All 16 people aboard a Eurocopter AS 332L2 Super Puma operated by Bond Offshore Helicopters died when the medium twin hit the surface of the North Sea on April 1, after what the UK’s Air Accidents Investigation Branch (AAIB) called a catastrophic failure of the main gearbox.
According to investigators, the failure took place in the epicyclic module. “This is supported by HUMS [health and usage monitoring system] data; however, this is not yet fully understood,” the report states. The failure resulted in the detachment of the main rotor head from the helicopter and was rapidly followed by main rotor blade strikes on the pylon and tail boom, which became severed from the fuselage.
The helicopter had been undergoing a daily inspection of the epicyclic module magnetic chip detector since March 25, when a particle was discovered on that part. In addition, the HUMS data was downloaded and analyzed each time the helicopter returned to its base at Aberdeen for the next 25 flying hours. According to the report, the operator noticed no further abnormalities in the week preceding the accident.
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