# Implementing and Testing a U-Space System: Lessons Learnt
## 3 The U-Space Services
### Monitoring  
The three following services of this category were implemented:  
* **Monitoring**. As aforementioned, when it comes to comply with the waypoint constraint related to the fourth dimension of the 4D trajectories, depending on the drone, it could be capable to try to comply with speed, ToA or none of them. The implemented conformance monitoring service may consider this while verifying whether the trajectory constraints were met. With respect to the 3D position, a light deviation warning was sent when the aircraft came notably apart from the planned route (10 m radius) but still inside a deconflect tube (of 20 m radius) reserved by the path planner around it. If leaving this tube, a severe deviation warning was sent, traffic around warned and the tactical separation service was triggered if conflicts appeared. * **Traffic Information**. Users received constant updates on the positions of the close traffic, warnings or information like flight cancellations and their reason. In the Web app, the icons of non-nominal flights appear with a warning icon, together with the mentioned red shield box (Figure 18, bottom right). Lost link events between the UAV and U-space or the GCS appear with different color icons in the flight strip that represents the flight status and its associated actions in the interface (Figure 18, top right), and some other events will print a textual message for the pilot, together with an aural warning for the important events or those requiring immediate attention. However, after watching the aircrew using the interface during the tests, it was obvious that an improvement in the usability of the Web app was required. Future work should be directed to allow for the filtering of some non-critical types of messages. This filtering could be set manually by the user or determined in a smart way by the system depending on the kind of user or the current situation, i.e., if a pilot is currently flying a drone, is it appropriate or necessary to display to the pilot in that moment messages about other canceled plans? Within which distance from the flying drone does it make sense to warn a pilot about other drone in distress? Also to reconsider was the way the textual warnings were shown to the pilot (Figure 18, left). To be sure that the pilot would read the important messages, pop ups were displayed in the right bottom corner of the screen and they would not disappear until the pilot clicked on them. The option of a warning displayed for some seconds was discarded because the pilot could be looking at the GCS in that moment and miss it. But when a series of important events happened, this resulted in a stack of messages (Figure 19) and an annoyed pilot struggling to close them or just ignoring them. A better way to display  
Figure 17: Drone in distress receives a wider separation, which is represented with a red cube. these events must be chosen to avoid adding more mental workload to the pilots while keeping them aware of the details of the safety-relevant events. Here again, a mix of a smart warning functionality able to evaluate the need of a warning for a specific user, and a more appropriate display element, could be the solution. Figure 19: Post-flight scenario. Bottom right: an accumulated stack of messages not attended by the pilot. Red cubes represent protective geo-fences created as a result of reporting inaccuracies or missing reports. The coloured continuous lines describe the trajectory followed by the drone given the reporting positions received. The vertical lines are the waypoints of the flight plan. Figure 18: Lost link warnings: yellow icon, between UAV and UTM; red icon, between UAV and GCS. Drone icon changes when the UAV suffers some non-nominal situation. * **Legal Recording. ** Communications related to the flights, events, user requests and errors were registered in log files for later analysis. These would also be used by the partner Austrian Institute of Technology (AIT) to train the algorithms that would detect unexpected values and therefore possible spoofing [31].