# Preliminary Impact Assessment of the Ad Hoc Separation Minima: A New Separation Mode
## 6 Conclusions  
The air transport system is expected to experience a continued increase in the number of movements. The current focus is to address the shortage of capacity to handle the forecasted demand while maintaining safety levels. Although the forecasts are long-term, ATM adopts strategic solutions to meet future challenges through the SESAR macro-program.  
One of the factors related to airspace capacity is separation minima. SESAR encourages an exploration of the evolution of the separation minima. A novel concept that was developed is Ad Hoc separation. This concept refers to the application of different separation minima values between aircraft flying in the same volume of airspace depending on certain factors.  
In this research, an analysis of the impact of the Ad Hoc separation concept's application in different en-route sectors (LECMZMU, LECMTLU, and LECMDGU) of Madrid ACC was presented. When new concepts are introduced in the system, generally, the complexity increases. Therefore, it is important to perform an analysis, even at a preliminary level, to check whether it is beneficial to apply this concept in a scenario or whether, instead, the complexity of the system is being increased in exchange of no benefit. En-route airspace capacity, \(CO_{2}\) emissions, fuel consumption, flow distance, and strategic delay indicators were selected for the impact assessment. The improvement in these last indicators (flight distance, fuel, \(CO_{2}\) emissions, and delay) stems from the reduction of ATCO interventions in aircraft trajectories. This is achieved by diminishing the number of \(LOS\) through the application of the Ad Hoc separation concept. FTS simulations were performed in RAMS to determine the benefits.  
The most significant outcomes were obtained in capacity KPA, with an increase of one aircraft per hour for the three scenarios studied. Although these results are positive, they highlight that the separation minima are not a key factor in estimating the capacity of an en-route scenario. Regarding the environment and the airspace user cost-efficiency, the results showcased favorable outcomes for both KPAs, although the impact may not be deemed very significant. The application of this concept in a broader scenario (ACC) than in a single sector would provide major benefits.  
Furthermore, through Ad Hoc separation, the number of ATCO interventions in the aircraft (for preventing or resolving \(LOS\)) is minimized, improving the aircraft and system performance (according to the previous findings). The outcomes obtained for these three sectors are representative and can be extrapolated to other sectors of similar complexity.  
Finally, according to the previous findings, it is suggested that continuing the development and research on this new separation mode could be beneficial for the ATM system. In addition, research areas were identified on which future work could focus: (1) ASMT verification and ATCO expert judgement for ASMT HMI graphical design; (2) more in-depth study of the E-OCVM validation methodology; (3) extending the application of the concept to Free Route airspaces; (4) generalization of the ADSM methodology.  
Conceptualization, L.S.-M. and L.P.S.; methodology, L.S.-M., J.A.P.-C. and M.P.M.; software, A.C.L.; validation, L.S.-M. and A.C.L.; formal analysis, L.S.-M. and J.A.P.-C.; resources, L.P.S. and E.S.A.; data curation, L.S.-M. and A.C.L.; writing--original draft preparation, L.S.-M; writing--review and editing, L.P.S., J.A.P.-C., A.C.L., E.S.A. and M.P.M.; funding acquisition, L.P.S. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Notably, the authors acknowledge ISA Software, who granted us the license to use RAMS Plus (6.7 version). This tool has been crucial for performing this research.  
The authors declare no conflict of interest.