formula means total noise is more sensitive to noise per flight than to the number of flights (Brueckner and Girvin, 2008) and it can be applied to any period of time (day, week, year, etc.). Noise data were obtained from ICAO on-line noise database 8. For each combination of aircraft type, engine type, MTOW and MLM (Maximum Landing Mass) the database provides the certified noise levels in EPNdB units for the three standards reference points around the runway: lateral, approach and flyover 9. EPNdB is the unit used to measure the Effective Perceived Noise Level (EPNL) and is the basic element for noise certification criteria. The EPNdB units are a single number to evaluate the subjective effects of airplane noise on human beings. To derive the noise from a specific aircraft, the noise certification levels at the three reference points were averaged to derive the noise from a specific aircraft. Not surprisingly, the larger the aircraft the more noise it creates overall and at each of the flight stages measured (Table 7). To account for the operation of wide-body aircraft on short-haul routes, the lowest MTOW version in the database was used. Still, the actual TOW (Take-Off Weight) of such aircraft flying short-haul routes will 8 (accessed August 2007). 9 The noise "reference measurement points" are: Lateral (full power) - the certified noise level corresponds to the average of two points located on a line parallel to and at a distance of 450m from the runway centre line. This is where the take-off noise level is at its maximum. Flyover (reduced power) - the point is located on the extended centre line of the runway, at a distance of 6500m from the start of roll. Approach - the point is located at the extended centre line of the runway, at a distance of 2000m from the runway threshold. On level ground this corresponds to a position of 120m vertically below the 3 0 descent path. Source: ICAO noise data base (

12 be much lower than that, thus the problem that data do not account for large aircraft flying short hall has not been really overcome. Table 7: Aircraft characteristics and certified noise levels Thrust (no. of Noise certification level at reference points Average noise per Aircraft (in service) engines) Lateral Flyover Approach LTO * A (11/88) kn (2) B (2/89) kn (4) A (5/96) kn (2) A (1/94) kn (2) * Note: the formula and literature do not suggest the use of weighted average. The fleet noise exposure from transporting different volumes of passengers by each type of aircraft is illustrated in Figure 1. The fleet noise exposure is lower when using the B747 rather than the A320, suggesting an advantage for using larger aircraft and lower frequency. A similar analysis which includes also the A319 (124 seats) and the A330 (335 seats) models shows that these models have a lower fleet noise exposure than the older A320 and B747 models. At each volume of passengers the A319 is only marginally quieter than the A330. This is illustrated in Table 8 for transporting 10000, and passengers by each type of aircraft. If a domestic version of the A330 existed, with a capacity of say 350 seats, such an aircraft fleet would outperform the other models examined above, resulting in a noise exposure level of units from transporting passengers (requiring 143 atms). Figure 1: The fleet noise exposure from A320 (150 seats) and B747 (525 seats) for transporting different volumes of passengers Fleet noise exposure Passenger volume A320 (150) B747 (524)

13 The non-linear property of noise volume, as heard by the human ear, makes it hard to interpret the magnitude of the difference in the fleet noise exposure that was revealed in Figure 1 and Table 8. Table 8: The fleet noise exposure level from different volumes of passengers passengers passengers passengers Aircraft (seats) atms * L fleet atms * L fleet atms * L fleet A (150) B (524) A (124) A (335) * Air Transport Movements - rounded up. The above analysis demonstrated that increasing aircraft size (and reducing service frequency) can result in lower noise impact provided the large aircraft are in high seating density configuration. The fact that large aircraft flying on short haul routes require to load substantially less fuel is also likely to lead to lower noise levels, but this effect could not be accounted for in full with the available data. The nature of noise measurement in the above analysis does not allow to assign monetary values to the noise pollution measured, mainly since this requires estimating the number of people exposed to noise from different aircraft which is not carried out here. Other studies (e.g. Pearce and Pearce, 2000; Dings et al., 2003) provide estimates of the marginal/average social cost of noise of different types of aircraft for a specific airport (e.g. Heathrow), but these cannot be used to estimate the cost of noise from more than one flight. Studies which estimate the welfare impact of airport noise regulations often assume a linear increase in noise as frequency increases, e.g. Brueckner and Girvin (2008) 10 and therefore cannot be used here. In a study on the effect on noise of a new runway at Sydney Airport (Department of Transport and Regional Services, 2000) the following was noted. For many people, the prime issue, as the number of movements to the north of the airport rose from 160 to 370 on a typical day, became not so much how many movements or how much noise they received in total, but whether they were able to get a break from the noise. This also suggests that using larger aircraft and lower frequency might be preferred. 6. Case studies There is a relatively small difference in the overall environmental cost of emissions from large and small aircraft, when accounting for both LAP and climate change impacts (Table 9). The result for the base models in this analysis, the A320 (150 seats) and the B747 (524 seats) is almost identical. These models are a better option, from an environmental perspective, than the A319 and the A330 which are newer. If airlines were to replace the A320 base model with a high-capacity (2-class) B747 then environmental benefits would result. When the B747 (524 seats) and B747D ( Brueckner and Girvin (2008) note with regard to their analysis that [an] unrealistic element is the linear fashion in which noise is added across flights (p. 21). Since their interest is more in a theoretical model and qualitative conclusions, this is not considered a major limitation.

