*4.4.1 General input for analysis*

*Environmental Impact of Aviation and Sustainable Solutions*

Data on aircraft unit cost used for verification was obtained from Centre for Asia Pacific Aviation [64]. A comparable unit cost drop between 2014 and 2016 can be observed for both FSDM results (25%) and CAPA data (20%). Likewise, the trend of the cost development throughout the period is comparable for both FSDM and CAPA, although absolute values are not equal. Although Groenenboom [65] recorded that the average age of passenger aircraft slightly decreased between 2010 and 2015, it does not precisely give the age for passenger aircraft. Average age of the passenger aircraft fleet depends on the rate of aircraft additions to the fleet, compared to retirements from the fleet. In addition, the average fleet age depends on jet fuel price. Lower fuel prices encourage airlines to keep older aircraft longer in service, especially when travel demand is strong [66, 67], thereby increasing the average fleet age. Therefore, a slight increase in the average age of the fleet

*Fuel price, unit cost, and average age of global pax fleet: 2008-2016. Source: Own calculations [65].*

Next, the reliability of the model in estimating future emissions and air passen-

For forecasts until 2050, passenger load factor is assumed steady at 2036 levels. Dray et al. [63] updated AIM to AIM2015 and used the UK Department of Energy and Climate Change (DECC) historical and forecast oil price levels [68]. In this verification study, the DECC medium oil price forecast was used. A review of the historical prices [year 2016 USD per gallon] between 1990 and 2015 shows that jet fuel prices were approximately 21% above DECC oil prices. The fuel price development according to the DECC has a price level in 2036 and beyond which is even

Furthermore, from year 2015, RPK growth rates of 3.8% per year were used in this verification process according to the SSP2 baseline scenario of Dray et al. [63]. In the SSP2 baseline scenario, zero carbon prices were assumed, so that ETS costs were set to zero. The assumptions in aircraft utilisation, load factor and technology improvements used for arriving at Boeing's future fleet composition are retained. As a result, the basic giant-leap technological improvements assumed were similar. Incremental improvements were excluded since they did not assume incremental technological improvements. **Figure 11** shows the jet fuel price development of the SSP2 baseline scenario. **Figure 12** shows estimates of fuel burn and air traffic in 2050 relative to 2015 from Dray et al. [63] and using FSDM. Because the long-term development is of

accompanies a decrease in the price of fuel from year 2012 to 2016.

*4.3.3 Verification of forecast fleet fuel burn and air passenger traffic*

ger traffic of the global passenger aircraft fleet is verified.

higher than Boeing's high-fuel price forecast.

interest, yearly changes in the results are not shown.

**162**

**Figure 10.**

Past and forecast RPK growth factors are used as given by Boeing [58]. After 2036, the annual growth rates are assumed constant at 2036 levels. Assumptions on seat and freight load factor are the same as in the verification according to Boeing's forecast. Past fuel price until 2016 and forecast prices by Airbus until 2025 are used

**Figure 12.**

*Verification of forecast passenger aircraft fuel burn and traffic. Source: Own calculations, based on [63].*

as shown in **Figure 6**. Fuel price after 2025 is assumed to increase annually by 0.1%, reaching 2.53 year 2016 US dollars per gallon in year 2050.

Fleet planning horizon and aircraft depreciation period are kept at 15 and 14 years, respectively. Aircraft production capacity and annual productivity are as earlier described. Furthermore, calibration input such as cost improvement assumptions is retained for all application scenarios.

## **5. Definition of scenarios**

A baseline scenario is assumed which is named *giant-leap plus incremental improvement baseline*. This scenario assumes that incremental improvements are applied to initial fleet and next-generation aircraft. Thus, it assumes that airlines always integrate the latest available fuel and cost improvements on aircraft programmes when adding new available aircraft to the fleet. The actual state of CO2 emissions from passenger air transport is expected to be similar to this baseline if in-service improvements on aircraft otherwise known as Performance Improvement Packages (PIPs), which are beyond the scope of this research, are considered. Incremental improvements refer all improvements shown in the Appendix (see **Table A-1**), excluding those comparing each aircraft to its previous aircraft generation.

Whereas the *Growth Strategy* has been used in the FSDM calibration and verification and is the strategy used for the baseline scenario, the *Replacement Strategy* is evaluated as a strategic measure to determine emission reduction benefits at the fleet level. Other assumptions of the baseline scenario are kept, except the fleet renewal sequence.

#### **6. Results**

Prioritising filling retirement gaps above growth gap implies that more aircraft production capacity is used for replacing economically inefficient aircraft. Compared to the *Growth Strategy*, the *Replacement Strategy* generates a higher wave of aircraft economic retirement. Between 2008 and 2050, the *Replacement Strategy* retires 7% more aircraft economically than the *Growth Strategy*. Between 2008 and 2024, the *Replacement Strategy* retires approximately 65% more aircraft economically and 44% more aircraft both economically and structurally. This can be seen in **Figure 13**.

However, in year 2024, few years after the JC, MR, LR and NB would be out of production; only a 3% improvement in CO2 emissions is realised using the *Replacement Strategy* compared to the *Growth Strategy*.

From **Figure 14**, the two benefits of the *Replacement Strategy* until 2024 can be seen—a maximum of 2% higher share of retired aircraft in the fleet and a slightly longer year-on-year growth in fleet specific fuel consumption (SFC). However, because these improvements are minimal, the CO2 emission improvement in the *Replacement Strategy* is also limited to about 3% in year 2024.

