Date: 201412
Local time of day: 0001-0600
Location: ZAB.ARTCC, NM
Aircraft: UAV - Unpiloted Aerial Vehicle
Flight plan: IFR
Flight phase: Cruise
Airspace: Class A ZAB
ATC / advisory: Center ZAB
Second aircraft: Super King Air 200
Reporter organization: Government
Reporter function: Enroute
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Training / Qualification
Anomaly: Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Due to poor staffing we had sector 46 combined over at R42. I am here on yet another overtime shift and even with me and another overtime we are still below numbers. So there is an issue right there but not the one we are here for. So I am working R42 with 46 combined. I am aware that we have an UAV returning. I have already been looking for him and have seen his code and started the track for him when he calls center. I tell him to go ahead and he says he is giving us a radio check 7 min south of VYLLA. I give him his code and have him ident and radar identify him 30 miles south of VYLLA. He is level at FL210. I go about work and have the supervisor call the inbound since I am busy with two sectors and two frequencies; so I'm already dealing with frequency congestion with the two sectors frequencies. I now have a BE20 call me south of VYLLA and I radar identify him level at FL200. Unexpectedly; the UAV starts descending. He is still south of VYLLA and about 4 miles east of the BE20. So separation is already lost. I call the UAV and tell him to climb to FL210. He doesn't respond and continues descent. I call again and he finally answers and I clear him back to FL210 and call the traffic. He acknowledges and says returning to FL210. I then try to ascertain why he was descending to FL200. He responds by saying he has just leveled at FL200 after I had cleared him and he acknowledged the climb to FL210! I again tell him to climb and maintain FL210 and I also turned him 20 right since he and the BE20 were both converging at VYLLA and since he clearly didn't understand my clearance to FL210. He again acknowledges the climb and turn and finally starts the climb. As soon as the BE20 enters my airspace I descend him to FL180. I keep trying to get the UAV pilot to give me his reason for his descent and I finally get that they had just made a 'pilot swap' and that the LOA states they cross into US airspace at FL200 so he just descended to FL200. I ask if the Controller had issued that crossing instruction and he says negative it is in the LOA. I advised him the LOA doesn't supersede ATC clearances and he cannot descend without a clearance from ATC. If we are expected to work more and more UAVs then the pilots of the UAVs need to be trained pilots in the NAS. They should hold current pilots licenses with proper ratings. They need to understand they must obey all ATC clearances and that an ATC clearance supersedes any other LOA or flight plan or anything. Also UAVs are notoriously hard to get a hold of sometimes and they often go NORDO for long periods of time. Their radios are poor and transmissions are hard to understand much of the time. If this UAV hadn't finally responded to me he could have been over VYLLA at FL200 at the same time as the BE20. Of course I would have tried to move the BE20 but when dealing with Foreign ATC sometimes they get lost in the transfer and they don't ship aircraft until they are over VYLLA. This could have been worse than a loss of separation. I feel that we need to relook at UAVs in the NAS. Are they safe? Are the pilots properly trained and do they understand how things operate in the NAS?




Synopsis: ZAB Controller reports a UAV descending without clearance; causing loss of separation with a BE20. The UAV pilot stated he was descending in compliance with the LOA. The reporter believes that UAV pilots should have licenses and be properly trained to fly an IFR clearance in the NAS.