What happened
On April 28, 2017, at approximately 16:05 local time, an SE 3160 helicopter, registration HB-XXM, was returning to Wilderswil/Interlaken (LSXI) following the completion of a proficiency check flight. While operating at an altitude of roughly 3,500 feet in the vicinity of Steffisburg, the crew heard a loud bang. Immediately following this sound, the flight instructor took control of the aircraft and initiated an autorotation procedure. Despite experiencing intense vibrations throughout the airframe, the instructor managed to perform a controlled landing on a nearby meadow. The aircraft sustained light damage during the landing, and there were no injuries to the crew.
The investigation
Following the incident, the Swiss Transportation Safety Investigation Board (SUST) opened an inquiry to determine the cause of the mechanical failure. Upon inspecting the aircraft on the ground, the crew identified that the tail rotor control cable had severed. The investigation focused on the circumstances surrounding the breakage of this critical flight control component.