What happened
On 20 October 2021, a Pilatus PC12/47E, registration LX-JFX, operated by Jetfly Aviation S.A., was conducting an IFR flight from Dieppe-Saint-Aubin to Brive-Souillac. During the descent phase, the aircraft exited a cloud mass and encountered severe turbulence.
As the aircraft approached another cloud mass at approximately 3,000 ft, the pilot flying (PF) disengaged the autopilot to perform a sudden right-hand avoidance maneuver. During this maneuver, the aircraft's speed decreased significantly, triggering the stall warning. The pilot responded by increasing engine power and leveling the wings. The aircraft lost approximately 55 and 600 ft of altitude during the maneuver before the crew regained the target altitude and continued the approach to land without further incident.
The investigation
The investigation utilized data from the Aircraft Condition Monitoring System (ACMS) to reconstruct the flight path, as the onboard flight recorder was found to have a power supply failure and yielded no usable data.
Investigators examined meteorological reports, noting that while the crew had access to forecasts indicating possible thunderstorms (TCUs/Cbs), the intensity of the turbulence was underestimated. The investigation also reviewed the aircraft's weather radar capabilities, noting that the installed Honeywell RDR2000 system displays precipitation intensity but does not provide a turbulence display. The crew's statements were also analyzed, revealing a disagreement regarding the necessity of the avoidance maneuver.