The Accident Investigation Board of Norway (AIBN) has released an update regarding the 29 April 2016 accident involving an Airbus Helicopters H225 that suffered a complete separation of its main rotor head.

The H225 registration LN-OJF , operated by CHC was en route from the Gullfaks B oil platform in the North Sea when it suffered a catastrophic gearbox failure, resulting in the separation of the main rotor head, and the the death of all thirteen people on board. The incident occurred over a small Island just East of Turøy.

According to the report, the failure was the result of a fatigue fracture in one of the eight second stage planet gears inside the H225’s gearbox. Even though the fracture has been identified in the investigation, the AIBN says that it has still not identified a route cause, and that the final report’s release date remains uncertain.

Planet gear parts from second stage epicyclic reduction gear module. (The fractured gear is on top of a sample gear that was not involved in the accident.) Photo: AIBN

“The investigation is complex, and has a wide scope. So far, the metallurgical studies have been a major focus. These are efforts to map and understand why fatigue cracks could form and evolve. This work has not yet been completed.”

“It appears that the fracture propagated in a manner which was unlikely to be detected by the mandatory or supplementary systems intended for warning of an imminent failure.”

The incident bears great resemblance to an earlier accident involving another H225 (G-REDL) off Scotland operated by Bond Helicopters, which also saw a main rotor separation, resulting in the death of sixteen people. Bond Helicopters had suffered another less serious incident involving one of their H225s that ditched on approach to the BP ETAP Oil Platform in the North Sea.

Following the accident in Norway, an Airworthiness Directive (A/D) issued by the The European Authority in Aviation Safety (EASA) saw the entire fleet of H225s grounded in Europe. CHC has since expressed intentions of removing the H225 from it’s fleet entirely.

The AIBN investigation could force Airbus Helicopters to re-evaluate the certification standards for the gearbox.

“At present time, the primary focus of the AIBN investigation is certification aspects of the main gearbox and the robustness of past and present design requirements. This includes the follow-up on safety recommendations issued by the AAIB in connection with the accident involving G-REDL and continuing airworthiness of the gearbox.”

LN-OJF’s main rotor captured falling from the skies:

The H225 has been in use with off-shore oil operations and Search and Rescue (SAR) work for a long time, but the spate of accidents has left operators with severely degraded confidence in the helicopter, which has become a big headache for Airbus Helicopters. The manufacturer will have to evaluate the viability of the continued production of the H225 family, having lost the crucial element of trust with it’s customers.

An Airbus Helicopters H225 similar to LN-OJF. Photo: Ronnie Robertson

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