However, after year 2024, having attained a more cost-efficient and fuel-efficient fleet than in the *Growth Strategy*, the growth in ASK over time and the absence of more efficient aircraft result in fewer numbers of aircraft being retired by the *Replacement Strategy*. On the other hand, in the *Growth Strategy*, the fleet in year 2024 is not as efficient, thereby giving a possibility of better fleet renewal afterwards. Between 2025 and 2050, the *Growth Strategy* retires 4% more aircraft both economically and structurally than the *Replacement Strategy*. Therefore, compared to the *Growth Strategy*, the *Replacement Strategy* gives a lower EMP of 2% in 2050.

**165**

**7. Conclusion**

**Figure 14.**

*consumption.*

**Figure 13.**

*Increasing the Emission Mitigation Potential by Employing an Economically Optimised…*

*Growth and replacement strategy: Number of aircraft economically retired and fleet level CO2 emissions.*

From the last fleet-level emission results of **Figure 13**, there is an identified shortterm benefit of the *Replacement* Strategy. However, in the long term, the benefits reduce because the absence of newer more cost-efficient aircraft. Despite this diminished benefit, about 2% of the emissions (40 Mt. CO2) could be saved at the global fleet level in year 2050 by using this fleet renewal strategy. Therefore, in order to achieve higher mitigation potentials, there is need for additional technological measures, in terms of more cost-efficient aircraft, with entry to service as from 2024.

*Growth and replacement strategy: Share of retired aircraft in fleet and year-on-year growth in specific fuel* 

*DOI: http://dx.doi.org/10.5772/intechopen.88219*

*Increasing the Emission Mitigation Potential by Employing an Economically Optimised… DOI: http://dx.doi.org/10.5772/intechopen.88219*

**Figure 13.**

*Environmental Impact of Aviation and Sustainable Solutions*

reaching 2.53 year 2016 US dollars per gallon in year 2050.

assumptions is retained for all application scenarios.

*Replacement Strategy* compared to the *Growth Strategy*.

*Replacement Strategy* is also limited to about 3% in year 2024.

**5. Definition of scenarios**

aircraft generation.

renewal sequence.

**6. Results**

as shown in **Figure 6**. Fuel price after 2025 is assumed to increase annually by 0.1%,

Fleet planning horizon and aircraft depreciation period are kept at 15 and 14 years, respectively. Aircraft production capacity and annual productivity are as earlier described. Furthermore, calibration input such as cost improvement

A baseline scenario is assumed which is named *giant-leap plus incremental improvement baseline*. This scenario assumes that incremental improvements are applied to initial fleet and next-generation aircraft. Thus, it assumes that airlines always integrate the latest available fuel and cost improvements on aircraft programmes when adding new available aircraft to the fleet. The actual state of CO2 emissions from passenger air transport is expected to be similar to this baseline if in-service improvements on aircraft otherwise known as Performance Improvement Packages (PIPs), which are beyond the scope of this research, are considered. Incremental improvements refer all improvements shown in the Appendix (see **Table A-1**), excluding those comparing each aircraft to its previous

Whereas the *Growth Strategy* has been used in the FSDM calibration and verification and is the strategy used for the baseline scenario, the *Replacement Strategy* is evaluated as a strategic measure to determine emission reduction benefits at the fleet level. Other assumptions of the baseline scenario are kept, except the fleet

Prioritising filling retirement gaps above growth gap implies that more aircraft production capacity is used for replacing economically inefficient aircraft. Compared to the *Growth Strategy*, the *Replacement Strategy* generates a higher wave of aircraft economic retirement. Between 2008 and 2050, the *Replacement Strategy* retires 7% more aircraft economically than the *Growth Strategy*. Between 2008 and 2024, the *Replacement Strategy* retires approximately 65% more aircraft economically and 44% more aircraft both economically and structurally. This can be seen in **Figure 13**. However, in year 2024, few years after the JC, MR, LR and NB would be out of production; only a 3% improvement in CO2 emissions is realised using the

From **Figure 14**, the two benefits of the *Replacement Strategy* until 2024 can be seen—a maximum of 2% higher share of retired aircraft in the fleet and a slightly longer year-on-year growth in fleet specific fuel consumption (SFC). However, because these improvements are minimal, the CO2 emission improvement in the

However, after year 2024, having attained a more cost-efficient and fuel-efficient fleet than in the *Growth Strategy*, the growth in ASK over time and the absence of more efficient aircraft result in fewer numbers of aircraft being retired by the *Replacement Strategy*. On the other hand, in the *Growth Strategy*, the fleet in year 2024 is not as efficient, thereby giving a possibility of better fleet renewal afterwards. Between 2025 and 2050, the *Growth Strategy* retires 4% more aircraft both economically and structurally than the *Replacement Strategy*. Therefore, compared to the *Growth Strategy*, the *Replacement Strategy* gives a lower EMP of 2% in 2050.

**164**

*Growth and replacement strategy: Number of aircraft economically retired and fleet level CO2 emissions.*

**Figure 14.**

*Growth and replacement strategy: Share of retired aircraft in fleet and year-on-year growth in specific fuel consumption.*

#### **7. Conclusion**

From the last fleet-level emission results of **Figure 13**, there is an identified shortterm benefit of the *Replacement* Strategy. However, in the long term, the benefits reduce because the absence of newer more cost-efficient aircraft. Despite this diminished benefit, about 2% of the emissions (40 Mt. CO2) could be saved at the global fleet level in year 2050 by using this fleet renewal strategy. Therefore, in order to achieve higher mitigation potentials, there is need for additional technological measures, in terms of more cost-efficient aircraft, with entry to service as from 2024.

As an outlook, having known the emission mitigation potential of the proposed *Replacement Strategy*, the cost analysis, i.e. advantage or disadvantage, of this measure should also be evaluated. Lastly, this study does not include effects of ticket price elasticity of fuel price changes.
