Accident
On 23 May 1970 at 1600 hours MEZ, a glider training flight took off from Olten airfield's grass runway 23 using aerotow. The aircraft was a Rhönlerche II, registration HB-655, operated by an instructor and a student. The instructor had briefed the student that he would perform a simulated rope-break exercise at the end of the field and would take control.
After a normal takeoff, the instructor released the tow rope at approximately 15 meters above ground (m/G) with an airspeed of 55 mph (90 km/h), according to the tow pilot. The instructor then took control, initially veering slightly right before initiating a left turn-back. Concerned about trees located about 120 meters south of the runway departure axis, he tightened the turn radius, increasing bank angle to 50° or more. At roughly 5 m/G, he attempted to raise the nose, but the glider responded sluggishly. Before completing the turn, the aircraft struck the ground at 1651 hours with a flight path angle of about 20° and bank of approximately 60°.
Injuries and Damage
The student sustained minor injuries; the instructor was uninjured. The glider suffered serious damage, and minor third-party damage occurred.
Crew and Aircraft Information
The instructor, born 1940, held a valid glider pilot license since 17 May 1961 with an instructor endorsement from 18 July 1969. He had a total flying experience of 184 hours, including 30 hours as an instructor. The student, born 1946, held a valid student pilot certificate with 18 flying hours and 129 landings. No evidence of health impairment was found. Neither pilot had any prior accidents or incidents recorded.
Weather Conditions
Weather in the accident area, as reported by the Swiss Meteorological Institute (MZA), was: total cloud cover 6/8, with 3/8 at 2000 m above sea level; visibility greater than 20 km; wind variable 2–5 knots, occasionally light north wind; temporary light thermic turbulence.
Investigation Findings
Examination of the glider wreckage revealed no evidence of pre-existing airworthiness issues. The investigation concluded that the instructor's decision to release the tow rope at only about 15 m/G and to initiate a turn-back was unreasonable, especially given the limited lateral obstacle clearance that necessitated a very tight turn. The glider likely dropped below minimum speed during the turn, causing a stall. Due to the low altitude, the instructor could not recover the aircraft in time.