Incident Summary
A helicopter conducting a post-maintenance check flight for oil leaks experienced a vibration shortly after takeoff. The pilot initiated a precautionary landing in a field, during which a passenger shifted seats, causing a center of gravity (CG) shift and subsequent loss of control.
Sequence of Events
The flight was intended to verify the absence of oil leaks following maintenance. Shortly after departure, at an altitude between 50 and 100 feet above ground level (AGL), the pilot detected a two-per-revolution vibration and decided to land in a field. As the helicopter descended to approximately 5 feet AGL, the pilot perceived what he described as a CG shift. The right skid then contacted the ground. The pilot lowered the collective, but control was lost and the helicopter rolled over.
The pilot stated that the vibration was not severe enough to have caused the loss of control.
Findings
Investigation revealed that in addition to the two front seat occupants, a 226-pound passenger was seated in the right center (rear-facing) seat. The passenger reported that he could not see much from that seat and, just prior to the skid contact, moved to the right rear (forward-facing) seat. This movement would account for a rearward shift in the helicopter's center of gravity.