What happened
On September 1, 2004, two light aircraft were engaged in a formation flight from Les Éplatures toward Luzern-Beromünster. The formation consisted of a Piper J3C-65/L-4, registration HB-OGG, acting as the leader, and a Luscombe 8A, registration HB-DVW, following behind.
During the return leg of the flight, the two aircraft experienced a mid-air collision near Altwyden, in the municipality of Utzenstorf. The impact caused severe structural damage to the Luscombe 8A, rendering the aircraft uncontrollable. The aircraft entered a spinning descent and crashed, resulting in one fatality (the pilot). The pilot of the HB-OGG was able to perform an emergency landing in a nearby flat field after sustaining minor damage to the aircraft's wings and propeller.
The investigation
Investigators from the Swiss Transportation Safety Investigation Board (SUST) performed a detailed reconstruction of the collision using deformation measurement techniques and wreckage analysis. The investigation examined the flight paths, the physical damage to both airframes, and the pilots' recent flight history.
Technical analysis of the wreckage confirmed that the aircraft became momentarily wedged together during the collision. The propeller of the HB-OGG struck the left aileron of the HB-DVW, and the tail section of the HB-DVW subsequently struck the cockpit area and wing strut of the HB-OGG. The investigation also looked into the pilots' recent activities, noting that they had been distracted by observing a model airplane and discussing potential changes to their flight route shortly before the impact.
Findings
- The primary cause of the accident was the mid-air collision between the two aircraft during formation flight.
- The Luscombe 8A sustained such extensive damage to its control surfaces and structure that flight could no longer be maintained.
- The pilots were experienced in flying these specific aircraft types and frequently flew together, but neither pilot had received formal training in formation flying.
- Distractions, including radio communications regarding local air traffic and observing a model aircraft, may have contributed to the aircraft drifting onto converging flight paths.
- The pilot of the HB-DVW may have lost sight of the lead aircraft due to the visual obstruction caused by the aircraft's own wing during an overtaking maneuver.