CEN10LA477

The pilot reported that the approach and landing were normal. After landing, he lowered the collective and began to decrease engine power by manipulating the throttle closed. Before the throttle was completely closed, the helicopter suddenly rolled to the right and came to rest on its right side, incurring damage to the airframe, main rotor, and tail boom. A postaccident examination did not reveal any anomalies consistent with a preimpact failure or malfunction. Dynamic rollover is the tendency of a helicopter to continue rolling when the critical angle is exceeded, if one skid is on the ground, and the helicopter is pivoting around that point. Dynamic rollover is possible when a skid is caught by a projection on the surface or when landing on a slope.

On August 13, 2010, about 1120 central daylight time, a Bell 206B helicopter, N54BE, piloted by an airline transport pilot, was substantially damaged during landing at the pilot's private helipad in Rocky Mount, Missouri. The personal flight was being conducted under 14 Code of Federal Regulations Part 91 without a flight plan. Visual meteorological conditions prevailed. The pilot, who was the sole occupant, was not injured. The helicopter departed Jefferson City Memorial Airport (JEF), Jefferson City, Missouri, about 1050. The pilot reported that the approach and landing were normal. He stated that after landing, he lowered the collective and began to "roll off" the throttle. However, before the throttle was completely off, the helicopter "suddenly rolled to the right." The aircraft came to rest on its right side with damage to the airframe, main rotor, and tail boom. A post accident examination did not reveal any anomalies consistent with a pre-impact failure or malfunction. Flight control continuity was confirmed. The pilot reported weather conditions as clear skies, with light and variable winds at the time of the accident. Weather conditions recorded at the Lee C. Fine Memorial Airport (AIZ), located about 14 miles southeast of the accident site, at 1115, included clear skies and winds from the southwest at 8 knots. The Federal Aviation Administration (FAA) Rotorcraft Flying Handbook noted that helicopters are susceptible to a lateral rolling tendency referred to as dynamic rollover. The handbook stated that, "Dynamic rollover is possible even during takeoff and landings on relative level ground, if one wheel or skid is on the ground and thrust (lift) is approximately equal to the weight of the helicopter. If the takeoff or landing is not performed properly, a roll rate could develop around the wheel or skid that is on the ground."