# Airline Network Planning Considering Climate Impact: Assessing New Operational Improvements  
[PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON]  
1 Section Air Transport and Operations, Faculty of Aerospace Engineering, Delft University of Technology, 2628 HS Delft, The Netherlands; [EMAIL_ADDRESS] (B.F.S. ); [EMAIL_ADDRESS] (A.S.) 1  
[PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON]  
1 Section Air Transport and Operations, Faculty of Aerospace Engineering, Delft University of Technology, 2628 HS Delft, The Netherlands; [EMAIL_ADDRESS] (B.F.S. ); [EMAIL_ADDRESS] (A.S.) 1  
[PERSON], [PERSON], [PERSON], [PERSON], [PERSON]  
2 Deutsches Zentrum fur Luft- und Raumfahrt, Institut fur Luftverkehr, 21079 Hamburg, Germany; [EMAIL_ADDRESS] (Z.L.Z. ); [EMAIL_ADDRESS] (C.M.W. ); [EMAIL_ADDRESS] (F.L.) 2  
[PERSON], Zare  
and operational improvements. Eventually, aviation emissions change the atmospheric concentrations of greenhouse gases and cloudiness, leading to an atmospheric radiation imbalance resulting in temperature changes. Climate metrics, e.g., the ATR [7], are used to evaluate the climate impact of aviation scenarios. The topic of mitigating the climate impact of aviation has been addressed in the academic literature in several studies. Based on the holistic overview offered by [8], there are three main research directions which are contributing to aviation climate impact mitigation. Firstly, there are sustainable energy resources advancement, as discussed, e.g., in [9; 10]. Secondly, novel aircraft design and aircraft performance improvements, are addressed, e.g., in [11; 12; 13]. Finally, there are operational improvements (OIs), which address the utilisation of the currently available fleet and technologies to improve aviation climate impact, as considered, e.g., in [14; 15; 16]. The first two research directions have mainly had a long-term impact on aviation. With the exception of sustainable aviation fuel (SAF), which is already used on a small scale by some airlines, it should take more than one decade for new aircraft designs or hydrogen-powered aircraft to start operating in the airline fleet [17]. They are not expected to contribute to the effort of reducing the aviation footprint in the short term [8]. Aviation stakeholders, particularly airlines, will have to adopt climate impact reduction goals in their decisions using current technologies to improve the sustainability of their operations. One way to do this is to rethink their operations and adopt OIs. These are changes in the operations that modify the airline processes and services to improve their operational efficiency and simultaneously mitigate the climate impact. In this paper, we particularly looked at OIs that can reduce the climate impact of airline operations. One well-studied OI is the concept of ISO. This OI aims to reduce the stage length of flights by performing one or more intermediate landings during a mission. Past studies on the ISO have covered the analysis of limited missions approaches [18; 19] and global-level assessments [16; 20]. These studies primarily evaluated the potential fuel savings and climate impact mitigation that could be achieved, suggesting fuel savings of between 4.8-14.0% [16] and climate impact reduction up to 40% [20]. Some studies considered new aircraft designs to better suit ISO operations [18; 21]. The fuel efficiency gains, in these cases, can be significantly higher, eventually doubling the values from the studies not considering aircraft redesign. Modifying the flying cruise altitude in the interest of climate impact reduction is another promising OI. As atmospheric chemical processes are highly sensitive towards the emission altitude, flying lower (FL) has a great potential to reduce the flights' climate impacts [22; 23]. Studies of this OI show that FL can decrease the climate impact up to 33% [15; 24; 25]. The combination of ISO and FL is another research aspect that may increase the advantages of both OIs in mitigating the climate impact.