What happened
On the afternoon of October 7, 197 and, a Bücker 131-150 (registration HB-UVA) departed from the Porrentruy airfield for a private flight to Courtelary. The aircraft was operated by a flight group and was being flown by two pilots who were trainees at the Porrentruy engine flight school.
At approximately 14:55, witnesses observed the aircraft flying at a very low altitude and low airspeed in the vicinity of Epiquerez. During this period, the aircraft suddenly pitched forward and entered a longitudinal roll. The aircraft struck a meadow at a nose-low angle of approximately 30 degrees, which triggered a post-impact fire that completely consumed the wreckage. Both occupants sustained fatal injuries.
The investigation
The investigation examined the flight path, the mechanical state of the aircraft, and the environmental conditions. Investigators noted that while the aircraft's engine was functioning normally and the fuel load was sufficient for the intended mission, the maintenance records were not in compliance with regulations, as the 50-hour inspection interval had been exceeded.
Technical analysis of the wreckage showed that the fuel tank ruptured upon impact, fueling the intense fire. The investigation also looked into the possibility of pilot error or environmental factors, such as the presence of high-voltage power lines in the area which, due to the sun's position, might have been difficult to detect. Additionally, the investigation noted that the pilot in the front seat had a blood alcohol level of 0.3 ‰, which can impair performance.
Findings
- The aircraft was flying below the minimum prescribed altitude and at a low airspeed immediately prior to the accident.
- The aircraft entered a spin following a sudden loss of airspeed.
- The investigation could not definitively determine if the loss of speed was caused by an optical illusion regarding the horizon while climbing, or an abrupt maneuver to avoid a nearby high-voltage power line.
- There was no evidence of mechanical failure contributing to the crash, as the engine was operating normally.