*3.4. Safety*

The bespoke statements regarding the perceived safety are shown in Figure 13. All statements regarding the general perceived safety received a mean rating higher than three (neither agree nor disagree) at the minimum. From this rating, it became apparent that the ATCOs seemed to feel in control and safe in controlling the traffic, including the area around the LMP where the traffic was converging as well.

During the debriefing, the ATCOs reported overall safe operation within the new airspace design. Nevertheless, some safety-critical situations were reported, which are also shown in the recorded data. Critical situations were mainly related to the simulation setup, technical issues or lack of experience with the system—for instance, difficulty in judging distances due to lack of measurement tools in unknown airspace. Although aircraft might need to keep adjusting their flying speed constantly to meet the negotiated target times, no further risk was produced. These results reflect the subjective feedback from ATCOs gathered through the questionnaire and debriefing.

**Figure 13.** Mean agreement to tailored statements regarding the perceived safety for all scenarios. Error bars represent standard deviations.

#### *3.5. Tactical Assistance Systems*

The feedback on the three tactical assistance systems was not free of contradictions. However, the main feedback was positive rather than negative, along with suggestions for possible improvements. All in all, the tactical assistance systems provided the required information about the projected aircraft's positions on the final approach in line with the sequences computed by the AMAN. The provided information was reported by ATCO as helpful to obtaining the whole picture of the traffic situation and to plan ahead. Participants made also several suggestions to further improve the provided data, indicating that there is room for improvements. Some examples of the suggested improvements are listed in the following paragraph.

Based on feedback collected from all ATCOs, the time-based ghosting tool was one of the most used and useful assisting tools made available during the validation trials. It was even considered by most of ATCOs as necessary and crucial for handling the 4D-FMS traffic safety-wise. Participants reported also that they would even like to have it for real operations to be used for other purposes. Nevertheless, some ATCOs felt distracted by the ghost symbol, which could tie up mental capacity. Some would only like to have the sequence number above the ghost symbol or to reduce the label by displaying only the callsign. Others would like to see a special marker when the real aircraft deviates too much from the planned route due to certain environmental conditions. This request could be accommodated by enabling the ATCO to individually customise the ghost symbol using different shapes and colour settings. The ATCOs perceived the TargetWindow as helpful and sufficient for handling the conventional 3D-FMS traffic, making the CSVT superfluous. Consequently, the CSVT was rarely used. Additionally, the ATCOs recorded some minor technical stability issues, which means that in some cases, aircraft did not have a TargetWindow, or the label was shown on the wrong side of the runway system. As an improvement, some features should be made available to ATCOs, enabling them to manually adjust the label, shape and colour settings for the TargetWindow itself. This feedback is in line with feedback on the ghosting.
