Accident Overview
On 20 November 1999 at 1010Z, a Bell 206 B helicopter (registration ZS-RFE) operated as a domestic charter flight from the V&A Waterfront departed on a sightseeing flight with a pilot and four foreign tourists. The flight was conducted in fine weather conditions. While flying at approximately 2,000 feet above ground level, the amber ENG CHIP warning light illuminated. About two minutes later, the red ENG OUT warning light and audio warning activated.
Sequence of Events
Upon receiving the engine out warning, the pilot immediately lowered the collective pitch lever and executed an autorotational landing in an open area near Groot Constantia Wine Farm in Cape Town. During touchdown, the left front skid dug into soft soil and failed, causing the helicopter to nose forward. One of the main rotor blades then severed the top section of the tail boom. All five occupants disembarked from the helicopter without injury.
Probable Cause
The engine chip warning was attributed to the initial failure of the inner housing of the 2½ bearing in the accessory gearbox of the engine. Both engine magnetic plugs, removed during the investigation, contained metal particles originating from the 2½ bearing inner housing. The engine out warning was attributed to the partial failure of the N1 tacho-generator bearing. As the generator assembly was only press-fitted into the housing, the heat generated by the partial bearing failure allowed the housing to expand sufficiently for the generator assembly to become dislodged in flight, resulting in the engine out warning.