What happened
On August 20, 1998, a Super Dimona HK 36 TTC, registration HB-2309, departed from Schänis airfield for a planned 2.5-hour recreational flight. The aircraft was carrying a pilot and one passenger. During the flight, witnesses observed the aircraft performing several extremely low-level maneuvers over various landmarks, including flying as low as 2 meters above the Sihlsee and 10 meters above the Wägitalersee.
Approximately 34 minutes into the flight, the aircraft approached the Höhronen mountains near Wyssenbach. While flying at an altitude of roughly 30 meters, the pilot initiated a left turn. During this maneuver, the right wingtip collided with trees on a forested slope, causing the aircraft to crash. The impact resulted in two fatalities. The aircraft was destroyed by the collision and a subsequent intense post-crash fire.
The investigation
The investigation examined the aircraft's condition, the pilot's experience, and the flight preparations. Technical analysis of the wreckage, including the propeller and engine instruments, indicated that the engine was producing approximately 68% power at the moment of impact. No pre-existing mechanical defects were found in the control linkages or engine components.
Investigators also reviewed the aircraft's weight and balance. At takeoff, the aircraft was 37 kg over its maximum allowable takeoff weight due to being fully fueled for a long-duration flight. Additionally, the altimeter was found to be incorrectly set, showing an altitude approximately 900 meters higher than the actual altitude. Medical examinations of the occupants confirmed no evidence of impairment from alcohol or drugs, and no health issues were identified as contributing factors.