What happened
During a preflight inspection around 0800, the pilot prepared the aircraft for a scheduled cargo mission. Although the night was clear, the temperature was -11 degrees F, and frost had accumulated on the airframe. The pilot used a broom to clear the frost from the wings and tail surfaces, but no deicing fluid was utilized during this process.
Shortly after takeoff, while maintaining an airspeed of 110 knots, the pilot retracted the flaps to approximately 5 degrees. The aircraft began experiencing a series of right-hand rolls, which the pilot described as a wave-like or vortex-like motion. In an attempt to stabilize the flight, the pilot applied left aileron and extended the flaps to 20 degrees, but the right-hand roll intensified. As the aircraft began descending toward the terrain, the pilot attempted to deploy the flaps fully. The aircraft subsequently collided with the ground.
Findings
Post-accident investigations of the aircraft revealed no evidence of mechanical failure. While the engine showed internal over-temperature damage and minor fire damage—suggesting a significant spike in fuel flow during the impact—the propeller blades were also found to be consistent with high power settings at the time of the crash.
Crucially, the observed rolling and vortex-like movements were consistent with airframe contamination caused by frost. The aircraft's operating manual explicitly warns against departing with any frost, ice, or snow on the flight surfaces due to the negative impact on flight characteristics. Furthermore, the manufacturer's guidelines specify that if temperatures are below 10 degrees C, a visual or tactile inspection must be performed, and approved deicing fluids or a heated hangar should be used to ensure the wings and horizontal stabilizer are completely clear of accumulation.