The latest report from the Accident Investigation Board Norway (AIBN) is formal, it is this small part seen here in the photo, which caused the Super Puma crash in Norway two months ago.
Thanks to detailed metallurgical examinations the investigators are now almost certain that it was fatigue failure due to premature wear, and thus disintegration, of one of the eight second stage planet gears in the main gearbox, which resulted in the detachment of the main rotor blade.
Following the in-flight detachment of another Super Puma main rotor blade in 2009, a fatigue warning detection system had however been installed by Airbus Helicopters. Nevertheless, the problem is that the system detects the presence of micro-splinters of metal, whilst in this case; a crack may have formed inside the gear before fracturing, and without projecting the least fragment.
The investigation is still on going to determine the origin of this premature wear. Meanwhile, the European Aviation Safety Agency (EASA) is maintaining a temporary ban on H225 commercial flights.