Accident Sequence
A student pilot was performing a practice autorotation under the supervision of a certified flight instructor (CFI). At approximately 10 feet above the ground, the student began increasing collective pitch to cushion the touchdown. The CFI noted that the main rotor RPM was low and added throttle to execute a touchdown with power. Upon touchdown, a ground resonance vibration developed. In response, the CFI lifted the helicopter off the ground. The vibration persisted, so the CFI rolled the throttle off and set the helicopter back on the ground. Immediately after, the helicopter rolled onto its side.
Post-Accident Inspection
Following the incident, the landing gear dampers and main rotor dampers were removed and tested at the factory. The right rear and left front main landing gear dampers had charge pressures below acceptable factory specifications. The right front and left rear landing gear dampers were found to be within factory specification ranges. All three main rotor dampers were adjusted to excessive friction torque values. Additionally, the red blade damper was assembled incorrectly, with a plate stack-up improper for any version of that damper assembly.
Maintenance History
The helicopter had been in storage for two years prior to June 1994, when it was leased to the operator. The red blade damper had been removed from another helicopter, overhauled, and placed in spare parts inventory. It was then installed on the red blade on July 20, 1994.