Stemme Gmbh & Co S10 VT N5021 accident near Telluride, Colorado

Probable cause

The pilot's encounter with a downdraft that exceeded the climb performance of the powered glider and resulted in his inability to maintain clearance from the trees. Contributing to the accident was the pilot's decision to fly near building clouds and rain shower activity.

NTSB analysis

The pilot was conducting a local sightseeing flight at the time of the accident. A witness reported seeing the powered glider climbing out after takeoff and the engine "sounded perfect." He subsequently heard the sound of a "strained engine" similar to a propeller-driven airplane maneuvering during aerobatic flight. Shortly afterward, the sound of the engine stopped. A second witness observed the powered glider fly by with the engine running. It subsequently went out of sight below the tree line. Shortly afterward, he heard a loud noise that he 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.

A postaccident examination and engine test run did not reveal any anomalies consistent with a preimpact failure or malfunction.

Witness statements and satellite imagery indicated that building cumuliform clouds were present near the accident site. Weather radar data depicted a rain shower over the site about the time of the accident that appeared to be dissipating. With dissipating rain shower activity, the glider was in a favorable area for the existence of downdrafts. It is likely that the pilot encountered a downdraft that exceeded the maximum climb performance of the powered glider.

Text from the NTSB. Open the NTSB docket for CEN16FA331 for the full record.