Accident Sequence
During a cruise climb, the turbo-prop airplane departed controlled flight after initiating a turn directed by air traffic control. Radar data showed the airplane climbing to a maximum altitude of 13,800 feet above mean sea level while heading northeast. Subsequently, the airplane entered an increasingly tighter right descending turn, with a calculated descent rate of 7,000 feet per minute. The airplane then impacted the terrain and exploded.
Witness Reports
A witness reported hearing an "unusually loud" engine sound before seeing the airplane in a nose-low descent. According to the witness, the airplane was "heading straight down, and did between a quarter and half of turn, but was not spinning wildly." The witness stated that the airplane disappeared behind a nearby ridgeline, followed by a "loud sound, and an immediate large cloud of black smoke."
Weather and Pilot Briefing
Instrument flight rules (IFR) conditions prevailed at altitude, while marginal visual flight rules (MVFR) conditions prevailed at the accident site. The instrument-rated pilot received a weather briefing prior to departure, during which he was informed of building thunderstorm activity near the departure airport and along the route of flight. The pilot told the briefer that he intended to depart shortly to keep ahead of the approaching weather. Additionally, a witness at the departure airport reported that the passenger expressed concern about flying in "bad weather," and the pilot responded that the weather was only going to worsen and that they "needed to go to get ahead of it."
Investigation Findings
A two-dimensional reconstruction determined that all primary airframe structural components, flight control surfaces, powerplant components, and propeller blades were present. Flight control continuity could not be established due to extensive damage to all components. Inspection of the recovered flight control components did not exhibit any evidence of pre-impact malfunction. The standby attitude indicator gyro and its case showed evidence of rotational damage, consistent with the gyro rotating at the time of impact. Both solid-state Attitude & Heading Reference System (AHRS) units were destroyed during the accident, and as a result no information was available.
Probable Cause
The official probable cause is: "The pilot's spatial disorientation while turning in a cruise climb in instrument meteorological conditions, which resulted in the pilot's loss of aircraft control, and his failure to recover from a resultant tight descending spiral."