# Airline Network Planning Considering Climate Impact: Assessing New Operational Improvements
## 3 Results
### ATRLISO Scenario  
The final comparison made between the lower-altitude ISO (LISO) and the ATR scenario is illustrated in Figure 7. Our analysis reveals that LISO is more effective than ISO in reducing the network's climate impact for both KLM and TAP, with potential reductions of 18% and 21% in ATR20, respectively. However, flying at a lower altitude for LISO OIs would require more fuel, resulting in a higher DOC. Furthermore, most emission types are slightly increased due to deviations from the optimal fuel altitude and increased fuel consumption. The profit loss for both airlines is approximately 6%, and most of the reduction in ATR20 is attributed to decreasing the long-haul ATR20. Overall, the combined use of ISO and FL shows promising results in mitigating the network's climate impact. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Scenarios**} & \multicolumn{2}{c}{**\# Direct Flights**} & \multicolumn{2}{c}{**\# ISO Flights**} & \multicolumn{2}{c}{**\(\Delta\) ATR20 (\%)**} & \multicolumn{2}{c}{**\(\Delta\) ATR100 (\%)**} & \multicolumn{2}{c}{**\(\Delta\) Profit (\%)**} \\ \cline{2-11}  & **S-Low** & **S-High** & **S-Low** & **S-High** & **S-Low** & **S-High** & **S-Low** & **S-High** \\ \hline BAU & 2322 & 2334 & & & & & & & & \\ ATR & 2368 & 2376 & & & \(-11\) & \(-12\) & \(-11\) & \(-12\) & \(-10\) & \(-6\) \\ ATRISO & 2256 & 2170 & 104 & 204 & \(-13\) & \(-14\) & \(-14\) & \(-14\) & \(-11\) & \(-6\) \\ ATRLISO & 2077 & 2020 & 271 & 334 & \(-44\) & \(-28\) & \(-26\) & \(-29\) & \(-16\) & \(-10\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Weekly flight type composition and relative changes in climate and profit KPIs—KLM. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Scenarios**} & \multicolumn{2}{c}{**\# Direct Flights**} & \multicolumn{2}{c}{**\# ISO Flights**} & \multicolumn{2}{c}{**\(\Delta\) ATR20 (\%)**} & \multicolumn{2}{c}{**\(\Delta\) ATR100 (\%)**} & \multicolumn{2}{c}{**\(\Delta\) Profit (\%)**} \\ \cline{2-11}  & **S-Low** & **S-High** & **S-Low** & **S-High** & **S-Low** & **S-High** & **S-Low** & **S-High** \\ \hline BAU & 1062 & 1136 & & & & & & & & \\ ATR & 1232 & 1286 & & & \(-24\) & \(-28\) & \(-25\) & \(-28\) & \(-23\) & \(-17\) \\ ATRISO & 1290 & 1092 & 4 & 10 & \(-22\) & \(-27\) & \(-24\) & \(-28\) & \(-20\) & \(-20\) \\ ATRLISO & 1104 & 1182 & 112 & 96 & \(-43\) & \(-40\) & \(-44\) & \(-40\) & \(-25\) & \(-23\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Weekly flight type composition and relative changes in climate and profit KPIs—TAP. Figure 7: Average annual changes of the KPIs for ATRLISO compared to the ATR scenario: **(a)** the assessment of the climate KPIs (%); and **(b)** assessment of the non-climate KPIs (%). The introduction of FL seems to increase the added value of ISOs. There are more ISO flights in the LISO results, and all the airports which are used in the ISO scenario are also used in the LISO scenario. There is also no proportional relationship between the number of ODs associated with a candidate ISO airport and the number of times it is visited per week. The ISO alternative would be selected based on the profit margin of the route and network-related constraints. Therefore, an airport located at the perfect spatial point will not necessarily be frequently visited for ISO flights. The flight type composition and the associated climate impact reduction compared to BAU for all the scenarios are reported in Tables 2 and 3. The ATR scenario has more flights than the BAU scenario because closer destinations are served, resulting in shorter flight times. Thus, the weekly schedule of an aircraft could accommodate more flights, which increases the total number of flights per week, and the optimisation subroutine could not find a significantly better solution than what we have in the ATR scenario for the TAP case study. As a result, we see a relatively close objective function value for both scenarios, even though the network structure and the number of flights differ.