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Investigators find metal fatigue caused fatal 2016 Airbus helicopter crash in Norway

10 July 2018

The crash of an Airbus Super Puma helicopter that killed all 13 people aboard was the result of metal fatigue in its gearbox, Norway’s Accident Investigation Board (AIBN) said in its final report into the incident published on July 5, 2018.  The crash occurred after the Super Puma’s main rotor blades separated from the helicopter as it was ferrying passengers from a Norwegian offshore oil platform to the mainland.

LN-OJF's detached main rotor - Image: AIBN
LN-OJF's detached main rotor - Image: AIBN

The H225 LP Super Puma LN-OJF, operated by CHC Helikopter Service AS, came down on the island of Turøy on the approach to Bergen Airport Flesland inbound from Equinor's Gullfaks B platform in the North Sea.

The aircraft had just descended to 2 000 feet and was in cruise at 140 knots at the time of the failure. The AIBN said cockpit recordings showed the crew had received no warnings before the main rotor detached. The cockpit recording ended almost immediately, but data from health and usage monitoring systems showed the aircraft yawing and rolling to the right, impacting the island about 13 seconds after the main rotor detached. It ultimately landed about 550 meters away from the main crash site.

“The accident was a result of a fatigue fracture in a second stage planet gear in the epicyclic module of the main rotor gearbox,” investigators said. “Cracks initiated from a micro-pit at the surface and developed subsurface to a catastrophic failure without being detected.”

Investigators said they had excluded material unconformity and mechanical failure, as well as maintenance actions by the helicopter operator, as causes for the crash. Nor was there any connection between the crew handling and the accident, said the report.

Among the 12 recommendations they made, investigators said Airbus should take another look at the design of the main gearbox of the Super Puma.

“The Accident Investigation Board Norway recommends that Airbus Helicopters revise the type design to improve the robustness, reliability and safety of the main gearbox in AS 332 L2 and EC 225 LP (helicopters).”

Airbus Helicopters said it welcomed the conclusion of the investigation and took note of the findings in the report.

“Airbus Helicopters is committed to the continuous improvement of the H225 MGB (main gear box) with the objective of increasing robustness, reliability and safety, as highlighted in the AIBN recommendation,” said an Airbus spokesman.

“This includes, among other initiatives, a roadmap for the development of new vibration monitoring methods which will be shared with industry in due course.”

The report also targeted the European Aviation Safety Agency (EASA), calling on the regulator to revise certification standards for large rotorcraft, initiate research into crack development in certain aircraft bearings, and ensure manufacturers’ continuing airworthiness programs cover the examination of critical components found to be beyond serviceable limits.

One of the main recommendations from AIBN is that EASA require a fail-safe main gearbox, in which no failure of an internal component leads to a catastrophic failure.

The unanticipated nature of the failure was an area of particular focus for investigators, given the clear parallels they draw to the fatal crash of an AS332 L2 off the coast of Scotland in 2009 that killed 16 people. In that aircraft (G-REDL), the main rotor also detached following what was later discovered to be a fatigue fracture in a second stage planet gear.

EASA’s response to the final report dismissed any implied criticism over its response to the G-REDL incident as “a number of opinions and hypotheses”.

It concluded: “Safety is EASA’s mission and utmost priority. We will continue developing our safety plan with improvements stemming from this report.” 

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