What happened
On December 7, 2023, a Beechcraft 35-C33, registration N5891J, was engaged in a private cross-country flight from Knoxville Downtown Island Airport to Benton, Arkansas. The flight proceeded normally following takeoff, with the aircraft climbing to 6,500 feet mean sea level (msl).
As the flight progressed, ADS-B data indicated that the aircraft began experiencing significant altitude and airspeed fluctuations. The airplane repeatedly climbed and descended by as much as 1,500 feet, with airspeeds varying between 100 and 160 knots. During this period, air traffic control notified the pilot that the aircraft was significantly left of course; the pilot acknowledged the instruction but failed to correct the track.
At approximately 11:03 CST, the pilot transmitted an emergency message. Shortly thereafter, a faint male voice was heard requesting help. The aircraft then entered a rapid descent, with the descent rate exceeding 10,000 feet per minute and groundspeed reaching approximately 230 knots, before impacting hilly, wooded terrain. The accident resulted in 2 fatal injuries.
The investigation
Investigators analyzed ADS-B data, which showed that the aircraft's vertical profile was consistent with pilot-induced oscillations. The aircraft was equipped with a Century 2000 autopilot, a system that requires the pilot to manually adjust the elevator trim when the autopilot prompts for a change.
Examination of the wreckage revealed that the airplane's engine was running at the time of impact. While the wreckage was highly fragmented due to the force of the impact and a post-impact fire, investigators found no mechanical irregularities that would have prevented normal operation. The elevator trim actuator was found with a 5-degree deflection in the trailing edge down direction.
Interviews with a former flight instructor indicated that the pilot had previously struggled with manual aircraft handling and often confused the direction of the trim control. The instructor noted that the pilot would frequently disconnect the autopilot when it became difficult to manage.
Toxicological analysis of the pilot's tissue revealed the presence of several medications, including alprazolam, trazodone, and buspirone. While these substances can cause sedation or impaired psychomotor performance, investigators could not definitively determine if they contributed to the accident.