What happened
On the morning of October 14, 1978, a pilot departed from Buttwil airfield in a SF 25 C Falke motor glider, registration HB-2021, for a planned flight over the Alps. The flight, which included a passenger, initially proceeded toward the Bernese Oberland. During the return leg, the aircraft flew via the Pilatus and Luzern regions, maintaining speeds between 150 and 160 km/h to ensure a timely return to the airfield.
Shortly after 13:00, the aircraft reappeared over Buttwil. An eyewitness observed the aircraft performing a downwind pattern for runway 34 at an altitude of approximately 200 meters. The aircraft then executed a 180-degree turn to establish the final approach. During the approach, the aircraft entered a brief sideslip with the airbrakes partially or fully extended. Following this maneuver, the aircraft's nose dropped sharply at an altitude of approximately 20 meters. At 13:07, the aircraft struck the ground roughly 100 meters before the threshold of runway 34 at a longitudinal pitch of 40 to 50 degrees.
The investigation
The investigation examined the aircraft's condition, the flight history, and the crew's experience. The wreckage showed that the engine was likely at idle during impact. While the airframe sustained heavy damage, including broken wings and a destroyed forward fuselage, investigators found no evidence of mechanical or technical failures that could have contributed to the accident. The aircraft's weight and center of gravity were within permissible limits, though the center of gravity was located toward the forward end of the allowable range.
Medical examinations confirmed that neither occupant was under the influence of alcohol. However, the investigation noted that the shoulder harnesses were improperly secured; they were looped around small mounting brackets rather than the intended steel tube, causing the anchors to tear during the impact. The passenger sustained injuries that led to his death two months later.
Findings
- The aircraft experienced a loss of control for undetermined reasons during the final approach.
- The center of gravity was positioned in the forward portion of the allowable range, a condition that can make the aircraft nose-heavy and difficult to trim across all speed ranges.
- Both the pilot and the passenger had relatively low flight experience, and the passenger was not legally authorized to fly in a motor glider without specific extensions.
- The cockpit ventilation was reportedly inadequate, and the pilot's side window was jammed.
- Improperly installed safety harnesses significantly reduced the occupants' chances of survival during the high-impact crash.