## 5 Conclusions  
This paper presented a conceptual analysis of the environmental and economic impact of introducing hybrid-electric propulsion in the context of regional aviation. In addition, the introduction of a new airframe such as the box-wing was considered as an incremental technological step, and an extensive comparative analysis with corresponding TW aircraft has been proposed.  
The obtained results can be analyzed from two different perspectives. Firstly, when analyzing the effects in terms of greenhouse gas reductions resulting from the introduction of hybrid-electric propulsion, it can be observed that the incremental technological contribution at the propulsion level is not sufficient to introduce general environmental benefits. In fact, emissions related to the current methods of electricity production mitigate the potential beneficial effects of emission reductions directly related to flight. Introducing more energy-efficient airframes, such as box wing, may introduce gains over the corresponding hybrid-electric TW, but if general benefits with respect to the state of the art are to be achieved, changes at the overall system level involving a marked transition to electricity production from renewable sources, should be provided.  
From an economic point of view, once again the box-wing configuration introduces benefits in terms of reduced value of DOC when directly compared to the corresponding TW hybrid-electric aircraft. These benefits, however, are lower than those found in terms of fuel consumption and CO\({}_{2}\) emissions, as they are averaged over a set of fixed costs that are the same for both architectures. On the other hand, when compared to the data of state-of-the-art regional thermal aircraft, both configurations introduce direct operational cost increases. This conceptual analysis, therefore, shows that, according to current estimates, a trade-off between economic and environmental performance should be addressed. In general, this scenario is in constant evolution, as both significant investment in research and development for electric propulsion for aeronautical applications and the gradual introduction of policies aimed at penalizing more polluting modes of transport, tend to mitigate the economic penalties that can be expected from the current outlook.  
Conceptualization, K.A.S., G.P. and A.A.Q.; methodology, K.A.S. and G.P.; software, G.P. and K.A.S.; validation, K.A.S. and G.P.; formal analysis, K.A.S. and G.P.; investigation, G.P. and K.A.S.; data curation, G.P. and K.A.S.; writing--original draft preparation, K.A.S. and G.P.; writing--review and editing, A.A.Q.; visualization, G.P. and K.A.S.; supervision, G.P., K.A.S. and A.A.Q.; funding acquisition, A.A.Q. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The data presented in this study are available on request from the authors [PERSON] and [PERSON].  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**MTOW [tons]** & **Span [m]** & **ICAO \(\textbf{{}^{\prime}}\textbf{{}^{\prime}}\leq 2\textbf{{}^{\prime}}\)m** & **ICAO \(\textbf{{}^{\prime}}\textbf{{}^{\prime}}\leq\textbf{{}^{\prime}}\) & **ICAO \(\textbf{{}^{\prime}}\textbf{{}^{\prime}}\leq\textbf{{}^{\prime}}\)6 m** \\ \hline  & **TW** & **BW** & **TW** & **BW** & **TW** & **BW** \\ \hline
23 & 28.8 & 23.8 & \(\star\) & \(\checkmark\) & \(\checkmark\) & \(\checkmark\) \\ \hline
30 & 32.8 & 27.8 & \(\star\) & \(\star\) & \(\checkmark\) & \(\checkmark\) \\ \hline
40 & 38.0 & 29.9 & \(\star\) & \(\star\) & \(\star\) & \(\checkmark\) \\ \hline
50 & 42.4 & 35.4 & \(\star\) & \(\star\) & \(\star\) & \(\checkmark\) \\ \hline \hline \end{tabular}
\end{table}
Table 9: Wingspan compliance with ICAO Aerodrome Codes for TW and BW hybrid-electric aircraft.