SEA01LA153 · LET Blanik L-13

The glider pilot reported that the towline prematurely released from the tow plane (Piper PA-18). He reported that this occurred shortly after takeoff from runway 28, about 200 feet above ground level (AGL). After the unscheduled disconnect, the glider pilot initiated a turn to the right in an effort to reach the departure runway. He reported that during the turn, the glider "pitched down" and did not respond to control inputs. Shortly thereafter, the glider impacted trees and terrain. This was the second failed attempt to launch the glider; the first attempt resulted in an unscheduled release immediately following the initiation of the tow. Following the first unscheduled release, the "Field Manager" reconnected to towline to the PA-18, and the second tow was initiated. In both cases, the towline prematurely released from the release hook on the tow aircraft, but remained attached to the latching mechanism on the glider. The handle for the tow-hitch is located on the floorboard of the tow plane's forward cockpit. To open the hitch, the handle is moved from the forward position to the aft position. According to the tow plane pilot, the handle had not been actuated and was in the forward position when the unscheduled releases occurred. Postaccident examination and testing of the tow-hitch revealed no discrepancies or anomalies that would explain the unscheduled release. In a written statement, the glider pilot indicated that he had not been briefed on potential emergency landing sites near the departure field. Additionally, he stated that had he been briefed, he would have "...made the decision to fly to such a site given my altitude at release." The elevation at Bergseth Field is approximately 1,100 feet mean sea level (MSL). Runway 10/28 is a 2,100 by 60 foot turf runway, with rising terrain to the east and sloping terrain to the west The terrain to the west slopes down to an elevation of approximately 500 feet MSL.

Verbatim NTSB analysis and probable cause from the NTSB dataset