Incident Overview
A commercial pilot experienced a loss of control while flying in instrument meteorological conditions (IMC) when the airplane encountered severe turbulence. The event occurred at 16,000 feet mean sea level (msl) during level cruise flight. The pilot reported an unanticipated severe downdraft that resulted in a rapidly descending spiral. Control was regained at 6,000 feet msl in visual meteorological conditions (VMC), after which the pilot executed a precautionary landing at the nearest suitable airport.
Preflight and Weather Conditions
Prior to the flight, the pilot obtained a thorough preflight weather briefing from the Flight Service Station (FSS). Due to severe weather reported in Kansas and Colorado, the pilot filed a route further north through Nebraska. At the time of the weather brief, there were no pilot reports (PIREPS) along the planned route. A review of air traffic control (ATC) tapes revealed that no communications regarding turbulence or severe weather occurred between the controller and the pilot before the upset.
Aircraft Damage and Inspection
During taxi to the ramp after the precautionary landing, the right landing gear collapsed. Subsequent inspection revealed that the right landing gear had collapsed, the wing spar was bent, and the wings were wrinkled. A representative from the airplane's manufacturer assessed that the damage indicated the airplane experienced approximately 12 g's of force during the recovery from the turbulence event. The airplane's storm scope was tested by a repair facility after the accident and performed within normal specifications.
Equipment and Communications
No malfunctions or anomalies were reported with aircraft systems beyond the damage sustained. The storm scope was verified to be operational. The pilot and ATC did not discuss turbulence or severe weather prior to the incident.