**5. Conclusions**

The development and implementation of the GreAT concept within the DLR realtime simulation environment ATMOS was realised. The HITL validation campaign was conducted with a total of five ATCOs from HungaroControl. The obtained results allow two conclusions to be drawn. The first one indicates that the developed GreAT concept has proved to be supportive for ATCO by sequencing arrival traffic in a safe and efficient manner. This has a proven influence on the mean flight distance per aircraft, and therefore, a positive impact on the reduction of overall fuel consumption. Furthermore, reducing the total fuel consumption mitigates the exhausted gas. These results indicate that through the implementation of the GreAT concept, a important reduction of aviation's environmental impact is feasible. The second conclusion is that the 4D-FMS aircraft guidance may to certain extent increase airport capacity. Increasing the number of aircraft equipped with advanced FMS leads to more landed aircraft with shorter flown distances, while keeping the mental workload, situation awareness and safety to acceptable levels. All in all, the GreAT concept carries the potential to lower aviation's impact on the environment while keeping airport capacity at least on the same level. Further research should focus on the large-scale implementation and gathering of statistically significant results by increasing the sample size. Additionally, a baseline for the human performance results could bring new insights on the impacts of the GreAT concept on mental workload and situation awareness.

**Author Contributions:** Conceptualisation, N.A., I.S., T.M. and M.-M.T.; methodology, N.A., T.M. and M.-M.T.; simulation and software, N.A.; validation, N.A., I.S., R.A. and M.-M.T.; formal analysis, N.A., I.S., R.A., T.M. and M.-M.T.; investigation, N.A.; resources, T.M.; data curation, N.A.; writing original draft preparation, N.A., I.S., R.A., T.M. and M.-M.T.; writing—review and editing, T.M. and M.-M.T.; visualization, N.A., I.S. and M.-M.T.; supervision, T.M.; project administration, T.M. and M.-M.T.; funding acquisition, M.-M.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement n◦ 875154.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** Data can be available by contacting the corresponding author, Nils Ahrenhold. Data for reference study were taken from https://opensky-network.org/datasets/ states/, accessed on 18 November 2022.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **Abbreviations**

