What happened
The aircraft was being repositioned for an air taxi operation when the pilot initiated takeoff on a runway covered with slush. As the aircraft accelerated down the runway, the nosewheel began to sling water and slush onto the windshield. To eliminate this visual distraction, the pilot raised the nosewheel slightly.
At approximately that moment, the aircraft swerved to the right. The pilot reportedly moved both power levers back to the reverse thrust position in an attempt to abort the takeoff. However, the aircraft then swerved abruptly to the left and continued off the right side of the runway, descending down an embankment.
As the plane skidded off the runway, the pilot brought both condition levers back to the emergency shut-off position. Upon inspection, frozen slush was found on the airframe. Additionally, a grayish-white residue, possibly from evaporated water or steam, was noted inside the exhaust stack of the right engine.
The investigation
Post-acc examination revealed specific mechanical states of the engines and propellers. Both propeller feather valves were found in the open position, and both engine shut-off valves were closed. Both propeller latch pins were engaged.
However, a discrepancy was noted between the two engines: the left propeller was fully feathered, while the right propeller remained in flat pitch. This asymmetry likely contributed to the directional control issues experienced during the aborted takeoff attempt.