CEN17FA103 · Bell Helicopter Textron Canada 429

While performing a dark night, cross-country flight, the helicopter cruised towards its destination. The helicopter impacted a marshy area of a lake. Impact signatures were consistent with the helicopter colliding with trees and terrain in a nose low attitude. Weather information for the time of the accident showed that the helicopter was operating in an area favorable for instrument flight rules (IFR) conditions due to precipitation and mist, cloud ceilings between 1,000 to 1,600 ft above ground level, and possible moderate turbulence. Due to cloud cover, it is likely that the Moon was not visible. There is no evidence that the pilot obtained a weather briefing prior to takeoff. The pilot's log books were not recovered during the investigation and the pilot's total time, and night experience is not known. While the pilot held a rating for instrument airplane, it is not known how much training the pilot obtained, if any, for an instrument helicopter rating. It is likely that the pilot had no more than 30 hours in make and model.

Data downloaded from onboard avionics found that the flight was uneventful until 4 minutes before the accident when the helicopter made a right turn and began flying to the southwest. As the helicopter tracked southwest, the altitude dropped to about 600 ft msl (500 ft above ground level [agl]). A minute later, the helicopter turned left turn and descended in the turn to about 420 ft agl before it pitched up to 40° nose high, resulting in a 2,500 ft per minute (fpm) climb. The helicopter momentarily stabilized on a 55° heading. At this time, the pilot armed the airspeed hold mode but did not turned on the force trim, so the autopilot would not engage. It is likely that the pilot expected the autopilot to engage, and when the helicopter began a left bank, he turned on the force trim but did not re-engage the autopilot. Shortly thereafter, the helicopter exceeded a 45° left bank and the pitch exceeded 40° nose low. The helicopter rapidly descended and impacted terrain. An examination of the avionics data, airframe, and engine did not identify any preimpact anomalies. While several substances were found in the pilot's toxicology, their use did not appear to contribute to the accident. The circumstances of the accident are consistent with the pilot's inadvertent encounter with instrument meteorological conditions, which resulted in in spatial disorientation, loss of control, and subsequent impact with terrain.

Verbatim NTSB analysis and probable cause from the NTSB dataset