Bell 206B Main Drive Shaft Failure During Commercial Flight (ZS-RFM)

Accident Overview and Flight Details On 2 July 2002, a Bell 206B helicopter registered ZS-RFM was operating a commercial flight from Harmony Gold Mine to Rand Refineries in Germiston. The aircraft was carrying the pilot, one passenger, and valuable cargo. The pilot-in-command held a valid ALTP license and had 10,080 total flying hours, including 550 hours on type. ## Accident Sequence During cruise flight, the helicopter experienced a failure of the main drive shaft assembly located between the main rotor gearbox and the engine. The pilot reported that the engine also failed shortly afterward. The pilot then executed an autorotational landing in an open field south of Alberton. On touchdown over uneven terrain, one main rotor blade struck the tail rotor drive shaft cowling and the tail rotor drive shaft. ## Post-Accident Actions and Damage Security precautions were implemented because of the cargo, and a serviceable helicopter was sent to transfer and deliver the valuable load. The wreckage was recovered by road to a maintenance facility, where investigators assessed the damage and the cause of the drive shaft failure. No persons were injured or killed. ## Probable Cause The investigation attributed the fracture of four fixation bolts to excessive heat generated between the mating faces of the outer and inner coupling teeth due to inadequate lubrication. The inadequate lubrication was linked to either incorrect installation of the grease seal or severe wear and tear of the seal before re-assembly, which may have failed shortly after the drive shaft assembly returned to service.