Bell 206B Helicopter Accident in South Africa (ZS-HMB)

Accident Overview and Flight Details On 30 March 2000 at 0740Z, a Bell 206B helicopter with registration ZS-HMB was operating an international charter flight from Nelspruit to Maputo. The aircraft was carrying one pilot and three passengers. The pilot held a commercial licence and had 4,919.0 total flying hours, including 640.0 hours on the aircraft type. ## Sequence of Events While navigating the Crocodile River Gorge to avoid cloudy conditions at higher altitudes, the helicopter experienced a sudden bang and yawed to the left. The pilot applied right rudder pedal to counteract the swing. Simultaneously, the ENG OUT warning light illuminated, followed by an audio warning. With the throttle at full power, the main rotor RPM began decreasing, and the helicopter entered autorotational flight. Due to limited landing options caused by the terrain, the pilot elected to land in an open area on the riverbank. ## Descent and Landing During the descent, the pilot observed that the power turbine RPM was greater than the main rotor RPM. Based on recent recurrent training that covered this specific scenario, the pilot kept the engine running until after landing to maintain tail rotor control. The ENG CHIP warning light also illuminated during the descent. Upon landing, one of the main rotor blades severed the tailboom and tail rotor drive shaft. With the throttle still open, the pilot observed the engine Ng at idle (58%), the power turbine at 100%, and the main rotor RPM at approximately 45% and decreasing. Once the main rotor blades stopped turning, all occupants disembarked uninjured. ## Technical Findings The main rotor brake was found to be inoperative due to the failure of the input drive shaft coupling from the engine to the main rotor gearbox.