What happened
On May 23, 1970, at approximately 16:00, a flight instructor and a student were conducting a training flight at the Olten airfield. The aircraft, a Rhönlerche II with registration HB-6xy, was being operated in a glider tow configuration. The instructor had planned to perform a rope-break maneuver near the end of the airfield, during which he intended to take control of the aircraft from the student.
After a successful takeoff from the grass runway, the instructor released the tow cable at an altitude of approximately 15 meters while the aircraft was traveling at 55 mph (90 km/h). To execute the planned maneuver, the instructor initiated a left-hand turn. Due to the proximity of trees located roughly 120 meters south of the runway departure axis, the instructor tightened the turn radius to avoid an obstacle, resulting in a bank angle of 50 degrees or more.
As the aircraft leveled out at an altitude of about 5 meters, the instructor attempted to recover the aircraft, but the glider responded sluggishly. The aircraft ultimately impacted the ground at 16:51 with a bank angle of approximately 60 degrees and a flight path inclination of 20 degrees. The student sustained minor injuries, while the instructor was uninjured. The glider suffered heavy damage, and minor damage was reported to third-party property.
The investigation
The investigation examined the flight conditions, the mechanical state of the aircraft, and the pilot's actions. Meteorological data indicated visibility exceeding 20 km, with scattered clouds and light, variable winds. An examination of the wreckage revealed no evidence of mechanical failure or lack of airworthiness prior to the impact. The investigation also reviewed the flight experience and medical fitness of both the instructor and the student, finding no impairments to the pilots' health or prior accident history in the federal aviation records.
Findings
- The instructor's decision to release the tow cable and initiate a turning maneuver at an altitude of only 15 meters was deemed unreasonable.
- The tight radius required to avoid nearby trees caused the glider to drop below its minimum flying speed.
- The resulting aerodynamic stall and the low altitude prevented the instructor from successfully recovering the aircraft before ground impact.