What happened
On October 24, 2004, at approximately 11:35 AM, a H36 Dimona motor glider, registration HB-2059, departed from runway 12 at Bad Ragaz airport. The pilot, intending to fly to Saanen with one passenger, initially planned to use runway 30 due to wind conditions but ultimately opted for runway 12 following a change in the wind direction.
During the takeoff roll, the aircraft drifted left of the runway onto the grass because the pilot did not sufficiently correct for the torque-induced yaw characteristic of this model. The aircraft lifted off after a ground roll of approximately 330 to 350 meters. Upon leaving the runway, the aircraft entered a flight profile with a high angle of attack, flying in a steep climb that prevented further acceleration or altitude gain. The aircraft then veered left toward the village of St. Leonhard, where it collided with a tree at a high vertical load of approximately 20 m/G. The impact caused the aircraft to rotate 180 degrees and crash tail-first. The collision resulted in two serious injuries for the occupants and the total destruction of the aircraft.
The investigation
The investigation conducted by the Swiss Transportation Safety Investigation Board (SUST) examined the aircraft's technical condition, the pilot's experience, and the environmental factors. Investigators found no evidence of pre-existing mechanical failures; the engine was producing high power at the time of impact, and the control linkages and structural components were intact. The aircraft's weight and center of gravity were within permissible limits.
Technical analysis revealed that at such a high angle of attack, the pitot tube was being affected by the propeller wash, making the airspeed indicator unreliable. This likely caused the indicated airspeed to increase even as the actual flight performance degraded. The investigation also noted that the pilot had relatively limited experience with this specific aircraft type, with only 40.5 hours of flight time on the model and very little recent experience on the specific runway used.
Findings
- The primary cause of the accident was that the motor glider maintained a highly pitched flight attitude immediately after takeoff, which prevented the aircraft from accelerating or climbing effectively.
- The pilot failed to adequately compensate for the leftward yawing moment caused by engine torque during the takeoff roll.
- The high angle of attack rendered the airspeed indication unreliable due to propeller wash interference with the pitot tube.
- The presence of a terrain elevation (the "Büel" hill) likely influenced the pilot to maintain the steep pitch to clear the horizon.
- The aircraft was operating within its weight and balance limits, and no mechanical malfunctions contributed to the crash.