## 3 System Requirements for BVLOS Flight Operations
### RAVEN-Proposed Small UAS DAA System
#### 3.5.4 Evasive Maneuvering Algorithm for Collision Mitigation Solutions  
In Figure 12, once NMACs are projected and the break-ins are predicted on the CAAT boundary in the next five seconds, the evasive maneuvering algorithm evaluates collision risks and triggers horizontal maneuvers, based on the traffic-detected relative bearing (\(\beta_{\text{train}}\)) and the traffic relative heading (\(\psi_{\text{train}}\)) with respect to the UA in four quadrants from 0\({}^{\circ}\) to 360\({}^{\circ}\). In each quadrant in Figure 12, when traffic is heading to the red regions (displayed as the red arc areas), the algorithm starts to initiate evasive maneuvers to steer the UA to the safe regions which are far away from traffic. The UA will then remain there until the horizontal range rate \(r>0\) and the horizontal range \(r>2\) nmi between the UA and traffic. Assume that maximum 2 g turns (turn rate at 6\({}^{\circ}\)/s) can be achieved on the UA. The UA horizontal maneuvering options at four quadrants in Figure 12 are designed differently and their details are described as follows:  
Figure 11: Summarized CAAT boundaries (bearing in deg, range in nmi, UA at 75 kt, and traffic at various airspeeds). (**a**) CAAT obtained without wind; (**b**) Summarized with various 20 kt gusty winds. Figure 10: Diagrams to locate CAAT boundaries (bearing in deg and range in nmi). (**a**) Alerting threshold boundaries; (**b**) Simulation web structure. **(1) Horizontal maneuvers in quadrant I:**  
As shown in Figure 13a,b, the maneuvering strategy in quadrant I is to let the UA fly to safe waypoints in quadrant II, which are located at a position 90\({}^{\circ}\) off the traffic break-in bearings on the WC boundary in quadrant II. Upon the traffic break-in bearings, the UA make left turns or right turns to fly to the predefined safe waypoints. The UA make right turns when the break-in bearing is less than 45\({}^{\circ}\); and the UA make left turns when the break-in bearing is greater than 45\({}^{\circ}\). **(2) Horizontal maneuvers in quadrant II and III**  
In Figure 13c,d, two maneuvering strategies are described for the cases when traffic are coming from the rear of the UA. In Figure 13c, the UA make left turns to fly to the predefined safe waypoints in quadrant III when the traffic break-in bearing is in quadrant II (rear right of the UA). In Figure 13d, the UA make right turns to fly to the predefined safe waypoints in quadrant II when the traffic break-in bearing is in quadrant III (rear left of the UA). **(3) Horizontal maneuvers in quadrant IV**  
In Figure 13e,f, the UA make left turns to fly to the predefined safe waypoints in quadrant III when the break-in bearing is greater than 315\({}^{\circ}\); and the UA make right turns to fly to the predefined safe waypoints in quadrant III when the break-in bearing is less than 315\({}^{\circ}\). **(4) Vertical maneuvering strategy in the three-dimensional evasive maneuvering algorithm**  
In collision mitigation, horizontal and vertical maneuvers are typically engaged at the same time to help small UAS escape from emergencies as soon as possible. The vertical maneuvering strategy is designed based on the vertical separation \(d_{h}\) and the traffic vertical rate \(\dot{h}_{\text{\tiny{maxive}}}\); namely, it is to increase the vertical separation between the UA and traffic, so that the vertical separation at the horizontal Closest Point of Approach (CPA) can be greater than 100 ft (\(h_{\text{\tiny{maxive}}}=\pm 100\) ft). This strategy is described in further detail with the corresponding diagrams for different encounter geometries in Table 2.  
Figure 12: Horizontal maneuvering strategies in the three-dimensional evasive maneuvering algorithm. Figure 13: Horizontal maneuvering strategies in quadrant I, II, III, and IV.