# ATC Human Factors Involved in RPAS Contingency Management in Non-Segregated Airspace
## 2 Method
### Nominal RPAS Conditions and Contingencies into Non-Segregated Airspace
#### 2.3.2 Loss of the Command-and-Control Link Contingency  
One of the main characteristics of an RPAS is that the aerial vehicle is remotely controlled by a communication system based on the C2-Link. If there is a failure in the communication link, then there is a lack of ability to transmit guidance to the RPAS and receive feedback regarding the state of the vehicle and its location. Eventually, the link may be regained after some time or become a total loss if the failure remains for the rest of the flight. Given that the C2-Link is independent of the other communication links, voice communication may still be relayed through the RPAS or ground infrastructure and ATC may still be able to see the mode-S or other transponder information from the RPAS. Those datalinks may remain fully operative as they depend on a separate infrastructure; rather, they operate on a broadcast configuration (ADS-B) or point-to-point through an alternative ground/satellite infrastructure (ADS-C). The failure of the ADS-B/ADS-C infrastructure would reduce the surveillance of the RPAS to basic radar surveillance (PSR/SSR) and render the pilot blind concerning the RPAS's whereabouts. In the event of a total loss of the C2-Link, the RPAS flight management system should still be able to detect that contingency and revert the vehicle's operation into a fully autonomous mode. Such contingency trajectories should be anticipated to ensure the safety of all airspace users. The loss of C2-Links may not necessarily imply a degradation of the RPAS airworthiness, but such a state implies an immediate declaration of an emergency. From an ATC perspective, either the loss of the C2-Link or the loss of the remote pilot to the ATC link is managed in an equivalent way. In both cases, the lack of ability to transmit clearances to the RPAS and receive appropriate feedback about the state of the flight is considered equivalent to a case of a total loss of communications in a manned aircraft. As a result, the command-and-control link loss would be treated accordingly, with a procedure based on ICAO Annex 10 \"Loss of communications procedure\" [23]. Under these circumstances, completing the full RPAS flight plan, including the mission segment, may be in doubt, but the initially planned landing site must remain the primary objective. The ICAO procedures for loss of radio should be strictly maintained. Full flight plan completion is assumed in airliner operations. However, in the specific case of RPAS operations, it becomes a big discussion point whether the targeted mission should be cancelled earlier, especially considering that some missions for high-performance RPAS platforms may last more than 24 h.  
When considering the mission cancellation and return routes, it should be noted that a certain margin of time is advisable before the RPAS performs any actual action. The RPAS pilot should use this buffer time to try to regain the C2-Link and the ATC to make the proper traffic arrangements to absorb the impact of the new situation. Hence, an RPAS under loss link should maintain the last assigned speed and level for a minimum of a few minutes before initiating any further manoeuvre. A final factor to consider is how the RPAS would descend to landing altitude. Again, two alternatives may be employed according to the ATC criteria or other context factors: (1) The RPAS may descend from a predefined top of descend point until the holding position associated with the landing Initial Approach Fix (IAF). The RPAS should wait there for 30 min as prescribed by ICAO procedures and then proceed to land. (2) The RPAS may remain at its last cleared altitude, flying to the selected IAF following the intended flight plan. Once over, the IAF at cruise altitude, the RPAS could continuously descend until the prescribed IAF altitude is reached. If more than 30 min were employed while descending, the landing could be initiated immediately. If not, the RPAS should hold for the remaining time and then initiate the landing procedure.