14 seats) are assumed to use lower thrusts at take-off and climb stages of the LTO cycle, the total environmental cost is 4.95 and 4.56 Euro/seat respectively. Table 9 shows that the impact of aircraft operation on climate change is higher then that on LAP and that new aircraft do not perform better from an environmental perspective. Table 9: The environmental cost (LAP and climate change) from aircraft emission during a flight of 500nm (Euro/seat) Aircraft LAP Climate Total A (150) A (164) B (524) B D (568) A (124) A (335) To put the above results in context, three case studies routes are analysed. The question on airlines choice of aircraft size is relevant to a specific type of routes, the short haul high density routes. On long-haul routes of over 6,000 km airlines can only use wide-body aircraft and on short-haul low density routes demand does not justify the use of large aircraft and the level of service will normally be low. Short-haul, high density routes are normally routes serving two hubs. On such routes low-cost carriers (LCC) will normally not operate and airlines which do operate usually offer (at least) economy and business class seating. These types of routes were chosen as case study routes. Table 10: Short-haul high density case study routes Observed route characteristics (2003) weekly (2-way) Route km atm Seats Seat/atm Barcelona-Madrid (BCN - MAD) Sapporo-Tokyo (CTS - HND) L.A. Chicago (LAX - ORD) atms to transport similar capacity using (seats) A320 B747 B747D (150) (524) (568) , , , The three case study routes chosen for analysis are described in Table 10. These routes vary in range but are considered short-haul routes. Despite the high demand for services on the Barcelona-Madrid and Los Angeles-Chicago routes airlines operating these routes opted, on average, for narrow-body (small) aircraft. In contrast, on the route between Sapporo and Tokyo airlines opted to operate, on average, wide body (large) aircraft 11. To evaluate the environmental impact of airlines choice of aircraft size on these routes the number of flights required to offer similar seating capacity 11 Givoni and Rietveld (2007) provide some explanations for these differences.

15 using the A320 (150 seats), B747 (524 seats) and B747D (568 seats) was calculated (Table 10). Given the seat capacity offered on each route the analysis provides information on the scale of difference in environmental impact from operating large and small aircraft (Table 11) and this is then compared to the actual (average) airlines choice of aircraft size. On all three routes, if airlines opted to use the large rather than the small aircraft reduction in noise would result, but it is not possible to conclude how substantial these reductions are. Table 11: The weekly environmental impact from the operation of large and small aircraft Aircraft Climate LAP + Take-off thrust / (seats) atm Noise 1 LAP 2 change 2 Climate 2 H 2 O impact? Barcelona-Madrid (BCN - MAD) A320 (150) , , ,963 75% / No B747 (524) , , ,582 75% / No Difference ,599 31,980 7,381 Sapporo-Tokyo (CTS - HND) A320 (150) , , ,263 90% / No B747 (524) , , ,212 75% / No Difference ,473 56,524 42,051 Los Angeles - Chicago (LAX - ORD) A320 (150) , ,514 1,042, % / Yes B747 (524) , , ,418 75% / Yes Difference ,057 68,614 70,671 1 Fleet noise exposure 2 Euro For the LAP analysis, it was assumed that on all three routes the B747 would only require 75% engine thrust at take-off (70% at climb), while for the A320 it was assumed that 75% engine thrust at take-off will suffice for the very short Barcelona- Madrid route, 90% thrust for the longer Sapporo-Tokyo route and 100% thrust for the much longer Los Angeles Chicago route. Under these assumptions, only on the last route (LAX-ORD) there will be LAP benefits from increasing aircraft size, thus the conclusion depends on the route distance. Reduction in climate change impact is expected on all routes from shifting services from the small to the large aircraft. For the routes of less than 1000 km, due to the very short cruise time 12, the impact of water vapour emission on climate change was not included. Overall, accounting for LAP and climate change impacts, environmental benefits are expected on the case study routes after changing from the A320 to the B747 aircraft and adjusting the service frequency to provide similar seating capacity. These benefits appear to increase with range. On two of the case study routes (BCN-MAD and LAX-ORD) airlines choose to use, on average, narrow body aircraft while on the third case study route (CTS-HND) they choose wide-body aircraft (Table 10). From an environmental perspective it appears 12 Cruise time was estimated to be 8.8, 32.4 and minutes for the Barcelona-Madrid, Sapporo- Tokyo and Los Angeles Chicago routes respectively.

