What happened
On 8 October 2010, a Hughes 269C helicopter, registration ZS-HTJ, was conducting a game darting operation at Farm Eulalie in the Marken district of Limpopo Province. The mission involved using a dart gun to tranquilize Eland antelope for later capture by ground teams.
While searching for the animals, the aircraft experienced a sudden surge in engine RPM, immediately followed by a significant decay in the main rotor RPM. Unable to maintain flight, the pilot attempted an emergency forced landing in dense, bushy terrain. The helicopter struck the ground heavily in an upright position. The impact caused the skid gear to collapse and separate from the airframe, leading the aircraft to roll onto its right side.
The pilot sustained serious injuries to his back, exacerbated by the failure of his shoulder harness, which was found to be in a dilapidated condition. The passenger, who had discarded the dart gun prior to impact, escaped with only minor cuts and bruises.
The investigation
SACAA AIID investigators examined the wreckage and the maintenance history of the aircraft. The investigation focused on the mechanical failure that preceded the loss of rotor power.
Technical analysis of the powertrain revealed that the lower coupling driveshaft (part number 269A5559-3) had failed. Although the component had a service life of 6,000 hours, it had only completed 1,442.8 hours of service since its last replacement. Metallurgical examination confirmed that the shaft failed due to fatigue.
Investigators also reviewed recent maintenance performed on the aircraft in September 2010, which had been initiated to address a reported engine vibration. During this period, the lower coupling driveshaft had been removed and refitted. While the investigation could not confirm if a previous engine overspeed event had occurred, it could not rule out such an event as a potential catalyst for the fatigue cracks.
Findings
- The primary cause of the accident was an unsuccessful forced landing following the failure of the engine-driven lower coupling driveshaft.
- The failure of this shaft resulted in a total loss of power to the main rotor transmission system.
- The pilot's shoulder harness failed during the impact because it was in a non-serviceable, dilapidated state.
- The aircraft's landing gear collapsed upon impact, causing the subsequent rollover.
- The aircraft was operating in high density altitude conditions (6,000 feet) with an ambient temperature of 34°C.