What happened
On August 24, 2012, a Pilatus PC-12/47, registration HB-FPZ, departed from Antwerp, Belgium, bound for Saanen, Switzerland. The flight, operated by Air Sarina, was carrying a pilot and three passengers. While flying under IFR conditions at 26,000 ft, the aircraft began to deviate from its assigned track.
During communications with Geneva air traffic control, the pilot reported a significant issue with the autopilot. Radar data and Swiss surveillance records indicated that the aircraft entered a period of increasing oscillations in roll and vertical speed. During this descent, the aircraft experienced extreme maneuvers, including a descent rate of 15,500 ft/min followed by a climb at the same rate. An overspeed alarm was audible during radio transmissions. Approximately 20 seconds after these maneuvers, the right wing suffered a structural failure at 12,750 ft. The aircraft subsequently struck the ground in a wooded area near Solemont at an indicated airspeed of 305 kt and a pitch angle of approximately 80 degrees. The impact resulted in four fatalities and the total destruction of the aircraft.
The investigation
The BEA examined the wreckage and recovered debris from the right wing as far as 10 km from the main impact site. Investigators determined that the right wing's forward spar had failed due to structural overload, with no evidence of prior damage. The investigation also analyzed meteorological data, which confirmed the presence of heavy icing conditions and convective cells (cumulonimbus) in the area.
Swiss radar data provided critical insight, showing that the aircraft's oscillations began even before the pilot reported autopilot issues. The investigation also reviewed a previous incident involving a similar aircraft in Canada, where icing had caused increased control forces. Additionally, the pilot's recent history was reviewed, noting a reported autopilot anomaly just days prior to the accident.
Findings
- The primary cause of the in-flight wing separation was structural overload resulting from a loss of control.
- The aircraft was operating in an environment characterized by heavy icing and high humidity, which likely caused ice accumulation on the airframe or around the aileron controls.
- The pilot may have misdiagnosed the situation as an autopilot failure, potentially due to a recent similar occurrence, whereas the aircraft was likely already experiencing aerodynamic degradation.
- The loss of control may have been triggered by the pilot's attempts to correct the aircraft's oscillations, which potentially amplified the unstable flight dynamics.
- The lack of flight recorders on this aircraft prevented investigators from definitively determining the exact sequence of pilot inputs leading to the loss of control.