The helicopter was engaged in cattle mustering on Ivanhoe Station. The pilot in command was training the other pilot in aerial mustering techniques. While the helicopter was being flown at about 50 feet agl, one main rotor blade grip failed. The associated main rotor blade separated from the helicopter and the resulting imbalance caused the other main rotor blade and transmission to be torn from the helicopter. The aircraft then fell to the ground, landing on its right side. The main rotor blade grip failed due to a combination of fatigue and overload forces. Examination of the aircraft records revealed that because of a error in the recording of component hours, the 5000 hour service life of the grip had been exceeded by 687 hours. During the investigation inspections of the blade grips on several other helicopters were carried out. Fatigue cracking was revealed in a significant number of the blade grips inspected. As a result, the manufacturer of the aircraft has recommended a reduction in the service life of the component.