What happened
On December 5, 1959, a training flight conducted by the Schaffhausen Gliding Group resulted in the destruction of a Kranich II glider, registration HB-479. During a dual instruction session, a flight instructor and a student pilot were performing maneuvers near Löhningen. The flight was intended as a circuit for landing, but due to the aircraft's altitude, the instructor ordered additional turns to bleed off height. During a left-hand turn, the student pilot increased the bank angle and applied significant right rudder, causing the aircraft to drop from an altitude of approximately 80 meters into a spin. The aircraft struck the ground after roughly two rotations, resulting in the total loss of the aircraft. The instructor sustained minor injuries, while the student pilot suffered severe injuries, including a serious concussion and multiple bone fractures.
The investigation
The investigation examined the flight controls, the qualifications of the crew, and the mechanical condition of the aircraft. It was noted that the instructor was performing training duties as part of a practical internship that had not been formally reported to the Federal Office of Civil Aviation, meaning no official supervisory instructor had been appointed. The investigation also scrutinized the aircraft's instrumentation, specifically the two different airspeed indicators installed in the front and rear cockpits. These instruments featured different scales and markings. Post-accident testing revealed significant inaccuracies in these gauges, with one indicating speeds much higher than actual and the other much lower. However, due to a lack of historical calibration records, the investigators could not definitively determine if these discrepancies contributed to the pilot's loss of situational awareness.
Findings
- The primary cause of the accident was the exceeding of the stall speed by the student pilot during a turn.
- The aircraft was at an altitude of only 80 meters, which provided insufficient margin for the instructor to recover the aircraft once the stall occurred.
- The student pilot had demonstrated a recurring tendency to fly below the prescribed normal speed of 70 km/h during the flight.
- The instructor's attempt to intervene in the controls was unsuccessful due to the rapid onset of the aerodynamic stall and the low altitude.