Primary finding
Probable cause
The operator’s incorrect input into the ground station controller, resulting in a loss of control during flight and subsequent impact with terrain.
Investigator assessment
Analysis narrative
The operator of the uncrewed aircraft system (UAS) reported that, he and an external emergency safety pilot were conducting an engineering test flight to fine tune the autopilot’s tail rotor yaw limits. While hovering at 50 ft agl, the operator incorrectly input a full left tail rotor command, causing the UAS to begin a rapid counterclockwise rotation. The auto pilot was unable to maintain a level attitude or stabilize the UAS during the rotation, and descended uncontrollably. The safety pilot attempted to stabilize the UAS manually, using the emergency RC controller, to no avail. The UAS impacted the surface, resulting in substantial damage to the tailboom. The operator of the UAS reported that there were no preaccident mechanical malfunctions or failures that would have precluded normal operation.