What happened
During an instructional flight intended to conduct simulated emergency governor operations, a single-engine helicopter performed a hard landing. The aircraft touched down in a near level flight attitude with a slight tail low attitude. Upon impact, the landing gear skids collapsed, causing the lower vertical fin and the tail rotor assembly to contact the ground. This impact bucked the tailboom at its forward attaching points. Following the impact, the helicopter slid 250 feet on its fuselage before coming to rest in an upright position. The crew performed an emergency engine shutdown and egressed the aircraft unassisted; there were no injuries reported.
The investigation
Investigators examined the helicopter systems and tested the throttle twist grip for anomalies, simulating the actions taken during the training flight. This included cycling the governor between auto and manual modes for several minutes to check for restrictions in manual throttle operation. The examination determined that the solenoid responsible for allowing manual throttle manipulation would not fully retract due to heat generated during activation, creating a restriction. Additionally, investigators examined the crash-attenuating seats. While the left front seat attenuated as designed, the right front seat did not appear to have fully attenuated. These seats were shipped to the manufacturer in France for further analysis.
Findings
Testing of the seats at the manufacturer's facility revealed that they met all specifications. Evidence indicated that while the attenuation on the right seat had initiated, it did not sustain sufficient forces to fully stroke.