What happened
On July 31, 1966, a Mucha 100 A glider, registration HB-647, was engaged in a soaring flight near Schaffhausen, Switzerland. After being towed to an altitude of approximately 200 meters, the pilot released from the towline and began flying along the western slope of the Siblinger Schlossranden. While initially experiencing light upward lift, the pilot noted a decrease in lift as the aircraft moved further into the valley.
While flying at approximately 75 km/le, the pilot attempted a left-hand turn to reverse course within the Churztal valley. During this maneuver, the aircraft experienced a sudden drop in airspeed. Despite the pilot's attempt to correct the flight path by pushing the control stick forward to regain speed, the aircraft's altitude was already too low to recover. The left wingtip struck trees, causing the glider to crash into the forest.
The investigation
The investigation examined the pilot's experience, the aircraft's performance, and the environmental conditions at the time of the accident. The pilot had approximately 51 hours of total glider flight experience, with very limited time specifically logged on the Mucha 100 A model. Meteorological data indicated moderate turbulence and winds from the west-southwest at 20 to 30 knots.
Investigators analyzed the aerodynamic limits of the Mucha 100 A, noting that while the stall speed in level flight is 50 km/h, it increases to approximately 54 km/h during a 30-degree banked turn. The investigation also reviewed the flight path relative to the terrain and the regulatory requirements for minimum flying altitudes in such environments.
Findings
- The pilot was flying at an altitude that was insufficient to allow for a recovery maneuver once the loss of airspeed occurred.
- The aircraft's altitude had dropped below the 50-meter minimum ground clearance required for glider operations in this terrain.
- The pilot's decision to enter the Churztal valley was problematic, as the wind conditions made it inevitable that the aircraft would encounter lee-side downdrafts.
- Improper flight tactics and a failure to maintain adequate altitude were the primary contributing factors to the accident.
Safety action
No specific safety recommendations were recorded in the final report, though the investigation highlighted the risks of flying in lee-side turbulence at low altitudes.