Background
On 16 July 1963, the Grunau Baby II glider, registration HB-246, was involved in an accident near Bad Ragaz, Switzerland. The aircraft was owned by the Segelfluggruppe Arosa des AeCS and possessed a current airworthiness certificate issued on 7 June 1961, as well as a traffic permit dated 2 August 1938 valid until 6 June 1964.
The pilot, born in 1933, held a glider pilot license issued on 27 June 1960, valid until 19 August 1963. His flight experience totaled approximately 38 glider flying hours in 122 flights, of which about 23 hours were accrued in 25 flights since obtaining his license. His training had been interrupted for over a year before the accident date.
The airfield at Bad Ragaz has a runway length of 515 m. Runway 29 presented unfavorable conditions because a high-voltage power line, approximately 30 m high, crossed the takeoff direction about 550 m beyond the end of the runway.
Accident Sequence
On the day of the accident, after a break of more than a year, the pilot resumed glider training. A first training flight of 15 minutes proceeded normally. At 17:45 MEZ, he launched for a second flight, again using aero-tow behind the motor aircraft Chipmunk HB-TUE. The pilot perceived the takeoff as somewhat slow. As the tow approached the high-voltage power line, he gained the impression that the tow plane would not clear the obstacle. Consequently, he released the tow rope and initiated a steep climb in an attempt to underfly the power line. He successfully avoided a collision with the lowest cable but was unable to recover the glider in time. The aircraft struck the ground at a steep angle.
During the accident, the pilot sustained only minor abrasions. The glider was completely destroyed. No third-party damage occurred.
Investigation
The investigation was opened on 23 July 1963. Weather played no role in the accident.
According to statements from both participating pilots (the glider pilot and the motor aircraft pilot), the tow likely had sufficient altitude to clear the power line. After the glider released, the motor aircraft overflew the line without contact, even with the tow rope hanging down. The glider pilot's position, having been above the tug, likely created a perspective that led him to misjudge the clearance distance, as he may have seen the power line cables approximately in line with the tow rope.
The subsequent actions support the conclusion that adequate height existed: to underfly the line after release, the pilot must have pitched down steeply, and then could not recover before ground impact. The pilot's limited flying experience (approximately 22 hours 45 minutes of gliding time) and the long break from training made such a misjudgment plausible.
Conclusion
The accident was attributed to the glider pilot's incorrect assessment of the situation. Fearing a collision between the tow and the power line, he released the tow just before the line and, during an attempt to underfly it, struck the ground because he was unable to recover the glider in time.