The AIBN today issued a preliminary report detailing its findings regarding the EC225 helicopter crash on Turøy, near Bergen. All 13 people on board lost their lives when the main rotor head detached from the helicopter causing the fatal accident.
The investigation has revealed that this accident has clear similarities to an AS 332 L2 accident off the coast of Scotland in 2009. The helicopters had near identical main rotor gearboxes installed. In both accidents, one of the eight second stage planet gears in the epicyclic module fractured as a result of fatigue. However, there was one warning of possible gear fracture in the case of the 2009 accident, while there was no advance warning in this accident.
The AIBN will continue the investigation into how and why two similar catastrophic accidents could happen to near identical helicopters only seven years apart.
What were the Main Findings?
- The flight was normal until the rotor detached. There were no warnings before mechanical noise was recorded on the Combined Voice and Flight Data Recorder immediately
before the rotor separated.
- The accident was a result of a fatigue fracture in one of the eight
second stage planet gears in the epicyclic module of the main rotor gearbox.
- The crack appears to have initiated as a surface micro-pit. However, the reason for formation of the micro-pit and the underlying driving mechanisms are not currently understood.
- No material conformity issues or discrepancies in the manufacturing process have been revealed during the investigation.
- The main rotor gearbox had been involved in a road accident during transport in 2015. It was inspected, repaired and released for flight by the helicopter manufacturer, Airbus Helicopters, and flew 260 flight hours prior to the incident. The AIBN has not found
any physical evidence to connect the ground transport accident to the subsequent initiation and growth of the fatigue cracks in the second stage planet gear.
What is a Preliminary Report?
The Accident Investigation Board Norway (AIBN) issues a preliminary report within 12 months following the accident. This is in accordance with Regulation (EU) No. 996/2010 Article 16.
The report is an extensive but incomplete representation of the AIBN’s investigations in connection with the accident.
As the investigation is incomplete the AIBN issues no safety recommendations at this stage.
Only the final report will represent the complete investigation and be the official document of the AIBN.
The European Aviation Safety Agency (EASA) said:
“While the accident investigation is not complete, EASA continues to implement robust and proven certification processes taking into account all available information.
“EASA will continue to provide its full support to the ongoing investigation until the cause of the accident will be found.”