The CFI reported that during the takeoff the left hook of the winch harness released, uncommanded, from the center of gravity attachment. The glider yawed to the left toward a ditch on the west side of the runway. The CFI applied right aileron and full right rudder in an attempt to avoid the ditch however the glider continued into the ditch. The glider came to rest bridging the ditch on a heading of east. He reported that the ditch was full of broken and cut down brush and saplings. During the impact, a broken branch penetrated the left side of the cockpit and impaled itself in the CFI's right calf. The CFI remained hospitalized for five days following the accident. Members of the glider club reported that they had hooked both the left and right side cables prior to the takeoff. Inspection of the tow winch failed to reveal any mechanical failure/malfunction.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
Ground crew personnel improperly connected the tow winch cable prior to takeoff which resulted in one side of the winch cable coming disconnected. Factors associated with the accident were the ditch and the tree branch which the airplane contacted.