# Airline Network Planning Considering Climate Impact: Assessing New Operational Improvements
## 4 Discussion
The findings suggest adopting new network design objectives or operational concepts may require re-evaluating the fleet composition from a fleet management perspective. In the KLM case study, the fleet allocation to the new network was found to be less efficient than the reference one, resulting in a relative drop in average fleet utilisation compared to other airlines. Airlines may need to make appropriate short- or long-term fleet management decisions to address the potential inefficiencies due to climate-aware network planning. These changes may cause the flight LF to deviate from the assumed average European values used for DOC and climate impact calculation. Therefore, in the ATR scenario, the reduced LF, compared to the BAU scenario, can further help mitigate climate impact and costs. We used the proposed framework to provide an overview of the actual network-level consequences of implementing the ISO and FL. We presented the results by comparing an OI-specific scenario with the ATR scenario. We discovered that ISO could help decrease the total ATR20 and expand the network (serve more destinations). According to the case studies, lowering the climate impact and network expansion ISO contributions may not coincide due to the fact that they have contracting effects in ATR20. This also may not be possible to be anticipated what would be the ultimate effect as it is highly case-dependent. We also observed that 4-7% of the flights adopted a weekly ISO operation, and the portion of ISO flights in S-high is more than it is in S-low. Further analysis showed that the average airfare in S-high is about 30% and 44% higher for TAP and KLM, respectively. Therefore, this season has a larger profit margin for both airlines, which allowed more ISO to be implemented. The additional cost of ISO is a noticeable impediment towards widely implementing it. In the case studies, extra landing and take-off in ISO resulted in increased CO and HC emissions by up to 10%. Considering the additional DOC, ISO may not be a realistic choice for all network routes for an airline. Nonetheless, it can provide additional flexibility in network planning while using the same fleet composition. On the other hand, LISO could produce a significant ATR20 reduction when combined with the network planning model. The increase in the DOC for LISO is slightly higher than ISO as the cruise altitude shifts from the optimal fuel altitude. At the same time, the reduction in the ATR20 is high enough to make LISO a better option than ISO. LISO emits non-CO\({}_{2}\) emissions at an altitude at which atmospheric reactions result in a lower ATR20, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Criteria**} & \multicolumn{2}{c}{**ATR Scenario**} & \multicolumn{2}{c}{**ATRISO Scenario**} & \multicolumn{2}{c}{**ATRLISO Scenario**} \\ \cline{2-7}  & [30] & **This Study** & [20] & **This Study** & [15] \({}^{*}\) & **This Study** \\ \hline \multirow{3}{*}{
\begin{tabular}{c} Profit loss \\ Climate impact mitigation \\ (ATR100) \\ LF \\ \end{tabular} } & Up to 12\% & 10\% & - & 10.5\% & - & 14\% \\ \cline{1-1} \cline{2-7}  & up to 12.5\% & 11\% & Up to 40\% & 15\% & up to 21\% & 17\% \\ \cline{1-1} \cline{2-7}  & Up to \(-\)30\% & \(-\)3\% & - & \(-\)2\% & - & \(-\)4\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison between the absolute results compared to the business-as-usual case obtained in the literature and the average annual results for each of the three scenarios in this study (KLM). \({}^{*}\) This study did not include the ISO OIs and only considered FL. and it helps reduce the ATR20 between 17 and 31% at the network level in our case studies. Most of the ATR20 reduction in this scenario was gained by modifying the long-haul route in both TAP and KLM. It can be concluded that a revision in planning long-haul routes should be the main focus of network climate-friendly planning revisions. Long-haul flight changes may necessitate changes to short-haul flights to maintain the connecting passenger flow at hub airport(s).