16 that airlines choice of aircraft on the Japanese route results in environmental gains, contrary to airlines choice on the US route. On the Spanish route, it appears that current choice of aircraft size does not carry a considerable environmental penalty and results in local benefits, which appears substantial, in terms of reduced LAP. There is potential for environmental benefits if airlines will replace the fleet used to serve the case study routes to an all B747 fleet. The significance of these benefits is hard to judge. What is clear and important is the runway capacity that will be freed from increasing aircraft size and lowering frequency accordingly. Changing from the fleet used in 2003 to an all B747 fleet will free up over 11% of the runway capacity used in Barcelona airport and over 8% of that in Madrid airport. In Sapporo, although the fleet used was of wide body aircraft, due to the relatively small size of the airport (87256 atms in 2003) changing the fleet to an all B747 fleet will free almost 11% of the airport runway capacity. At Chicago O Hare airport, largest in the world and probably the busiest, over 12,000 atms can be freed, but this is only a fraction (1.4%) of the airport capacity. This reduction in the number of services, if not replaced by other services, might have other environmental benefits (see below). A concern from a public perspective is that increasing aircraft size and adjusting frequency will result in very low level of service, but for the three routes considered here this seems to be limited. After moving to an all B747 fleet, the level of service of the case study routes will remain relatively high with 20, 33 and 10 services per day (one way) on the Barcelona-Madrid, Sapporo-Tokyo and Los Angeles-Chicago routes respectively. 7. Conclusions The comparison of the environmental impact from the operation of large (wide-body) and small (narrow-body) aircraft on short haul routes showed the following. Increasing aircraft size, switching from an A320 (150 seats) fleet to a B747 (524 seats) fleet and adjusting the service frequency to offer similar seating capacity will increase LAP but decrease climate change impact. When these impacts are monetized and aggregated the analysis showed that environmental benefits will result. In addition, increasing aircraft size will also reduce noise pollution around airports. Given the nature of data available, the methodology used, the differences between large and small aircraft appear to be modest and sensitive to the assumptions made. However, the main data limitation, the fact that actual data for large aircraft flying short-haul was not available (instead the analysis relied on data for large aircraft flying long haul) suggests that the environmental impact from the operation of large aircraft has been overestimated, and therefore the potential benefits from upsizing the fleet underestimated. In addition, the reduction in aircraft movements when upsizing aircraft fleet and adjusting service frequency can have two environmental benefits which were not accounted for in the above analysis. First, reduction in aircraft movements can reduce delays, on the ground and in the sky, and therefore reduce flight time leading to lower LAP and climate change impacts. Second, reduction in the number of movements means airport capacity can be maintained or increased without constructing new runways. As noted, on the majority of air transport routes airlines do not have a real choice in terms of the trade-offs between service frequency and aircraft size. But those routes on which they do, often take a substantial part of an airport capacity (as illustrated for

