Incident Overview
A pilot conducted a pre-flight run-up procedure before an intended helicopter takeoff. During this procedure, she disengaged the hydraulic system to check the rotor tip path plane. After completing the check, she did not reengage the system before proceeding.
Sequence of Events
The pilot lifted the helicopter into a hover. Immediately upon becoming airborne, the helicopter began to experience a pilot-induced oscillation. The pilot reported that this oscillation was due to heavy cyclic control forces, which she attributed to the disengaged hydraulic system. In an attempt to correct the oscillation, she overcompensated on the controls. This overcompensation led to the helicopter rolling over.
Pilot Report
The pilot stated that there was no mechanical malfunction or failure of any system. She acknowledged that she had forgotten to reengage the hydraulic system after the pre-flight check. The heavy cyclic control forces were a direct result of the hydraulic system being disengaged.
Conclusion
The rollover occurred because the pilot failed to reengage the hydraulic system prior to lifting into a hover. This caused abnormally heavy cyclic forces, leading to a pilot-induced oscillation and subsequent loss of control.