What happened
On 14 December 2008, a Robinson R44 Raven II, registration ZS-RYR, was conducting a domestic charter flight from Cleopatra Mountain Lodge in KwaZulu-Natal. The aircraft was carrying the pilot and three passengers when it entered the Langabalele Pass at an altitude of 9,500ft AMSL.
While the pilot was preparing to exit the pass and turn north, the aircraft was suddenly hit by a powerful downdraft. Realizing that the rate of descent was too high to safely execute a turn without hitting the terrain, the pilot attempted to land the helicopter straight ahead on the top of the pass. The aircraft skidded onto the surface at approximately 20kt. Because of the 25-degree downward slope of the terrain, the left skid struck the ground first and detached from the fuselage. The force of this hard landing caused the main rotor blades to strike the tail boom, severing both the boom and the tail rotor assembly. The aircraft came to a stop shortly after impact.
Despite the significant damage to the airframe, there were no fatalities. The pilot and two passengers escaped without injury, while one passenger sustained minor bruising.
The investigation
SACAA AIID investigators examined the aircraft's performance capabilities and the environmental conditions at the time of the accident. The investigation established that while the aircraft was well below its maximum takeoff weight, the atmospheric conditions were critical.
Although the pressure altitude was 9,500ft, the high temperature of 28°C resulted in a density altitude of approximately 12,800ft. This high density altitude significantly degraded the engine performance and aerodynamic lift available to the helicopter. The investigation also reviewed the maintenance history, noting the aircraft had undergone a scheduled inspection less than 70 hours prior to the event.