Overview
An aircraft with registration N5LN was conducting a test flight to perform an in-flight Negative Torque Sensing (NTS) check on its left engine, which had recently been overhauled. The check required shutting down the left engine during the flight. The test took place at night.
Weather and Briefing
The pilots were briefed that icing conditions existed, with moderate rime icing mixed below 15,000 feet in clouds and precipitation. Cloud bases were reported between 2,500 and 2,900 feet above ground level (agl).
Flight Sequence
After departure, the pilot reported to air traffic control (ATC) that the aircraft was clear of clouds and on top of the cloud layer at approximately 6,500 feet mean sea level (msl). ATC assigned N5LN a heading of 180 degrees at an assigned altitude of 8,000 feet. Without notifying ATC, N5LN subsequently turned to a southeast heading, descended from 7,700 feet to about 5,500 feet, and decelerated from approximately 182 knots to about 138 knots.
ATC then assigned N5LN a block altitude of 6,000 to 8,000 feet and a VFR-On-Top clearance. ATC instructed the flight to turn right to remain within the assigned airspace. N5LN turned right but continued to descend from about 5,500 feet to the last radar indication of 4,500 feet.
Impact and Wreckage Examination
The airplane impacted the ground in a steep attitude. Examination of the wreckage revealed that the landing gear was down, the right rudder trim was at full deflection, and the elevator trim was set to approximately six degrees nose-up. Examination of both engines indicated they were rotating and operating at the time of impact. Inspection of the airframe and propellers found no pre-existing anomalies that would have precluded normal operation.
Probable Cause
No probable cause was stated in the investigation source.