OK, here's the letter which went from Helicoptères Guimbal to their customers on this incident along with an associated SB...
An incident happened recently where a Cabri G2 was forced to perform emergency landing. The crew initially heard a noise and after some minutes of ensuing flight the helicopter developed significant engine vibration, followed by another loud noise and eventual loss of power. The pilot with his trainee made a safe autorotation landing.
The damage to the helicopter is minor.
The investigation by the authorities is under way with the assistance of Helicopteres Guimbal. The initial conclusion is that the engine cooling fan wheel broke and released a sector which caused extensive damage to the surrounding shroud, transmission belt and clutch cylinder.
The reason for the wheel failure was not determined. It could include foreign object ingestion, local damage of the wheel ring, or contact corrosion. No overspeed was reported and the wheel design has been tested to extreme overspeed of about 200% (5300 RPM), well above maximum engine speed.
The helicopter had 1180 hrs TT. The concerned parts manufacturing history and quality records were analyzed. These parts have a complete traceability.
Helicopteres Guimbal is today issuing a mandatory Service Bulletin to direct initial and periodic inspection of parts in service.
The development of a redesigned part, including enhanced damage tolerance, is already in progress with the goal of removing this periodic inspection requirement. The highest priority is being given to this effort in order to deliver safer parts soon.
I apologize for the inconvenience and kindly ask you to trust that we are doing our best to ensure the highest safety.