What happened
On 18 June 2007, a Robinson R22 helicopter, registration ZS-RUZ, was conducting a private flight departing from Cape Town International Airport. The pilot was flying toward Wellington to accumulate the necessary flight hours for a commercial license. The flight proceeded normally for approximately 15 minutes while cruising at 1,000 feet above mean sea level with an indicated airspeed of 80 knots.
During the cruise phase, the aircraft suddenly experienced intense vibrations and random yawing motions. This was accompanied by a partial loss of engine power and a subsequent loss of altitude. The pilot managed to execute a successful autorotative landing in an open field located in the Brackenfell area, approximately 8 nautical miles northeast of Cape Town International Airport. There were no injuries and the aircraft remained undamaged.
The investigation
Following the incident, the aircraft was retrieved by an approved maintenance organization for a technical examination. The investigation focused on the engine's performance and mechanical integrity. Maintenance inspections revealed that several teeth on the left-hand magneto distributor drive gear had sheared off. This mechanical failure was identified as the source of the engine's power loss and the resulting vibrations.
Records indicated that the most recent mandatory periodic inspection (MPI) had been completed on 19 April 2007. At the time of the incident, the aircraft had flown 94.5 hours since that inspection. The maintenance organization responsible for the previous MPI was found to be properly certified and had undergone a recent audit with no significant deficiencies noted.