What happened
On August 2, 1975, a formation of three aircraft—two Bücker-Jungmeister models and one Bücker-Lerche, registration OE-AKK—departed Trausdorf, Austria, for a VFR flight to Porrentruy, Switzerland. The group intended to perform aerobatic displays at a horse racing event in Tramelan. Following intermediate stops in Salzburg and Altenrhein, the group refueled in Sitterdorf before proceeding to the final destination.
Upon arriving at the Porrentruy airfield, the formation performed various maneuvers, including Immelmann turns and rolls. The Bücker-Lerche executed a tight right-hand turn on runway 07, conducting the approach at low power and close to the airfield. During the turn, the pilot utilized significant rudder and minimal lateral bank, causing the aircraft to drift off the runway centerline. As the pilot attempted to realign with the runway, the aircraft fell below its minimum flying speed. Despite a last-second attempt to apply power, the aircraft struck the ground approximately 44 meters before the runway threshold. The impact caused the landing gear to collapse, and the aircraft slid for about 38 meters before coming to a halt.
The investigation
The investigation examined the pilot's experience, the aircraft's technical condition, and the flight parameters. The pilot was an experienced Austrian aviator with over 169 flight hours, including significant time in the accident type. The aircraft was found to be airworthy, though it was approximately 15 kg over its maximum takeoff weight of 670 kg at the time of the accident. The investigation also reviewed the flight path, noting that the approach did not follow the standard procedures outlined in the AIP Switzerland, opting instead for a much tighter pattern.
Findings
- The pilot's approach was characterized by insufficient airspeed and an improper flight path.
- The landing pattern was executed much tighter than the prescribed procedure.
- The pilot's concentration may have been impaired due to fatigue, as the total flight duration exceeded four hours.
- The pilot failed to execute a go-around when it became apparent that the approach was too close to the runway threshold.
- The engine was at approximately idle RPM (1400 RPM) at the moment of impact.