On August 16, 1999, at 1637 eastern daylight time, a Robinson R-22, N20879, was substantially damaged when it rolled over and impacted terrain at Mansfield Municipal Airport, Mansfield, Massachusetts. The student pilot received minor injuries, and visual meteorological conditions prevailed for the local solo flight. No flight plan was filed, and the flight was conducted under 14 CFR Part 91. According to the student pilot's flight instructor who witnessed the accident, the student was attempting to bring the helicopter to a hover after executing a landing. With the left skid in the air and the entire right skid on the ground, the instructor watched the helicopter roll over. The student added that he felt the helicopter leaning to the right. "The next thing I knew it rolled over." Neither the flight instructor nor student pilot reported any pre-impact failures. Also, they did not report any flight control problems with the helicopter the day of the accident. In addition, the Federal Aviation Administration Inspector that responded to the accident did not report identifying any pre-impact malfunctions or failures with the helicopter. Federal Aviation Administration Advisory Circular 90-87 (Helicopter Dynamic Rollover) states the following: "Helicopter pilots in general are required to be skillful in operations on both improved or unimproved surfaces. During normal or slope takeoffs and landings with...one skid/wheel on the ground, the bank angle or side drift can place the helicopter in a situation where it is pivoting (rolling) about a skid/wheel which is still in contact with the ground. When this happens, lateral cyclic control response becomes more sluggish and less effective than for a free hovering helicopter. Consequently, if a roll rate is permitted to develop, a critical bank angle (the angle between the helicopter and the horizon) may be reached where roll cannot be corrected, even with full lateral cyclic." According to the NTSB Pilot/Operator Aircraft Accident Report, the student pilot had logged a total of 27 hours of flight experience with all 27 hours in helicopters.