History of Flight
On 23 November 2011, a Robinson R44 helicopter (registration ZS-RSU) was involved in tracking a stolen vehicle north of Pretoria. After completing the task, the helicopter returned to Grand Central Airport (FAGC). The pilot contacted air traffic control, who instructed the helicopter to remain east of the runway and report ready to cross active runway 35. ATC subsequently cleared the helicopter to cross runway 35 for landing. The pilot extended the downwind approach into wind for taxiway 35, rather than a crosswind landing.
During the approach, as the helicopter passed the eastern perimeter fence of FAGC, the low rotor RPM warning horn sounded, indicating a main rotor RPM of approximately 80%. The pilot observed that the engine RPM exceeded allowable limits. He reduced collective and entered autorotation in an attempt to regain rotor RPM, and also rolled down the throttle to reduce engine RPM, but this had no effect. The pilot made a brief radio transmission announcing “entering autorotation.”
As the helicopter neared the ground, the pilot flared to arrest descent and reduce forward speed, then levelled the aircraft for landing. The skids impacted the ground with forward speed, causing the helicopter to nose over and roll onto its left side. The main rotor blades were still turning during the rollover.
Occupants and Injuries
The helicopter carried a pilot and one crew member. No injuries were sustained by either occupant. Both were observed standing outside the helicopter after the accident. The passenger assisted the pilot by unbuckling his seatbelt, as the pilot was hanging against it in suspension.
Aircraft Damage
The helicopter sustained substantial damage. The left side of the fuselage was damaged, the main rotor blades were damaged during the rollover, and the tailboom separated from the main wreckage. There was no evidence of fire.
Investigation Findings
The maintenance organization did not find a mechanical failure that could have caused the engine RPM exceedance and loss of main rotor RPM.
Probable Cause
The probable cause was listed as unsuccessful autorotation.