What happened
On August 1, 1973, at approximately 14:30 CEST, a pilot was conducting a glider tow operation from the Schänis airfield using a Champion aircraft, registration HB-UAV. After successfully releasing the glider, the pilot returned to the airfield to land on the dry, paved runway 17.
Upon touchdown in a three-point position, the aircraft veered sharply to the right. Despite the pilot applying opposite rudder and engaging the left wheel brake, the aircraft drifted off the runway. The aircraft crossed an 8-meter wide stabilized grass strip and entered an adjacent area of marshy ground covered in tall grass. While traveling at a relatively low speed through this terrain, the aircraft overturned at approximately 14:43.
The investigation
The investigation confirmed that the pilot held a valid private pilot license and was authorized to perform the glider tow. At the time of the accident, the aircraft's weight was 581 kg, well within the maximum allowable limit of 750 kg. The center of gravity was also found to be within the permitted range.
Technical inspections revealed that the Champion was airworthy and properly registered. There were no evidence of mechanical failures; specifically, the wheel brakes and tailwheel steering mechanism were found to be in good working order. Weather conditions at the time were reported as having light, variable winds and good visibility.
Findings
- The aircraft's movement into the marshy area was caused by a lateral excursion during the landing roll.
- The aircraft type is known to be prone to veering or ground looping during landings on paved surfaces, particularly when landing with a forward-moving tendency.
- The overturn was primarily caused by the aircraft rolling through the soft, swampy terrain.
- The position of the center of gravity, which was at the forward limit of the allowable range, contributed to the tendency of the aircraft to overturn once it entered the marsh.