Flight Sequence
On Sunday, 26 August 1973, at 1359 hours Central European Time, a student pilot departed from Olten airfield in a Schleicher Ka 8B glider (registration HB-668) towed by a Robin DR 400/180R (HB-EUY). The tow pilot reported that at a point approximately 400 meters above ground, he signaled the glider to release by moving the ailerons, but the glider did not respond. Shortly thereafter, fog patches appeared on the left side of the flight path. The tow pilot reduced power and transitioned to level flight, during which the speed increased to 140 km/h. While turning, he felt a sudden, stronger-than-normal jerk. He then observed that the glider was no longer attached. After landing, he was informed that he had released only the tow ring.
Witnesses on the ground reported seeing the glider perform what appeared to be a looping maneuver. One witness stated that as the glider became inverted, an object resembling a package fell out. The glider then entered a spiral descent. The crash occurred at 1405 hours on the southern slope of the Born, at an elevation of about 500 meters above sea level.
Wreckage and Injuries
The glider came to rest horizontally on treetops. The tow cable was still attached to the nose hook and was wrapped around the wings. The weak link on the tug aircraft was broken. The right elevator was found approximately 90 meters above the crash site; its outer portion was missing. The canopy lay about 100 meters from the glider and was only slightly damaged. The pilot was found 30 meters from the wreckage, still strapped in his parachute. The parachute sack was open, the lines were deployed, but the canopy had not inflated. The release handle was torn off. The pilot was killed on impact.
Examination of the glider showed the outboard third of the left aileron torn off, the rear part of the right inner wing heavily damaged, and the right elevator missing. The fuselage was lightly damaged, and the cockpit was intact. Control connections were secure, and no technical defects were found. The tow release functioned normally. The seat belts were intact, but the buckle was open.
Weather Conditions
According to the Swiss Meteorological Institute, the weather at the time was overcast with rain. Cloud cover was 8/8 of stratus at approximately 1000 meters above ground. Visibility was 4 to 5 km. Surface wind was weak and variable; at 1500 meters, wind was from northeast to southeast at about 5 knots. Temperature was 20°C, dew point 15°C. Local thunderstorms were possible. The tow pilot reported high fog, wind from 050° to 070° at 5 to 10 knots, visibility 3 to 4 km, and moderate turbulence at the Born.
Probable Cause
The accident is attributable to the glider becoming entangled in the tow cable and consequently becoming uncontrollable. Contributing factors were the student's low flight experience, unfavorable weather conditions, and flight maneuvers by the tow pilot that overstretched the glider pilot's flying ability.