What happened
On the morning of 5 April 2005, a Bell 206L-3 helicopter, registration ZS-HUP, was engaged in commercial power line maintenance near the Three Rivers power station. The mission involved servicing the Eskom Glockner Lethabo 2, 275 Kilo Volt line. Following a standard pre-flight inspection and a safety briefing with the live-line crew, the aircraft was utilized to transfer personnel between towers.
After the maintenance team had disembarked from the aircraft, the pilot positioned the helicopter to the left of tower 43, facing north-west. While maintaining a 100-foot hover out of ground effect, the engine experienced a sudden loss of power. Unable to sustain the hover, the pilot initiated a hovering autorotation from the 100-foot altitude. The aircraft subsequently performed a hard landing in a maize field located adjacent to the power lines. The pilot, who was the only person on board, escaped the incident without injury.
The investigation
The investigation into the incident examined the mechanical state of the aircraft and the operational conditions at the time of the accident. Records indicated that the aircraft's last Mandatory Periodic Inspection (MPI) had been completed on 15 March 2005, with 55.6 flight hours accumulated since that inspection. The operator, Sapphire Air, held a valid Air Operating Certificate, and the pilot possessed the appropriate license and significant experience on the type.
Findings
Technical analysis determined that the engine power loss was caused by the fracture of the pneumatic Pc tube. This specific component, situated between the Fuel Control Unit (FCU) and the Power Turbine (PT) Governor, broke and separated from its connection at the FCU. This mechanical failure caused the engine to decelerate to ground idle levels (approximately 54-56% N1), which deprived the engine of the necessary power to maintain flight, necessitating the forced landing.