History of Flight
On 7 April 2008, at approximately 09:15 UTC, a Robinson R22 Beta II (registration ZS-RNB) was conducting a demonstration flight in the Grand Central helicopter general flying area, south of Allendale Road in Midrand, South Africa. The flight instructor and a passenger (a potential student pilot) had just completed a demonstration of helicopter flying techniques. The helicopter climbed to about 350 ft above ground level (AGL) when the instructor decided to demonstrate an autorotation to the passenger. The maneuver was initiated in a northerly direction with the wind from the east. Four to five seconds after entering autorotation, the low main rotor RPM audio warning sounded and the amber warning light illuminated. The pilot observed the main rotor RPM had decayed to approximately 88%, which was substantially lower than expected. Despite immediately lowering the collective pitch lever and rolling on the throttle as per the pilot's operating handbook, the pilot could not recover from the low RPM condition. The helicopter descended rapidly and struck the ground hard. The left skid touched down first, followed by the right skid about 1 meter further on. The left skid collapsed, causing the helicopter to nose over and cartwheel, coming to rest on its right side. The tail boom was severed by the main rotor blades. The pilot and passenger both sustained cuts and bruises; the pilot was taken to hospital for stitches to a forehead cut.
Injuries to Persons
Both the pilot and the passenger sustained minor injuries. The pilot received stitches for a cut on the forehead.
Damage to Aircraft
The helicopter sustained substantial damage, including failure of the left skid and severing of the tail boom. Damage was also noted to the main rotor blades, tail rotor, windshield, and skid gear.
Probable Cause
The investigation determined the probable cause to be a hard landing following a fairly high descent rate as a result of a low rotor RPM/blade stall.