On July 26, 2013, approximately 18:50 Alaska Daylight Time, a National Aeronautics and Space Administration (NASA) Sensor Integration Evaluation Remote Research Aircraft (SIERRA) single-engine fixed wing unmanned aircraft system (UAS) was substantially damaged following an engine power loss and uncontrolled descent into the Beaufort Sea, 65 nautical miles north of Oliktok Point, Alaska. The flight was conducted as a non-military public aircraft operation under the provisions of Title 49 of the United States Code (U.S.C.) Sections 40102 and 40125, and a Federal Aviation Administration (FAA) Certificate of Authorization (COA). There were no injuries. The UAS was on it's maiden science flight for the Marginal Ice Zone Observations and Processes Experiment (MIZOPEX) and lost engine power 4.5 hours into the 6 hour scheduled flight. The UAS was powered by a 26 horsepower Herbrandson Dyad 290B 2-cycle carbureted engine with a belt driven pusher fixed pitch propeller. The flight crew noted a loss of engine RPM and electrical bus voltage on the CloudCap Piccolo Autopilot (AP) system display that was part of the ground control system (GCS). The UAS was beyond the range of the hand held radio and under the control of the Piccolo AP, upon losing power the GCS operator was unable to issue any commands to the aircraft. Telemetry data revealed that for a period of about 60 minutes prior to the accident, RPM and altitude fluctuated, and throttle demand increased, indicating the possibility of engine intake icing. Weather conditions at the time of the accident were included relative humidity (RH) from 85% to 95%, at 4 degrees C. The nearest observation sites to the accident were Deadhorse (62 km) and Nuiqsut (52 km). Both of these stations reported temperatures ranging from 9 to 14 degrees Celsius during the flight time. The National Center for Atmospheric Research examined the weather conditions and concluded a high risk for carburetor ice existed. The MIZOPEX Project was under significant time and budget constraints due to a change in project plan from a larger UAS platform requiring payload bay changes within the original funding timeline. A full NASA Mishap Investigation Team report of this accident is available in the public docket for this case.