Accident Overview
On September 11, 2008, about 1630 mountain standard time, a Robinson Helicopter R-22, registered N227GH, impacted the taxiway and terrain during a practice 180-degree autorotation at the Ernest A. Love Field Airport (PRC) in Prescott, Arizona. The helicopter was operated by Guidance Helicopters, Inc., under 14 Code of Federal Regulations Part 91. The certified flight instructor (CFI) and the student pilot undergoing instruction (PUI) sustained minor injuries. The helicopter incurred substantial damage to the rotor system and tail boom. The instructional flight had departed PRC about 1545. Visual meteorological conditions prevailed, and no flight plan had been filed.
Sequence of Events
The CFI reported that four 180-degree autorotations had been completed successfully before the accident. The final autorotation was progressing normally until turning final. At that point, the helicopter experienced a sudden drop in airspeed approximately 150 feet above ground level (agl). The indicated airspeed was 52 knots, and rotor rpm was 101 percent. The PUI responded by pushing forward on the cyclic. The rotor rpm dropped to 95 percent, and the helicopter altitude decreased to 75 feet agl, resulting in lower rpm and an excessive descent rate. The CFI attempted a power recovery, but the rpm did not build quickly enough to prevent the skids from striking the taxiway. The CFI leveled the helicopter before impact. The right front skid contacted slightly first. The rotor then struck the tail boom, and the helicopter entered a right spin. After spinning several times, the helicopter drifted to the left, the skids contacted sod, and the helicopter rolled over.
The PUI confirmed the practice of 180-degree autorotations. As they rolled out on final, the airspeed began to drop. The PUI pushed forward on the cyclic and applied a little down collective. The helicopter descended faster than expected, with rpm dropping below 101 percent. Both the PUI and the CFI rolled on the throttle and leveled the aircraft. The helicopter hit the taxiway with the right skid first, began to spin, then hit the dirt and rolled over.
Pilot Reports
Both pilots reported that there were no mechanical failures or malfunctions during the flight.