What happened
On November 20, 1999, a Bell 206 B helicopter, registration ZS-RFE, was conducting a domestic charter flight near Cape Town. The aircraft, carrying a pilot and four foreign tourists, departed from the V&A Waterfront with the intention of returning to the same location. While cruising at an altitude of approximately 2,000 feet, the pilot observed the amber engine chip warning light illuminate.
Roughly two minutes after the initial warning, the red engine out light activated, accompanied by an audible engine out alert. In response to the loss of engine power, the pilot immediately lowered the collective pitch lever and initiated an autorotational descent. The helicopter successfully reached an open area near the Groot Constantia Wine Farm. During the touchdown, the left front skid sank into soft soil and failed, causing the aircraft to pitch forward. This movement resulted in a main rotor blade striking and severing the upper portion of the tail boom. Despite the structural damage to the airframe, all five occupants disembarked from the aircraft with no injuries.
The investigation
Investigators examined the engine components to determine the source of the warnings. Upon inspection, both magnetic plugs were removed from the engine. The investigation established that both plugs contained metal particles. These particles were traced back to the inner housing of the 2½ bearing located within the engine's accessory gearbox.
Findings
- The initial engine chip warning was likely caused by the failure of the inner housing of the 2½ bearing in the accessory gearbox.
- The subsequent engine out warning was potentially caused by a partial failure of the N1 tacho-generator bearing.
- It is believed that heat generated by the failing bearing caused the housing to expand sufficiently to allow the press-fitted generator assembly to become dislodged during flight.