CIRCUMSTANCES: "While the helicopter was flying at about 60 knots and 400 feet above the ground, the pilot heard a loud bang. The helicopter yawed slightly and the pilot felt an airframe vibration. As the pilot reduced airspeed and initiated a descent, he saw the red fire warning light illuminated and realised that the engine had failed. After a successful autorotative landing, the pilot extinguished several small scrub fires under the helicopter tail boom. These fires were ignited by hot metal ejected from the engine. He also extinguished a small oil fire in the engine bay. The engine failure resulted from the failure of the intermediate gear/pinion in the reduction gearbox. The gear failed due to fatigue cracking which commenced at an overstress crack. This crack, plus similar cracks found in the root of five adjacent gear teeth, probably occurred as a result of main rotor blade strikes which occurred when the helicopter rolled over during a ground run approximately 765 hours time-in-service earlier. After this earlier rollover accident, the reduction gearbox was inspected and returned to service in accordance with the Turbomeca Arriel 1 Engine Maintenance Manual. The engine manufacturer is aware of two other total ruptures of intermediate gears of the same modification status as was fitted in the reduction gearbox of VH-HRR. Eight more failures of intermediate gears of a later modification status have been detected by pilots, without ensuing engine failures, because of warning lights triggered by metal particles on an electric magnetic plug." RECCOMENDATIONS: It is recommended that the CAA liaise with the engine manufacturer to consider the desirability of incorporating more stringent inspection requirements in the engine maintenance manual to detect cracks in components after rotor blade strikes/sudden stoppages. RESPONSE TO S The CAA has been in contact with the engine manufacturer (Turbomeca) and the relevant certification authority (DGAC) with respect to reduction gearbox failures. Turbomeca intends to be more precise in the wording of the Engine Maintenance Manual concerning inspections to be carried out after rotor blade strikes/sudden stoppages.