What happened
On July 4, 1971, a training flight was underway at Samedan Airport involving a flight instructor and a student pilot. The flight was intended as an orientation mission for the student, who was unfamiliar with the local flying conditions. The aircraft, an SZD-9 "Bocian", registration HB-648, was being operated via a winch takeoff method.
During the takeoff sequence, the glider reached an altitude of approximately 10 to 15 meters, at which point the aircraft was flown at a very steep angle of attack. This maneuver caused the airspeed to drop significantly, leading to visible oscillations around the longitudinal and vertical axes. At an altitude between 70 and 100 meters, the glider began to veer to the left. During this period of instability, the tow rope likely released from the aircraft's release mechanism, possibly triggered by the increased rope angle caused by the lateral deviation.
Following the release, the crew failed to sufficiently apply nose-down elevator to compensate for the loss of tension. Consequently, the airspeed dropped below the minimum stall speed. The aircraft entered a right-hand spin and struck the paved runway at 14:45 with a pitch angle of approximately 75 degrees. The impact resulted in two fatalities and the total destruction of the glider.
The investigation
Investigators examined the aircraft, the winch mechanism, and the flight conditions. The investigation confirmed that the SZD-9 "Bocian" was properly maintained and that the release mechanism functioned correctly within prescribed parameters. The winch itself was found to be in good working order and operated appropriately.
Technical analysis of the safety harnesses revealed a significant safety deficiency: the strength of the seatbelts and their attachment points was far below the required 680 kg standard, having failed at only about 210 kg due to inadequate welding. However, investigators concluded that the occupants likely would not have survived the impact regardless of the harness integrity.
Findings
- The primary cause of the accident was the undershooting of the minimum airspeed.
- The takeoff was executed with an excessively steep angle of attack.
- The crew did not apply sufficient nose-down input following the release of the tow rope.
- The student pilot had not performed a winch takeoff in this specific aircraft type recently, and the instructor had not performed a winch takeoff in eight years.