HISTORY OF FLIGHTOn August 24, 2016, about 1410 mountain daylight time, a Stemme Gmbh S10-VT self-launching (powered) glider, N5021, was substantially damaged during an in-flight collision with trees and terrain near Telluride, Colorado. The pilot and passenger sustained fatal injuries. The glider was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a local sightseeing flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The flight originated from the Telluride Regional Airport (TEX), Telluride, Colorado, about 1315. A witness reported seeing the powered glider climbing out from TEX. The engine "sounded perfect" at a constant power setting at the time. About 15 minutes later, he heard the sound of a "strained engine." It sounded as if there was a "strain on the propeller," similar to a propeller-driven airplane maneuvering during aerobatic flight. About 15 seconds later, the sound of the engine stopped. He subsequently overheard radio communications of mountain staff personnel responding to a downed aircraft. A second witness observed the powered glider fly by with the engine running. His co-worker commented that the glider seemed to be flying unusually low. It subsequently went out of sight below the tree line. About 10 seconds later, they heard a loud noise, which they initially attributed to work going on in the area. However, with thoughts of the low flying glider, he decided to drive to a nearby ridge where he observed the accident site. He reported the accident to the local authorities. PERSONNEL INFORMATIONThe pilot's logbook was not available to the NTSB and, as a result, his flight experience could not be determined. The pilot did not hold a current Federal Aviation Administration airman medical certificate, nor was one required to operate a glider. In February 1998, on his most recent application for a medical certificate, the pilot reported a total civilian flight time of more than 4,000 hours. No subsequent applications were on file. The pilot provided 30-minute and 1-hour sightseeing flights from TEX. Advertisement flyers were available at the TEX fixed based operator. The pilot maintained a website advertising the sightseeing flights. AIRCRAFT INFORMATIONThe pilot purchased the glider in July 2004. A review of the available maintenance records revealed that the most recent entry, dated September 20, 2012, was unsigned. The entry noted the completion of an annual inspection at airframe and engine total times of 1,824.2 hours and 496.3 hours, respectively. METEOROLOGICAL INFORMATIONOne witness reported light rain and steady surface wind about 8 mph from the northeast about the time of the accident. He stated that there was no thunderstorm activity in the immediate area; however, there was thunderstorm activity across the valley to the north and closer to the airport. Another witness reported that "dark rain clouds" began building near the site about 1 hour before the accident. Satellite imagery depicted growing cumuliform clouds near the accident site that were moving southeastward at the time. The cloud-top heights over the accident site were about 18,000 feet mean sea level (msl). Weather radar data depicted a rain shower over the site about the time of the accident. The rain shower activity was moving south-southeast and appeared to be dissipating. With dissipating rain shower activity directly above the site at the time of the accident, the glider was in a favorable region for downdrafts. No Significant Meteorological Information (SIGMET) advisories were in effect for the site at the time of the accident. An Airmen's Meteorological Information (AIRMET) advisory for mountain obscuration due to clouds and mist was in effect at the time of the accident. A full weather study is available in the docket for this accident case. AIRPORT INFORMATIONThe pilot purchased the glider in July 2004. A review of the available maintenance records revealed that the most recent entry, dated September 20, 2012, was unsigned. The entry noted the completion of an annual inspection at airframe and engine total times of 1,824.2 hours and 496.3 hours, respectively. WRECKAGE AND IMPACT INFORMATIONThe powered glider came to rest within a small cluster of trees about 5 miles south-southeast of KTEX at an elevation of 11,200 feet. The vicinity of the accident site consisted of mountainous terrain, densely wooded areas, and small meadows. The terrain gradually sloped downhill toward the north/northwest from the accident site. The elevations of ridgelines to the east and south of the site exceeded 12,500 feet. A postaccident examination and engine test run were conducted by the NTSB investigator-in-charge with the assistance of technical representatives from the airframe and engine manufacturers. The examination and engine run did not reveal any anomalies consistent with a preimpact failure or malfunction. MEDICAL AND PATHOLOGICAL INFORMATIONThe Montrose Memorial Hospital Division of Forensic Pathology, Montrose, Colorado, performed an autopsy under the order of the San Miguel County Coroner's Office, and attributed the pilot's death to multiple traumatic injuries sustained in the accident. Toxicology testing performed by the FAA's Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, was negative for all drugs in the testing profile. No carbon monoxide or ethanol was detected in blood specimens.