The Accident Investigation Board of Norway (AIBN) has released another update in their investigation of the Airbus EC225 accident which happened on 29th April as the CHC aircraft was returning from the Gullfaks platform to Bergen Airport. Of particular note, they state

“At this stage of the investigation, the AIBN finds that the accident most likely was a result of a fatigue fracture in one of the eight second stage planet gears. It appears that the fracture has propagated in a manner which is unlikely to become detected by existing mandatory or supplementary systems for warning of an imminent failure. What initiated the fracture has not yet been determined”

That last sentence remains central – What initiated the fracture has not yet been determined.

Another key aspect to consider is the close similarity to the 2009 accident to AS332L2 G-REDL. In that report, the UK AAIB noted “An extensive and complex investigation revealed that the failure of the MGB initiated in one of the eight second stage planet gears in the epicyclic module. The planet gear had fractured as a result of a fatigue crack, the precise origin of which could not be determined”. AIBN also notes some clear differences to the G-REDL report.

While the latest document from AIBN is not the final report, the key information reveals puts much more weight on the design and/or manufacture process rather than the maintenance or safety management – ie on Airbus, not CHC. One line of investigation being followed is an accident when the Main Rotor Gearbox from the accident helicopter was being transported by road.

Please also refer to our article “Who should we blame when an aircraft crashes”

Jeremy Parkin – HeliHub.com