UAV - Unpiloted Aerial Vehicle
Flight Crew Last 90 Days 10; Flight Crew Total 50; Flight Crew Type 4
Situational Awareness
Deviation / Discrepancy - Procedural FAR; Inflight Event / Encounter Loss Of Aircraft Control
General None Reported / Taken
Environment - Non Weather Related; Human Factors
I was flying a small UAS. During the flight; the aircraft passed in front of the sun and I lost visual contact for approx. 10 seconds. Afterwards; I could not reacquire visual contact. I could hear the propeller and executed what I estimated was a 180 degree turn with the throttle at mid-position to bring the plane back to my location. After waiting approximately the time the plane had been flying away from me; I scanned the likely area of sky but could not see it. I then executed a 90-degree banked turns to put the increase the visibility of the plane (the plane was flying in a stabilized mode with a roll limit of 90 degrees; so full aileron stick-deflection would cause a consistent 90-degree bank angle). When I was unable to see the plane (I could still hear the propeller at this point) I executed a series of turns while monitoring the RSSI (receiver signal level transmitted from the plane back to the transmitter) and tried to find a course that would increase the RSSI level indicating the plane was flying closer. Unfortunately; the RSSI telemetry system is not very accurate at this range and I was unable to get a stable enough signal. At this point the telemetry link was lost (the transmitted signal has a substantially longer range). To minimize any potential damage on landing; I closed the throttle and applied full back elevator to slow the forward speed and descent rate until I estimated the plane would have landed (approximately one minute). The primary initiation of this event was a brief loss in awareness of the plane's path relative to the sun. Normally I avoid flying near the sun but in this case I misjudged.
UAV operator reported losing sight of the drone while controlling it in-flight.