What happened
On August 8, 2017, a Piper PA-46-350P departed Zurich-Kloten, Switzerland, on a private IFR flight destined for Hamburg-Fuhlsbüttel, Germany. The aircraft was carrying a pilot and one passenger. During the climb, the aircraft encountered a line of convective showers characterized by heavy precipitation and significant liquid water content.
As the aircraft climbed through the freezing level, it entered an area of intense convective activity. Radar data and meteorological analysis indicate the aircraft passed through a region of high turbulence and icing between FL 130 and FL 165. At approximately 11:50 UTC, the aircraft's groundspeed dropped from 156 knots to 130 knots while maintaining altitude, a pattern consistent with increasing ice accumulation or a pilot's attempt to reduce speed for turbulence. Shortly thereafter, the aircraft entered an uncontrolled descent. At 11:52 UTC, the pilot attempted to declare an emergency via radio, but the transmission was cut short. Witness video captured the aircraft emerging from the cloud base in a vertical dive, during which the left and then the right wings separated due to extreme structural loads. The aircraft impacted the surface of Lake Constance northwest of Mainau island, where the wreckage was recovered at a depth of 50 meters. Both occupants sustained fatal injuries.
The investigation
The BFU examined radar tracks from Swiss and German air traffic control, as well as meteorological data from the German Weather Service (DWD). The investigation analyzed the aircraft's flight path, the engine and propeller performance, and the structural integrity of the wreckage. Investigators also reviewed the pilot's flight experience and the aircraft's maintenance history. The investigation confirmed that the engine and propeller were functioning normally prior to the breakup, as loud engine noises were audible on witness recordings. The investigation also focused on the meteorological conditions, specifically the presence of supercooled large droplets (SLD) and extreme turbulence predicted for that altitude range.
Findings
- The aircraft encountered severe icing and turbulence during its climb.
- The aircraft entered an uncontrolled flight attitude, likely due to aerodynamic changes caused by ice accretion on the wings or tail, or a pilot error during turbulent conditions.
- The extreme structural loads experienced during the high-rate descent caused the wings to separate from the fuselage.
- The pilot's flight experience in these specific weather conditions was likely very limited.
- There was no evidence of engine failure or mechanical malfunction of the flight control systems prior to the loss of control.