What happened
On October 7, 1967, a student pilot was conducting a series of training circuits at the Speck-Fehraltorf airfield. After successfully completing two landings, the pilot initiated the approach for a third landing. The approach began normally, and the pilot executed a right-hand sideslip to align with the runway. While the aircraft was at an altitude of only 20 to 30 meters, it suddenly pitched forward into a steep dive at an angle between 50 and 70 degrees. The Jodel D-II, registration HB-SOV, struck the ground approximately 175 meters before the start of the runway. The impact resulted in the death of the pilot and the total destruction of the aircraft.
The investigation
The investigation examined the aircraft's maintenance history, the pilot's training records, and the mechanical state of the aircraft following the crash. The aircraft had been well-maintained, with its last inspection describing its condition as "very good." Investigators found no evidence of pre-existing technical defects in the control surfaces or the engine; notably, the tachometer was found to have stopped at approximately 640 RPM, indicating the engine was at idle during impact.
Testing conducted by the Federal Office of Civil Aviation with the same aircraft type revealed that while the aircraft has stable stall characteristics, it can enter an abnormal flight state—specifically a spin—if a sideslip is performed at speeds around 75 km/h. The investigation also noted that the trim levers were found heavily deformed in the neutral position, and the physical layout of the cockpit required the pilot to lean forward to operate the airbrake lever, which is positioned near the trim controls.
Findings
- The aircraft entered an uncontrolled dive for reasons that could not be definitively determined.
- Possible contributing factors included a loss of airspeed following the right-hand sideslip, an accidental and abrupt movement of the trim levers, or an unintentional forward push of the control column while attempting to reach the airbrake lever.
- The aircraft's high glide efficiency requires low approach speeds (80–95 km/h), placing the aircraft in a critical speed range where sideslips can lead to instability.