Preflight and Takeoff
At approximately 0800, a commercial pilot conducted a preflight inspection of the accident airplane in preparation for a cargo flight. Dark night visual meteorological conditions prevailed, with clear skies and a temperature of -11°F. The pilot observed frost on the airplane but described it as not bonded to the skin. Using a broom, he cleaned the frost from the wing and tail surfaces, which he believed resulted in clean surfaces. No deicing fluid was applied.
Loss of Control
After takeoff, the pilot retracted the flaps to about 5 degrees at 110 knots of airspeed. The airplane then rolled to the right approximately three times in a motion the pilot described as a wave or vortex-like movement. He applied left aileron and lowered the flaps to 20 degrees, but the roll to the right became more severe. The pilot reported that engine power was "good." Noticing the airplane descending toward the ground, he attempted to lower the flaps completely. His next memory was being outside the airplane after it collided with the ground.
Manufacturer Warnings
The airplane's information manual contains several pages of limitations and warnings regarding departure with even small amounts of frost, ice, snow, or slush, which it states adversely affects the airplane's flight characteristics. The manufacturer requires a visual or tactile inspection of the wings and horizontal stabilizer to ensure they are free of ice or frost when the outside air temperature is below 10°C (50°F), and notes that a heated hangar or approved deicing fluids should be used to remove ice, snow, and frost accumulations.
Post-Accident Examination
Post-accident examination of the airplane revealed no observed mechanical malfunction. The engine displayed internal over-temperature damage and minor external fire damage consistent with a massive spike of fuel flow at the time of ground impact. Damage to the propeller blades was consistent with high power at impact. The rolling and vortex motion experienced by the airplane was consistent with airframe contamination due to frost.