Aircraft and Pilots
The Piper J3C, registration HB-OSL, was a two-seat high-wing monoplane built around 1942, powered by a Rolls-Royce O-200 A engine. It was not certified for glider towing but had a tow hook and indicator installed. The glider was a SZD-9 bis Bocian (HB-596), a two-seat shoulder-wing design. The motor plane pilot, born in 1933, held private and commercial pilot licenses, including a towing endorsement, and had 208 hours of motor flight experience (107 hours on type). The glider pilot, born in 1922, held private and glider licenses, with 270 hours motor and 52 hours glider flight time. The glider carried a passenger, the pilot's son.
Accident Sequence
On Saturday, 24 August 1968, at 1634 local time, the tow plane and glider departed from Sitten airfield. After takeoff, the tow proceeded upwind towards the Mont d'Orge ridge. At 1639, the glider released south of the crest at approximately the same altitude. Shortly after release, the motor plane stalled and struck rocky terrain about 10 meters below the ridge at an elevation of 776 meters. The pilot was killed and the aircraft was destroyed.
Investigation Findings
Weather conditions included clear skies with 1/8 cumulus cloud cover, visibility 12 km, wind from 240° at 20 knots gusting to 30 knots, and moderate to strong turbulence near the ground. The tow rope was 60 meters long with breaking strengths of 952 kg forward and 749 kg aft. The motor plane's weight and center of gravity were within limits. The aircraft had been refueled before the flight and was inspected during a prior tow that day with no issues noted. The motor plane was not equipped with a rearview mirror, which was required for towing certifications. Logbook entries showed the aircraft had been used for towing on multiple occasions despite its lack of towing certification, leading to a mistaken belief among pilots that it was authorized.
Probable Cause
The official investigation concluded that the accident was due to inappropriate towing flight tactics, possibly toxically conditioned.