Accident Summary
During lift-off from soft, uneven terrain, the rear portion of the helicopter's right main skid contacted the ground, initiating a dynamic rollover. The event occurred as the pilot attempted to depart from an area described as clumpy and lumpy with grass ruts approximately 1 to 2 feet in height.
Pilot Report
The pilot reported making a slow ascent after lifting the helicopter off the ground. When the skids were about 1 foot above the terrain, the helicopter momentarily stopped as if something had caught the right side, followed by a slight lateral roll to the right. The pilot recognized the situation too late and applied full left cyclic while lowering the collective. By that time, the helicopter had exceeded the critical angle of bank into the low skid, making recovery impossible. The helicopter subsequently rolled 90 degrees to the right.
Terrain Conditions
The departure area consisted of soft, uneven ground with clumps and ruts of grass 1 to 2 feet high. This uneven surface contributed to the skid contacting the ground during the lift-off.
Dynamic Rollover Mechanism
The Rotorcraft Flying Handbook (FAA-H-8083-21) describes dynamic rollover as pivoting around a skid or landing gear wheel that causes the helicopter to reach its critical rollover angle. Beyond this point, main rotor thrust continues the roll and recovery is impossible. In this event, the skid contact led to such a scenario.
No mechanical deficiencies with the engine or airframe were noted. The pilot's actions, including the late application of corrective controls, were consistent with the dynamics described in the handbook.