What happened
On June 26, 1978, at 16:51 local time, a student pilot initiated a solo flight in a K-8B glider, registration HB-975, via aero-tow from Grenchen Airport. The tow was performed by a Robin HB-EXL aircraft. Shortly after takeoff, the glider began exhibiting increasingly severe undulating vertical oscillations. During a steep climb, while positioned approximately 10 meters above the tow plane, the glider pilot released the tow rope.
Following the release, the glider entered a tight, high-performance right-hand turn before transitioning into a near-vertical descent. During this maneuver, the cockpit canopy became detached from the fuselage. The aircraft struck the ground at high velocity at approximately 16:52, resulting in the death of the pilot and the total destruction of the glider. Minimal damage was sustained to ground structures.
The investigation
Investigators examined the aircraft wreckage and interviewed witnesses, including the tow pilot and a flight instructor who was traveling as a passenger in the tow plane. The investigation focused on the flight dynamics leading up to the release and the state of the aircraft's controls.
Technical examination of the release mechanism confirmed it was fully functional, suggesting the pilot intentionally released the rope. While the wreckage was too severely damaged to definitively determine if the elevator controls were operational, the investigation noted that the pilot was not properly secured in his harness at the time of impact, as the buckle was found open. Additionally, the tow aircraft, HB-EXL, was found to be approximately 26 kg over its maximum allowable takeoff weight during the flight.
Findings
- The primary cause of the accident was the loss of control of the glider due to undetermined reasons.
- The aircraft experienced significant turbulence and high wind gusts, with wind speeds reaching up to 25 knots.
- The flight instructor's presence as a passenger in the tow aircraft did not comply with established training guidelines or the aircraft's flight manual.
- The pilot was not properly restrained by his safety harness during the impact.
- The detachment of the cockpit canopy occurred during the high-G maneuver preceding the dive.