What happened
On May 19, 2013, an ASK 23 glider was performing a local flight via a winch launch at the Unterwössen glider field. The takeoff from runway 06 began normally, but shortly after liftoff, the aircraft failed to maintain a steady climb. The winch operator reported that the climb angle remained flat, causing the tow rope to develop significant slack.
At an altitude of approximately 10 meters, the rope disconnected from the glider. The pilot, perceiving insufficient upward pull, manually released the rope. In an attempt to maintain altitude, the pilot applied significant downward elevator pressure, which resulted in a steep descent at an angle of 30 to 40 degrees. Despite radio instructions from the launch controller to "pull, pull, pull," the aircraft continued its descent and struck the ground with a high sink rate. The impact caused the cockpit area to compress and the fuselage to buckle.
The investigation
The BFU examined the aircraft, the winch setup, and the flight conditions. The investigation included interviews with the pilot, the winch operator, and an eyewitness. The winch operator noted that he had increased the speed pre-selector by 5% to compensate for the windless conditions. The aircraft's flight data from a GPS device (Flarm) confirmed a maximum altitude of only 14 meters above ground level. The investigation also reviewed the pilot's recent flight experience and the aircraft's maintenance history, noting the glider had recently been re-registered in Germany.
Findings
- The pilot had set the trim to a nose-heavy configuration, whereas the flight manual recommends a neutral to slightly tail-heavy setting for winch launches to facilitate self-lifting.
- The loss of rope tension led the pilot to manually release the tow rope.
- The pilot's heavy application of elevator pressure during the descent contributed to the steep angle of impact.
- There were no technical defects found in the ASK 23 or the winch equipment.