17 the case studies routes). An analysis of routes from Heathrow on which air-rail substitution might take place (all short haul in airline terms) found that such routes consumed about 20% if Heathrow s runway capacity in (Givoni and Banister, 2006). Thus, overall the environmental benefits from upsizing the fleet might be substantial, but at the same time, might come at the cost of higher LAP around airports, which (locally and even nationally) might be more important. Although reducing service frequency would be a disadvantage for passengers the current level of service on most high-density short haul routes means that also if an all B747 fleet will be adopted the level of service will remain relatively high (see Table 11). In the longer term, if demand for air transport continues growing and current level of competition maintained, encouraging airlines to meet demand through more services rather than larger aircraft, many more routes will reach the level of service offered on routes such as the above case studies. The largest air transport markets and largest growing markets are particularly short-haul routes markets and include North- America, Europe, China and India. Airbus (2007) forecasts that in 2025 such markets will account for almost 35% of the world airlines RPKs (Revenue Passenger Kilometres) 14, and in terms of movements this probably translates to over 70%. Current evidence from the world s major airports show that scarce runway capacity and high level of congestion and delays do not deter airlines from offering very high levels of service on short haul routes. In the future, and if assuming that technological developments will provide similar environmental gains in large and small aircraft, the conflict between local and global concerns with air transport operation will be greater, favouring current practice of meeting demand through higher frequency in terms of LAP and calling for reducing service frequency and increasing aircraft size in terms of climate change and noise. The debate surrounding the development of the air transport industry, and the transport system in general, now focuses very much on sustainability. Whatever definition is given to sustainability, and where the balance is put between economic and environmental concerns, there seems to be an agreement that one way forward is to make best use of available capacity. This is supported both by research (e.g. Rietveld and Bruinsma, 1998) and by policy (e.g. Eddington, 2006). Therefore, after a certain level of service has been reached increasing supply through larger aircraft rather than additional services (and similar or smaller aircraft size) will represent better use of existing capacity. But such strategy, it appears, would not necessarily result in considerable environmental benefits and, at least in terms of LAP, would carry an environmental penalty. A basic result from a stylized transport economic model is that when demand increases, the response in capacity should be both in terms of higher frequencies and larger aircraft. This is known as Mohring's square root formula, implying that when demand increases with 10%, aircraft size should increase with 5% (Mohring, 1976). However, in the air transport industry the evidence suggest that the choice of aircraft size depends on market size with an elasticity of 0.35, indicating that in the airline 13 The nature of the analysis, air-rail substitution, means that routes such as London-Dublin and London-Madrid were not accounted for. 14 Domestic US: 13.1% of the world airlines RPKs in 2026 (2.4% annual growth from 2006), Intra western Europe: 8.6% (3.8%), Domestic China: 7.9% (8.4%), Domestic India: 2.3% (11.5%), and Domestic Asia: 1.4% (5.2%) (Airbus, 2007).

18 industry carriers give priority to increases in frequency (Givoni and Reitveld, 2007). Although given the present level of technology there is not a clear advantage for large aircraft, there certainly are advantages in terms of coping with airport congestion problems and making better use of existing runway capacity. Making best use of available capacity from an environmental perspective also means, as the analysis clearly show, higher seating densities on aircraft (naturally, the environmental benefits only occur if the load factor is maintained when the aircraft seating capacity is increased). However, it can be expected that in this case, airlines already optimize the trade-offs between passenger welfare and their operating costs 15. The above analysis demonstrated that there are no large economics of scale, in terms of environmental impact, in aircraft operation. This is mainly the result of the current strategy by aircraft manufactures to couple range and capacity in aircraft design. To make a better use of available runway capacity and to reduce the environmental impact from aircraft operation, especially at large airports, a large (wide body) aircraft designed for short haul operation would be required. At present, it is hard to see a market for such an aircraft. This is evident in airlines choice of relatively small aircraft (and high frequency service) also on routes to/from and between congested airports. This situation, however, might change when pricing of runway capacity will better represent the scarcity of runway capacity at the major airports. To some extent the new generation of wide body aircraft, the Airbus A350 and the Boeing B787 which are expected to enter service in the coming years might be considered as the aircraft required to reduce air transport impact on the environment. These aircraft are supposed to bring a marked change in fuel efficiency, assumed to be 20% more fuel efficient than their nearest existing equivalent at the beginning of this decade, the Boeing B767 (DfT, 2007). The question remains if these models will also be used by airlines on short haul routes. The market for a large short haul aircraft depends on demonstrating that large aircraft designed for short haul operation can produce considerable savings in fuel consumption. The current practice by low cost carriers, around the world, to relay on narrow body aircraft fleet (and often the smaller aircraft in that group) provides some indication that small aircraft are more fuel efficient, and therefore cost effective, than large aircraft. Cost savings is at the heart of the low cost carrier model and these airlines would normally not see service frequency as an important element (but rather price) in their competition for market share 16. At present, the market share of European low cost carriers, in terms of seat capacity, is 30% (Airbus, 2007). Further substantial increases in fuel prices and in addition a mechanism in which airlines and airports pay for the environmental impact they impose are likely to create the conditions for the development of a large short haul aircraft. This in turn can lead 15 This can be seen in the choice of 1-class configuration by low cost carriers compared to the 2-class configuration chosen by most other airlines on short haul routes. 16 An exception to this is the need to use small aircraft in regional airports where runways might not be large enough to support the operation of large aircraft, but this is probably not the case for most of the routes operated by a low cost carrier.