Primary finding
Probable cause
The pilot's encounter with sinking air conditions that resulted in a loss of lift and a subsequent loss of control.
Investigator assessment
Analysis narrative
The flight instructor reported that after demonstrating maneuvers he noticed that the glider had quickly descended to pattern altitude, so he proceeded into the traffic pattern. He slowed the glider to minimum sink airspeed and then turned onto the base leg about 200 to 250 ft above ground level. During the base leg turn, the glider continued to turn and descend, and the flight instructor was unable to maintain control. The glider impacted terrain short of the runway and sustained substantial damage to the fuselage, empennage, and both wings. The flight instructor reported that there were no preimpact mechanical malfunctions or failures with the glider that would have precluded normal operation. The flight instructor reported that there was sinking air in the flight area.