What happened
A flight involving N5LN, a turboprop aircraft, was conducting a night test flight to perform a required Negative Torque Sensing (NTS) check on the left engine following an overhaul. The procedure necessitated shutting down the left engine during the flight. Prior to departure, the crew was informed of icing conditions, including moderate rime ice, below 15,000 feet within clouds and precipitation, with cloud bases situated between 2,500 and 2,900 feet AGL.
After departing, the pilot notified air traffic control that the aircraft had climbed above the cloud layer at approximately 6,500 feet MSL. Although assigned a 180-degree heading at 8,000 feet, the aircraft turned southeast without notifying controllers. During this period, the aircraft descended from 7,700 feet to roughly 5,500 feet and slowed from 182 knots to 138 knots. Despite receiving a VFR-On-Top clearance and instructions to turn right to remain within assigned airspace, the aircraft continued to descend. The final radar contact showed the plane at 4,500 feet before it struck the ground in a steep attitude.
Findings
Post-accident inspections of the wreckage revealed that the landing gear was in the down position. The aircraft was found with full right rudder trim and approximately six degrees of nose-up trim. Investigation of the engines confirmed that both engines were rotating and operational at the moment of impact. Furthermore, the airframe and propellers showed no evidence of mechanical failures or anomalies that would have prevented the aircraft from operating normally.