## 3 Results
### Cooperative Detect and Avoid Approach  
The UTM-supported, cooperative collision avoidance approach was tested with two multicopter, each equipped with a MMT device. The trajectories of both UAVs are shown in Figure 11. Uas1 (ownship) performed a fully automated flight, while the intruder was flown manually. To rule out a mid-air collision even in the event of system failure, different flight altitudes were chosen for ownship (10 m) and intruder (25 m).  
Discrepancies could be observed in the reported altitude of uas1 via the UTM network and via ADS-B. Figure 12 shows the visualisation of the received traffic information from uas1 as seen by uas2 in experiment V5. Via the UTM network, a flight altitude of 25 m Above Ground Level (AGL) (i.e., including the elevation of approx. 550 m corresponds to 575 m or 1886 ft Above Mean Sea Level (AMSL)) was reported for uas1 (green dot in Figure 12 named _uas1_), whereas the MMT received via ADS-B a flight altitude of 495 m or 1624 ft AMSL (red dot in Figure 12 named _UNIBWT01_). This results in an altitude difference of \(-80\) m or \(-262\) ft. Figure 13 shows the received altitude information in more detail.  
Figure 10: Flight path (clockwise, starting at the leftmost waypoint) of uas1 (**blue solid line**) inside and outside a virtual control zone (**red dashed line**) with clearance-free (**blue circles**) and clearance-mandatory waypoints (**red rectangles**). Waypoints filled in green indicate where the UAV has automatically transitioned into hovering to request clearance for the next waypoint from ATC.  
Figure 11: Flight path of uas1 (**blue solid line**) and real cooperative Intruder uas2 (**red solid line**). Green dots indicate where uas1 has independently transitioned into hovering to avoid a collision with uas2.  
Figure 12: GUI of the UserApp (from the perspective of a user with ownship _uas2_) with different received altitude information from _uas1_ (**green dot** = traffic information received from UTM network, indicating an aircraft at an altitude of 25 m AGL, **red dot** = traffic information obtained by ADS-B, indicating an aircraft with callsign _UNIBWT01_ at an altitude of 495 m and another one with callsign _UNIBWM_\(A\) at an altitude of 472 m AMSL).  
The cause of this deviation can be attributed to the difference between the barometric setting of the MMT and the actual prevailing air pressure situation. The MMT has its own certified barometer which is set to the standard QNH setting in accordance with the applicable regulations. SAE AS8003 [37] specifies a barometric encoder accuracy of \(\pm 125\,\mathrm{ft}\) and a resolution of \(100\,\mathrm{ft}\). However, modern barometric encoders support accuracies of \(25\,\mathrm{ft}\), including the MMT. Via the OnboardApp, the MMT receives the fused positioning data from the FMS (based on non-certified COTS GNSS, inertial and pressure sensors with a stated vertical positioning accuracy of \(\pm 0.5\,\mathrm{m}\) or \(\pm 1.6\,\mathrm{ft}\)[38]), but only takes over the latitude/longitude information and combines it with its own barometric altitude information before the data is eventually broadcasted as an ADS-B Out signal. On the day of the flight test, the temperature was approximately \(T=8\,\mathrm{\SIUnitSymbolCelsius}\) with an air pressure of around \(P=1023\,\mathrm{hPa}\). According to the hyposymetric equation (see Equation (A4) in Appendix A), the altitude difference is ca. \(h=-79\,\mathrm{m}\) or \(-259\,\mathrm{ft}\), which corresponds approximately to the measured values.