What happened
On the afternoon of May 20, 1977, a Piper PA-28R-200 Cherokee Arrow II, registration HB-OQM, departed from the Bienne-Kappelen airfield for a planned one-hour local flight. The aircraft was carrying the pilot and three passengers. At the time, the region was experiencing unstable weather, with heavy cloud cover and developing thunderstorms along the Jura mountains.
Around 16:15, a witness observed the aircraft climbing through a gap in the clouds near Tavannes, surrounded by significant vertical cloud development. Shortly thereafter, at approximately 16:25, witnesses near Châtelat reported seeing the aircraft emerge from the clouds performing erratic maneuvers. During this period, observers noted that a portion of the wing was already missing. The aircraft then underwent a sudden mid-air disintegration, with the main wreckage falling into a forest near Monible and a large wing fragment landing over a kilometer away in a field.
All four occupants of the aircraft perished in the accident, and the aircraft was destroyed.
The investigation
The investigation focused on the structural integrity of the aircraft and the pilot's performance. Technical examination of the wreckage revealed that the left wing failed at station 118 due to the buckling of the upper spar cap. This failure was caused by a high positive load factor applied during flight. Laboratory analysis confirmed that the wing materials and construction met all required specifications and that no pre-existing fatigue or corrosion contributed to the break.
Medical examinations of the pilot revealed a blood alcohol concentration of 0.9‰, while the passengers showed varying levels of alcohol, including one at 1.0‰. The investigation also looked into the pilot's flight capabilities, noting he was qualified for visual flight rules (VFR) but not for instrument flight rules (IFR).
Findings
- The pilot continued a VFR flight into unfavorable meteorological conditions involving thunderstorms.
- The aircraft was subjected to structural loads exceeding the design limits, leading to the separation of the left wing.
- The pilot's decision-making and ability to manage the flight were impaired by alcohol consumption.