What happened
On 1s September 2018, a Bell Helicopter Textron 206B Jetranger-III, registration ZT-RAT, was conducting a commercial ferry flight from Wonderboom Airport to Lanseria Airport. The flight, carrying a pilot and one passenger, proceeded normally after takeoff until approximately 30 minutes into the journey.
While flying over the Mooiplaas area, the pilot observed a simultaneous drop in several critical engine parameters, including N1, N2, and turbine outlet temperature. This sudden loss of power resulted in an engine flameout. The pilot immediately initiated an autorotation procedure, identifying an open field for an emergency landing. However, the maneuver resulted in a hard impact with the ground, causing the aircraft's skids to break upon contact. There were no injuries reported for the occupants.
The investigation
SACAA AIID investigators examined the engine and the components of the fuel control system to determine the cause of the power loss. The inspection of the Allison 250-C20J engine revealed that the Pc Safety Valve had suffered a structural failure, specifically that the valve stem had broken off.
Further technical review showed that the valve, an aftermarket modification used to protect engine components during cleaning, had broken into two pieces. The investigation also looked into the maintenance history of the aircraft, noting that while a mandatory periodic inspection had been performed recently, there was no documented evidence that the operator had complied with the specific airworthiness instructions regarding the inspection intervals for this particular safety valve.