What happened
On 2 November 2021, a Bell 206L helicopter, registration ZS-HDX, was performing a repositioning flight from Rand Airport to Buffels Mine. Approximately 35 minutes into the cruise phase, the pilot observed an engine-out warning light, followed by a sudden drop to zero for oil pressure, torque, and gas generator (Ng) readings. Shortly after, a loud bang originated from the engine compartment, and the aircraft entered autorotation.
The pilot managed to turn the aircraft into the wind and executed a successful forced landing on a private farm located 16nm southwest of F/Fochville. Although a fire broke out in the engine bay following the landing, the pilot extinguished it using an on-board extinguisher. There were no injuries to the pilot or the passenger, though the helicopter sustained substantial damage to the engine, fuselage, tail rotor drive shaft, and one main rotor blade.
The investigation
SACAA AIID investigators examined the wreckage and conducted a metallurgical analysis of the engine components. The investigation confirmed that the pilot was properly licensed and that weather conditions were suitable for the flight. The analysis focused on the engine's internal failure mechanism to determine why the oil pressure vanished so abruptly.
Findings
The investigation established that the engine failure was triggered by the separation of an anti-rotation tab from the gas producer bearing thrust plate. This metal fragment traveled through the oil system and became lodged between the oil pump scavenge gear and the pump wall. This obstruction prevented the oil pump from providing adequate lubrication to the number 6 and 7 bearings, leading to thermal damage and subsequent failure of various turbine parts.