Flight Details
While descending for an instrument approach in instrument meteorological conditions, the airplane's airspeed exceeded its never exceed velocity (Vne) of 196 knots. The elevators subsequently fluttered and separated from the airplane. Following the elevator separation, the stabilizers departed, the nose pitched downward, and both wings failed in a negative direction.
Earlier during the flight, the pilot cruised at approximately 19,000 feet, tracking in a southerly direction at a ground speed of 191 knots. Winds aloft were reported as westerly.
Weather and Communications
The pilot communicated with flight watch and radar controllers, indicating that the airplane was not equipped with deicing equipment. The pilot was advised that icing conditions existed between 13,000 and 15,000 feet, and the freezing level was at 7,000 feet.
At 0923, due to traffic, the controller cleared the pilot to descend to 15,000 feet. The pilot accepted the clearance and requested a clearance to divert to a nearby airport, which the controller approved.
During the last 24 seconds of radar-recorded flight, the airplane's rate of descent increased to 3,500 feet per minute, and over its southerly course its ground speed increased to 240 knots. Shortly after at 0930:21, the sound of an emergency locator beacon was recorded in the radar control facility.
Pilot reports covering the area of the accident around the time of the event reported light to moderate turbulence and light to moderate rime/clear icing conditions.
Structural Failure Sequence
A ground witness heard a 'pop' sound and observed airplane parts falling from the low clouds. The surface winds were reported by the witness as gusty.
Engineering analysis and testing by the airframe manufacturer predicted the onset of flutter to occur at 241 knots. The airplane was modified by the installation of a larger engine with 95 additional horsepower available.